Current date: 2025-12-23

Setting default datestamp limit: 0

Datestamp limit: 2025-12-23 (0 days ago)

Created/updated limit: 2025-12-16 (7 days ago)

Suggested sets: physics, physics:astro-ph, physics:gr-qc, physics:physics

Setting default set: physics

OAI-PMH request: http://export.arxiv.org/oai2?verb=ListRecords&from=2025-12-23&until=2025-12-23&set=physics&metadataPrefix=arXiv

Scoring abstracts

Number of records retrieved: 1199

Keyword score statistics

score 13 -- 2 abstracts

score 10 -- 2 abstracts

score 9 -- 1 abstracts

score 7 -- 1 abstracts

score 6 -- 2 abstracts

score 5 -- 4 abstracts

score 4 -- 11 abstracts

score 3 -- 12 abstracts

score 2 -- 27 abstracts

in total -- 62 abstracts

Articles that appeared on 2025-12-23

[abstract 1 / 62] Wow! (score: 13)
arXiv:2507.14002 [pdf, ps, other]

Title: Reconnection-driven Flares in M87*: Proton-Synchrotron-powered GeV Emission

Authors: Hayk Hakobyan, Amir Levinson, Lorenzo Sironi, Alexander Philippov, Bart Ripperda,

Comments: 14 pages, 6 figures

Subjects: astro-ph.HE physics.plasm-ph

Created: 2025-12-21; Updated: 2025-12-23; Datestamp: 2025-12-23

Magnetic RECONNECTion in current layers that form intermittently in radiatively inefficient accretion flows onto BLACK HOLEs is a promising mechanism for particle acceleration and high-energy emission. It has been recently proposed that such layers, arising during flux eruption events, can power the rapid TeV flares observed from the core of M87. In this scenario, inverse Compton scattering of soft radiation from the accretion flow by energetic electron-positron pairs produced near the RECONNECTion layer was suggested as the primary emission mechanism. However, detailed calculations show that radiation from pairs alone cannot account for the GeV emission detected by the FERMI observatory. In this work, we combine analytic estimates with 3D radiative particle-in-cell simulations of pair-proton plasmas to show that the GeV emission can be naturally explained by SYNCHROTRON radiation from protons accelerated in the current sheet. Although the exact proton content of the layer is uncertain, our model remains robust across a broad range of proton-to-pair number density ratios. While protons are subdominant in number compared to pairs, our simulations demonstrate that they can be accelerated more efficiently, leading to a self-regulated steady state in which protons dominate the energy budget. Ultimately, proton SYNCHROTRON emission accounts for approximately 5%-20% of the total dissipation power. The majority is radiated as MeV photons via pair SYNCHROTRON emission, with a smaller fraction emitted as TeV photons through inverse Compton scattering.

[abstract 2 / 62] Wow! (score: 13)
arXiv:2512.19193 [pdf, ps, other]

Title: The IXPE and multifrequency polarimetric view of the extreme BLAZARs 1ES 1101-232 and RGB J0710+591

Authors: Fabrizio Tavecchio, Dawoon E. Kim, Gabriel Emery, Ioannis Liodakis, Iván Agudo, Paolo Coppi, Giampiero Tagliaferri, Laura Di Gesu, Tullia Sbarrato, Lucia Ballo, Alberto Sciaccaluga, Steven R. Ehlert, Giacomo Bonnoli, Francisco José Aceituno, Carolina Casadio, Víctor Casanova, Immacolata Donnarumma, Juan Escudero, Daniel Morcuende, Jorge Otero-Santos, Alfredo Sota, Vilppu Piirola, Pouya M. Kouch, Elina Lindfors, Kari Nilsson, Ioannis Myserlis, Mark Gurwell, Garrett Keating, Ramprasad Rao, Emmanouil Angelakis, Alexander Kraus, Ryo Imazawa, Mahito Sasada, Yasushi Fukazawa, Koji S. Kawabata, Makoto Uemura, Tsunefumi Mizuno, Tatsuya Nakaoka, Sumie Tochihara, Takahiro Akai, Hiroshi Akitaya, Rumen Bachev, Anton Strigachev, Petra Benke, Lena Debbrecht, Julia Eich, Florian Eppel, Andrea Gokus, Steven Hämmerich, Jonas Heßdörfer, Matthias Kadler, Sanghyun Kim, Dana Kirchner, Georgios Filippos Paraschos, Florian Rösch, Wladislaw Schulga,

Comments: 11 pages, submitted to A&A

Subjects: astro-ph.HE

Created: 2025-12-22; Updated: 2025-12-23; Datestamp: 2025-12-23

Multiwavelength polarimetry is a powerful tool to probe MAGNETic field and flow geometries in the RELATIVISTIC JETs of BLAZARs. In this respect, particularly interesting are the sources whose SYNCHROTRON emission covers a broad range of frequencies, from radio to X-rays, such as the BL Lac objects of the HSP type. Previous measurements including radio, optical and X-ray data show a clear trend, with the degree of POLARIZATION increasing with frequency. Here we report radio, optical and X-ray observations ($SWIFT$, $Nustar$ and $IXPE$) of 1ES 1101-232 and RGB J0710+591, two BLAZARs belonging to the puzzling subclass of extreme BL Lacs (EHBL). For 1ES 1101-232 we found a strong frequency-dependency of the degree of POLARIZATION (with a ratio $Π_X/Π_O\simeq 5.2$). For RGB J0710+591, IXPE derived a 1$σ$ upper limit $Π_X<11.6\%$, comparable with the measured optical degree of POLARIZATION (average $Π_O\sim 12\%$). We discuss the results in the framework of current interpretations and, in particular, we report an improved version of the stratified shock model that is able to reproduce the observed data of both sources.

[abstract 3 / 62] Wow! (score: 10)
arXiv:2507.02583 [pdf, ps, other]

Title: Measuring BLACK HOLE spins with x-ray reflection spectroscopy: A GRMHD outlook

Authors: Swarnim Shashank, Askar B. Abdikamalov, Honghui Liu, Abdurakhmon Nosirov, Cosimo Bambi, Indu K. Dihingia, Yosuke Mizuno,

Comments: 21 pages, 12 figures. v2: refereed version. Supplemental material available at http://link.aps.org/supplemental/10.1103/4sth-rnwv

Subjects: astro-ph.HE gr-qc

Created: 2025-12-21; Updated: 2025-12-23; Datestamp: 2025-12-23

X-ray reflection spectroscopy has evolved as one of the leading methods to measure BLACK HOLE spins. However, the question is whether its measurements are subjected to systematic biases, especially considering the possible discrepancy between the spin measurements inferred with this technique and those from gravitational wave observations. In this work, we use general RELATIVISTIC MAGNETohydrodynamic (GRMHD) simulations of thin accretion disks around spinning BLACK HOLEs for modeling the accretion process, and then we simulate NUSTAR observations to test the capability of modern reflection models in recovering the input spins. For the first time, we model the electron density and ionization profiles from GRMHD-simulated disks. Our study reveals that current reflection models work well only for fast-rotating BLACK HOLEs. We model the corona as the base of the JET and we find that reflection models with lamppost emissivity profiles fail to recover the correct BLACK HOLE spins. Reflection models with broken power-law emissivity profiles perform better. As we increase the complexity of the simulated models, it is more difficult to recover the correct input spins, pointing toward the need to update our current reflection models with more advanced accretion disks and coronal geometries.

[abstract 4 / 62] Wow! (score: 10)
arXiv:2512.18794 [pdf, ps, other]

Title: Recurrence plot analysis of BLAZAR gamma-ray light curves: Exploiting the time-domain capabilities of FERMI-LAT

Authors: Andrea Gokus, Rebecca Phillipson,

Comments: Proceedings of the 8th Heidelberg International Symposium on High-Energy Gamma-ray Astronomy, in review with "Memorie della Società Astronomica Italiana" (MemSAIt)

Subjects: astro-ph.HE

Created: 2025-12-21; Updated: 2025-12-23; Datestamp: 2025-12-23

Variability studies of JETted AGN, in particular BLAZARs, have been used to gain a better understanding of the particle acceleration mechanisms in JETs. However, statistical methods used for the characterization of variability often rely on stationary time series data, which is not fulfilled for most BLAZAR light curves. We introduce the recurrence plot method for long-term $γ$-ray light curves sampled by FERMI-LAT and present our results for the BL Lac object Mkn 421 and the FSRQ PKS 1424-41. Using surrogates to determine the significance of our findings, we conclude that Mkn 421 exhibits more determinism than PKS 1424-41, and that both sources potentially show nonlinearity. However, the latter has to be tested against more advanced surrogates that are able to replicate the nonstationarity of the original light curves. In future work, we will extend our recurrence analysis to a sample of $\sim50$ $γ$-ray bright sources to probe the JET dynamics of different BLAZAR classes.

[abstract 5 / 62] Wow! (score: 9)
arXiv:2512.19259 [pdf, ps, other]

Title: Sensitivity of CTAO to axion-like particles from BLAZARs: a machine learning approach

Authors: Francesco Schiavone, Leonardo Di Venere, Francesco Giordano,

Comments:

Subjects: astro-ph.HE

Created: 2025-12-22; Updated: 2025-12-23; Datestamp: 2025-12-23

Blazars are a class of ACTIVE GALACTIC NUCLEi, supermassive BLACK HOLEs located at the centres of distant galaxies characterised by strong emission across the entire electroMAGNETic spectrum, from radio waves to gamma rays. Their RELATIVISTIC JETs, closely aligned to the line of sight from Earth, are a rich and complex environment, characterised by the presence of strong MAGNETic fields over parsec-scale lengths. Owing to their cosmological distance from Earth, these sources serve as ideal targets to probe non-standard gamma-ray propagation. In particular, axion-like particles (ALPs) could be detected through their coupling to photons, which enables ALP-photon conversions in external MAGNETic fields, leading to distinct signatures in the BLAZARs' gamma-ray spectra. In this work, we explore a novel approach to constrain the ALP parameter space using gamma-ray observations, based on the use of machine-learning classifiers. We apply this technique to simulated observations of two bright BLAZARs -- Mrk 501 and PKS 2155$-$304 -- with the Cherenkov Telescope Array Observatory (CTAO), a next-generation gamma-ray facility well suited to probe such features, thanks to its improved energy resolution and point-source sensitivity with respect to present ground-based gamma-ray telescopes. The obtained $2σ$ exclusion regions on the ALP parameter space are consistent with those found by applying a standard likelihood-ratio test, and suggest that the CTAO sensitivity to ALPs could be extended beyond existing constraints over a wide mass range.

[abstract 6 / 62] Wow! (score: 7)
arXiv:2510.05324 [pdf, ps, other]

Title: On the statistical characterization of the SYNCHROTRON multi-zone POLARIZATION of BLAZARs

Authors: Andrea Tramacere,

Comments: published in A&A (final version after language editing and proofs)

Subjects: astro-ph.HE

Created: 2025-12-21; Updated: 2025-12-23; Datestamp: 2025-12-23

Multiwavelength polarimetric observations of BLAZARs reveal complex, energy-dependent POLARIZATION behavior, including a decrease in POLARIZATION fraction from X-rays to millimeter bands and significant variability in the electric vector position angle (EVPA). These trends challenge simple single-zone SYNCHROTRON models and suggest a more intricate, turbulent JET structure with multiple emission zones. We develop a statistical framework to model the observed energy-dependent POLARIZATION patterns in BLAZARs, focusing on the behavior captured by IXPE in the X-ray band and RoboPol in the optical. The goal is to statistically characterize multi-zone models in terms of the distributions of cell size and the physical parameters of the electron energy distribution (EED). A Monte Carlo approach, implemented with the JetSeT code, is used to generate synthetic multi-zone SYNCHROTRON emission from a spherical region filled with turbulent cells with randomly distributed physical properties. Simulations explore scenarios ranging from identical cells to power-law distributions of cell sizes and EED parameters with variable cutoff and low-energy slopes. The results show that a purely turbulent, multi-zone model can reproduce the observed energy-dependent POLARIZATION without requiring correlations between cell size and EED parameters. The POLARIZATION degree is primarily determined by the effective, flux-weighted, number of emitting cells, modulated by the dispersion in cell properties, particularly the EED cutoff energy at high frequencies and the low-energy spectral index at low frequencies. With a fractional dispersion in cutoff energy of about 90% and a low-energy spectral index dispersion of ~0.5-1.5, the model reproduces the chromatic mm-to-X-ray POLARIZATION trends seen by IXPE and the optical POLARIZATION limiting envelope observed in the RoboPol dataset.

[abstract 7 / 62] Yes (score: 6)
arXiv:2507.06766 [pdf, ps, other]

Title: Effects of Lorentz invariance violation on charged particles and photon production in astrophysical sources

Authors: Matheus Duarte, Vitor de Souza,

Comments:

Subjects: astro-ph.HE hep-ph

Created: 2025-12-20; Updated: 2025-12-23; Datestamp: 2025-12-23

We investigate the impact of Lorentz invariance violation (LIV) on radiation processes in astrophysical sources, focusing on SYNCHROTRON and inverse Compton interactions. We derive modified expressions for radiated power and photon energy under LIV assumptions and incorporate them into first-order FERMI acceleration models. Our analysis reveals energy thresholds beyond which LIV, within a kinematic framework, significantly alters particle dynamics and photon spectra, introducing non-physical divergences that highlight limitations in perturbative approaches. We model SYNCHROTRON self-Compton (SSC) emission in the presence of LIV and assess its consequences for photon fluxes from BLAZARs, including Markarian 501 and the BL Lac population. LIV introduces distinct high-energy emission regions that deviate from standard expectations. Comparisons with observational data, particularly upper limits from the Pierre Auger Observatory, suggest that future multi-messenger observations, together with the full analysis of particle's trajectories, could constrain LIV parameters through the non-detection of such excesses.

[abstract 8 / 62] Yes (score: 6)
arXiv:2512.18276 [pdf, ps, other]

Title: Discovery of a Luminosity-dependent Continuum Lag in NGC 4151 from Photometric and Spectroscopic Continuum Reverberation Mapping

Authors: Hai-Cheng Feng, Sha-Sha Li, Mouyuan Sun, Ciro Pinto, Shuying Zhou, Yerong Xu, J. M. Bai, Elena Dalla Bontà, ZhongNan Dong, Neeraj Kumari, Jiaqi Lin, H. T. Liu, Kai-Xing Lu, Bin Ma, Ji-Rong Mao, Emanuele Nardini, Enrico Piconcelli, Fabio Pintore, Jian-Guo Wang, Ding-Rong Xiong,

Comments: 13 pages, 6 figures, 2 tables. Accepted for publication in The Astrophysical Journal

Subjects: astro-ph.GA astro-ph.CO astro-ph.HE

Created: 2025-12-20; Updated: 2025-12-23; Datestamp: 2025-12-23

Accretion onto supermassive BLACK HOLEs (SMBHs) powers ACTIVE GALACTIC NUCLEi (AGNs) and drives feedback that shapes galaxy evolution. Constraining AGN accretion disk structure is therefore essential for understanding BLACK HOLE growth and feedback processes. However, direct constraints on disk size remain rare -- particularly from long-term, multi-season spectroscopic reverberation mapping (RM), which is critical for isolating the intrinsic disk response from the broad-line region (BLR). We present results from an intensive multi-wavelength RM campaign of NGC 4151 during its brightest state in nearly two decades. This represents the third high-cadence monitoring over the past decade, capturing accretion states spanning the transitional regime between thin and thick disks, making NGC 4151 the only AGN with continuum RM observations across such a wide range in accretion states. Combining spectroscopy from the Lijiang 2.4 m telescope with coordinated SWIFT UV/X-ray monitoring, we measure inter-band continuum lags from UV to optical. The wavelength-dependent lags follow a tight $τ\propto λ^{4/3}$ relation, consistent with reprocessing in a thin disk, but exceed theoretical predictions by a factor of 6.6. Our lag spectrum reveals clear excesses near the Balmer and possibly Paschen jumps, confirming diffuse continuum (DC) contamination from the BLR. By comparing the three campaigns, we discover a non-monotonic lag-luminosity trend ($>3σ$), which cannot be explained by DC emission alone. We propose the lags reflect combined disk and BLR contributions, and present the first evidence that the DC component follows an intrinsic Baldwin effect. These results offer new insights into SMBH mass measurements and theoretical models of AGN inner structure.

[abstract 9 / 62] Yes (score: 5)
arXiv:2509.22779 [pdf, ps, other]

Title: Ultra-long Gamma-ray Bursts from Micro-Tidal Disruption Events: The Case of GRB 250702B

Authors: Paz Beniamini, Hagai B. Perets, Jonathan Granot,

Comments: 10 pages, 1 figure. Submitted

Subjects: astro-ph.HE

Created: 2025-12-21; Updated: 2025-12-23; Datestamp: 2025-12-23

Ultra-long GAMMA-RAY BURSTs (ULGRBs), a rare class of high-energy transients with durations $>10^3$s, remain poorly understood. GRB 250702B is notable for its multi-hour prompt emission, an X-ray pre-peak emission starting $\sim$1 day earlier, off-nuclear host position, and hard, rapidly variable gamma-rays. This combination is difficult to explain with standard ULGRB progenitors such as blue-supergiant collapsars, MAGNETar engines, or white-dwarf tidal disruptions by intermediate-mass BLACK HOLEs. We interpret the event as a micro-tidal disruption event ($μ$TDE), where a stellar-mass BLACK HOLE or neutron star partially or fully disrupts a main-sequence star. Three $μ$TDE pathways can reproduce the observed pre-peak emission to main flare delay: (i) a dynamical (partial/repeating) disruption, in which a grazing passage yields a faint precursor and the core returns after $\sim$day for a deeper encounter; (ii) a natal-kick disruption, where the delay reflects the ballistic motion of a newborn compact object relative to its companion, leading to full disruption; and (iii) a hybrid natal-kick + partial case, in which the kick seeds the close encounter but the first passage is only partial, with the core returning on the day-scale period. Cross-section scalings imply comparable rates for partial and full outcomes in both dynamical and natal-kick scenarios. The highly variable, hard $γ$-ray emission supports association with a stellar-mass compact object. Fallback and viscous accretion naturally explain the ultra-long duration, energetics, and ks-scale X-ray variability. We outline observational discriminants between the three channels and argue that $μ$TDEs offer a compelling framework for ULGRBs such as GRB 250702B.

[abstract 10 / 62] Yes (score: 5)
arXiv:2510.02079 [pdf, ps, other]

Title: The very faint X-ray transient SWIFT J174610-290018 at the Galactic center

Authors: Giovanni Stel, Gabriele Ponti, Nathalie Degenaar, Lara Sidoli, Sandro Mereghetti, Kaya Mori, Tong Bao, Giulia Illiano, Samaresh Mondal, Mark Reynolds, Chichuan Jin, Tianying Lian, Shifra Mandel, Simone Scaringi, Shuo Zhang, Grace Sanger-Johnson, Rudy Wijnands, Jon M. Miller, Jamie Kennea, Zhenlin Zhu,

Comments: Accepted for publication in A&A. Minor revisions. Title changed

Subjects: astro-ph.HE

Created: 2025-12-22; Updated: 2025-12-23; Datestamp: 2025-12-23

Very Faint X-ray Transients (VFXTs) are a class of X-ray binary systems that exhibit occasional outbursts with peak X-ray luminosities (L_X< 1e36 erg s^-1) much lower than typical X-ray transients. On 22nd February 2024, during its daily Galactic center monitoring, SWIFT-XRT detected a VFXT, 7 arcmin from Sgr A* dubbing it SWIFT J174610--290018. We aim to characterize the outburst that occurred in 2024, and a second, distinct outburst in 2025, to understand the nature and accretion flow properties of this new VFXT. SWIFT-XRT light curves are used to constrain the duration of the two events. We carried out X-ray spectral analysis exploiting XMM and NUSTAR data. We used Chandra and XMM observations of the last 25 years to constrain the quiescent luminosity of the source. During the 2024 outburst, which lasted about 50 days, the source reached a luminosity in the 2-10 keV band of L_X = 1.2e35 erg s^-1 (assuming it is located at the Galactic center). The 2025 outburst is shorter (about 5 days), and reached L_X = 9e34 erg s^-1. The spectral features of the source include an excess at 6.5-7 keV, which can be associated either with a single reflection line or with the ionized Fe XXV and XXVI lines. The same source was identified in both the XMM and Chandra catalogs of point sources (known as 4XMM J174610.7--290020). During previous detections, the source displayed luminosity levels ranging from L_X= 2e32 to L_X = 3e34 erg s^-1 between 2000 and 2010. Moreover, it exhibited a potential type I X-ray burst in 2004. The analysis of the outbursts and the potential type I burst strongly suggests the neutron star low mass X-ray binary (NS-LMXB) nature of the VFXT. The source can be described by an accretion disk corona (as has been recently proposed by the XRISM/Xtend analysis). This scenario explains the overall low luminosity of this transient and the peculiar iron lines in the spectrum.

[abstract 11 / 62] Yes (score: 5)
arXiv:2512.18323 [pdf, ps, other]

Title: On Lorentz Variability of Magnetically Dominated Relativistic Outflows

Authors: V. I. Berezhiani, N. L. Shatashvili, A. G. Tevzadze,

Comments: 4 pages, 1 figure

Subjects: astro-ph.HE

Created: 2025-12-20; Updated: 2025-12-23; Datestamp: 2025-12-23

In this Letter, we show that MAGNETized RELATIVISTIC outflows can exhibit a RELATIVISTIC effect in which Lorentz transformation maps MAGNETic field topology into apparent temporal variability in the observer's frame. Using a force-free Beltrami configurations as representative equilibria of MAGNETically dominated outflows, we demonstrate that Lorentz mapping of stationary helical MAGNETic field produces quasi-periodic modulation of observable electroMAGNETic signatures, without invoking intrinsic plasma variability. This effect may be described as an aberration of force-free MAGNETic fields under Lorentz transformation. The characteristic frequency of the time variability is determined by the helical wave-number of the MAGNETic field, the viewing angle, and the bulk Lorentz factor of the JET outflow, and scales linearly with $Γ$. This establishes a purely kinematic RELATIVISTIC origin of variability and introduces the concept of MAGNETic Lorentz seismology: the inference of MAGNETic field structure in RELATIVISTIC outflows directly from observed temporal variability.

[abstract 12 / 62] Yes (score: 5)
arXiv:2512.19403 [pdf, ps, other]

Title: Diagnosing the AGN population origin of TeV neutrinos with their spatial correlation

Authors: Xiao-Bin Chen, Ruo-Yu Liu, Xiang-Yu Wang,

Comments:

Subjects: astro-ph.HE

Created: 2025-12-22; Updated: 2025-12-23; Datestamp: 2025-12-23

The recent IceCube detection of TeV neutrinos from some nearby Seyfert galaxy (e.g., NGC~1068) suggests that ACTIVE GALACTIC NUCLEi (AGN) could make a significant contribution to the diffuse flux of astrophysical neutrinos. The absence of TeV gamma-rays from NGC~1068 indicates neutrino production in compact gamma-ray-opaque region. The vicinity of the supermassive BLACK HOLE, such as disk-corona, is an ideal region, where the high radiation density leads to efficient neutrino production as well as the gamma-ray attenuation. Disk-corona models predict that the neutrino emission from AGNs correlates with X-ray emission, which traces the coronal activity. In this paper, we assess whether the X-ray AGN population origin for TeV neutrinos can be tested by using the spatial correlation between the neutrino population and X-ray AGN population with future neutrino telescopes. By performing simulations, we find that, the AGN origin of the neutrino background above 100\,TeV can be tested at a confidence level of $\sim2.4σ$ with five-year observations of IceCube-Gen2, which has an angular resolution of $\sim0.2$ degree. With better angular resolution and sensitivity in the energy range of above $300$\,TeV, a 30-${\rm km^3}$ underwater neutrino telescope, such as High-energy Underwater Neutrino Telescope (HUNT), is expected to reach a significance of $\sim8.6σ$ in testing the association after five years of exposure.

[abstract 13 / 62] Yes (score: 4)
arXiv:2506.07852 [pdf, ps, other]

Title: The link between galaxy merger, radio JET expansion and molecular outflow in the ULIRG IRAS 00183-7111

Authors: Ilaria Ruffa, Marilena Spavone, Enrichetta Iodice, Santiago Garcia-Burillo, Timothy A. Davis, Kazushi Iwasawa, Henrik W. W. Spoon, Rosita Paladino, Michele Perna, Cristian Vignali, Stanislav S. Shabala,

Comments: 18 pages, 11 figures. Accepted for publication in MNRAS

Subjects: astro-ph.GA

Created: 2025-12-22; Updated: 2025-12-23; Datestamp: 2025-12-23

The ultraluminous infrared galaxy (ULIRG) IRAS 00183-7111 ($z=0.328$) is one of the three ULIRGs that are currently known to host an ACTIVE GALACTIC NUCLEus (AGN) with small-scale radio JETs. We present a detailed study of the link between galaxy merger, AGN ignition, radio JET expansion and kpc-scale molecular outflow in IRAS 00183-7111, using high-resolution Atacama Large Millimeter/sub-millimeter Array (ALMA) observations of the $^{12}$CO(1-0) and $^{12}$CO(3-2) lines and very deep $i$-band VLT Survey Telescope (VST) imaging. The latter allows us to put constraints on the assembly history of the system, suggesting that it formed through a major merger between two gas-rich spirals, likely characterised by a prograde encounter and no older than $\approx2$~Gyr. The recent merger channelled about $(1.5\pm0.3)\times10^{10}$~M\textsubscript{$\odot$} of molecular gas in the central regions of the remnant, as traced by the CO detections. The spatial correlation between the CO distribution and the radio core suggests that this gas likely contributed to the ignition of the AGN and thus to the launch of the radio JETs. Furthermore, by comparing the relative strength of the two CO transitions, we find extreme gas excitation (i.e.\,$T_{\rm ex}\gg50$~K) around the radio lobes, supporting the case for a JET-ISM interaction. A qualitative study of the CO kinematics also demonstrates that, despite the overall disturbed dynamical state with no clear signs of regular rotation, at least one non-rotational kinematic component can be identified and likely associated to an outflow with $v_{\rm out}\approx439$~km~s$^{-1}$ and $\dot{M_{\rm out}}\approx 609$~M$_{\odot}$~yr$^{-1}$.

[abstract 14 / 62] Yes (score: 4)
arXiv:2509.14400 [pdf, ps, other]

Title: Electron Inertia and Magnetic Reconnection

Authors: Allen H Boozer,

Comments:

Subjects: physics.plasm-ph astro-ph.SR

Created: 2025-12-19; Updated: 2025-12-23; Datestamp: 2025-12-23

When electron inertia is the only non-ideal effect in the evolution of a MAGNETic field $\vec{B}$, the field lines of $\vec{B}$ RECONNECT, but the lines of a related field $\vec{\mathcal{B}}$ do not. $\vec{\mathcal{B}} \equiv \vec{B} + \vec{\nabla}\times \left( (c/ω_{pe})^2μ_0\vec{j} \right)$ with $ω_{pe}$ the plasma frequency and $\vec{j}$ the current density. The non-RECONNECTing evolution of $\vec{\mathcal{B}}$ was known in systems that depend on only two spatial coordinates. That result is extended to systems that depend on all three spatial coordinates. In three dimensional space, the practical importance of the non-RECONNECTing evolution of $\vec{\mathcal{B}}$ appears limited. When the evolution velocity of $\vec{\mathcal{B}}$ is chaotic, RECONNECTion naturally occurs on a timescale that depends only logarithmically on any non-ideal effect that is diffusive, such as resistivity.

[abstract 15 / 62] Yes (score: 4)
arXiv:2512.17994 [pdf, ps, other]

Title: Diffusive or Ballistic? Distributions and Spectra of PeV Cosmic Rays around MicroQUASARs

Authors: Yutaka Fujita, Rohta Takahashi, Norita Kawanaka,

Comments: 6 pages, 3 figures

Subjects: astro-ph.HE

Created: 2025-12-19; Updated: 2025-12-23; Datestamp: 2025-12-23

In the standard Galactic cosmic-ray (CR) paradigm, protons are accelerated up to ~1 PeV by Galactic sources. While SUPERNOVA remnants (SNRs) have been traditionally considered as the primary accelerators, recent observations by LHAASO and HAWC have detected very-high-energy (VHE) gamma rays exceeding 100 TeV from several microQUASARs, suggesting that these X-ray binaries can accelerate CRs beyond 1 PeV. We investigate the escape process of CRs from microQUASARs, focusing on the energy-dependent transport mechanisms. High-energy CRs are likely to have long mean free paths and move ballistically on scales smaller than their mean free path, while lower-energy CRs undergo diffusive propagation. This transition results in a spectral break in the CR distribution around the microQUASAR. We calculate CR energy spectra within a 10-30 pc radius for various diffusion coefficients and timescales. Our model predicts a spectral break and hardening at E_p ~10-100 TeV when the standard diffusion coefficient for the interstellar space is assumed. However, current VHE gamma-ray observations do not show clear spectral breaks, suggesting that the diffusion coefficient may be significantly reduced near microQUASARs, possibly due to MAGNETic field amplification by CR-driven turbulence.

[abstract 16 / 62] Yes (score: 4)
arXiv:2512.17997 [pdf, ps, other]

Title: Pulsational Instability of Quasi-Stars: Interpreting the Variability of Little Red Dots

Authors: Matteo Cantiello, Jake B. Hassan, Rosalba Perna, Philip J. Armitage, Mitchell C. Begelman, Yan-Fei Jiang, Taeho Ryu, Richard H. D. Townsend,

Comments: 11 pages, 6 figures, submitted to ApJL

Subjects: astro-ph.HE astro-ph.GA astro-ph.SR

Created: 2025-12-19; Updated: 2025-12-23; Datestamp: 2025-12-23

The JWST discovery of "Little Red Dots" (LRDs) has revealed a population of compact, red sources at $z \sim 5-10$ that likely host supermassive BLACK HOLEs (SMBHs). Recent observations of the gravitationally lensed LRD R2211-RX1 reveal century-scale photometric variability and a hysteresis loop in the luminosity-temperature plane, strongly suggesting that the optical emission originates from a pulsating, stellar-like photosphere rather than an accretion disk. This supports the "quasi-star" hypothesis, where a rapidly growing BLACK HOLE seed is embedded within a massive, radiation-pressure supported envelope. In this work, we investigate the stability of these envelopes using the stellar evolution code MESA coupled with the non-adiabatic oscillation code GYRE. We identify a theoretical "Quasi-Star Instability Strip" with a blue edge at $T_{\mathrm{eff}} \approx 5000-5200$ K. Models hotter than this threshold are stable, consistent with the non-variable LRD R2211-RX2 ($T_{\mathrm{eff}} \approx 5000$ K), while cooler models are unstable to radial pulsations driven by the $κ$-mechanism in helium and hydrogen ionization zones. For quasi-star masses in the range $M_\star \sim 10^4-10^5 M_\odot$, we find that the unstable fundamental radial modes ($\ell =0$, n$_{\rm p}=1$) have periods in the range $\sim 20-180$ years. The first overtone ($\ell =0$, n$_{\rm p}=2$) is also unstable or marginally stable in some of our models, with typical pulsation timescales $\sim 10-30$ years. These oscillations match the co-moving frame variability timescale of RX1. We argue that these violent pulsations likely drive enhanced mass loss analogous to super-AGB winds, which could affect the duration of the quasi-star phase and regulate the final mass of the seeded BLACK HOLE.

[abstract 17 / 62] Yes (score: 4)
arXiv:2512.18401 [pdf, ps, other]

Title: Energy-Dependent Shifts of Medium-Scale Anisotropies in Very-High-Energy Cosmic Rays Observed by LHAASO-KM2A

Authors: The LHAASO collabration,

Comments:

Subjects: astro-ph.HE

Created: 2025-12-20; Updated: 2025-12-23; Datestamp: 2025-12-23

Small deviations from isotropy in the arrival directions of Galactic COSMIC RAYs serve as a unique probe of the local MAGNETic environment. In this Letter, we report observations of medium-scale anisotropies (MSA) at energies above 10 TeV using the LHAASO-KM2A array. Our analysis identifies four regions of excess and four regions of deficit, each spanning angular scales of approximately ten degrees. Crucially, we detect significant energy-dependent shifts in the centroids of two excess regions: Region B and the newly identified Region $\mathrm{\widetilde{D}}$. We also characterize the energy evolution of the fractional relative intensity across both excess and deficit regions. These findings imply that the observed anisotropies are shaped by the specific realization of the local turbulent MAGNETic field within the COSMIC RAY scattering length. Such energy-dependent behaviors impose strict constraints on local turbulence models and COSMIC RAY propagation theories.

[abstract 18 / 62] Yes (score: 4)
arXiv:2512.18543 [pdf, ps, other]

Title: Searches for Prompt Low-Frequency Radio Counterparts to Gravitational Wave Event S250206dm with the OVRO-LWA Time Machine

Authors: Nikita Kosogorov, Gregg Hallinan, Casey Law, Jack Hickish, Jayce Dowell, Kunal P. Mooley, Marin M. Anderson, Judd D. Bowman, Ruby Byrne, Morgan Catha, Bin Chen, Xingyao Chen, Sherry Chhabra, Larry D'Addario, Ivey Davis, Katherine Elder, Dale Gary, Charlie Harnach, Greg Hellbourg, Rick Hobbs, David Hodge, Mark Hodges, Yuping Huang, Andrea Isella, Daniel C. Jacobs, Ghislain Kemby, John T. Klinefelter, Matthew Kolopanis, James Lamb, Nivedita Mahesh, Surajit Mondal, Brian O'Donnell, Kathryn Plant, Corey Posner, Travis Powell, Vinand Prayag, Andres Rizo, Andrew Romero-Wolf, Jun Shi, Greg Taylor, Jordan Trim, Mike Virgin, Akshatha Vydula, Sandy Weinreb, Scott White, David Woody, Sijie Yu, Thomas Zentmeyer, Peijin Zhang,

Comments: Accepted for publication in The Astrophysical Journal (ApJ). 19 pages, 6 figures

Subjects: astro-ph.HE

Created: 2025-12-21; Updated: 2025-12-23; Datestamp: 2025-12-23

We report on a search for prompt, low-frequency radio emission from the gravitational-wave (GW) merger S250206dm using the Owens Valley Radio Observatory Long Wavelength Array (OVRO-LWA). Early alerts favored a neutron-star-containing merger, making this a compelling target. Motivated by theoretical predictions of coherent radio bursts from mergers involving a neutron star, we utilized the OVRO-LWA Time Machine system to analyze voltage data recorded around the time of the event. The Time Machine is a two-stage voltage buffer and processing pipeline that continuously buffers raw data from all antennas across the array's nearly full-hemisphere instantaneous field of view, enabling retrospective beamforming, dedispersion, and fast-transient candidate identification. For this event, we analyzed a 30-minute interval beginning 3.5 minutes after the merger, which included two minutes of pre-alert data recovered by the ring buffer. We searched the 50% localization probability region with millisecond time resolution in the 69-86 MHz frequency band. No radio counterpart was detected above a 7-sigma fluence detection threshold of ~150 Jy ms. Using Bayesian analysis, we place a 95% confidence upper limit on the source luminosity of L95 = 4 x 10^41 erg s^-1. These constraints start to probe the bright end of the coherent-emission parameter space predicted by JET-ISM shock processes, MAGNETar and blitzar-like mechanisms, and recent simulation-based scenarios for neutron-star-containing mergers. This study presents the first sensitive, large-area, millisecond-timescale search for prompt low-frequency radio emission from a GW merger with the OVRO-LWA, establishing a framework in which about ten additional events will yield stringent population-level constraints.

[abstract 19 / 62] Yes (score: 4)
arXiv:2512.18786 [pdf, ps, other]

Title: Addendum to "Cygnus~X-3 as a semi-hidden PeVatron'' discussing the LHAASO 2025 data

Authors: M. Kachelriess, E. Lammert,

Comments: 3p addendum to arXiv:2503.11448 [astro-ph.HE]

Subjects: astro-ph.HE

Created: 2025-12-21; Updated: 2025-12-23; Datestamp: 2025-12-23

In a recent work, we have argued that the high-mass X-ray binary Cygnus~X-3 can accelerate COSMIC RAYs (CR) beyond PeV energies. Meanwhile, the LHAASO collaboration published the measurement of an orbitally modulated photon flux from Cygnus~X-3 extending up to 4 PeV. These observations point towards CR acceleration in the JET, and secondary production in CRs scattering on gas from the wind and on stellar UV photons from the companion star. The latter channel leads naturally to a contribution to the photon flux peaking around PeV energies which is orbitally modulated.

[abstract 20 / 62] Yes (score: 4)
arXiv:2512.18839 [pdf, ps, other]

Title: Accretion geometry in neutron star low-mass X-ray binaries during the hard spectral state

Authors: Emmi Meyer-Hofmeister, Yilong Wang, B. F. Liu,

Comments: 8 pages, 5 figures; Accepted for publication in MNRAS

Subjects: astro-ph.HE

Created: 2025-12-21; Updated: 2025-12-23; Datestamp: 2025-12-23

We investigate the accretion geometry in neutron star low-mass X-ray binaries (LMXBs) in the hard spectral state. It is commonly accepted that, for low mass transfer rates, an advection-dominated accretion flow (ADAF) is present in the inner region. But the observed RELATIVISTICally broadened emission lines in the reflection spectra clearly indicate the existence of discs near the innermost stable circular orbit $(R_{\rm{ISCO}})$. We investigate the interaction between the coronal flow and the disc in neutron star LMXBs, and find that gas condensation from the dominant, coronal accretion flow to an inner disc is enhanced as compared to that in BLACK HOLE LMXBs as a consequence of irradiation of the corona by the neutron star surface. Computations show that for low mass transfer rates ($\sim 0.005-0.02$ Eddington rate) a persistent weak disc can coexist with a coronal flow in the innermost region, where a pure ADAF would have been expected. The inner disc extends outwards from $R_{\rm{ISCO}}$ to $\sim 10 R_{\rm{ISCO}}$ for Eddington ratios ($L/L_{\rm{Edd}}$) as low as $\sim 0.002$, covers a larger region for higher Eddington ratios, and eventually connects to the outer disc at $L/L_{\rm{Edd}} \sim 0.02$, thereby transiting to a soft state. We demonstrate that the observationally inferred region of the broad iron lines in the hard-state sources generally lies within the extension of the inner discs predicted by the condensation model. Disappearance of the broad iron lines is predicted at very low luminosities, either caused by very low accretion rates or disc truncation by strong MAGNETic fields.

[abstract 21 / 62] Yes (score: 4)
arXiv:2512.19144 [pdf, ps, other]

Title: Height and Energy Evolution of X-ray Double Sources in a Solar Flare

Authors: Hanya Pan, Astrid M. Veronig, Rui Liu,

Comments: submitted to ApJ

Subjects: astro-ph.SR astro-ph.HE

Created: 2025-12-22; Updated: 2025-12-23; Datestamp: 2025-12-23

In the standard model, MAGNETic RECONNECTion at a vertical current sheet above the flare arcade is key to explaining many aspects of solar eruptions. The supra-arcade region is where the vertical current sheet is supposedly located, and X-ray/EUV emission therein reflects underlying energy release and transport processes, therefore providing valuable insight into the structure and evolution of the current sheet. Previous studies have focused primarily on the impulsive phase of flares, but phenomena in the decay phase are also crucial for understanding the complete flaring scenario. In this paper, we investigated an M6.7-class limb flare that occurred on August 28, 2022, combining observations from the Solar Orbiter (SolO) and Solar Dynamics Observatory (SDO). Coronal X-ray sources are continually observed by the Spectrometer/Telescope for Imaging X-rays (STIX) onboard SolO for over two hours, revealing a multi-phase evolution with varying velocities and multiple substructures, with higher-energy components consistently appearing at higher altitudes. Such a height-energy relation is notably observed in a double coronal source during the decay-phase, which is dominated by thermal emission. The energy distribution of the double source distinguish itself from previous studies that showed a symmetric distribution, with the higher-energy components being closer to the center of the double source during the impulsive phase. Obtained from two opposite side-on perspectives on the supra-arcade region, these findings reveal the spatio-temporal complexity of the energy release process in the post-flare current sheet during the decay phase.

[abstract 22 / 62] Yes (score: 4)
arXiv:2512.19448 [pdf, ps, other]

Title: Confining nonlinear electrodynamics BLACK HOLEs: from thermodynamic phases to high-frequency phenomena with accretion process

Authors: Erdem Sucu, Izzet Sakallı, Orhan Donmez, G. Mustafa,

Comments: 27 pages, 14 figures

Subjects: astro-ph.HE gr-qc

Created: 2025-12-22; Updated: 2025-12-23; Datestamp: 2025-12-23

We investigate a static, spherically symmetric BLACK HOLE solution arising from Einstein gravity coupled to a confining nonlinear electrodynamics model that reproduces Maxwell theory in the strong-field regime while introducing confinement-like corrections at large distances. The resulting metric function is asymptotically Schwarzschild but carries a characteristic Q^3/(9ξ^2 r^4) correction, where $Q$ is the MAGNETic charge and $ξ$ is the nonlinear electrodynamics parameter, with the conventional Reissner-Nordström term Q^2/r^2 absent. We analyze the horizon structure and construct three-dimensional embedding diagrams to visualize spatial geometry. Using the Gauss-Bonnet theorem, we compute the weak-field deflection angle in vacuum, cold plasma, and axion-plasmon media, finding that the nonlinear electroMAGNETic corrections reduce the total bending compared to Schwarzschild at fixed Arnowitt-Deser-Misner mass. The gravitational redshift, Joule-Thomson expansion coefficient, and heat capacity are derived, revealing phase transitions and inversion curves that depend on the model parameters. We obtain closed-form expressions for the photon sphere radius, Lyapunov exponent, and shadow size, demonstrating their sensitivity to Q and $ξ$ along observable Intensities. Fully RELATIVISTIC hydrodynamical simulations of Bondi-Hoyle-Lyttleton accretion show that the confining geometry produces a $\sim 40\%$ enhancement in mass accretion rate relative to Schwarzschild and generates quasi-periodic oscillations with stable 3:2 and 2:1 frequency ratios matching observations from BLACK HOLE X-ray binaries. These results establish the confining nonlinear electrodynamics BLACK HOLE as a testable model that can reproduce high-frequency quasi-periodic oscillation pairs without invoking BLACK HOLE spin.

[abstract 23 / 62] Yes (score: 4)
arXiv:2512.19471 [pdf, ps, other]

Title: Revealing the intricacies of RADIO GALAXies and filaments in the merging galaxy cluster Abell 2255. II. Properties of filaments using multi-frequency radio data

Authors: E. De Rubeis, M. Bondi, A. Botteon, R. J. van Weeren, J. M. G. H. J. de Jong, G. Brunetti, L. Rudnick, M. Brüggen, L. Bruno, E. L. Escott, C. Gheller, L. K. Morabito, K. Rajpurohit, H. J. A. Röttgering,

Comments: 18 pages, 13 figures, proposed for acceptance on Astronomy and Astrophysics

Subjects: astro-ph.CO astro-ph.GA

Created: 2025-12-22; Updated: 2025-12-23; Datestamp: 2025-12-23

In this paper, we aim to further analyze the filaments in Abell 2255 combining LOFAR data with uGMRT (1260 MHz) and VLA (1520 MHz) data to constrain the spectral shape of the filaments. This allows studying their morphological properties, required to understand their origin, at unprecedentedly high resolution (~2.3 kpc), crucial to disentangle the different COSMIC RAY components that populate the Original TRG. We produced a LOFAR-VLBI map at 1.5" resolution using the wide-field technique with 56 hours of observations. This was the first time this technique was used for a galaxy cluster, especially for such deep observations. uGMRT and VLA data have been calibrated and imaged to produce spectral index maps and to apply further techniques to extract additional information, such as the radiative ages of the filaments or their equipartition MAGNETic field. Polarization information was also obtained using VLA through the rotation measure synthesis technique. Thanks to the LOFAR-VLBI wide-field image at 144 MHz, we revealed additional, very steep ($α> 2$) filaments beyond those attached to the RADIO GALAXy, extending for around 250 kpc and previously known as the Trail. Combining LOFAR-VLBI with uGMRT and VLA, we found integrated spectral values between 1.1-1.7 for the filaments. Spectral analysis revealed also that the Original TRG has a complex structure, showing overlapping features with distinct spectral indices that extend throughout its tail. Polarized emission emerges only from the tail and the brightest part of the filaments, with values up to $22\%$. Although there is no clear scenario regarding the formation of filaments, we highlight the importance of the Original TRG as the main driver of such structures, even at larger distances from the core.

[abstract 24 / 62] (score: 3)
arXiv:2501.10509 [pdf, ps, other]

Title: Stellar Stripping and Disruption in Disks around Supermassive Black Hole Binaries: Repeating nuclear transients prior to LISA events

Authors: Daniel J. D'Orazio, Christopher Tiede, Lorenz Zwick, Kimitake Hayasaki, Lucio Mayer,

Comments: Published in ApJ

Subjects: astro-ph.HE astro-ph.CO

Created: 2025-12-22; Updated: 2025-12-23; Datestamp: 2025-12-23

If supermassive BLACK HOLE binaries (SMBHBs) are driven together by gas disks in galactic nuclei, then a surrounding nuclear star cluster or in-situ star-formation should deliver stars to the disk plane. Migration through the circumbinary disk will quickly bring stars to the edge of a low-density cavity cleared by the binary, where the stellar orbit becomes trapped and locked with the binary decay. Here we explore the scenario where the trapped stellar orbit decays with the binary until the binary tidally strips the star in a runaway process. For Sun-like stars, this occurs preferentially for $10^4-10^6 M_{\odot}$ SMBHBs, as the SMBHB enters the LISA band. We estimate that the runaway stripping process will generate Eddington-level X-ray flares repeating on hours-to-days timescales and lasting for decades. The flaring timescales and energetics of these circumbinary-disk tidal-disruption events (CBD-TDEs) match well with the recently discovered Quasi-Periodic Eruptions. However, the inferred rates of the two phenomena are in tension, unless low-mass SMBHB mergers are more common than expected. For less-dense stars, stripping begins earlier in the SMBHB inspiral, has longer repetition times, lasts longer, is dimmer, and can occur for more massive SMBHBs. Whether CBD-TDEs are a known or a yet-undiscovered class of repeating nuclear transients, they could provide a new probe of the elusive SMBH mergers in low mass / dwarf galaxies, which lie in the sweet-spot of the LISA sensitivity.

[abstract 25 / 62] (score: 3)
arXiv:2507.12278 [pdf, ps, other]

Title: Boosted DARK MATTER versus DARK MATTER-induced neutrinos from single and stacked BLAZARs

Authors: Andrea Giovanni De Marchi, Alessandro Granelli, Jacopo Nava, Filippo Sala,

Comments: References added, matches the version published in JHEP

Subjects: hep-ph astro-ph.HE

Created: 2025-12-20; Updated: 2025-12-23; Datestamp: 2025-12-23

The physics responsible for the production of observed high-energy neutrinos have not been established so far, neither for the diffuse astrophysical ones nor for those detected from single BLAZARs. We recently proposed that both could be explained by deep inelastic scatterings between sub-GeV DARK MATTER (DM) around BLAZARs and protons within their JETs. Here, we compute the proton-recoil signals at the neutrino detectors Super-Kamiokande, KamLAND, Borexino, JUNO, Hyper-Kamiokande and DUNE induced by DM that is itself boosted by the scatterings with protons in BLAZAR JETs. We do it for the four cases of vector, axial, scalar and pseudoscalar mediators of DM-QUARK interactions. We perform the analysis for the single BLAZAR TXS 0506+056 and for a sample of more than 300 stacked BLAZARs. We find that searches for such BLAZAR-boosted DM leave room for a variety of DM models to explain observations of high-energy neutrinos. We check that the depletion of the DM spike induced by DM-proton and DM-DM interactions does not compromise the DM interpretation for high-energy neutrinos, but challenges other BLAZAR-DM signals.

[abstract 26 / 62] (score: 3)
arXiv:2509.12352 [pdf, ps, other]

Title: Predicting stellar collision outcomes of main sequence stars

Authors: Pau Amaro Seoane,

Comments: Accepted for publication, A&A

Subjects: astro-ph.GA astro-ph.CO

Created: 2025-12-19; Updated: 2025-12-23; Datestamp: 2025-12-23

Stellar collisions in dense galactic nuclei might play an important role in fueling supermassive BLACK HOLEs (SMBHs) and shaping their environments. The gas released during these collisions can contribute to SMBH accretion, influencing phenomena such as ACTIVE GALACTIC NUCLEi and tidal disruption events of the remnants. We address the challenge of rapidly and accurately predicting the outcomes of stellar collisionsincluding remnant masses and unbound gasacross a broad parameter space of initial conditions. Existing smoothed-particle-hydrodynamic (SPH) simulation techniques, while detailed, are too resource-intensive for exploratory studies or real-time applications. We develop a machine learning framework trained on a dataset of $\sim 16,000$ SPH simulations of main-sequence star collisions. By extracting physically meaningful parameters (e.g., masses, radii, impact parameters, and virial ratios) and employing gradient-boosted regression trees with Huber loss, we create a model that balances accuracy and computational efficiency. The method includes logarithmic transforms to handle dynamic ranges and regularization to ensure physical plausibility. The model achieves predictions of collision outcomes (remnant masses, and unbound mass) with very low mean absolute errors respect to the typical mass scale. It operates in fractions of a second, enabling large-scale parameter studies and real-time applications. Parameter importance analysis reveals that the impact parameter and the relative velocity dominate outcomes, aligning with theoretical expectations. Our approach provides a scalable tool for studying stellar collisions in galactic nuclei. The rapid predictions facilitate investigations into gas supply for SMBH accretion and the cumulative effects of collisions over cosmic time, particularly relevant to address the growth of SMBHs.

[abstract 27 / 62] (score: 3)
arXiv:2509.19763 [pdf, ps, other]

Title: Energy transfer from MHD-scale slow-mode waves to kinetic-scale ion acoustic waves

Authors: Xiaofei Shi, Xin An, Vassilis Angelopoulos,

Comments:

Subjects: physics.plasm-ph

Created: 2025-12-22; Updated: 2025-12-23; Datestamp: 2025-12-23

Large-amplitude slow-mode waves are commonly observed near Earth's MAGNETopause. Recent observations show that these waves can occur simultaneously with kinetic-scale ion acoustic waves. The amplitude of the ion acoustic waves is enhanced near the MAGNETic field peaks of the slow-mode wave, suggesting that the slow-mode waves may drive the generation of ion acoustic waves. To test this hypothesis, we conduct a hybrid simulation using observation-based parameters. The simulation results demonstrate that large-amplitude slow-mode waves generate counter-streaming ion beams, which in turn excite ion acoustic waves and relax the ion beams. Our study reveals a clear energy transfer channel from MHD-scale slow-mode waves to kinetic-scale ion acoustic waves.

[abstract 28 / 62] (score: 3)
arXiv:2510.12620 [pdf, ps, other]

Title: Formation of protostars and the launching of stellar core outflows with moving-mesh radiation non-ideal MAGNETohydrodynamics

Authors: Alexander C. Mayer, Rüdiger Pakmor, Thorsten Naab, Oliver Zier, Alexei V. Ivlev, Tommaso Grassi, Paola Caselli, Volker Springel,

Comments: 16 pages, 12 Figures; accepted, updated for proof

Subjects: astro-ph.SR astro-ph.GA

Created: 2025-12-20; Updated: 2025-12-23; Datestamp: 2025-12-23

We present an implementation of radiative transfer with flux-limited diffusion (FLD) for the moving-mesh code {\small AREPO} and use the method in a physical model for the formation of protostars with non-ideal radiation-MAGNETohydrodynamics (RMHD). We follow previous work in splitting the additional terms to the hydrodynamical equations arising from the inclusion of radiation into terms to be integrated explicitly and implicitly, as the diffusion and coupling terms would impose very restrictive timestep criteria. We validate the scheme with standard test problems for radiation diffusion, matter-gas coupling, and radiative shocks from the literature. Our implementation is compatible with local timestepping, which often presents problems for implicit schemes, and we found very good agreement with results obtained with global timesteps. We present an example application of the new implementation to the collapse of a $1\,{\rm M}_\odot$ molecular cloud core to a second Larson core modelled with radiation non-ideal MAGNETohydrodynamics. A high-velocity JET with v$_{\rm rad}> 10\, {\rm km\,s^{-1}}$ is self-consistently launched from the second core, nested within the first core, which produces a lower-velocity MAGNETorotational outflow. We observe MAGNETic field amplification up to more than $\vert \mathbf{B}\vert_{\rm max}>10^5$ G in the second core, which is surrounded by a small (<0.5 au) disk. This application demonstrates the robustness of our scheme in multi-scale and high-resolution simulations on arbitrary meshes and, as such, the model can be readily used for further simulations of protoSTAR FORMATION at high resolution.

[abstract 29 / 62] (score: 3)
arXiv:2510.27188 [pdf, ps, other]

Title: Magnetically supramassive and hypermassive compact stars

Authors: Koji Uryu, Shijun Yoshida, Eric Gourgoulhon, Charalampos Markakis, Kotaro Fujisawa, Antonios Tsokaros, Keisuke Taniguchi, Mina Zamani, Lambros Boukas,

Comments: 13 pages

Subjects: gr-qc astro-ph.HE

Created: 2025-12-19; Updated: 2025-12-23; Datestamp: 2025-12-23

It is known that the mass of MAGNETized RELATIVISTIC compact star is larger than that of non-MAGNETized one for the same equation of state and central density, albeit the excess of mass is sizable only if the MAGNETic fields are strong enough B~10^17-10^18G. Using our recently developed numerical code COCAL, we systematically compute such compact star solutions in equilibrium associated with mixed poloidal and toroidal MAGNETic fields, and show the MAGNETically supramassive solutions whose masses exceed by more than 10% of the maximum mass of the static and spherically symmetric solutions. For some extremely strong MAGNETic field configurations, we also obtain solutions more massive than the maximum mass of the uniformly rotating solutions at the Kepler (mass-shedding) limit, namely MAGNETically hypermassive solutions.

[abstract 30 / 62] (score: 3)
arXiv:2512.10811 [pdf, ps, other]

Title: Spectroscopic characterization of a remarkable temporally varying, triple-lensed QUASAR at z=2.67

Authors: Charlie Lind-Thomsen, Kasper E. Heintz, Albert Sneppen, Kostas Valeckas, Stefan Geier, Jens-Kristian Krogager, Johan Richard, Johan P. U. Fynbo,

Comments: 9 pages including references. 9 figures. A&A submitted

Subjects: astro-ph.GA astro-ph.CO

Created: 2025-12-21; Updated: 2025-12-23; Datestamp: 2025-12-23

Gravitationally lensed QUASARs are viable cosmic tools for constraining a diversity of fundamental astrophysical phenomena; They enable identification of faint, low-mass supermassive BLACK HOLEs, provide unique constraints on the intervening intergalactic or interstellar medium in their sightlines, and can be used to determine key cosmological quantities such as the Hubble constant, $H_0$. However, they are rare phenomena, and it has proven difficult to define efficient, unbiased selection methods.} In this study, we report the independent spectroscopic identification of a remarkable triple-lensed QUASAR at $z=2.67$, identified based on astrometric measurements from the {\em Gaia} mission, previously identified in Pan-STARRS. Furthermore, a larger spectroscopic follow-up survey of {\em Gaia}-detected candidate lensed QUASARs. We characterize in detail the three mirror images of the QUASAR and their spatial and temporal spectroscopic coverage, with focus on the emission-line properties which shows variation across sigthlines and temporal evolution over the $\sim 11$months spectroscopic campaign. We construct a lens model of the foreground source from a combination of the multiple spectra and deep optical imaging, providing a robust halo mass of $M_{\rm h} = (2.78 \pm 0.05)\times 10^{10}M_\odot$. Based on the lens model, the time delay between each sightline is translated into an intrinsic QUASAR time, allowing us to construct a QUASAR timeseries over $\sim18$months with monthly cadence. Over months timescales the broad emission lines vary in both velocity offset and equivalent width (EW) as well as an overall increase in ionization. This exemplary triple-lensed QUASARs demonstrates the viability of identifying such rare lens configurations based purely on the astrometric measurements from the {\em Gaia} mission, which we here provide optimized selection criteria for, for future studies.

[abstract 31 / 62] (score: 3)
arXiv:2512.16157 [pdf, ps, other]

Title: Understanding pulsar MAGNETospheres with the SKAO

Authors: L. S. Oswald, A. Basu, M. Chakraborty, B. C. Joshi, N. Lewandowska, K. Liu, M. E. Lower, A. Philippov, X. Song, P. Tarafdar, J. van Leeuwen, A. L. Watts, P. Weltevrede, G. Wright, J. Benacek, A. Beri, S. Cao, P. Esposito, F. Jankowski, J. C. Jiang, A. Karastergiou, K. J. Lee, N. Rea, D. Vohl, The SKA Pulsar Science Working Group,

Comments: Published in the Open Journal of Astrophysics

Subjects: astro-ph.HE

Created: 2025-12-18; Updated: 2025-12-23; Datestamp: 2025-12-23

The SKA telescopes will bring unparalleled sensitivity across a broad radio band, a wide field of view across the Southern sky, and the capacity for sub-arraying, all of which make them the ideal instruments for studying the pulsar MAGNETosphere. This paper describes the advances that have been made in pulsar MAGNETosphere physics over the last decade, and details how these have been made possible through the advances of modern radio telescopes, particularly SKA precursors and pathfinders. It explains how the SKA telescopes would transform the field of pulsar MAGNETosphere physics through a combination of large-scale monitoring surveys and in-depth follow-up observations of unique sources and new discoveries. Finally, it describes how the specific observing opportunities available with the AA* and AA4 configurations will achieve the advances necessary to solve the problem of pulsar radio emission physics in the coming years.

[abstract 32 / 62] (score: 3)
arXiv:2512.18421 [pdf, ps, other]

Title: The evolution of obscured AGN across cosmic time -- A large QUASAR survey for the 2040s

Authors: Tanya Urrutia, Darshan Kakkad, Paula Sánchez-Sáez, Mojtaba Raouf, Swayamtrupta Panda, Sarah E. I. Bosman, Francisco Pozo Nunez, Annagrazia Puglisi, Sophia Flury, Dragana Ilic, Andjelka B. Kovacevic, Mamta Pandey-Pommier, Giustina Vietri, Sarath Satheesh-Sheeba, Francesco Salvestrini, Susanna Bisogni, Eduardo Bañados, Ana Monreal Ibero, Sabine Thater, Pratika Dayal, Filippo D'Ammando, José Afonso, Paramita Barai, Valentin Ivanov,

Comments: White paper in response to ESO's "Expanding Horizons" call

Subjects: astro-ph.GA

Created: 2025-12-20; Updated: 2025-12-23; Datestamp: 2025-12-23

We propose a large QUASAR demographic optical multi-object spectroscopic (MOS) survey targeting over 50 million AGN candidates up to the highest redshifts possible in the optical (z~6.5), with repeat visits, using a variety of selection criteria available by 2040. A large MOS survey combining all AGN selection methods is the only way to unify a diverse range of different obscured AGN populations within a single, variability- and spectroscopy-based framework, rather than as disjoint classes selected by different methods.

[abstract 33 / 62] (score: 3)
arXiv:2512.19056 [pdf, ps, other]

Title: On the Diversity of Pulsar's Frequency-Dependent Circular Polarization

Authors: Shunshun Cao, Yanjun Guo, Jinchen Jiang, Kejia Lee, Weiyang Wang, Renxin Xu,

Comments: 16 pages, 9 figures, submitted to ApJL

Subjects: astro-ph.HE

Created: 2025-12-22; Updated: 2025-12-23; Datestamp: 2025-12-23

The nature of coherent radio emission is still challenging even after more than half a century of pulsar discovery, but it is generally a consensus that single-pulse observations are essential for probing the MAGNETospheric dynamics, especially with the largest single-dish telescope FAST (Five-hundred-meter Aperture Spherical radio Telescope). The frequency-dependent circular POLARIZATION of single pulses, with high signal-to-noise ratios, is recorded by the FAST, which shows great diversity, and we are trying an effort to understand such circular POLARIZATION based on the wave mode coupling in the limiting POLARIZATION region, and consequently to constrain the dynamical parameters. By quantitatively comparing models with data using Bayesian analysis, it is found that the plasma multiplicity is approximately between $10^0$ and $10^{2}$, while the Lorentz factor of the particles between $10^{0.5}$ and $10^{2}$. This study presents a systematic framework for integrating pulsar emission theories with observational data.

[abstract 34 / 62] (score: 3)
arXiv:2512.19211 [pdf, ps, other]

Title: Magnetically confined charged particles: From steep density profiles to the breaking of the adiabatic invariant

Authors: Aurélien Cordonnier, Yohann Lebouazda, Xavier Leoncini, Guilhem Dif-Pradalier,

Comments:

Subjects: physics.plasm-ph

Created: 2025-12-22; Updated: 2025-12-23; Datestamp: 2025-12-23

This study examines the stability of Vlasov equilibrium solutions for MAGNETically confined plasmas, derived through the principle of maximum entropy. By treating the toroidal limit as a perturbation from an analytical cylindrical solution, we demonstrate that these equilibria align well with the inviscid MAGNETohydrodynamic (MHD) description. Using the aspect ratio as a perturbation parameter, we compute particle trajectories sampled from the kinetic equilibrium distribution, confirming the overall stability of the solutions. However, under burning plasma conditions, chaotic dynamics emerge for particles with supra-thermal and even thermal energies. This destroys the adiabatic invariance of the MAGNETic moment. The exact consequences are unclear, but they could undermine the foundational assumptions of gyrokinetic modelling in burning plasmas. Nevertheless, these results suggest the possibility of unaccounted transport losses in future burning plasma operations. The interplay between turbulence and energetic particles in the presence of Hamiltonian chaos certainly warrants further investigation.

[abstract 35 / 62] (score: 3)
arXiv:2512.19547 [pdf, ps, other]

Title: Shock-induced MAGNETic RECONNECTion driving Ellerman bomb emission and a spicule

Authors: Mats Ola Sand, Quentin Noraz, Guillaume Aulanier, Juan Martínez-Sykora, Mats Carlsson, Luc Rouppe van der Voort,

Comments: Accepted for publication in A&A. Movies can be found at http://tsih3.uio.no/lapalma/subl/recon_eb_spic/

Subjects: astro-ph.SR

Created: 2025-12-22; Updated: 2025-12-23; Datestamp: 2025-12-23

The mechanism that forms dynamic type II spicules has remained elusive for many years. Their dynamical behaviour has long been linked to MAGNETic RECONNECTion, yet no conclusive evidence has been provided. However, one recent observational study found signs of RECONNECTion, as traced by Ellerman bombs (EBs), at the footpoints of many spicules. The triggering of EBs is generally linked to RECONNECTion due to flux emergence and convective motions in the photosphere. We aim to explore whether we can connect EBs to type II spicules, and to what extent we can use EBs as an observational proxy to probe RECONNECTion in this dynamic. We also aim to provide further insight into the mechanisms that trigger EBs. We used a simulation run with the radiative MAGNETohydrodynamics code Bifrost to track spicules and study the physical processes behind their formation. To detect EBs and classify the spicules, we synthesised the H-alpha line using the multilevel radiative transfer code RH1.5D. We also traced shocks and current sheets to decipher the origin of EBs and spicules. We selected one type II spicule with a strong EB near its footpoint and studied their formation in detail. A MAGNEToacoustic shock advects the MAGNETic field lines towards an oppositely directed ambient field, creating a current sheet. The current sheet accelerates dense plasma via a whiplash effect generated by RECONNECTion into the inclined ambient field, launching the spicule. Several EB profiles trace shock- and MAGNETic-RECONNECTion-induced dynamics during this process at the spicule footpoint. We present a new EB triggering mechanism in which a shock-induced current sheet RECONNECTs, triggering an EB in the lower solar atmosphere. The shock-induced current sheet generates the launch of a type II spicule via RECONNECTion outflows. These results provide a physical origin for the observed connection between EBs and spicules.

[abstract 36 / 62] (score: 2)
arXiv:2501.13681 [pdf, ps, other]

Title: A projection method for particle resampling

Authors: Mark F. Adams, Daniel S. Finn, Matthew G. Knepley, Joseph V. Pusztay,

Comments:

Subjects: physics.plasm-ph physics.comp-ph

Created: 2025-12-19; Updated: 2025-12-23; Datestamp: 2025-12-23

Particle discretizations of partial differential equations are advantageous for high-dimensional kinetic models in phase space due to their better scalability than continuum approaches with respect to dimension. Complex processes collectively referred to as particle noise hamper long time simulations with particle methods. One approach to address this problem is particle mesh adaptivity or remapping, known as particle resampling. This paper introduces a resampling method that projects particles to and from a (finite element) function space. The method is simple; using standard sparse linear algebra and finite element techniques, it can adapt to almost any set of new particle locations and preserves all moments up to the order of polynomial represented exactly by the continuum function space. This work is motivated by the Vlasov-Maxwell-Landau model of MAGNETized plasmas with up to six dimensions, 3X in physical space and 3V in velocity space, and is developed in the context of a 1X + 1V Vlasov-Poisson model of Landau damping with logically regular particle and continuum phase space grids. Stable long time dynamics are demonstrated up to T = 500 and reproducibility artifacts and data with stable dynamics up to T = 1000 are publicly available.

[abstract 37 / 62] (score: 2)
arXiv:2503.08875 [pdf, ps, other]

Title: The effect of split endcaps on the flow dynamics in a tall Taylor-Couette setup

Authors: A. Mishra, P. Personnettaz, G. Mamatsashvili, V. Galindo, F. Stefani,

Comments: 15 pages, 15 figures, 2 Tables, accepted for publication in Physical Review Fluids

Subjects: physics.flu-dyn astro-ph.HE astro-ph.SR

Created: 2025-12-22; Updated: 2025-12-23; Datestamp: 2025-12-23

The effects of axial boundaries, or endcaps are of fundamental interest in many Taylor-Couette (TC) flow experiments. A main challenge in those experiments has been to minimize these effects, which can substantially alter the flow structure compared to the axially unbounded idealized case. Therefore, understanding and disentangling the influence of endcaps on the TC flow dynamics is essential for the unambiguous interpretation of experimental results, particularly when other dynamical processes (instabilities) in TC flows are involved. In this paper, we study the hydrodynamic evolution of a quasi-Keplerian TC flow in the presence of split endcaps for high Reynolds numbers, $Re$, up to $2\times 10^5$, which are larger than those considered in related previous studies. At these $Re$, the flow deviates from the ideal TC flow profile without endcaps, resulting in about $15\%$ deviation in angular velocity at the mid-height of the cylinders. Aside from turbulent fluctuations caused by shearing instability near the endcaps, the bulk flow remains nearly axially independent and exhibits overall Rayleigh-stability. We characterize the scalings of the Ekman and Stewartson layer sizes with $Re$ as well as examine the effect of the ratio of the outer to inner cylinders' angular velocities on the flow. The implications of these findings for ongoing MAGNETorotational instability (MRI) experiments based on the similar axially bounded TC setup are also discussed. Specifically, it is shown that when imposing a constant axial MAGNETic field in all the considered configurations, the flow profile modified by the endcaps lowers the critical threshold for the onset of MRI that in turn can facilitate its emergence and detection in those experiments.

[abstract 38 / 62] (score: 2)
arXiv:2504.12500 [pdf, ps, other]

Title: In situ axion generation and detection in LASER-plasma wakefield interaction

Authors: Xiangyan An, Min Chen, Jianglai Liu, Zhan Bai, Liangliang Ji, Zhengming Sheng, Jie Zhang,

Comments:

Subjects: physics.plasm-ph hep-ph

Created: 2025-12-20; Updated: 2025-12-23; Datestamp: 2025-12-23

We propose a LASER-plasma wakefield interaction based scheme for in situ axion generation and detection through the Primakoff process. Strong electroMAGNETic fields ($\gtrsim 10^{11}$\,V/m) in the wakefield can enhance axion production rates by 2 orders of magnitude compared to conventional light-shining-through-a-wall experiments. By replacing the axion generation stage with LASER-wakefield interaction, the axion-photon coupling constraints can achieve the level of $\gagg \sim 10^{-10}\,\text{GeV}^{-1}$ for axion mass less than 0.1\,meV. Besides, the generated axions can convert back into photons in the background fields, leading to axion-regenerated electroMAGNETic fields (AREM) with unique POLARIZATION, frequency, and transverse modes. This provides a new promising way to search axions by detecting the filtered AREM fields from the background LASER and plasma fields.

[abstract 39 / 62] (score: 2)
arXiv:2505.23731 [pdf, ps, other]

Title: The ambiguous AT2022rze: Changing-look AGN mimicking a SUPERNOVA in a merging galaxy system

Authors: P. J. Pessi, R. Lunnan, J. Sollerman, L. Yan, A. Le Reste, Y. Yao, S. Nordblom, Y. Sharma, M. Gilfanov, R. Sunyaev, S. Schulze, J. Johansson, A. Gangopadhyay, C. Fremling, K. Tristram, M. J. Hayes, C. Fransson, Y. Hu, S. J. Brennan, S. Rose, K. De, K-R. Hinds, C. Liu, A. A. Miller, Y-J. Qin, P. Charalampopoulos, A. Gkini, M. J. Graham, C. P. Gutiérrez, S. Mattila, T. Nagao, I. Pérez-Fournon, F. Poidevin, J. S. Bloom, J. Brugger, T. X. Chen, M. M. Kasliwal, F. J. Masci, J. N. Purdum,

Comments: 18 pages, 13 figures. Published in MNRAS

Subjects: astro-ph.HE

Created: 2025-12-22; Updated: 2025-12-23; Datestamp: 2025-12-23

AT2022rze is a luminous, ambiguous transient located South-East of the geometric center of its host galaxy at redshift z = 0.08. The host appears to be formed by a merging galaxy system. The observed characteristics of AT2022rze are reminiscent of ACTIVE GALACTIC NUCLEi (AGN), tidal disruption events (TDEs), and superluminous SUPERNOVAe (SLSNe). The transient reached a peak absolute magnitude of -20.2 +- 0.2 mag, showing a sharp rise (trise,1/e = 27.5 +- 0.6 days) followed by a slow decline (tdec,1/e = 382.9 +- 0.6). Its bumpy light curve and narrow Balmer lines indicate the presence of gas (and dust). Its light curve shows rather red colors, indicating that the transient could be affected by significant host extinction. The spectra reveal coronal lines, indicative of high-energy (X-ray/UV) emission. Archival data reveal no prior activity at this location, disfavoring a steady-state AGN, although an optical spectrum obtained prior to the transient is consistent with an AGN classification of the host. Based on this, we conclude that the transient most likely represents a Changing-look AGN at the center of the smallest component of the merging system.

[abstract 40 / 62] (score: 2)
arXiv:2509.01664 [pdf, ps, other]

Title: Mysteries of Capotauro: investigating the puzzling nature of an extreme F356W-dropout

Authors: Giovanni Gandolfi, Giulia Rodighiero, Marco Castellano, Adriano Fontana, Paola Santini, Mark Dickinson, Steven Finkelstein, Michele Catone, Antonello Calabrò, Emiliano Merlin, Laura Pentericci, Laura Bisigello, Andrea Grazian, Lorenzo Napolitano, Benedetta Vulcani, Anthony J. Taylor, Pablo Arrabal Haro, Allison Kirkpatrick, Bren E. Backhaus, Benne W. Holwerda, Marika Giulietti, Alessandro Bianchetti, Paolo Cassata, Nikko J. Cleri, Emanuele Daddi, Henry C. Ferguson, Giorgia Girardi, Michaela Hirschmann, Anton M. Koekemoer, Andrea Lapi, Fabio Pacucci, Pablo G. Pérez-González, Alexander de la Vega, Amelia Vietri, Stephen Wilkins, L. Y. Aaron Yung, Micaela Bagley, Rachana Bhatawdekar, Jeyhan Kartaltepe, Casey Papovich, Nor Pirzkal,

Comments: Accepted for publication in A&A

Subjects: astro-ph.GA astro-ph.SR

Created: 2025-12-20; Updated: 2025-12-23; Datestamp: 2025-12-23

JWST has uncovered a diverse population of extreme near-infrared dropouts, including ultra high-redshift ($z>15$) galaxy candidates, dust-obscured galaxies challenging dust production theories, sources with strong Balmer breaks - possibly compact AGN in dense environments - and cold, sub-stellar Galactic objects. This work presents Capotauro, a F356W-dropout in the CEERS survey with F444W AB magnitude of $\sim27.68$ and a sharp $>3$ mag flux drop between $3.5{-}4.5\,μ$m, undetected below $3.5\,μ$m. We combine JWST/NIRCam, MIRI, and NIRSpec/MSA data with HST/ACS and WFC3 observations to perform a spectro-photometric analysis of Capotauro using multiple SED-fitting codes. Our setup tests $z\geq15$ as well as $z<10$ dusty, Balmer-break or strong-line galaxy solutions, and the possibility of Capotauro being a Milky Way sub-stellar object. Among extragalactic options, our analysis favors interpreting the sharp drop as a Lyman break at $z\sim32$, consistent with the epoch of formation of the first stars and BLACK HOLEs, with only $\sim0.5\%$ of the posterior volume at $z<25$. Lower-redshift solutions struggle to reproduce the extreme break, suggesting that if Capotauro lies at $z<10$, it must show a non-standard combination of strong dust attenuation and/or Balmer breaks, making it a peculiar interloper. Alternatively, its properties match a very cold (Y2-Y3 type) brown dwarf or a free-floating exoplanet with a record-breaking combination of low temperature and large distance ($T_{\mathrm{eff}}<300\,\mathrm{K}$, $d\gtrsim130\,\mathrm{pc}$, up to $\sim2\,\mathrm{kpc}$). While current data cannot determine its nature, Capotauro emerges as a remarkably unique object in all plausible scenarios, and a compelling target for follow-up.

[abstract 41 / 62] (score: 2)
arXiv:2509.07100 [pdf, ps, other]

Title: Active galactic nuclei-heated dust revealed in "little red dots"

Authors: I. Delvecchio, E. Daddi, B. Magnelli, D. Elbaz, M. Giavalisco, A. Traina, G. Lanzuisi, H. B. Akins, S. Belli, C. M. Casey, F. Gentile, C. Gruppioni, F. Pozzi, G. Zamorani,

Comments: Published in A&A. 8 pages + Appendix. 4 tables, 6 figures

Subjects: astro-ph.GA

Created: 2025-12-20; Updated: 2025-12-23; Datestamp: 2025-12-23

Little red dots (LRDs) are a puzzling population of extragalactic sources whose origin is highly debated. In this {work}, we performed a comprehensive stacking analysis of NIRCam, MIRI, and ALMA images of a large and homogeneously selected sample of LRDs from multiple JWST Legacy fields. We report clear evidence of hot-dust emission in the median stacked spectral energy distribution (SED) that features a rising near-infrared continuum up to rest-frame $λ_{\rm rest}$$\sim$ 3$μ$m, which is best explained by a standard dusty ACTIVE GALACTIC NUCLEus (AGN) structure. Although LRDs are likely to be a heterogeneous population, our findings suggest that most ($\gtrsim$50 %) LRDs show AGN-heated dust emission, regardless of whether the optical and ultraviolet (UV) continua are stellar or AGN-dominated. In either case, the best-fit dusty-AGN SED, combined with the lack of X-ray detection in the deep Chandra stacks, suggests that Compton-thick ($N_{\rm H}$$>$3$\times$10$^{24}$ cm$^{-2}$) gas obscuration is common, and likely confined within the dust sublimation radius ($R$$_{\rm sub}$$\sim$0.1 pc). Therefore, we argue that AGN-heated dust does not directly obscure either the optical-UV continuum or the broad-line region emission, in order to explain the observed blue UV slopes and prominent Balmer features. While a gas-dust displacement is in line with several models, the formation scenario (in-situ or ex-situ) of this pre-enriched hot dust remains unclear.

[abstract 42 / 62] (score: 2)
arXiv:2509.11631 [pdf, ps, other]

Title: Hurst Index of Gamma-Ray Burst Light Curves and Its Statistical Study

Authors: Ruo-Yu Guan, Feifei Wang, Yuan-Chuan Zou,

Comments: submitted to Journal of Hign Energy Astrophysics

Subjects: astro-ph.HE

Created: 2025-12-22; Updated: 2025-12-23; Datestamp: 2025-12-23

Gamma-ray bursts (GRBs) rank among the most powerful astrophysical phenomena, characterized by complex and highly variable prompt emission light curves that reflect the dynamics of their central engines. In this work, we analyze a sample of 163 long-duration GRBs detected by the Burst and Transient Source Experiment (BATSE), applying detrended fluctuation analysis (DFA) to derive the Hurst index as a quantitative descriptor of temporal correlations in the light curves. We further explore statistical correlations between the Hurst index and 12 other observational parameters through regression and correlation analyses. Our results reveal anti-correlations between the Hurst index and the burst durations (T50, T90), and a negative trend with the low-energy spectral index α. We also find that correlations with peak photon flux are strongest at the shorter timescale (64 ms) and systematically weaken at longer timescales (256-1024 ms), indicating that the persistence of temporal correlations is most evident in the rapid variability component of GRB emission. The results offer new perspectives on the temporal structure of the GRB emission and its potential link to the underlying physical mechanisms driving these bursts.

[abstract 43 / 62] (score: 2)
arXiv:2511.06330 [pdf, ps, other]

Title: Conceptual design of Thomson scattering system with high wavelength resolution in MAGNETically confined plasmas for electron phase-space measurements

Authors: Kentaro Sakai, Kentaro Tomita, Takeo Hoshi, Akito Nakano, Motoshi Goto, Kenichi Nagaoka, Ryo Yasuhara,

Comments: 14 pages, 11 figures, 1 table

Subjects: physics.plasm-ph

Created: 2025-12-20; Updated: 2025-12-23; Datestamp: 2025-12-23

We discuss the conceptual design of a spatially-resolved spectroscopy system of Thomson scattering with high wavelength resolution capable of measuring the shape of electron velocity distribution functions in MAGNETically confined plasmas. We design a spatially-resolved spectrometer with 2560 wavelength channels. The estimated number of scattered photons in a single spectrometer channel is much larger than unity under the experimental setup and plasma parameters of the Compact Helical Device (CHD), indicating sufficient photon statistics for single-shot measurements. Simulations of the scattered spectra show that the signal-to-noise ratio exceeds 5 even under the most unfavorable conditions expected in CHD at full spectral resolution, and further improves with post-processing pixel binning. Bayesian inference applied to the simulated spectra demonstrates that the inferred plasma parameters agree with the input values within the estimated uncertainties. Comparisons between spectra generated from non-Maxwellian electron velocity distribution functions and their Maxwellian fits indicate that deviations from Maxwellian distributions can be identified using the proposed system.

[abstract 44 / 62] (score: 2)
arXiv:2512.11790 [pdf, ps, other]

Title: GLIMPSE-D: An Exotic Balmer-Jump Object at z=6.20? Revisiting Photometric Selection and the Cosmic Abundance of Pop III Galaxies

Authors: Seiji Fujimoto, Yoshihisa Asada, Rohan P. Naidu, John Chisholm, Hakim Atek, Gabriel Brammer, Danielle A. Berg, Daniel Schaerer, Vasily Kokorev, Lukas J. Furtak, Johan Richard, Alessandra Venditti, Volker Bromm, Angela Adamo, Adelaide Claeyssens, Miroslava Dessauges-Zavadsky, Qinyue Fei, Tiger Yu-Yang Hsiao, Damien Korber, Julian B. Munoz, Richard Pan, Alberto Saldana-Lopez,

Comments: 20pages, 16 figures, 4 tables. Submitted to the Open Journal of Astrophysics. Comments and feedback are warmly welcomed!

Subjects: astro-ph.GA astro-ph.CO

Created: 2025-12-20; Updated: 2025-12-23; Datestamp: 2025-12-23

We present deep JWST/NIRSpec G395M spectroscopy of GLIMPSE-16043, a promising $z\sim6$ Pop III candidate originally identified through NIRCam photometry as having weak [OIII]$λ\lambda4959,5007$ emission. Our follow-up reveals clear [OIII] emission, ruling out a genuine zero-metallicity nature. However, the combination of the measured line fluxes and photometry indicates that its spectral energy distribution requires an extraordinarily strong Balmer jump ($-1.66 \pm 0.47$ mag) and H$α$ equivalent width ($3750\pm1800$ Å), features that cannot be reproduced by current stellar+nebular or pure nebular photoionization models. The only models approaching the observations to almost within $1σ$ involve a hot ($T_{\rm eff}\!\simeq\!10^{4.7}$ K) single blackbody embedded in a low-$T_{\rm e}$ nebular environment, suggestive of scenarios such as a tidal-disruption event or a microQUASAR with strong disk winds. This cautions that photometric Pop~III selections are vulnerable to contamination when the rest-frame optical continuum is undetected. Motivated by this, we refine the photometric Pop III selection criteria to exclude the locus of extreme Balmer-jump objects. The revised criteria also recover the recently reported spectroscopic candidate AMORE6, demonstrating that the updated selection preserves sensitivity to genuine Pop III-like sources while removing key contaminants. Applying the refined criteria across legacy survey fields and five newly released CANUCS lensing cluster fields, we revisit the Pop III UV luminosity function and estimate the Pop III cosmic star-formation rate density to be $\approx[10^{-6}$--$10^{-4}]$~$M_{\odot}$~yr$^{-1}$~cMpc$^{-3}$ at $z\simeq6$--7, falling in the range of current theoretical predictions.

[abstract 45 / 62] (score: 2)
arXiv:2512.18052 [pdf, ps, other]

Title: Divertor Detachment Characterization in Negative Triangularity Discharges in DIII-D via 2D Edge-Plasma Transport Modeling

Authors: Menglong Zhao, Filippo Scotti, Thomas Rognlien, Marvin Rensink, Alessandro Marinoni, Dinh Truong, Huiqian Wang, Kathreen Thome, Carlos Paz-Soldan,

Comments:

Subjects: physics.plasm-ph

Created: 2025-12-19; Updated: 2025-12-23; Datestamp: 2025-12-23

Edge fluid modeling of the first divertor-plasma detachment experiments in negative triangularity discharges on DIII-D is presented using the 2D multi-fluid code UEDGE, including cross-field particle drifts. Density scans are performed to reproduce the experimental roll-over of the outer-target ion saturation current and to investigate detachment physics for both forward and reverse toroidal MAGNETic field configurations. Consistent with experiments, the simulations show that approximately 40% higher density is required to reach detachment onset for forward BT compared to reverse BT, and that deep detachment is not achieved for reverse BT. Comparisons with positive triangularity Ohmic discharges further demonstrate that negative triangularity requires substantially higher densities, at or above the Greenwald limit, to access detachment. The modeling indicates that the increased difficulty of achieving detachment in negative triangularity arises from a shorter midplane-to-target connection length, a reduced outer divertor leg length, and lower cross-field transport compared to positive triangularity configurations.

[abstract 46 / 62] (score: 2)
arXiv:2512.18086 [pdf, ps, other]

Title: A recurrent 70-100 minute quasi-periodic pulsation in the intermediate-aged mid-M dwarf GJ 3512

Authors: J. López-Santiago, F. Reale, G. Micela, L. Martino, G. Vázquez-Vilar, J. Miguez,

Comments: Accepted for publication in MNRASL. 5 pages. 5 figures

Subjects: astro-ph.SR

Created: 2025-12-19; Updated: 2025-12-23; Datestamp: 2025-12-23

We report the discovery of a {recurrent} quasi-periodic pulsation (QPP) in the late-M dwarf GJ 3512 (M5.5V) using multiple TESS datasets. A strong signal with a period of 70-100 minutes was detected in wavelet analyses of the two-minute cadence light curve from Sector 20. This signal was detected also in observations from Sectors 47 and 60. The QPP persisted for weeks in sector 20 and spanned nearly three years of TESS coverage. There was no significant damping between major flares. This behavior contrasts with that of previously reported stellar QPPs, which are confined to individual flares and decay on timescales of minutes to hours. The oscillation amplitude is at the milli-magnitude level. A pulsation origin is discarded since theoretical instability strips for 100-minute pulsations are restricted to pre-main sequence stars, while GJ 3512 is an intermediate age (2-8 Gyr) main-sequence dwarf. The persistence across independent TESS sectors discards an instrumental artifact origin and points to a likely coronal origin instead, such as oscillatory RECONNECTion or thermal non-equilibrium cycles in large active regions. This represents the first detection of a likely sustained QPP with these characteristics in a late-type star, highlighting the need for further investigation into physical mechanisms behind such variability.

[abstract 47 / 62] (score: 2)
arXiv:2512.18093 [pdf, ps, other]

Title: New Multi-messenger Probe of Dark Matter-Nucleon Interactions from Ultra-high Energy Cosmic Ray Acceleration

Authors: Stephan A. Meighen-Berger, P. S. Bhupal Dev, Matheus Hostert,

Comments: 7 pages, 4 figures, CETUP 2025-005, Comments are welcome

Subjects: hep-ph astro-ph.HE

Created: 2025-12-19; Updated: 2025-12-23; Datestamp: 2025-12-23

It has been suggested that the density of DARK MATTER (DM) halo can be highly enhanced around supermassive BLACK HOLEs at the centers of massive galaxies. If real, these DM \emph{spikes} would offer new opportunities to probe the properties of DM. In this work, we point out that DM spikes can significantly impact the composition and survivability of ultra-high-energy COSMIC RAYs accelerated near supermassive BLACK HOLEs. A large DM-nucleon cross section would fragment heavy nuclei into lighter elements and prevent them from attaining the energies observed at Earth. While the origin of COSMIC RAYs remains a mystery, we show that if the highest-energy COSMIC RAYs on Earth come from sources like NGC1068, then cross sections of size $σ_{χp} \leq 3 \times 10^{-34} \left( \frac{m_χ}{\mathrm{GeV}}\right)\;\mathrm{cm^{2}}$ would be excluded by COSMIC RAY data. These bounds can be competitive with other existing probes in the DM mass region $m_χ\in [5\;\mathrm{MeV}, 50\;\mathrm{MeV}]$. While the uncertainties on the acceleration mechanism of COSMIC RAYs prevent us from setting robust limits, our study highlights an important connection between DM spikes and COSMIC RAY physics that is complementary to existing cosmological and direct detection constraints.

[abstract 48 / 62] (score: 2)
arXiv:2512.18157 [pdf, ps, other]

Title: Continuous Wide-Field Optical Monitoring for Very Early-Phase Transient Discovery

Authors: Massimo Della Valle, Maria Teresa Botticella, Enrico Cappellaro, Roberto Ragazzoni, Matteo Aliverti, Carmelo Arcidiacono, Lorenzo Amati, Andrea Baruffolo, Maria Grazia Bernardini, Giovanni Boato, Fabrizio Bocchino, Francesco Borsa, Mohamed Yahia Bournane, Enzo Brocato, Giovanni Bruno, Paolo D'Avanzo, Nancy Elias-Rosa, Silvio Di Rosa, Diego Farias, Jacopo Farinato, Davide Greggio, Adriano Ingallinera, Luca Izzo, Marco Limongi, Demetrio Magrin, Marco Marongiu, Andrea Melandri, Giusi Micela, Matteo Murgia, Valerio Nascimbeni, Salvatore Orlando, Antonino Petralia, Vincenzo Petrecca, Maura Pilia, Silvia Piranomonte, Andrea Possenti, Kalyan Radhakrishnan, Oleksandra Rebrysh, Simone Riggi, Irene Salmaso, Giovanni Scandariato, Corrado Trigilio, Simone Zaggia,

Comments: Submitted in response to the call for White Papers for the definition of the ESO next transformational facility. https://next.eso.org/. 6 pages

Subjects: astro-ph.IM

Created: 2025-12-20; Updated: 2025-12-23; Datestamp: 2025-12-23

The study of transient phenomena in a multimessenger context is expected to remain a major pillar of astrophysical discovery in the decades ahead. Supernovae, Kilonovae, Black-Hole formation, Novae, GRBs, and tidal disruption events are prime examples, as their earliest phases link electroMAGNETic radiation to gravitational waves, neutrinos, and high-energy emission. Yet, the physics connecting these messengers unfolds within minutes to hours, while traditional surveys revisit the same region of the sky on the scale of days/weeks, missing when the event begins. Current survey facilities excel at answering what happened and how often, but essentially fail in addressing how it happened and how it couples to gravitational waves, neutrinos, or high-energy emission. Continuous wide-area optical monitoring, as proposed here, removes this limitation. The traditional approach, where a GW or neutrino alert triggers electroMAGNETic follow-up, is now complemented, and sometimes reversed: early electroMAGNETic discoveries can prompt searches for weaker gravitational waves or neutrino signals that would otherwise be missed. In the Einstein Telescope era, wide-field optical monitoring will allow us to find the optical counterparts of gravitational-wave events and understand their physics. At the same time, a telescope capable of continuous monitoring provides immediate scientific value for planetary defense, space-debris tracking, stellar variability, exoplanets transit monitoring, accretion-driven activity, and when we step into a new observational territory, the true discoveries are often the ones we did not expect. In this vision, continuous time-domain astronomy does not replace classical surveys: it completes them by supplying the missing temporal dimension. Follow-up observations remain essential, but they now begin at the physical onset of the event rather than after its evolution is underway.

[abstract 49 / 62] (score: 2)
arXiv:2512.18281 [pdf, ps, other]

Title: Measurements of QUASAR proximity zones with the Lyman-$α$ forest of DESI Y1 QUASARs

Authors: Ryuichiro Hada, Paul Martini, David H. Weinberg, Zheng Zheng, J. Aguilar, S. Ahlen, D. Bianchi, D. Brooks, T. Claybaugh, A. Cuceu, A. de la Macorra, S. Ferraro, A. Font-Ribera, J. E. Forero-Romero, E. Gaztañaga, G. Gutierrez, J. Guy, H. K. Herrera-Alcantar, K. Honscheid, M. Ishak, R. Joyce, D. Kirkby, T. Kisner, A. Kremin, C. Lamman, M. Landriau, L. Le Guillou, A. Meisner, R. Miquel, A. Muñoz-Gutiérrez, N. Palanque-Delabrouille, W. J. Percival, C. Poppett, F. Prada, I. Pérez-Ràfols, G. Rossi, E. Sanchez, D. Schlegel, M. Schubnell, J. Silber, D. Sprayberry, G. Tarlé, B. A. Weaver, H. Zou,

Comments: 21 pages, 7 figures, 1 table; submitted to ApJ

Subjects: astro-ph.GA astro-ph.CO

Created: 2025-12-20; Updated: 2025-12-23; Datestamp: 2025-12-23

The intergalactic medium (IGM) around QUASARs is shaped by their dense environments and by their excess ionizing radiation, forming a "QUASAR proximity zone" whose size and anisotropy depend on the QUASAR's halo mass, luminosity, age, and radiation geometry. Using over 10,000 QUASAR pairs from the Dark Energy Spectroscopic Instrument (DESI) Year 1 data, with projected comoving separations $r_{\perp} < 2\,h^{-1}{\rm Mpc}$, we investigate how the proximity zone of foreground QUASARs at $z\sim2{\rm-}3.5$ affects Lyman-alpha absorption in their background QUASARs. The large DESI sample enables unprecedented precision in measuring this "transverse proximity" effect, allowing a detailed investigation of the signal's dependence on the projected separation of QUASAR pairs and the luminosity of the foreground QUASAR. We find that enhanced gas clustering near QUASARs dominates over their ionizing effect, leading to stronger absorption on neighboring sightlines. Under the assumption that QUASAR ionizing luminosity is isotropic and steady, we infer the IGM overdensity profile in the vicinity of QUASARs, finding overdensities as high as $Δ\sim 10$ at comoving distance $\sim 1\,h^{-1}{\rm Mpc}$ from the most luminous systems. Surprisingly, however, we find no significant dependence of the proximity profile on the luminosity of the foreground QUASAR. This lack of luminosity dependence could reflect a cancellation between higher ionizing flux and higher gas overdensity, or it could indicate that QUASAR emission is highly time variable or anisotropic, so that the observed luminosity does not trace the ionizing flux on nearby sightlines.

[abstract 50 / 62] (score: 2)
arXiv:2512.18565 [pdf, ps, other]

Title: Formation of Be stars via wind accretion: Case study on Black hole + Be star binaries

Authors: Zhenwei Li, Shi Jia, Dandan Wei, Hongwei Ge, Hailiang Chen, Yangyang Zhang, Xuefei Chen, Zhanwen Han,

Comments: 16 pages, 7 figures; accepted for publication in The ApJL

Subjects: astro-ph.SR astro-ph.HE

Created: 2025-12-21; Updated: 2025-12-23; Datestamp: 2025-12-23

Be stars are rapidly rotating main-sequence (MS) stars that play a crucial role in understanding stellar evolution and binary interactions. In this letter, we propose a new formation scenario for BLACK HOLE (BH) + Be star binaries (hereafter BHBe binaries), where the Be star is produced through the Wind Roche Lobe Overflow (WRLOF) mechanism. Our analysis is based on numerical simulations of the WRLOF process in massive binaries, building upon recent theoretical work. We demonstrate that the WRLOF model can efficiently form BHBe binaries under reasonable assumptions on stellar wind velocities. Using rapid binary population synthesis, we estimate the population of such systems in the Milky Way, predicting approximately $\sim$ {1800-3200} currently existing BHBe binaries originating from the WRLOF channel. These systems are characterized by high eccentricities and exceptionally wide orbits, with typical orbital periods exceeding 1000 days and a peak distribution around $\sim$10000 days. Due to their long orbital separations, these BHBe binaries are promising targets for future detection via astrometric {and interferometric} observations.

[abstract 51 / 62] (score: 2)
arXiv:2512.18637 [pdf, ps, other]

Title: A Framework for Lorentz-Dirac Dynamics and Post-Newtonian Interaction of Radiating Point Charges

Authors: Suhani Verma, Siddarth Mediratta, Nanditha Kilari, Prakhar Nigam, Ishaan Singh, Daksh Tamoli, Aakash Palakurthi, Valluru Ishan, Tanmay Golchha, Sanjay Raghav R, Sugapriyan S, Yash Narayan, P Devi, Prathamesh Kapase, G Prudhvi Raj, Lakshya Sachdeva, Shreya Meher, K Nanda Kishore, G Keshav, Jetain Chetan, Rickmoy Samanta,

Comments: 42 pages, 6 figures

Subjects: gr-qc astro-ph.HE hep-th

Created: 2025-12-21; Updated: 2025-12-23; Datestamp: 2025-12-23

We examine classical radiation reaction by combining the covariant Lorentz--Dirac formulation, its Landau--Lifshitz (LL) order reduction, and a post-Newtonian (PN) Hamiltonian treatment of interacting and radiating charges. After reviewing the LL reduction and its removal of runaway and preacceleration behavior, we verify energy balance in several RELATIVISTIC single-particle scenarios by demonstrating agreement between the LL Larmor power and the loss of mechanical energy. We then construct an N-body framework based on the conservative Darwin Hamiltonian supplemented with the leading 1.5PN radiation--reaction term. Numerical simulations of charge-neutral binary systems of both symmetric and asymmetric mass configurations show orbital decay, circularization, and monotonic Hamiltonian decrease consistent with dipole radiative losses. The resulting framework provides a simple analogue of gravitational PN radiation reaction and a tractable system for studying dissipative and potentially chaotic electroMAGNETic dynamics.

[abstract 52 / 62] (score: 2)
arXiv:2512.18657 [pdf, ps, other]

Title: Solar JET-induced perturbation propagating through coronal loops and in-loop electron beam transport indicated by type II and type N radio bursts

Authors: Yingli Cui, Xiangliang Kong, Zhentong Li, Bing Wang, Yadan Duan, Ze Zhong, Hao Ning, Zhao Wu, Manqing Wang, Yang Liu, Feiyu Yu, Zelong Jiang, Wei Chen, Yang Su, Yao Chen,

Comments:

Subjects: astro-ph.SR

Created: 2025-12-21; Updated: 2025-12-23; Datestamp: 2025-12-23

Solar type II radio bursts are commonly attributed to coronal shocks driven by coronal mass ejections (CMEs). However, some metric type II bursts have occasionally been reported to occur in the absence of a CME and to be associated with weak solar activities. This study aims to identify the driver of the coronal shock in this kind of type II event. We investigate a high-frequency metric type II burst with clear band splitting, observed simultaneously by the Chashan Broadband Solar radio spectrograph and the Nançay Radioheliograph. It is associated with a C3.1-class flare and a small-scale JET, but without a detectable CME in the coronagraphs. The type II burst is preceded by multiple type III bursts, one of which exhibits characteristics of a type N burst. The type II burst source is associated with the JET-induced perturbation front propagating through nearby closed loops at a speed of $\sim$880 km s$^{-1}$, rather than the much slower JET front. This suggests that the disturbance initiated by the JET can convert to a shock wave within low Alfvénic coronal loops, providing the necessary conditions for electron acceleration and subsequent radio emission. Our findings offer new insights into the formation mechanism of high-frequency type II bursts associated with weak flares and JETs.

[abstract 53 / 62] (score: 2)
arXiv:2512.18881 [pdf, ps, other]

Title: Optical appearance, Hawking radiation, and Barrow thermodynamics of Letelier BLACK HOLE in electroMAGNETic universe

Authors: İzzet Sakallı, Erdem Sucu, Ahmad Al-Badawi, Faizuddin Ahmed,

Comments: 31 pages, 15 Figures, 8 Tables. Comments are welcome

Subjects: gr-qc astro-ph.HE hep-th

Created: 2025-12-21; Updated: 2025-12-23; Datestamp: 2025-12-23

We present an investigation of a static, spherically symmetric Letelier BLACK HOLE (BH) immersed in an electroMAGNETic universe (EMU), characterized by the cloud of strings (CoS) parameter $α$ and the EMU parameter $a$. The photon sphere and shadow radius are derived analytically, revealing how both parameters modify the apparent BH silhouette compared to the Schwarzschild case. We extend the shadow analysis to homogeneous and inhomogeneous plasma environments, demonstrating systematic reductions in the observed shadow size, and compute the weak gravitational lensing deflection angle in plasma using the Gauss-Bonnet theorem. The perturbative dynamics are investigated for scalar, electroMAGNETic, and Dirac fields, with quasinormal mode frequencies obtained via the sixth-order WKB approximation and greybody factors calculated using the rigorous bounds method. The resulting Hawking radiation spectra reveal distinct signatures for BOSONic and fermionic emission channels. We further analyze quasi-periodic oscillations by deriving the fundamental orbital frequencies and applying both parametric resonance and RELATIVISTIC precession models, obtaining constraints from observations.

[abstract 54 / 62] (score: 2)
arXiv:2512.18941 [pdf, ps, other]

Title: Non-Inductive Current Start-Up Using Multi-Harmonic Electron Cyclotron Wave and Current Ramp-Up Through Combined Electron Cyclotron Wave and Ohmic Heating in EXL-50U Spherical Torus

Authors: Xinchen Jiang, Yuejiang Shi, Yueng-Kay Martin Peng, Shaodong Song, Wenjun Liu, Xianming Song, Xiang Gu, Ji Qi, Dong Guo, Debabrata Banerjee, Lili Dong, Zhenxing Wang, Chunyan Li, Junquan Lin, Pingwei Zheng, Haojie MA, Huasheng Xie, Jiaqi Dong, Qingwei Yang, Yunfeng Liang, Baoshan Yuan, Xianmei Zhang, Minsheng Liu, EXL-50U team,

Comments:

Subjects: physics.plasm-ph

Created: 2025-12-22; Updated: 2025-12-23; Datestamp: 2025-12-23

The non-inductive current start-up by multi-harmonic electron cyclotron wave has been systematically investigated in the EXL-50U spherical torus. Significant enhancements of the driven current with increasing number of resonance layers have been demonstrated by variation of the number of harmonic resonance layers of the ECW through adjustment of the MAGNETic field or plasma cross section. The critical role of multi-harmonic ECW in enhancing the driven current has been experimentally verified for the first time. To explain the related experimental observations, a physical mechanism involving multi-harmonic heating, multiple reflections, and multi-pass absorption - leading to the generation of high-energy electrons via X-mode wave or electron Bernstein wave has been proposed. The current drive capacity of the first harmonic extraordinary mode of the ECW has also been experimentally confirmed for the first time. After the application of Ohmic heating during the current ramp-up phase, the current drive efficiency of ECW is further enhanced. Leveraging the synergistic effect between ECW and Ohmic heating, EXL-50U achieved a plasma current of 1 MA, with the non-inductively driven current fraction reaching 70%.

[abstract 55 / 62] (score: 2)
arXiv:2512.18992 [pdf, ps, other]

Title: Fragmenting Filaments and Evolving Cores -- Insights from Dust Polarisation Study of a filament in Northern Orion B

Authors: Kshitiz K. Mallick, Doris Arzoumanian, Satoko Takahashi, Ray S. Furuya, Yoshiaki Misugi, Yoshito Shimajiri, Kate Pattle, Shu-ichiro Inutsuka,

Comments: 28 pages, 12 figures, Accepted in The Astrophysical Journal (ApJ)

Subjects: astro-ph.GA

Created: 2025-12-22; Updated: 2025-12-23; Datestamp: 2025-12-23

We present an analysis of polarised dust emission at 850 micron for a parsec long filament in the northern part of the Orion B molecular cloud. The region was observed by the JCMT SCUBA-2/POL-2 polarimeter. The filament has a line mass (~80 Msun/pc) larger than the critical (MAGNETic) line mass (~37 Msun/pc); and hosts one starless, three prestellar, and four protostellar cores, with masses in the range 0.13 to 9.13 Msun. The mean (debiased) polarisation fraction of the filament and core pixels was calculated to be 5.3+/-0.3% and 3.2+/-0.3%, respectively, likely reflecting their distinct physical conditions. The polarisation fraction for the cores does not depend on the type of core, and was found to decrease with increasing column density, varying from 6-11% at the filament edges to 1$^{+0.7}_{-0.1}$% in the denser parts ($N_{H2}\gtrsim$2x10$^{22}$cm$^{-2}$). Magnetic field orientation of the protostellar cores, in contrast to prestellar cores, appears to be relatively aligned with the MAGNETic field orientation of the local filament in this region. Using the Davis-Chandrasekhar-FERMI formalism the plane-of-sky MAGNETic field strength for the protostellar cores (~39-110 microG) was found to be higher than that of the prestellar cores (~22-61 microG); and weakest for the starless core (~6 microG). The average value for the filament was found to be ~31 microG. The MAGNETic field-volume density relation for the prestellar/starless cores and protostellar cores suggests a transition from weak field case to strong field case as the cores evolve from prestellar to protostellar phase.

[abstract 56 / 62] (score: 2)
arXiv:2512.19073 [pdf, ps, other]

Title: Measurement of inclusive diJET cross-sections in proton-proton collisions at $\sqrt{s} = 13$ TeV with the ATLAS detector

Authors: ATLAS Collaboration,

Comments: 51 pages in total, author list starting page 34, 14 figures, 3 tables, submitted to EPJ C. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2021-18

Subjects: hep-ex

Created: 2025-12-22; Updated: 2025-12-23; Datestamp: 2025-12-23

Inclusive diJET cross-sections have been measured in proton-proton collisions at a centre-of-mass energy of 13 TeV using data with an integrated luminosity of 140 fb$^{-1}$, recorded by the ATLAS detector at the Large Hadron Collider during 2015-2018. Jets are identified using the anti-$k_{t}$ algorithm with a radius parameter of $R = 0.4$. The inclusive diJET double-differential cross-sections are measured first as a function of the invariant diJET mass and the half absolute rapidity separation between the two leading JETs, $(m_{\mathrm{jj}}$, $y^{\ast})$, and second as a function of the invariant diJET mass and the total longitudinal boost of the diJET system, $(m_{\mathrm{jj}}$, $y_{\mathrm{boost}})$. The measured diJET system covers the invariant mass range from 240 GeV to almost 10 TeV, with diJET separation $y^{\ast} < 3.0$ and diJET boost $y_{\mathrm{boost}} < 3.0$. The results are unfolded to the particle level and compared with state-of-the-art next-to-next-to-leading-order full colour perturbative QCD calculations, corrected for non-perturbative and electroweak effects.

[abstract 57 / 62] (score: 2)
arXiv:2512.19218 [pdf, ps, other]

Title: Multi-wavelength study of the pre-eruption dip in the recurrent nova T Coronae Borealis preceding imminent nova eruption

Authors: Songpeng Pei, Xiaowan Zhang, Renzhi Su, Yongzhi Cai, Ziwei Ou, Qiang Li, Xiaoqin Ren, Taozhi Yang, Mingyue Li,

Comments: 12 pages, 4 figures. Accepted by Astronomy and Astrophysics

Subjects: astro-ph.HE astro-ph.SR

Created: 2025-12-22; Updated: 2025-12-23; Datestamp: 2025-12-23

We present a multi-wavelength study of the symbiotic recurrent nova (RN) T Coronae Borealis (T CrB) using SWIFT Burst Alert Telescope (BAT) / X-Ray Telescope (XRT) / UltraViolet Optical Telescope (UVOT) and American Association of Variable Stars Observers (AAVSO) observations from 2005 to 2025. Our analysis spans quiescent, high, and pre-eruption dip states. We find that brightening amplitudes increase toward shorter wavelengths in both optical and UV bands, while the UV and X-ray fluxes are generally anti-correlated throughout all phases. During the 2023-2024 pre-eruption dip, soft and hard X-rays increased as optical and ultraviolet (UV) brightness declined, consistent with a transition from an optically thick to thin boundary layer driven by a reduction in the accretion rate. We also report, for the first time, a second, lower-amplitude dip occurring between September 2024 and February 2025 following the primary 2023-2024 pre-eruption dip. The observed variability supports an accretion-variation scenario as a unifying explanation for both the high and dip states, and may signal an imminent nova eruption.

[abstract 58 / 62] (score: 2)
arXiv:2512.19236 [pdf, ps, other]

Title: Dynamically close galaxy pairs from the unWISE survey: Testing the merger-AGN-STAR FORMATION connection

Authors: Josephine Chishala, Roberto De Propris, Mirjana Pović,

Comments: 20 Figures, 8 Tables, accepted for publication in A&A

Subjects: astro-ph.GA

Created: 2025-12-22; Updated: 2025-12-23; Datestamp: 2025-12-23

Galaxy mergers are expected to have a profound influence on the STAR FORMATION histories of galaxies. It is generally expected that mergers are the main drivers of galaxy mass growth through the accretion of mass and the triggering of new STAR FORMATION episodes, while the shocks and torques induced by the merger may drive gas and dust to central supermassive BLACK HOLEs and fuel ACTIVE GALACTIC NUCLEi (AGN) activity and producing both positive and negative feedback. We test whether a merger-AGN-STAR FORMATION connection exists by selecting samples of galaxy pairs of stellar masses log(M/Msun) approximately 10.2 and 11.4 within the redshift of 0.25 at various projected separation and velocity differences in an increasing order, and therefore having a decreasing probability of being truly bound and interacting. We identify galaxies in close pairs and then measure their STAR FORMATION rates (SFRs) (via their NUV - r colours) and the degree of AGN activity (from X-rays, radio emission at 20cm, WISE infrared colours, and emission line ratios) as a function of their projected separation and velocity difference. We find only weak evidence that galaxies in pairs have higher SFRs as galaxies become closer in projected and velocity separation, except possibly for pairs at closest separation of less than 20 kpc and velocity difference less than 500 km/s. Similarly, we see no strong evidence that AGN are more common for galaxies in closer pairs, irrespective of the method used to detect AGN. For this sample, we do not find any clear evidence that mergers and interactions may play a significant role in triggering STAR FORMATION and AGN activity, opposite to expectations from theoretical models invoking feedback episodes. Secular processes may be more important, although this may depend on the selection of galaxies and indicators for STAR FORMATION and AGN activity.

[abstract 59 / 62] (score: 2)
arXiv:2512.19241 [pdf, ps, other]

Title: Formation of external particle JETs on a spherical particle bed subjected to strong explosive loading

Authors: Yifeng He, Junsheng Zeng, Baolin Tian, Yue Yang,

Comments:

Subjects: physics.flu-dyn

Created: 2025-12-22; Updated: 2025-12-23; Datestamp: 2025-12-23

We report the mechanism for the formation of external particle JETs on a spherical particle bed subjected to strong explosive loading, revealing a critical dependence on particle size. Under strong explosive loading, the formation of external particle JETs is primarily driven by a drag-coupled mechanism. We conducted Eulerian-Lagrangian simulations, with up to $2048^3$ effective cells and $1.8$ million tracked parcels on an adaptive mesh, for both small- and large-particle cases. Pronounced JETs are observed only with small particles, alongside accelerated bed thickening. By defining characteristic inner and outer radii, the particle bed thickness evolution is quantified, showing an initial linear growth followed by a nonlinear deceleration. Particle dynamics analysis indicates that drag force dominates particle motion and JET formation during the nonlinear stage. The initial angular non-uniformity of the particle bed induces a non-uniform gas radial velocity. Through drag coupling, this flow asymmetry generates a radial velocity difference in small particles, thereby promoting pronounced JET formation, whereas large particles resist this drag-induced effect. The greater drag-induced deceleration on smaller particles leads to an increased velocity difference across the particle bed, explaining the accelerated thickening. A characteristic radius model that integrates the Gurney model for the linear stage with a drag-dominated deceleration model for the nonlinear stage is established and shows good agreement with numerical results across different particle sizes.

[abstract 60 / 62] (score: 2)
arXiv:2512.19377 [pdf, ps, other]

Title: Critical phenomenon inside asymptotically flat BLACK HOLEs with spontaneous scalarization

Authors: Li Li, Ze Sun, Fu-Guo Yang,

Comments: 10 pages, 16 figures

Subjects: gr-qc

Created: 2025-12-22; Updated: 2025-12-23; Datestamp: 2025-12-23

We study the interior dynamics of spontaneously scalarized BLACK HOLEs in Einstein-Maxwell-Scalar theory with zero cosmological constant, revealing novel critical phenomena. We demonstrate that, for a wide range of scalar-electroMAGNETic couplings, scalarized BLACK HOLEs possess no smooth inner Cauchy horizon and instead evolve into a spacelike Kasner singularity. The scalar hair triggers a rapid collapse of the Einstein-Rosen bridge at the would-be Cauchy horizon. Near the critical point where scalarized BLACK HOLEs bifurcate from the Reissner-Nordstrom solution, we establish a robust scaling relation between the Kasner parameter and the charge-to-mass ratio of the hairy BLACK HOLE, opening a new window into the remarkable simplicity underlying BLACK HOLE interiors.

[abstract 61 / 62] (score: 2)
arXiv:2512.19474 [pdf, ps, other]

Title: Low-redshift 3D Lyman-α Forest Correlations with China Space Station Telescope

Authors: Ting Tan, Huanyuan Shan, Eric Armengaud,

Comments:

Subjects: astro-ph.CO

Created: 2025-12-22; Updated: 2025-12-23; Datestamp: 2025-12-23

While the Lyman-$α$ (Ly$α$) forest traces the large-scale matter distribution over a wide range of redshift, its three-dimensional (3D) clustering at $z < 2$ has not yet been measured. We investigate the prospects for measuring low-redshift Ly$α$ correlations with the UV slitless spectroscopic instrument of the China Space Station Telescope (CSST). We construct mock CSST QUASAR spectra that reproduce the expected survey depth, spectral resolution and noise properties, and derive Ly$α$ auto-correlation functions and cross-correlations with QUASARs (QSO) and emission-line galaxies (ELG) in the range $1.1 < z < 2.0$. We then interpret these three-dimensional correlation functions with a standard anisotropic redshift-space clustering model and obtain forecast constraints on the Ly$α$ and tracer parameters. At an effective redshift $z_{\rm eff}=1.59$ (1.58 for ELGs), the Ly$α$ bias parameters will be measured with a 10-30\% precision, depending on priors on other tracer's biases. We also forecast a marginal $2.5σ$ ($3.7σ$) detection of the BAO feature, corresponding to a $\sim$10\% (7\%) constraint on the isotropic BAO scale, from the combination of Ly$α$ auto- and Ly$α$-QSO (ELG) cross-correlations. These results show that CSST can provide the first three-dimensional characterization of the low-redshift Ly$α$ forest and a complementary Ly$α$-based BAO measurement at $z < 2$, helping to link galaxy clustering surveys with high-redshift Ly$α$ forest studies.

[abstract 62 / 62] (score: 2)
arXiv:2512.19603 [pdf, ps, other]

Title: Probing Dark Sectors with Exploding Black Holes: Gamma Rays

Authors: Michael J. Baker, Joaquim Iguaz Juan, Aidan Symons, Andrea Thamm,

Comments: 34 pages, 13 figures and 1 table

Subjects: hep-ph astro-ph.CO astro-ph.HE

Created: 2025-12-22; Updated: 2025-12-23; Datestamp: 2025-12-23

The Hawking radiation from the explosion of a BLACK HOLE would provide definitive information on the particle spectrum of nature. Here we quantify the potential of current and future gamma ray telescopes to probe new dark sectors. We improve on the analysis used in previous work by making careful use of the experimental response functions, deriving a more realistic estimate of the backgrounds and optimizing the statistical analysis. We compute the sensitivity of the current experiments (HAWC and LHAASO) and estimate the reach of the future experiments (SWGO and CTA North and South), for various sky positions of the explosion. We find that for a BLACK HOLE exploding at $0.01\,\text{pc}$ the gamma ray signal observed by HAWC could probe dark sectors with 10-20 (or more) new Dirac fermions up to masses around $10^5\,\text{GeV}$, while CTA will be able to probe 2-15 new Dirac fermions with masses up to $10^6\,\text{GeV}$. CTA North and South will have sensitivity to 10 dark fermions up to a distance of 0.1 pc and 50 up to a distance of 0.6 pc.