Current date: 2026-09-10
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Number of records retrieved: 847
Keyword score statistics
score 11 -- 1 abstracts
score 8 -- 1 abstracts
score 7 -- 2 abstracts
score 6 -- 3 abstracts
score 5 -- 1 abstracts
score 4 -- 7 abstracts
score 3 -- 11 abstracts
score 2 -- 21 abstracts
in total -- 47 abstracts
Articles that appeared on 2026-09-10
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[abstract 1 / 47] Wow! (score: 11)
- Title: First Detection of Radio Polarization During Jet Formation in the Changing-Look AGN 1ES 1927+654Authors: Onic I. Shuvo, Eileen T. Meyer, Sibasish Laha, Agniva Roychowdhury, Dev R. Sadaula, Tracy E. Clarke, Wendy M. Peters, Mitchell C. Begelman, Markos Georganopoulos, Rostom Mbarek, Amelia M. Hankla, Alexander Philippov, Navin Sridhar,Comments: 22 pages, 10 figures, 2 tables. Submitted to ApJSubjects: astro-ph.HE astro-ph.GACreated: 2026-09-08; Updated: 2026-09-10; Datestamp: 2026-09-10
We present a multiwavelength radio study of the changing-look AGN 1ES 1927+654 following its renewed X-ray brightening since mid-2022, combining VLBA imaging with multi-band and time-resolved VLA observations. Our main results are: (i) VLBA observations continue to reveal the bipolar JET structure first reported in Meyer et al. (2025), with new X-band detections confirming the morphology at larger separation and K-band imaging revealing a bridge of emission consistent with a continuous outflow; (ii) the VLBA core exhibits a GHz-peaked spectrum, and VLA/VLITE observations from 340 MHz to 45 GHz show emission from an inhomogeneous SYNCHROTRON source, self-absorbed below ~3 GHz and optically thin above; (iii) VLA and VLBA flux densities are consistent above 8 GHz, indicating emission dominated by a compact core; (iv) linear POLARIZATION is detected above ~3 GHz, with fractional POLARIZATION increasing with frequency from ~0.2% to ~6% and EVPAs exhibiting non-linear lambda^2 behavior; (v) long-term VLA X-band monitoring reveals a large, smooth rotation of the EVPA of ~137 degrees over ~81 days in 2026, followed by a partial return, at stable total intensity and suppressed fractional POLARIZATION <~1.4%, consistent with a propagating disturbance crossing the compact emitting region; and (vi) circular POLARIZATION is not detected at any epoch. These observations demonstrate that 1ES 1927+654 has transitioned from an X-ray-dominated, non-JETted state to a radio-loud AGN (Laha et al. 2025) hosting a newly launched RELATIVISTIC JET, a unique laboratory for studying JET birth and early MAGNETic field evolution.
[abstract 2 / 47] Wow! (score: 8) - Title: Hadronic origin of gamma rays and neutrinos from BLAZARs: Multi-messenger implications and observational constraintsAuthors: Rodrigo Sasse, Rita de Cássia dos Anjos,Comments: 17 pages, 5 figuresSubjects: astro-ph.HECreated: 2026-09-09; Updated: 2026-09-10; Datestamp: 2026-09-10
We investigate whether cosmogenic gamma rays and neutrinos from ultra-high-energy COSMIC RAYs (UHECRs) produced in hadronically active BLAZARs can significantly contribute to the observed spectral energy distribution (SED), and examine the potential of the Cherenkov Telescope Array Observatory (CTAO) to detect and discriminate this component. For four nearest neutrino bright BLAZARs modeled by Rodrigues (2024), specifically AP Librae, TXS 1700+685, PKS 2326$-$502, and PKS 2345$-$16, we constrain the UHECR luminosity by requiring that the total emission does not overshoot available multi-wavelength data, assuming acceleration in the optically thin large scale JET, propagate UHECRs through realistic Galactic and extragalactic MAGNETic fields, and forecast CTAO performance. We find that cosmogenic gamma rays contribute up to about 7.5% of the total gamma-ray emission at the highest energies ($10^{20}$ eV), and thus remain subdominant in the SED. In contrast, the associated neutrino emission, at approximately $10^{44}$ to $10^{46}$ erg s$^{-1}$, offers a robust propagation signature of hadronic acceleration. Our simulations of 50 hour CTAO exposures show that the observatory can accurately reconstruct the intrinsic gamma ray spectrum, enabling strong constraints on the hadronic origin and propagation of UHECRs. These results demonstrate the power of combining CTAO gamma-ray measurements with neutrino observations to probe BLAZAR hadronic processes.
[abstract 3 / 47] Wow! (score: 7) - Title: Accretion, Jets, and Recoil in a Merging Supermassive Black Hole Binary: A Prompt ElectroMAGNETic Postmerger Counterpart for LISAAuthors: Maria Chiara de Simone, Manuela Campanelli, Lorenzo Ennoggi, Carlos O. Lousto, Yosef Zlochower,Comments: 12 pages, 6 figuresSubjects: astro-ph.GA astro-ph.HE gr-qcCreated: 2026-09-09; Updated: 2026-09-10; Datestamp: 2026-09-10
We report the first three-dimensional general RELATIVISTIC MAGNETohydrodynamic simulation to follow, self-consistently in a dynamical spacetime, the MAGNETized gas around a misaligned-spin supermassive binary BLACK HOLE, from late inspiral through merger to the gravitational-wave recoil of the remnant. The equal-mass binary, in a $\textit{hang-up kick}$ configuration, is embedded in an equilibrated circumbinary disk (CBD), relaxed for 165 binary orbits before we evolve the final $\sim\!40$ orbits. During the inspiral, each BLACK HOLE hosts a strongly warped minidisk whose JET follows the local spin axis near the horizon before aligning with the binary's angular momentum farther out. The merger imparts a recoil of $\simeq\!1032$ $km\,s$$^{-1}$ to the remnant, which nonetheless retains its gravitationally bound CBD, and the relaunched JET preserves its pre-merger orientation. The bolometric luminosity brightens by a factor $\sim\!2.2$, powered by merger-driven shocks concentrated within $r \lesssim 15\,M$, and the enhancement persists through the recoil. We identify a distinctive postmerger electroMAGNETic signature: MAGNETized structures, generated at coalescence, drive correlated quasi-periodic modulations of the horizon MAGNETic flux, the Poynting flux, and the thermal output, decoupled from the accretion rate. The postmerger radiative efficiency $L_{\rm EM}/\dot{M}c^2$ rises by a factor $\simeq 2.6$ at nearly constant accretion rate, showing that this emission is powered by the merger rather than accretion. The transient turns on within minutes and lasts at least several hours for a $10^6 \ M_{\odot}$ LISA source, establishing recoiling remnants as prompt postmerger counterparts to massive BLACK HOLE mergers and a first-principles framework for interpreting candidates such as 3C186.
[abstract 4 / 47] Wow! (score: 7) - Title: The Evolution of Thermal and Non-thermal Emission Components in GRB 250920CAuthors: Jia-Ming Chen, Ke-Rui Zhu, Shan Chang, Dan Zhu, Yu-Lu Gong, Zhao-Yang Peng, Yong-Gang Zheng, Li Zhang,Comments: 31 pages, 12 figures,accepted for publication in RAASubjects: astro-ph.HECreated: 2026-09-09; Updated: 2026-09-10; Datestamp: 2026-09-10
We present a temporal and time-resolved spectral analysis of GRB 250920C using \textit{FERMI}/GBM and \textit{SWIFT}/BAT data. The prompt emission consists of two distinct episodes, EI and EII, separated by a significant quiescent interval. We perform Bayesian spectral fitting with empirical, thermal, composite, and physical SYNCHROTRON models. In EI, the spectra show clear evidence for an additional thermal component. The BB+PL model is preferred in most bright time bins, and joint \textit{FERMI}/GBM+\textit{SWIFT}/BAT fits further support the presence of this component. The blackbody temperature generally decreases with time, the blackbody flux follows the pulse profile, and the thermal flux fraction remains high. Fireball-parameter estimates give a photospheric Lorentz factor of a few hundred and an initial radius of $r_{0}\sim10^{9}$--$10^{10}$ cm, with $1+σ_{0}$ of order unity and $η\gg1$, supporting a thermally dominated baryonic outflow. In contrast, EII is dominated by non-thermal emission. Its low-energy photon indices do not significantly exceed the SYNCHROTRON line of death, and the spectra are well described by fast-cooling SYNCHROTRON radiation in a decaying MAGNETic field. The MAGNETization constraint gives $σ_{\min}\sim1.1$--$4.3$. Since these values exceed unity, they suggest that EII may be Poynting-flux dominated. These results therefore suggest a possible transition in GRB 250920C from a fireball-dominated EI phase to a Poynting-flux-dominated EII phase.
[abstract 5 / 47] Yes (score: 6) - Title: 1LHAASO J1852+0050u: GeV-100TeV Gamma-ray emission Powered by Star-forming Region?Authors: The LHAASO Collaboration,Comments: Accepted for publication in MNRAS. 14 pages. 7 figures & 5 tables includedSubjects: astro-ph.HE astro-ph.SRCreated: 2026-09-09; Updated: 2026-09-10; Datestamp: 2026-09-10
Star-forming regions (SFRs), including HII regions, have recently attracted significant attention as potential sites of particle acceleration capable of producing PeV COSMIC RAYs, i.e. as potential Galactic PeVatrons. Yet, SFRs known as candidate PeVatrons are still very rare. Here we report a highly likely physical association between the UHE gamma-ray source 1LHAASO J1852+0050u and coincident star-forming regions. Using $\sim$4 years of LHAASO data, the extended source 1LHAASO J1852+0050u (called J1852 in this study) was reanalyzed with a significance of $\sim$13$σ$ and 39%-containment radius of 0.35$°$. This extended source projectively covers dozens of HII regions and an energetic pulsar PSR J1853+0056. We reanalyzed $\sim$16 years of FERMI-LAT data and found a GeV source (named SrcAG) coincident with the LHAASO source J1852. The CO-line observation shows a molecular clump which coincides with the gamma-ray sources and is related with the ultra-compact HII region G34.26+0.15 at the distance of $\sim$3.3 kpc. Fitting to the spectral energy distribution indicates that PSR J1853+0056 cannot afford the observed gamma-ray flux either for J1852 or SrcAG. Although the contribution from hidden pulsars to the gamma-ray emission could not be excluded, it is most likely that the GeV-100TeV gamma-ray emission is dominantly powered by SFR through p-p hadronic interaction between the protons accelerated in the SFR and MCs: the GeV emission is ascribed to the protons accelerated by protostars' activities, while the TeV emission ascribed to the protons accelerated by massive stars in the SFR.
[abstract 6 / 47] Yes (score: 6) - Title: Search for refractive substructure in ACTIVE GALACTIC NUCLEi using ground-based VLBI observationsAuthors: Tatiana A. Koryukova, Alexander V. Plavin, Alexander B. Pushkarev, Yuri Y. Kovalev,Comments: 11 pages, 6 figures, 3 tables; Submitted to MNRASSubjects: astro-ph.HE astro-ph.GACreated: 2026-09-09; Updated: 2026-09-10; Datestamp: 2026-09-10
We present the results of the first systematic search for refractive scattering substructure in ACTIVE GALACTIC NUCLEi (AGN) using ground-based very long baseline interferometry (VLBI) data. We selected 1074 AGNs showing a steep frequency dependence of their angular sizes and compared the observed long-baseline visibility amplitudes with the predictions of the refractive substructure model for scatter-broadened images. Nine sources showed consistency with the expected level of refractive noise, including the QUASAR TXS 2005+403 (J2007+4029), which confirms previously reported results for this source. Remarkably, the majority of these AGNs are located in the Cygnus region -- one of the key ``hotspots'' of strong Galactic scattering. For five selected AGNs, we identified at least two epochs with sufficiently high data quality showing long-baseline detections, suggesting the presence of scattering substructure. We showed that refractive scattering substructure in AGN is a rare effect, requiring high sensitivity, sufficient source brightness, and lines of sight with particularly strong turbulence in the interstellar medium. Nevertheless, AGNs can serve as powerful probes of the turbulent interstellar medium. We discuss strategies for improving the sensitivity of VLBI observations and identify the most promising sources for reliable detection and investigation of refractive substructure in future observations.
[abstract 7 / 47] Yes (score: 6) - Title: MHD Modelling of MAGNETic RECONNECTion heating and JETs in the solar coronaAuthors: P. Pagano, C. Argiroffi, F. Reale, A. Petralia, G. Cozzo, P. Testa,Comments:Subjects: astro-ph.SRCreated: 2026-09-09; Updated: 2026-09-10; Datestamp: 2026-09-10
Magnetic RECONNECTion is seen as the lead mechanism to explain the persistent and bursty heating of the solar corona that keeps its thermal structure. Lately the observations and modelling of MAGNETic RECONNECTion outflows, i.e. nanoJETs, has empowered our capabilities to scrutinise this mechanisms, however more needs to be understood on the relation between the energetic and kinematic events. The aim of this paper is to study in details the properties of the heating events (nanoflare) and the kinematic counterparts (nanoJETs) in order to augment detection capabilities of MAGNETic RECONNECTion events. We use MHD simulations of the interaction of two MAGNETic flux tubes where MAGNETic RECONNECTion occurs and such RECONNECTion outflows are generated. We vary key parameters, such as the critical current and the size of the domain to study the heating and slingshot mechanisms. We find that the properties of the nanoJETs can give away much information on the MAGNETic RECONNECTion that generated it, while it is difficult to directly link the amount of heating and the JET speeds. We also find that such RECONNECTion model can explain a wide range of heating events. Magnetic RECONNECTion still is invariably linked to both heating and outflows and our simulations show the complex interplay between these two byproducts of the MAGNETic RECONNECTion and how their properties can be studied in observations.
[abstract 8 / 47] Yes (score: 5) - Title: Bright flare in the obscured state of GRS 1915+105 as seen by NICER and SWIFTAuthors: Shuaitongze Zhao, Honghui Liu, Menglei Zhou, Swarnim Shashank, Cosimo Bambi, Andrea Santangelo,Comments: 16 pages, 13 figures. v2: refereed versionSubjects: astro-ph.HECreated: 2026-09-09; Updated: 2026-09-10; Datestamp: 2026-09-10
We report time-resolved NICER and SWIFT X-ray spectroscopy of a bright flare from the BLACK HOLE X-ray binary GRS 1915+105 during its obscured state, which is characterized by heavy line-of-sight absorption by dense material with complex geometry. In April 2023, an unexpected flare was detected, with the observed X-ray flux increasing by nearly an order of magnitude relative to the typical obscured-state level. The spectra show pronounced variability, including significant evolution of the Fe K emission features. Time-resolved spectral modeling indicates that the main flare is associated with a combination of enhanced intrinsic emission and reduced obscuration. We further find that neutral and ionized reflection components are subject to distinct absorbers, whose evolving visibility implies a stratified absorber-reflector geometry. These properties are consistent with a re-illumination phase following a failed disk wind. A delayed radio flare detected about 2.5 days later suggests a coupling between accretion and JET activity.
[abstract 9 / 47] Yes (score: 4) - Title: Inflationary Magnetogenesis with $f(R,ϕ)$ CouplingAuthors: Shuang Liu, Bo-yu Zhao, Yu Li, Yao-chuan Wang,Comments: 19 pages, 8 figuresSubjects: astro-ph.CO gr-qcCreated: 2026-09-09; Updated: 2026-09-10; Datestamp: 2026-09-10
Inflationary MAGNETogenesis provides a promising mechanism for generating primordial large-scale MAGNETic fields, but faces challenges such as the strong coupling problem and backreaction issues. In this paper, we extend the Ratra model by introducing a coupling between the electroMAGNETic field and the background geometry, parameterized as $K(R)I^2(ϕ)$. Starting from a general action with $f^2(R,ϕ)F_{μν}F^{μν}$, we adopt $f^2(R,ϕ)=K(R)I^2(ϕ)$ as a concrete realization. Rather than focusing on the slow-roll inflationary stage (which reduces to the standard Ratra scenario), we concentrate on the post-inflationary reheating epoch, where the broken-power-law evolution of the scale factor and coupling function across the inflation-to-reheating transition allows us to derive analytic expressions for the MAGNETic and electric energy density spectra. Three key theoretical constraints are imposed on the model parameter space: the strong coupling condition, the backreaction constraint, and the CMB isotropy requirement. We obtain predictions for the present-day MAGNETic field strength $B_0$ and coherence length $L_{c0}$ for various combinations of the inflationary energy scale $H_f$ and the reheating temperature $T_r$. By comparing with observational constraints from radio observations and FERMI-LAT gamma-ray data, we demonstrate that the inflationary energy scale $H_f$, the reheating temperature $T_r$, the parameter $β$, and the e-folding numbers $N_f$, $N_r$ must satisfy stringent joint constraints. This work provides a viable theoretical framework for inflationary MAGNETogenesis that simultaneously satisfies theoretical consistency conditions and current observational bounds, with the reheating-stage nonlinear MHD evolution serving as a crucial ingredient for producing observationally compatible MAGNETic fields.
[abstract 10 / 47] Yes (score: 4) - Title: SHELLQs. Black Hole Mass and Eddington Ratio Distributions of Intermediate-Luminosity Quasars at 6[abstract 11 / 47] Yes (score: 4)Authors: Masafusa Onoue, John D. Silverman, Yoshiki Matsuoka, Xuheng Ding, Camryn L. Phillips, Michael A. Strauss, Junya Arita, Takuma Izumi, Mahoshi Sawamura, Nobunari Kashikawa, Irham Andika, Kentaro Aoki, Shunsuke Baba, Anna-Christina Eilers, Seiji Fujimoto, Tomotsugu Goto, Masatoshi Imanishi, Kohei Inayoshi, Kazushi Iwasawa, Knud Jahnke, Yuki Kaneko, Toshihiro Kawaguchi, Kotaro Kohno, Chien-Hsiu Lee, Alessandro Lupi, Tohru Nagao, Dragan Salak, Malte Schramm, Yoshiki Toba, Hideki Umehata, Marta Volonteri, Fabian Walter, Feige Wang, Jinyi Yang,Comments: 36 pages, 16 figures, submitted to ApJSubjects: astro-ph.GACreated: 2026-09-08; Updated: 2026-09-10; Datestamp: 2026-09-10
We present near-infrared spectroscopy of 21 QUASARs at 6.07 < z < 6.90 obtained with JWST/NIRSpec and Subaru/MOIRCS. These targets have absolute ultraviolet magnitudes of -25 < M_1450 < -22 and are drawn from a sample of z>6 QUASARs identified in the Subaru High-z Exploration of Low-Luminosity Quasars (SHELLQs) project. These QUASARs occupy the intermediate-luminosity regime between luminous QUASARs and the faint high-redshift AGNs uncovered by JWST. We detect broad Balmer emission lines and MgII 2798 with underlying continua from the NIRSpec and MOIRCS targets, respectively. The virial BLACK HOLE masses of this sample span a wide range of 7.2 < log M_BH/M_sun < 9.4, with Eddington ratios of -1.3 < log L_bol/L_Edd < 0.4. Combining these measurements with our previous mass estimates for other SHELLQs QUASARs, we construct a sample of 27 QUASARs with M_BH estimates at 6 < z < 7 and derive the distributions of M_BH and L_bol/L_Edd. When compared with luminosity-matched QUASARs at z ~ 1.3, we find median offsets of delta log M_BH/M_sun = -0.4 and Delta log L_bol/L_Edd = 0.2 in the high-redshift sample. In addition, 11% of the high-redshift QUASARs are accreting near or above the Eddington limit. As a systematic check, adopting the Eddington-ratio-dependent calibration of single-epoch M_BH estimates increases the inferred super-Eddington fraction to 22%. These results indicate that a representative population of distant supermassive BLACK HOLEs undergo a rapid accretion phase, although not as extreme as that seen in the most luminous QUASAR population, consistent with the anti-hierarchical growth scenario of supermassive BLACK HOLEs.
arXiv:2609.09274 [pdf, ps, other]Little Red Dots (LRDs) display singular properties unlike any known class of AGN or galaxies, motivating novel mass estimators for their central engines. Inspired by their similarities to stellar phenomena, here we interpret the LRD continuum as being produced by a pseudo-photosphere. We fit tailored stellar atmosphere models to host-subtracted LRD central engines ("BLACK HOLE stars," BH*s) represented by stacks of $117$ objects. Typical BH* continuum spectra are well fit by models in a narrow range of temperatures ($T_{\rm eff}\approx4200-4800$ K), with bolometric luminosities $\approx10^{43-45}$ erg s$^{-1}$, implying pseudo-photospheric radii $\approx700-2000$ au. Based on these parameters, we explore four different approaches to deriving BH* masses: 1) using the surface gravity from atmosphere models; 2) appealing to the resemblance to super-Eddington phenomena; 3) approximating the escape velocity from the outflowing material; and 4) exploiting the lack of variability to bound the dynamical time. For the typical BH*, all of these methods yield remarkably consistent masses of $\approx10^{4-5}\,M_\odot$, implying a highly super-Eddington luminosity of $L_{\rm{bol}}/L_{\rm{Edd}}\sim5-50$. These mass estimates place BH*s within the scatter of the local scaling relation between BLACK HOLE mass and host galaxy stellar mass, providing a self-consistent alternative to "overmassive" BLACK HOLEs that lie $2-3$ dex above it. Crucially, our derived masses are consistent with BH*s arising from single supermassive stars (SMSs), whose masses cannot exceed $\approx10^{5-6}\,M_\odot$ due to general RELATIVISTIC instabilities. Furthermore, for our derived $L_{\rm bol}/L_{\rm Edd}$, the sharp cutoff of the LRD luminosity function matches the maximum theoretical mass of an SMS. With LRDs, we may therefore be directly observing the birth of heavy BLACK HOLE seeds.
arXiv:2609.09314 [pdf, ps, other]Circumbinary disks around supermassive BLACK HOLE binaries (SMBHBs) are expected to form across a broad range of inclinations, with retrograde configurations potentially a common occurrence. Here we present the first grid-based hydrodynamical simulations of retrograde circumbinary disks around eccentric SMBHBs, solving an energy equation that balances viscous and shock heating against blackbody radiative cooling. We investigate different initial disk Mach numbers $\mathcal{M}_a \in \{10, 20, 40\}$ and consider binary eccentricities $e_\mathrm{b}\in[0.0,\,0.8]$, finding that multiple stable states exist for the same binary eccentricity and Mach number. These states differ by the sense of rotation of their minidisks; both retrograde ($\downarrow\downarrow$), both prograde ($\uparrow\uparrow$), or one of each ($\uparrow\downarrow$), a property set by the initial conditions. Our findings indicate that each state produces qualitatively distinct orbital evolution: $\downarrow\downarrow$ and $\uparrow\downarrow$ minidisks drive circular inspirals whereas $\uparrow\uparrow$ minidisks drive eccentric inspirals with potentially observable eccentricity in the LISA band. We measure the electroMAGNETic emission produced by the disk, finding that a binary of mass $M_\mathrm{b}=8\times10^6\mathrm{M}_\odot$ at redshift $z=1$ would be detectable by both current and upcoming optical and UV instruments. We demonstrate that the time- and azimuthally-averaged disk profiles are well described by 1D models, which naturally set a cavity radius within which angular momentum transport is dominated by Reynolds stresses rather than viscosity.
arXiv:2609.09327 [pdf, ps, other]We present the identification of the co-spatial and co-temporal small scale JETs -- sometimes also named as JETlets -- at the base of the coronal hole plume associated with chromospheric and transition region (TR) flows. We identified 19 JETs with coordinated observations recorded on March 19, 2016 using the Solar Dynamics Observatory (SDO) and the Interface Region Imaging Spectrograph (IRIS). Our analysis of \ion{Si}{4} 1393.7~Å line suggests blueshifts mostly in the range of 10 to 33~km~s$^{-1}$, but few less than -10~km~s$^{-1}$, while analysis of co-spatial \ion{Mg}{2}~h~\&~k lines show both blueshifts and redshifts in the range of {--}9 to 17~km~s$^{-1}$. We observed highly asymmetric, enhanced intensity in \ion{Si}{4} line during these events. The upflows observed in transition region through \ion{Si}{4} is strongly correlated with chromospheric downflows observed in \ion{Mg}{2}. We interpret these results as a signature of interchange RECONNECTions creating bi-directional flows -- giving rise to upflows (downflows) in transition region (chromosphere).
arXiv:2609.10041 [pdf, ps, other]Bow-shock pulsar wind nebulae (PWNe) are SYNCHROTRON sources formed when the outflow of supersonic pulsars is confined by the surrounding interstellar medium. These sources are dominated by freshly injected particles, thus providing a unique laboratory for studying particle acceleration in RELATIVISTIC outflows. The Mouse is a prototypical bow-shock PWN and is bright in the radio and X-ray bands, enabling detailed multi-wavelength spectral modeling. Using data from 17 telescopes, the Mouse is detected from 118 MHz to 353 GHz, covering over 3 decades in frequency, and in X-rays from 0.5 to 30 keV. A clear spectral break is identified at 3.7 GHz. The radio spectrum exhibits a rising trend at low frequency, peaks at the break, and then declines. We find a change in spectral index $Δα=0.65\pm0.05$ across the break. We attribute this to an intrinsic cutoff or steepening in the injected particle distribution. This could indicate the characteristic energy of leptons leaving the pulsar MAGNETosphere, or energy dissipation after the particles cross the termination shock.
arXiv:2609.10073 [pdf, ps, other]Motion of plasma in pulsar MAGNETospheres essentially follows bent MAGNETic field lines which may result in radiation beams sweeping past the observer's sightline. We show that under certain conditions such a passing beamlet can produce two orthogonal POLARIZATION modes (OPMs) solely from averaging of radiative contributions, without involving birefringence. This requires that radiation from different stages of the passage is contributed incoherently, hence that the timescale for the coherence is much shorter than the typical sampling time. The model produces two OPMs of comparable amount, with a wide range of (single-pulse) polarized fractions, which is consistent with general observed pulsar properties. Under the specific conditions required (essentially incoherent summation of signal at appropriate time scale) the averaging effects alone can thus lead to the appearance of two orthogonal POLARIZATION tracks with OPM jumps.
arXiv:2510.21555 [pdf, ps, other]Spacetimes arising from nonlinear electrodynamics (NED) are a good laboratory for studying both the nature of regular BLACK HOLE (RBH) solutions and the imprints of nonlinear electroMAGNETic fields within this context. Over the past few decades, NED-sourced BLACK HOLE (BH) spacetimes have attracted considerable attention, but electrically charged RBHs obtained in the so-called $F$ framework have been less addressed in the literature. We consider two electrically charged, fully regular members of the h-family that are solutions to general relativity minimally coupled to NED. Because of their potential astrophysical and astronomical applications, we mainly focus our investigation on the motion of photons and its implications for the gravitational and kinematic redshifts, as well as for the shadow radius, considering the effective geometry followed by photons in NED. Moreover, we consider the observational data for Sagittarius A$^{\star}$ and Messier 87$^{\star}$ BHs to impose some constraints on the charge-to-mass ratio of the fully RBHs. We obtain the general equations that govern the gravitational and kinematic redshifts of NED-sourced BH spacetimes. In particular, for fully RBHs with BH charge-to-mass ratios above some moderate value, we observe discrepancies in their physical and geometrical properties compared to those of the Reissner--Nordström (RN) BH. Therefore, our results indicate that it is possible to distinguish NED-based RBH solutions from RN BHs, from the perspective of gravitational and kinematic redshifts, suggesting potential astrophysical relevance.
arXiv:2601.20210 [pdf, ps, other]We present a detailed analysis of $γ$-ray emission from the middle-aged SUPERNOVA remnant (SNR) S147 (G180.0$-$1.7) using approximately 16.5 years of FERMI-LAT data. Spatially, a new extended $γ$-ray component distinct from the emission associated with the H$α$ filaments of the SNR shell is identified. This new component exhibits a strong spatial correlation with dense molecular clouds (MCs) identified in CO emission at Local Standard of Rest velocities of $0$--$5\,\mathrm{km\,s^{-1}}$. Spectrally, the cloud-associated emission implies an underlying cosmic-ray (CR) proton population described by a hard power-law with an index of $Γ\approx 2.1$, compatible with the standard diffusive shock acceleration prediction. We interpret the $γ$-ray emission in this region with a hadronic scenario involving two distinct CR populations: trapped CRs reaccelerated within the radiative SNR shell as proposed in previous work, and escaping CRs illuminating the nearby MCs. The derived CR proton intensity in the MC region significantly exceeds the local Galactic background measured by AMS-02, consistent with the interpretation that the cloud is illuminated by particles accelerated by S147. These findings provide observational support for a CR-escape scenario during the earlier evolutionary phases of this middle-aged SNR and highlight the S147 MC component as a potential candidate for detection at TeV energies by LHAASO.
arXiv:2607.11761 [pdf, ps, other]Kinetic instabilities, notably the whistler heat-flux instability (WHFI), are known to suppress thermal transport significantly in the moderate- to high-$β$ plasmas relevant to many astrophysical systems. This paper explores WHFI-regulated heat transport in a new regime: ultra-high-$β$ plasmas with $β_{e} \gtrsim L_{\mathrm{T}}/ρ_e$. Extrapolating previous theories of the WHFI to ultra-high-$β$ plasmas, we propose that the MAGNETic energy in unstable whistler fluctuations becomes comparable to that of the background MAGNETic field at saturation. We corroborate this hypothesis using 1D3V and 2D3V kinetic simulations using the particle-in-cell code OSIRIS. We find that, in ultra-high-$β$ plasmas, the heat flux is localised and no longer regulated primarily by resonant pitch-angle scattering of electrons; instead, thermal energy is transported predominantly by advection at the whistler phase velocity. Heat-flux suppression is observed in 1D3V and 2D3V simulations; however, we show that the saturation of the WHFI and the regulation of heat flux are sensitive to dimensionality in the ultra-high-$β$ regime. The amplitude and phase velocity of the heat-flux-regulating whistler waves scale differently with $β_e$, yielding parallel heat fluxes, normalised to the free-streaming value, of $q_{e\parallel} / q_\mathrm{fs} \approx 4.7 β_{e}^{-1}$ and $q_{e\parallel} / q_\mathrm{fs} \approx 0.3 β_{e}^{-1/2}$ in 2D3V and 1D3V simulations, respectively. We perform 2D3V simulations with background MAGNETic fields inclined to the temperature gradient, showing perpendicular heat transport remains negligible. We develop a heuristic theory from kinetic equations that explains these phenomena. Our work extends our understanding of how the WHFI modifies thermal transport to regimes applicable to high-energy-density physics and the reionised intergalactic medium.
arXiv:2609.09197 [pdf, ps, other]We study circular geodesics of neutral test particles in the static charged solution of Scalar--Tensor--Vector Gravity (STVG), and we use the twin kilohertz quasiperiodic oscillations (QPOs) of twelve accreting compact objects to bound its parameters. Starting from the effective potential we obtain closed forms for the specific energy, the specific angular momentum and the Keplerian angular velocity, and from these the radial and vertical epicyclic frequencies. The horizon, photon sphere, shadow radius and innermost stable circular orbit are given in closed form as well, and each one reduces to the RN and Schwarzschild value in the appropriate limit. Null geodesics are integrated numerically and show how the enhanced coupling widens the capture cross section while leaving the logarithmic divergence of the deflection angle at the photon sphere intact. Within the RP model we then run Metropolis--Hastings MCMC simulations on the QPO pairs of eight neutron stars and four microQUASARs, comparing the Schwarzschild spacetime, the RN spacetime, STVG with vanishing charge and the full STVG solution. The best fits are obtained mainly for the charged solutions in the neutron star sample, while all four models describe the BLACK HOLE sample equally well. We show that the orbital dynamics depends on the mass $M$, the coupling $α$ and the charge $Q$ only through the two combinations $\Meff=(1+α)M$ and $\Qeff^{2}=(1+α)(αM^{2}+Q^{2})$, which accounts for the multimodal posteriors found in the neutron star sample and sets a model-independent limit on what QPO timing alone can measure. The astrophysical implications of these bounds, in particular for inferred masses above the Tolman--Oppenheimer--Volkoff limit, are discussed in detail.
arXiv:2609.09285 [pdf, ps, other]Magnetars became favored engines of fast radio bursts (FRBs) following the discovery of a luminous radio burst coincident with a hard X-ray flare from a Galactic MAGNETar. Several repeating FRB sources exhibit time-variable rotation measures and compact, spatially coincident persistent SYNCHROTRON radio emission, consistent with energetic-particle nebulae and confined by young SUPERNOVA ejecta. Secular changes in the dispersion measure (DM) of repeating FRBs have also been observed, offering a complementary probe of their local environments; for example, the DM of FRB 121102 rose until 2019 before declining in recent years. Although rising DM evolution has been attributed to shock ionization, shocked ejecta can cool efficiently through metal-line emission and may recombine, especially if it mixes turbulently with cooler gas. Here we argue that DM variations of the observed magnitude and timescale instead arise from changes in the ionization state of SUPERNOVA ejecta irradiated by X-rays from a time-variable central engine. The dominant rapidly variable contribution comes from the dense, weakly ionized shell swept up by the expanding nebula, whose ionization and recombination times are much shorter than those of the more extended ejecta. The model predicts that enhanced FRB activity should be accompanied by rising DM, with a response smoothed over the ionization/recombination time, superposed on a slower secular decline from the expanding ejecta; in FRB 121102, the DM maximum occurred close to the burst-rich 2018--2019 activity episodes, including the 2019 FAST burst storm. If the recently reported renewed activity of FRB~121102 is sustained, the model predicts that its DM decline should flatten and may reverse into a fresh rise over the coming years.
arXiv:2609.09447 [pdf, ps, other]We consider main-sequence stars orbiting close to a supermassive BLACK HOLE (SMBH), which are potential gravitational wave (GW) sources for LISA if their orbital periods are of the order of an hour. At such a short orbital period, mass transfer from the star to the SMBH occurs. The evolution of the semi-major axis and GW frequency depends on the evolution of the stellar mass and radius. We use MESA to study stars that transfer mass to SMBHs similar to Sagittarius A* starting on the zero-age main sequence (MS). We identify 4 evolutionary phases. (I) Stars initially with mass $>2 M_\odot$ remain on the MS as their mass and radius decrease. (II) Below $2 M_\odot$, the separation is sufficiently small so that the GW timescale is too short for the stars to maintain thermal equilibrium. They evolve adiabatically off the MS and shrink rapidly as they lose their high-entropy envelope. (III) Below $0.5-1 M_\odot$, depending on the initial mass, the uniform low-entropy core is exposed and stars expand adiabatically. (IV) Below $0.15-0.4 M_\odot$, the thermal and GW timescales become comparable, and stars cool and shrink while maintaining this balance. Overall, mass transfer causes the orbit to expand, slowing down the orbital evolution and leading to GW emission at lower frequencies making the GW signal harder to detect. If located around Sagittarius A*, mass transferring stars spend most of the time relatively close to the LISA sensitivity curve, with maximal SNR reaching around 600 during the transition between stages II and III.
arXiv:2609.09886 [pdf, ps, other]We report the first very long baseline interferometry (VLBI) experiment conducted in the 690 GHz atmospheric window. On 2024 November 21, observations with the Atacama Large Millimeter/submillimeter Array, the Atacama Pathfinder EXperiment (APEX), and the James Clerk Maxwell Telescope (JCMT) were carried out using ALMA's newly developed Band 9 phasing capability. Fringes were detected on the ALMA-APEX baseline during a scan of the QUASAR J0423-0120, with a signal-to-noise ratio of ~12 and useful fringe recovery over solution intervals of order tens of seconds, representing the highest-frequency ground-based VLBI fringe detection reported to date. No fringes were found on the ALMA-JCMT baseline, despite excellent weather conditions, consistent with sensitivity predictions and supporting baseline performance models. The ALMA Phasing System maintained stable phasing at Band 9 for ~1-2 minutes before gradually degrading, indicating limitations under these observing conditions. Our analysis shows that, under excellent weather conditions, 690 GHz VLBI can still support fringe recovery over short solution intervals, despite rapid atmospheric phase fluctuations at these frequencies. This work validated key elements of near-terahertz VLBI operation and establishes a technical foundation for routine observations in the 690 GHz atmospheric window.
arXiv:2609.09926 [pdf, ps, other]Neutron star-BLACK HOLE (NSBH) mergers are promising multimessenger sources, but only a subset is expected to produce detectable electroMAGNETic (EM) counterparts, depending on the binary mass ratio, BLACK HOLE (BH) spin, and neutron star (NS) equation of state (EoS). We investigate the prospects for detecting kilonova counterparts to NSBH mergers in the LIGO-India era using the Vera C. Rubin Observatory (Rubin). We simulate GW230529-motivated NSBH populations with two effective tidal deformability ranges, estimate gravitational-wave detections for the LHV (LIGO-Livingston, LIGO-Hanford, Virgo) and LHVA (LHV with LIGO-India at Aundha) detector networks, and model the detectability of the associated kilonova emission with Rubin. We find that adding LIGO-India approximately doubles the number of EM follow-ups, primarily by increasing the duty cycle and reducing the median sky-localization area, and notably increases the number of such detections at large distances. For fixed-exposure strategies, the EM detection rate saturates at exposure times of a few hundred seconds, reflecting the trade-off between depth and sky coverage. We therefore introduce an event-specific exposure-time optimization strategy based on the expected counterpart brightness and sky-localization area. With this strategy, the expected NSBH GW+EM detection rate per year is 4.19(-3.58,+9.66) for the optimistic and 0.79(-0.68,+1.83) for the conservative population with the LHVA network, compared to 1.46(-1.25,+3.37) and 0.27(-0.23,+0.62), respectively, for LHV. The required Rubin follow-up time remains within the expected Target-of-Opportunity allocation. These results show that in the next decade, a few such NSBH follow-ups may take place, with a fraction of them in the redshift range of about 0.1-0.2, which will not only be useful for measuring the Hubble constant but can also help us in probing the Hubble parameter.
arXiv:2609.10035 [pdf, ps, other]Circumplanetary disks (CPDs) regulate gas accretion onto forming giant planets and provide the environment in which their satellites may form. We use high-resolution, global three-dimensional simulations to investigate the early formation, orientation, and outflows of a CPD around a Jupiter-mass planet embedded in a turbulent MAGNETized protoplanetary disk. Within a locally isothermal, ideal-MHD framework, we evolve disks threaded by net vertical MAGNETic fields, corresponding to initial plasma parameters $875\leqβ\leq3500$, until MAGNETorotational-instability-driven turbulence is established before inserting the planet. We also perform a hydrodynamic control simulation. In the most strongly MAGNETized model, with $β=875$, the CPD forms already highly inclined and reaches a maximum tilt of approximately $87^\circ$. By contrast, the hydrodynamic CPD and the MHD models with $β\gtrsim1000$ remain nearly coplanar. A control simulation in which the planet is inserted before global MRI turbulence develops also remains coplanar, despite producing local turbulence and bipolar outflows. The large tilt is therefore associated with the pre-existing global turbulent state and its evolved velocity and toroidal MAGNETic-field structure, although our current diagnostics do not distinguish between a direct MAGNETic torque and the accretion of misaligned angular momentum. All MHD models launch bipolar outflows; in the highly tilted case, these develop a curved, helical morphology that persists until the end of our short-term simulations. These results identify pre-existing global MAGNETized turbulence as a viable route to generating strongly inclined CPDs and twisted planetary outflows.
arXiv:2609.10176 [pdf, ps, other]There is growing evidence for cosmic-ray acceleration in massive stellar clusters. Furthermore, extended gamma-ray emission suggests that particle transport in the vicinity of their sources is influenced by physical processes markedly different from large-scale diffusion in the Milky Way. We characterize extended gamma-ray emission in the direction of the Westerlund 1 stellar cluster and Kes 41 SUPERNOVA remnant using > 16 years of data from the FERMI Large Area Telescope (LAT) at energies > 0.8 GeV. We test whether clusters of gamma-ray sources not associated to multiwavelength counterparts are better described by extended emission components. We report the detection of three new extended emission components with soft spectra towards regions of high gas column density in the Galactic plane. One extended component associated with the natal cloud of Kes 41 is statistically preferred over the point source previously reported towards the SUPERNOVA remnant shell. The other two extended components overlap with neutral gas within ~100 pc from the edge of the Westerlund 1 superbubble. The extended emission may be explained either by mismodeled gas in the interstellar background model or by the local injection of particles. Under the latter hypothesis, explaining the component associated with Kes 41 requires converting $\lesssim 5\%$ of the SUPERNOVA remnant energy into accelerated particles, while accounting for the two components near Westerlund 1 requires converting $10^{-4}$ of the cluster wind mechanical power into gamma rays. Nevertheless, our results strengthen the evidence for gamma-ray emission structures arising at intermediate spatial scales between isolated objects and the large-scale diffuse emission from the interstellar medium. This could explain a part of the soft unassociated Galactic sources detected by the FERMI LAT. (Abridged)
arXiv:2609.10285 [pdf, ps, other]Binary BLACK HOLEs (BBHs) have been theorised to form through various different channels, but current LIGO-Virgo-KAGRA (LVK) sky locations make the direct study of formation channels a challenge. Association of strongly lensed BBHs to their hosts has been shown to be possible with current detector networks at upgraded sensitivity and survey telescopes like Euclid, with localisations that can reach sub-galactic scales in the source plane. With Hubble Space Telescope-like high-resolution imaging, we report that strong-lensing localisation of BBHs allows us to confidently associate the BBH with specific structures within their host galaxies, specifically, galactic centres (GCs). We demonstrate that a BBH localised to the GC of the galaxy can reject light-tracing BBH populations ($p < 5\%$) in a single observation, and in most cases demonstrate high confidence rejection ($p < 1\%$), providing a conservative basis to exclude light-tracing spatial distributions associated with field-like or non-central formation channels. Such association therefore directly supports formation channels confined to GCs, such as ACTIVE GALACTIC NUCLEi and nuclear stellar clusters.
arXiv:2512.22938 [pdf, ps, other]Continuous gravitational waves have the potential to transform gravitational wave astronomy and yield fresh insights into astrophysics, nuclear and particle physics, and condensed matter physics. We evaluate their detectability by combining various theoretical and observational arguments from the literature and systematically applying those arguments to known astronomical objects and future gravitational wave detectors. We detail and update previous estimates made in support of Cosmic Explorer [M. Evans et al., arXiv:2306.13745; I. Gupta et al., Class. Quantum Grav. 41, 245001 (2024)]. It is commonly argued that the spins of accreting neutron stars are regulated by gravitational wave emission and that millisecond pulsars contain a young pulsar's MAGNETic field buried under accreted material. If either of these arguments holds, the first detection of continuous gravitational waves is likely with near future upgrades of current detectors, and many detections are likely with next generation detectors such as Cosmic Explorer and the Einstein Telescope. A lack of detections in the next several years would begin to raise serious doubts about current theories of millisecond pulsar formation.
arXiv:2512.24544 [pdf, ps, other]Modern stellarator designs routinely attain high levels of MAGNETic-field quasi-symmetry through flux-surface shaping. Here, we examine different methods for characterizing stellarator flux-surface shapes in a manner analogous to flux-surface shaping in tokamaks. The methods considered use a Fourier analysis to define the shaping modes (e.g. elongation, triangularity, squareness, etc.) of equilibrium cross-sections. Relative to an axisymmetric equilibrium, the additional degree of freedom in a non-axisymmetric equilibrium manifests as a rotation of each shaping mode about the MAGNETic axis. This analysis is performed on non-axisymmetric configurations with a high degree of quasi-symmetry and equilibria with varying quasi-symmetry quality from the QUASR database. One method in particular is shown to reduce shape complexity in quasi-symmetric equilibria by defining a set of cross-sections that efficiently fill out an equilibrium volume. This is accomplished by defining a cross-section as the set of points that occupy the shortest distance between the MAGNETic axis and an equilibrium flux-surface across all quasi-symmetry contours. Using this method, we find empirically an equilibrium geometry can be described with significantly fewer non-negligible shaping modes relative to other shape characterization methods. Moreover, the method reveals that quasi-symmetry quality is strongly correlated with equilibrium shapes that exhibit a highly constrained linear distribution of shaping modes, where an increase in shape complexity is proportional to an increase in shape rotation about the MAGNETic axis. It is therefore argued this method provides a way to efficiently characterize the shape of quasi-symmetric equilibria in a manner analogous to how equilibrium shapes are described in tokamaks.
arXiv:2608.22240 [pdf, ps, other]We study the thermal history of the primordial Universe in the presence of non-zero lepton and baryon asymmetries. Considering different scenarios, we determine the equation of state (EoS) of the Universe from T = 10 GeV down to T = 1 keV, spanning the QCD transition, hadron gas phase and neutrino decoupling epochs. Using a combination of numerical codes, we track the cosmic trajectories of chemical potentials associated with the baryonic, leptonic and electric charges, and follow the evolution of lepton asymmetries including through the era where neutrino oscillations take place. Combining peak theory with numerical-relativity simulations of the collapse threshold, we show the EoS-induced modifications to the primordial BLACK HOLE (PBH) mass spectrum. We determine the associated Gravitational Wave (GW) signal, showing how lepton asymmetries and a particular spectral index of curvature perturbations can be hinted at by current ground interferometer-based GW observations. Finally, we discuss constraints and positive evidence for PBHs.
arXiv:2609.02674 [pdf, ps, other]This study investigates an Einstein-nonlinear electrodynamic BLACK HOLE generated by a Yukawa-screened electroMAGNETic potential and examines its thermal properties through the calculation of the fundamental thermodynamic potentials and variables. The effect of thermal fluctuations on the calculated standard thermodynamic quantities is analyzed through two different correction terms added to the Bekenstein-Hawking entropy. In this work, the thermodynamic behavior in cases where the BLACK HOLE has a relatively large event horizon is investigated using a logarithmic correction term representing corrections arising from quantum fields in constant backgrounds. In addition, thermal fluctuations occurring in cases where the event horizon is small are analyzed through an exponential correction term added to the entropy, reflecting non-perturbative quantum effects. Finally, the thermodynamic functions for all obtained cases are examined graphically, and the stability properties of the BLACK HOLE are discussed in detail.
arXiv:2609.09026 [pdf, ps, other]Open clusters remain among the most powerful laboratories for calibrating how fundamental stellar properties such as rotation, MAGNETic activity, surface chemistry, and internal structure evolve over the pre-main-sequence to main-sequence and post-main-sequence stellar lifetime. Because cluster members share a common age, galactic environment, and initial composition, they provide empirical anchors upon which age-dating techniques such as gyrochronology, activity-age relations, and chemical clocks are built. This paper summarizes the Cool Stars 23 splinter session - Open Clusters as Laboratories for Cool Star Evolution, held on 15 June 2026 in Tokyo, Japan. The session comprised one invited review, ten contributed talks, and ten poster pop-up presentations, organized around three themes: the evolution of rotation, MAGNETic activity, and chemical abundances (Li-depletion, [C/N], [Y/Mg], and neutron-capture elements). We close with a summary of the open questions identified in the panel discussion and the observational and theoretical work that new surveys (e.g. Gaia DR4, 4MOST, WEAVE) and missions (e.g. PLATO, Roman) will enable over the coming years. Together, these efforts will help assess the current state of the field and shape its future directions.
arXiv:2609.09297 [pdf, ps, other]In this work, we investigate the physical properties and cosmic evolution of galaxies and AGN in a sample of 280 protoclusters identified in the TNG300 simulation, selected to end up in $z = 0$ clusters with $M_{200, \rm c} > 10^{14} \, {\rm M_{\odot}}$. Our goal is to provide the first statistical view of AGN activity enhancement in a uniformly defined sample of overdense environments, and to identify the physical mechanisms driving it. We identify protoclusters as the progenitors of present-day galaxy clusters through merger-tree reconstruction and compare their galaxy and AGN populations with a control sample of field galaxies across the redshift range $0 \leq z \leq 6$. We investigate galaxy and SMBH demographics, AGN fractions, bolometric luminosity functions, and the SMBH accretion rate density, consistently applying homogeneous selection criteria in all environments. We find that TNG300 protoclusters host systematically more massive galaxies and SMBHs than the field by up to $1 \, {\rm dex}$ at all redshifts, with signatures of accelerated galaxy evolution already visible at $z \sim 3-4$. The AGN fraction increases with stellar mass in both environments and, at fixed host-galaxy stellar mass, is broadly consistent between protoclusters and field galaxies, indicating no strong environmental triggering of SMBH accretion. However, when analysed as a function of redshift, protoclusters exhibit a significant enhancement of AGN activity (by a factor $> 2$), particularly at high luminosities and early cosmic times. We show that this enhancement primarily arises from differences in the stellar-mass distributions of galaxies in overdense regions, where massive systems assemble earlier than in the field. Consistently, protoclusters dominate the bright end of the AGN bolometric luminosity function and contribute up to $\sim 50\%$ of the total SMBH accretion rate density at $z \sim 6$.
arXiv:2609.09419 [pdf, ps, other]We study linear gravitational perturbations and the corresponding quasinormal-mode spectra of electrically and MAGNETically charged BLACK HOLEs in the presence of higher-order corrections to the Einstein-Hilbert action. In particular, we consider a four-derivative interaction that couples the Riemann tensor to the electroMAGNETic field strength in the unique (Horndeski) combination that preserves second-order equations of motion. We provide a comprehensive analysis of the stability conditions. We numerically confirm the absence of exponentially growing modes throughout the physically admissible region of parameter space where the theory remains free of pathologies. We then investigate in detail the properties of the quasinormal-mode spectra and identify several distinctive features induced by the higher-order interaction.
arXiv:2609.09517 [pdf, ps, other]The MAGNETic field strength is a central design object in the theory of MAGNETic confinement of plasma. Desirable confinement properties such as quasi-symmetry and omnigenity are characterized by special forms of the field strength when it is given in the particular coordinate system called ``Boozer coordinates." We ask a basic realizability question: which functions of Boozer coordinates can arise as the magnitude of a MAGNETic field that is written in Boozer coordinates? Using exterior differential systems and the Cartan-Kähler theorem, we show that every positive analytic function is locally realizable. Thus there is no local analytic obstruction to prescribing the field strength in Boozer coordinates; though further restrictions might arise from global geometric or additional physical constraints.
arXiv:2609.09555 [pdf, ps, other]We introduce {\it TransRAT}, a self-consistent time-domain framework that follows the coupled dynamical response of dust to transient irradiation and predicts its observable signatures. We apply {\it TransRAT} to a Type~IIP SUPERNOVA illuminating a one-zone molecular cloud. Radiative heating raises the grain temperature, modifying the MAGNETic susceptibility and Larmor precession, while the enhanced radiation field accelerates radiative precession and can switch the alignment axis from the MAGNETic field (B-RAT) to the radiation direction (k-RAT). Simultaneously, strong RATs align grains faster than gas randomization, extending {\it fast alignment} to smaller grain sizes, and disrupt large grains through RAT disruption (RAT-D), irreversibly modifying the grain size distribution. As the transient fades, the alignment axis returns to ${\bf B}$ at a rate controlled by the MAGNETic susceptibility, whereas the enhanced aligned-grain population and RAT-D-modified grain size distribution can persist long after the radiation has faded- referred to as \emph{physical memory effects}. The time-dependent evolution of grain alignment and disruption produces distinctive observational signatures: a flare in extinction and thermal dust POLARIZATION followed by a RAT-D-induced dip; a blueward shift of the POLARIZATION peak $λ_{\max}$; a POLARIZATION-angle rotation equal to the projected ${\bf B}$--${\bf k}$ separation ($45^{\circ}$ for our adopted geometry) when RAT-D removes large high-$J$ aligned grains and leaves low-$J$ grains aligned with kRAT followed by angle reverberation as alignment returns to ${\bf B}$; and a non-monotonic evolution of $R_V$. The persistent observational manifestations of the transient irradiation, including enhanced POLARIZATION, blueshifted $λ_{\max}$, modified $R_V$, and POLARIZATION-angle evolution, constitute \emph{fossil imprints} of past cosmic transients.
arXiv:2609.09651 [pdf, ps, other]Magnetized ion transport in weakly ionized plasmas ranges from gyroangle-dependent kinetics to Hall-Pedersen drift-diffusion as collisionality and MAGNETization vary. We develop a polar-harmonic unified gas-kinetic scheme (PH-UGKS) for the ion Vlasov-BGK equation in a uniform MAGNETic field. The scheme evolves the full ion distribution by coupling a conservative density update to exponential evolution of its nonequilibrium component. Exact collision-rotation integration in gyroangle Fourier space is combined with a time-averaged kinetic flux that incorporates spatial transport and electric acceleration, together with a compact Hall-Pedersen correction to the density flux. The scheme conserves ion number, and analysis establishes second-order temporal consistency and asymptotic preservation of the Hall-Pedersen density limit at fixed MAGNETization. Numerical tests reproduce ion Bernstein dispersion and Dory-Guest-Harris growth rates and resolve changes in the gyroharmonic spectrum as the collision-to-gyrofrequency ratio varies. The driven ion-flux response agrees with an independent characteristic-Volterra reference, including finite-frequency departures from the instantaneous Hall-Pedersen relation. In collisional tests, accurate responses are obtained with time steps far larger than both the collision time and the gyroperiod. Fixed-resolution density tests confirm convergence to the corresponding Hall-Pedersen discretization. The same kinetic formulation thus connects kinetic response and macroscopic transport without switching to a fluid solver or subcycling microscopic time scales.
arXiv:2609.09655 [pdf, ps, other]The present thesis is a work in progress on improving the simulation of integrated pulse profiles of pulsars. Pulsars, highly MAGNETized rotating neutron stars, serve as precise cosmic clocks useful for studying gravity and the interstellar medium. Although periodic pulses from many pulsars are observed and modeled at differ- ent radio frequencies, a robust realistic simulation of their profiles utilizing their parameters remain underdeveloped. The present study focuses on developing a physically consistent model to reproduce observed pulse shapes across multiple frequencies. This study will be useful in coherently understanding the various as- pects of the pulsar emission mechanism. These integrated pulse profiles are the time-averaged properties of pulsar emission and are obtained after averaging indi- vidual pulses over a few thousand rotations. Observed to be highly stable, these are indicative of the global properties of the pulsar MAGNETosphere. By refining simulation techniques and incorporating the propagation effects of the interstellar medium, this work will prove to be helpful in generating synthetic, yet realistic models. The results are expected to contribute to the interpretation of observa- tional data and to the development of improved timing and emission models for pulsars
arXiv:2609.09725 [pdf, ps, other]The origin of the optical emission in tidal disruption events (TDEs) remains one of the major outstanding questions in the field, in part due to the limited number of nearby events with high-cadence monitoring to track their evolving photometric and spectroscopic properties. We present multi-wavelength observations of the nearby ($z=0.01368$) TDE\,2025aarm, including near-daily spectroscopic coverage prior to the optical peak. Its proximity makes it one of the brightest TDEs discovered, reaching a peak magnitude of $m_r\sim15.5$ ($M_r\sim-18$). The light curve deviates from a smooth evolution, exhibiting multiple rebrightening episodes visible in both the individual filter light curves and the bolometric luminosity. Blackbody modelling reveals that these rebrightenings are associated with an increase in temperature of $> 5,000-10,000$\,K, while the inferred photospheric radius remains approximately constant. Simultaneously, the H$α$ line not only increases in blueshift but also broadens, suggesting a link between the continuum rebrightenings to changes in the kinematics of the line-forming gas. We identify a persistent absorption component at $\sim-3900$\,km\,s$^{-1}$ in multiple Balmer lines, providing further evidence for outflowing material. The H$α$ profile also exhibits excess flux compared to a Gaussian on both sides of the line, inconsistent with simple scattering-dominated outflow models. Disk-profile modelling provides evidence for the emergence of a disk-like component least $\sim20$ days after peak, with substantial changes in the disk properties between $\sim50$ and 60 days. These observations highlight the complexity of TDE emission processes and demonstrate how dense multi-wavelength monitoring can disentangle the roles of accretion, reprocessing, and outflows in shaping TDE emission.
arXiv:2609.09767 [pdf, ps, other]We investigate the influence of current helicity on the turbulent MAGNETic diffusivity $β$ using three complementary derivations of the $α$ and $β$ coefficients, based on the large-scale MAGNETic field $\overline{\mathbf{B}}$, the turbulent velocity $\mathbf{u}$, and the turbulent MAGNETic field $\mathbf{b}$. Applying these coefficients to raw DNS data, we reconstruct $\overline{\mathbf{B}}$ and compare the results with the original simulations. In the kinematic regime all models agree well with the DNS data. In the nonlinear regime, however, $β_{\mathrm{vv-vw}}$ alone produces unbounded growth of $\overline{\mathbf{B}}$. Including the contribution from turbulent MAGNETic fields ($β_{\mathrm{bb+jb}}$) suppresses this unphysical growth and restores agreement with the DNS results. We find that kinetic helicity drives $β$ more negative, while current helicity shifts it back toward zero. Weighted combinations of the coefficients further show that the $β$ effect dominates the evolution of $\overline{\mathbf{B}}$ throughout, whereas the $α$ effect becomes important mainly for sustaining the field in the nonlinear regime. The corresponding IDL analysis scripts are provided to facilitate practical implementation of the theoretical models.
arXiv:2609.09816 [pdf, ps, other]In this work, we extend the thermodynamic analyses of the neutral and specially charged Kerr-Bertotti-Robinson BLACK HOLEs to the general Kerr-Newman-Bertotti-Robinson family, in which the electric and external-field parameters are independent. Using covariant surface charges and canonical integrability methods, we determine the total angular momentum and the canonical mass. The angular momentum follows analytically from the combined gravitational and electroMAGNETic surface charges. However, the infinitesimal charge associated with coordinate time translations is not integrable in solution space, so the mass must be associated with a more general symmetry generator. Imposing the canonical integrability conditions on this generator, together with the Kerr-Newman mass as the zero-field boundary condition, selects the Christodoulou-Ruffini mass and determines the associated thermodynamic potentials. The first law and Smarr formula take the same form as the ones in usual Kerr-Newman case, and the two previously studied Kerr-Bertotti-Robinson cases are recovered as special limits.
arXiv:2609.09913 [pdf, ps, other]We present a study of the MAGNETic field (B-field) in the Eagle Nebula (M16) using data from the James Clerk Maxwell Telescope (JCMT) B-fields In STar-forming Region Observations (BISTRO) survey. We extend our previous study of the well-known `Pillars of Creation' region of the nebula to study two other structures in the region, the `Spire' and the bright-rimmed cloud (BRC) known as `SFO30'. These structures show similar B-field morphologies to the Pillars. We calculate B-field strengths using the Davis-Chandrasekhar-FERMI (DCF) method and thereby estimate the MAGNETic potential energy in each of these regions for comparison with the local gravitational, turbulent and thermal energies, as well as the pressure energy of the shocks from nearby O-type stars. We find approximate equipartition between the energies supporting the regions and those tending towards collapse, with the B-field support playing a significant role. This agrees with our earlier hypothesis that B-fields help support pillar-like structures in molecular clouds and make them longer-lived than they would otherwise have been.
arXiv:2609.10213 [pdf, ps, other]Over the coming years, the number of tidal disruption events (TDEs) is expected to substantially increase with observations from the Vera Rubin Observatory (g and r band) and {\it ULTRASAT} (near UV) wide-field surveys. These future samples have great promise to characterize the bottom end of the massive BLACK HOLE mass function, but existing detections of intermediate mass BLACK HOLE TDEs are primarily in X-rays, leaving their optical/UV emission largely unexplored. We present a time- and angle-dependent analysis of the outflow produced by dissipation near pericentre in a three-dimensional end-to-end radiation-hydrodynamics simulation of a TDE by a $10^4 M_\odot$ BLACK HOLE with realistic parameters, run with the code RICH. We find that outflow anisotropy produces viewing-angle-dependent observables. Towards the poles and the pericentre region, mass-loss rates are low and bolometric luminosities reach $\sim2$--$3$ times the Eddington luminosity. Towards the stream, the properties show a stronger dependence on latitude: the mass-loss rate increases and the bolometric luminosity decreases as the line of sight approaches the orbital plane. These denser regions favour H$α$ and H$β$ emission. Despite these variations, all viewing directions show a common spectral evolution, with an initial soft X-ray flare followed (around $1.25t_{\rm fb}\approx3$~days) by the reprocessing of shock-powered emission into the UV and optical bands. Although the optical/UV luminosities we predict for this TDE are likely too dim for past surveys (e.g. ASAS-SN, ZTF), they are within the detection capabilities of LSST and ULTRASAT to horizons of $\sim 790$ and $\sim 340$ Mpc, respectively, for the brightest viewing directions.
arXiv:2609.10270 [pdf, ps, other]Face-on spiral galaxies offer a favorable geometry for studying MAGNETic-field structures and cosmic-ray (CR) propagation because projection effects and structural overlap are reduced. We investigate cosmic-ray electron (CRE) transport in the nearby face-on spiral galaxy NGC 2442 and assess how its environment and MAGNETic-field structure influence propagation. We combine radio continuum (RC) observations from ASKAP at 943 MHz, MeerKAT at 1.28 and 1.7 GHz, and ATCA at 5 GHz with optical H$α$ and infrared data, and compare them with 2D CRE transport simulations. NGC 2442 has a steep integrated RC spectrum, with $α=-0.96\pm0.04$ for the total emission and $α_{\rm nt}=-1.21\pm0.04$ for the SYNCHROTRON emission over 408 MHz-5 GHz. A break near 1 GHz indicates substantial radiative aging. Under equipartition, we derive a mean MAGNETic-field strength of $10.8\,μ{\rm G}$. RC-SFR smoothing gives effective CRE propagation lengths of $\sim0.65$-$0.89$ kpc at 943-1700 MHz and $\sim0.44$ kpc at 5 GHz, corresponding to diffusion coefficients of order $10^{28}\,{\rm cm^2\,s^{-1}}$. We identify a steep-spectrum SYNCHROTRON ``island'' in the southeast, with $α\sim-1.09$ and no clear H$α$, infrared, FUV, or NUV counterpart, indicating that CREs are unlikely to be injected in situ. Our 2D CRPropa simulations show that anisotropic diffusion along ordered MAGNETic fields enables CREs to reach the island more efficiently than isotropic diffusion. NGC 2442 therefore shows that environmental disturbances and ordered MAGNETic fields can strongly regulate CRE propagation in disturbed spiral galaxies.
arXiv:2609.10319 [pdf, ps, other]Little red dots (LRDs) are a recently identified population of compact, red sources characterised by a distinctive V-shaped UV-to-optical continuum and broad emission lines. Their physical structure and evolution remain uncertain, while their properties at intermediate redshifts are largely unexplored. We identify and characterise LRD-like sources at 0.5
arXiv:2609.10332 [pdf, ps, other]We develop a Plebański--Demiański-adapted parametrization of the general Ovcharenko--Podolský solution and construct new families of generalized BLACK HOLEs in four-dimensional Einstein--Maxwell theory. These Petrov type~D spacetimes possess non-null, fully non-aligned electroMAGNETic fields. A restriction imposed in the previous parametrization is not required by the field equations in shifted coordinates. Removing it retains an independent charge parameter $q$, which may be real or purely imaginary. For $q^2\geq0$, both the metric and electroMAGNETic field admit a smooth aligned limit to the charged Plebański--Demiański solution with $Λ=0$ and $e^2+g^2=q^2$. We impose angular conditions in the Griffiths--Podolský form allowing Killing horizon cross sections with spherical topology. The resulting eight-parameter class extends the seven-parameter class of Ovcharenko and Podolský [arXiv:2508.04850]. The remaining normalization condition is generically quartic, defining four algebraic branches. We give explicit metrics and electroMAGNETic fields for the non-twisting and $l=0$ twisting families and analyze their BLACK HOLE and acceleration horizons, extremality, conicity, and further limits. We determine the effective-NUT-free branches of the latter family and their degenerate cases. Using the genuine Griffiths--Podolský form, we establish an explicit correspondence between the non-accelerating effective-NUT-free subclass and the Kerr--Newman--Bertotti--Robinson family and express its electroMAGNETic flux charges in our parameters. The $q^2<0$ sector includes the genuine uncharged Kerr--Bertotti--Robinson solution recently identified by Ovcharenko and Podolský [arXiv:2608.21672].
arXiv:2609.10384 [pdf, ps, other]Rapid, precise localization of GAMMA-RAY BURSTs (GRBs) requires continuous wide-field imaging at hard X-ray and soft gamma-ray energies. We develop a fixed (non-rotating) modulation-collimator architecture to address this challenge. A bigrid collimator, a pair of aligned, periodic slit grids in front of a simple, non-imaging photon-counting detector, transmits an off-axis source through a triangular fringe pattern whose local angular position, the source phase, is recovered from simultaneous count rates in several grid pairs at fixed relative phase offsets, rather than by mechanically rotating a single grid pair as in the classical rotating modulation collimator. Four-phase demodulation of these count rates robustly cancels detector background and grid leakage without requiring rotation. Because the fringe pattern repeats across the sky, a phase measurement corresponds to many candidate source positions; we resolve this ambiguity over an arbitrarily wide field of view using a cascade of progressively coarser-pitched grid stages, generalizing the two-grid vernier-scale technique originally used to localize Sco X-1. This vernier cascade technique reduces the required photon counts and grid-calibration accuracy required to achieve fine angular resolution over a broad field of view. Generalized to two dimensions with orthogonal cascades, the resulting architecture achieves wide-field localization with no moving parts, no time modulation, and only simple photon-counting detectors, a promising candidate for simple, inexpensive, continuous-monitoring instruments supporting time-domain and multi-messenger astrophysics.
arXiv:2609.10422 [pdf, ps, other]Title: Wave Emission and Absorption in a Near-Sun Proton-Cyclotron Wave StormAuthors: Kristopher G Klein, Daniel Verscharen, Mihailo Martinovic, Niranjana, Ali Rahmati, Roberto Livi, Davin Larson, Michael Stevens,Comments: 20 pages, 10 figures, under review at Solar PhysicsSubjects: astro-ph.SR physics.plasm-ph physics.space-phCreated: 2026-09-09; Updated: 2026-09-10; Datestamp: 2026-09-10Quantification of energy transport and dissipation in weakly collisional heliospheric plasmas that are far from local thermodynamic equilibrium is an outstanding scientific problem. A central challenge is determining how non-Maxwellian velocity-space structure affects damping and emission of coherent ion-scale waves, especially compared to simplified analytical models for background plasma velocity distributions. In this work, we study the damping and emission of parallel-propagating proton cyclotron waves for two models of proton velocity distributions measured by the SPAN-I instrument on board Parker Solar Probe during an extended storm of waves with left-hand POLARIZATION in the solar wind at a heliocentric distance of 30.1 solar radii. Using the measured velocity distribution rather than a two-component bi-Maxwellian model predicts instabilities consistent with the observed coherent waves. For intervals in which both models predict net damping, the observed VDF model yields weaker damping in 90\% of cases, with a reduction in the integrated heating rate of 0.44 relative to the bi-Maxwellian model. These results suggest that simplified analytical velocity distribution models may overestimate cyclotron damping and underestimate wave emission in the near-Sun solar wind.
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