Current date: 2025-10-02
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Number of records retrieved: 633
Keyword score statistics
score 10 -- 1 abstracts
score 9 -- 1 abstracts
score 8 -- 3 abstracts
score 7 -- 3 abstracts
score 6 -- 1 abstracts
score 5 -- 5 abstracts
score 4 -- 1 abstracts
score 3 -- 5 abstracts
score 2 -- 17 abstracts
in total -- 37 abstracts
Articles that appeared on 2025-10-02
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[abstract 1 / 37] Wow! (score: 10)
- Title: Multiband Optical Photometric and Spectroscopic Monitoring of the 2024 Flare Event in Transition Blazar OP313Authors: TianFang Zhang, Mitsuru Kokubo, Mamoru Doi, Haruna Hagio, Hibiki Seki, Ichiro Takahashi, Katsuhiro L. Murata, Kazuya Matsubayashi, Keisuke Isogai, Koji Kawabata, Mahito Sasada, Masafumi Niwano, Masaki Hashizume, Megumi Shidatsu, Narikazu Higuchi, Ryo Imazawa, Shigeaki Joshima, Shigeyuki Sako, Shunsuke Hayatsu, Yoichi Yatsu, Wataru Iwakiri, Yoshiyuki Kubo,Comments:Subjects: astro-ph.HECreated: 2025-10-01; Updated: 2025-10-02; Datestamp: 2025-10-02
Blazars are ACTIVE GALACTIC NUCLEi known for their extreme variability, offering unique opportunities to study JET physics and high-energy emission mechanisms. In 2024, the Flat Spectrum Radio Quasar (FSRQ) OP313 underwent a remarkable flare event, during which the gamma-ray flux observed by the FERMI Large Area Telescope (FERMI/LAT) increased by a factor of 60 over its average value. The flare peak lasted less than two days. Using optical telescopes, we conducted 100-day time-scale observations. Multi-wavelength data revealed that OP313 entered an active state 50 days prior to the flare and remained active for at least 50 days afterward. We propose that this prolonged activity results from variations in electron density within the shock front due to changes in the accretion rate. Concurrently, OP313's spectrum transitioned from an FSRQ-like state to a BL Lac-like state, characterized by a significant increase in the SYNCHROTRON peak frequency and the disappearance of broad-line region emission lines. In the post-flare phase, we observed a decoupling between SYNCHROTRON radiation and inverse Compton scattering, along with a possible decrease in the MAGNETic field strength within the shock front.
[abstract 2 / 37] Wow! (score: 9) - Title: Modelling multiwavelength afterglows of the VHE-GRB populationAuthors: Monica Barnard, Ankur Ghosh, Jagdish C. Joshi, Soebur Razzaque,Comments: 17 pages, 20 figures, Accepted for publication in MNRASSubjects: astro-ph.HECreated: 2025-10-01; Updated: 2025-10-02; Datestamp: 2025-10-02
The recent detection of very high energy (VHE, $\gtrsim$ 100 GeV) $γ$-ray emission from GAMMA-RAY BURSTs (GRBs) has provided new insights into afterglow physics. Understanding the temporal and spectral evolution of VHE GRBs requires detailed modelling of multiwavelength observations spanning radio to VHE $γ$ rays. Previous studies interpreted afterglow of VHE GRBs using a range of frameworks, including single- and multi-zone JET configurations, SYNCHROTRON radiation from forward and reverse shocks, SYNCHROTRON self-Compton (SSC) processes, as well as hadronic emission processes. We have modeled five long-duration VHE GRBs - GRB 180720B, GRB 190114C, GRB 190829A, GRB 201216C and GRB 221009A; using the NAIMA code and modifications to it. The results from our analysis indicate that SSC is the dominant VHE emission mechanism, with negligible contribution from external Compton. Most VHE GRBs are well described by the forward shock model in a spherical JET configuration, where constant density interstellar medium is preferred over wind medium. Additionally, we find that VHE GRBs tend to occur in environments with lower MAGNETic fields and higher ambient medium densities. Interestingly, VHE GRBs lie at the edge of the $3σ$ region of the $E_{\rm k,iso}$ - $ε_B$ correlation observed in other energetic GRBs. Our model slightly over predicts the radio fluxes, indicating that a more complicated modelling might be required in some cases. These findings provide crucial constraints on VHE GRB emission sites and mechanisms and serve as a benchmark for future observations and theoretical studies in the era of CTA and next-generation $γ$-ray observatories.
[abstract 3 / 37] Wow! (score: 8) - Title: Comprehensive X-ray Observations of the Exceptional Ultra-long X-ray and Gamma-ray Transient GRB 250702B with SWIFT, NUSTAR, and Chandra: Insights from the X-ray Afterglow PropertiesAuthors: Brendan O'Connor, Ramandeep Gill, James DeLaunay, Jeremy Hare, Dheeraj Pasham, Eric R. Coughlin, Ananya Bandopadhyay, Akash Anumarlapudi, Paz Beniamini, Jonathan Granot, Igor Andreoni, Jonathan Carney, Michael J. Moss, Ersin Göğüş, Jamie A. Kennea, Malte Busmann, Simone Dichiara, James Freeburn, Daniel Gruen, Xander J. Hall, Antonella Palmese, Tyler Parsotan, Samuele Ronchini, Aaron Tohuvavohu, Maia A. Williams,Comments: Submitted to ApJLSubjects: astro-ph.HECreated: 2025-10-01; Updated: 2025-10-02; Datestamp: 2025-10-02
GRB 250702B is an exceptional transient that produced multiple episodes of luminous gamma-ray radiation lasting for $>25$ ks, placing it among the class of ultra-long GAMMA-RAY BURSTs (GRBs). However, unlike any known GRB, the \textit{Einstein Probe} detected soft X-ray emission up to 24 hours before the gamma-ray triggers. We present comprehensive X-ray observations of the transient's afterglow obtained with the Neil Gehrels SWIFT Observatory, the Nuclear Spectroscopic Telescope Array, and the Chandra X-ray Observatory between 0.5 to 65 days (observer frame) after the initial high-energy trigger. The X-ray emission decays steeply as $\sim t^{-1.9}$, and shows short timescale X-ray variability ($ΔT/T < 0.03$) in both SWIFT and NUSTAR, consistent with flares superposed on an external shock continuum. Serendipitous detections by the SWIFT Burst Alert Telescope (BAT) out to $\sim$0.3 days and continued NUSTAR variability to $\sim$2 days imply sustained central engine activity; including the precursor, the required engine duration is $\gtrsim 3$ days. Afterglow modeling favors the combination of forward and reverse shock emission in a wind-like ($k \approx 2$) environment. These properties, especially the long-lived engine and early soft X-ray emission, are difficult to reconcile with a collapsar origin, and GRB 250702B does not fit neatly with canonical ultra-long GRBs or RELATIVISTIC tidal disruption events (TDEs). A hybrid scenario in which a star is disrupted by a stellar-mass BLACK HOLE (a micro-TDE) provides a plausible explanation, although a RELATIVISTIC TDE from an intermediate-mass BLACK HOLE remains viable. Decisive discrimination between progenitors will require sensitive late-time X-ray observations.
[abstract 4 / 37] Wow! (score: 8) - Title: Automated Modeling with AAP-Imfit: Astrometry and Photometry via CASAAuthors: Alfredo Amador-Portes, Eva Palafox, Víctor M. Patiño-Álvarez, Vahram Chavushyan, Andrei P. Lobanov, Sergio A. Dzib,Comments: 15 pages, 10 Figures, 1 Table. Accepted for publication in ApJSubjects: astro-ph.IM astro-ph.GA astro-ph.HECreated: 2025-09-30; Updated: 2025-10-02; Datestamp: 2025-10-02
Very Long Baseline Interferometry (VLBI) provides the highest-resolution radio intensity maps, crucial for detailed studies of compact sources like ACTIVE GALACTIC NUCLEi (AGN) and their RELATIVISTIC JETs. Analyzing JET components in these maps traditionally involves manual Gaussian fitting, a time-consuming bottleneck for large datasets. To address this, we present an automated batch-processing tool, based on the Gaussian fitting capabilities of CASA, designed to streamline VLBI JET component characterization (AAP-Imfit). Our algorithm sets a detection limit, performs automatic 2D Gaussian fitting, and removes model artifacts, efficiently extracting component flux densities and positions. This method enables systematic and reproducible analysis, significantly reducing the time required for fitting extensive VLBI datasets. We validated AAP-Imfit by using VLBI observations of the BLAZARs 3C 279 and 3C 454.3, comparing our results with published fits. The close agreement in residual root mean square (RMS) values and model/residual-to-map RMS ratios confirms the accuracy of our automated approach in reproducing original flux distributions. While visual inspection remains important for complex or faint features, this routine significantly accelerates VLBI component fitting, paving the way for large-scale statistical studies of JET dynamics.
[abstract 5 / 37] Wow! (score: 8) - Title: Diffuse neutrino flux from coronal MAGNETospheric current sheets of accreting BLACK HOLEsAuthors: Despina Karavola, Maria Petropoulou, Damiano F. G. Fiorillo, Luca Comisso, Lorenzo Sironi,Comments: 8 pages, 2 figures, ICRC 2025 proceedingSubjects: astro-ph.HECreated: 2025-10-01; Updated: 2025-10-02; Datestamp: 2025-10-02
Non-JETted AGN exhibit hard X-ray emission with a power law spectrum above $\sim$2 keV, which is thought to be produced through Comptonization of soft photons by electrons and positrons (pairs) in the vicinity of the BLACK HOLE. The origin and composition of this plasma source, known as the corona, is a matter open for debate. Our study focuses on the role of RELATIVISTIC protons accelerated in black-hole MAGNETospheric current sheets in the neutrino production of AGN coronae. We present a model that has two free parameters, namely the proton plasma MAGNETization $σ_{\rm p}$, which controls the peak energy of the neutrino spectrum, and the Eddington ratio $λ_{\rm Edd}$ (defined as the ratio between X-ray luminosity $L_{\rm X}$ and Eddington luminosity $L_{\rm Edd}$), which controls the amount of energy transferred to secondary particles. Furthermore, we combine our coronal model with an AGN population in order to provide a prediction for the diffuse neutrino flux measured on Earth. We compare our results with the observational data by IceCube and we find a satisfactory agreement on both the flux value and the slope of the neutrino distribution when we assume a $σ_{\rm p}$ value of $10^5$ for all the sources in our sample.
[abstract 6 / 37] Wow! (score: 7) - Title: Atacama Cosmology Telescope: Observations of supermassive BLACK HOLE binary candidates. Strong sinusoidal variations at 95, 147 and 225 GHz in PKS 2131$-$021 and PKS J0805$-$0111Authors: Adam D. Hincks, Xiaoyi Ma, Przemek Mróz, Sigurd K. Naess, Sebastian Kiehlmann, Roger D. Blandford, J. Richard Bond, Mark Devlin, Jo Dunkley, Allen Foster, Matthew J. Graham, Yilun Guan, Carlos Hervías-Caimapo, John C. Hood, Arthur Kosowsky, Aretaios Lalakos, Elias R. Most, Michael D. Niemack, John Orlowski-Scherer, Lyman A. Page, Bruce Partridge, Anthony C. S. Readhead, Cristóbal Sifón, Suzanne T. Staggs, Andrew G. Sullivan, Cristian Vargas,Comments: 20 pages, 11 figures, 9 tables. Revised version after referee's report, resubmitted to A&A on 17 Sept. 2025Subjects: astro-ph.HE astro-ph.GACreated: 2025-10-01; Updated: 2025-10-02; Datestamp: 2025-10-02
Large sinusoidal variations in the radio light curves of the BLAZARs PKS J0805$-$0111 and PKS 2131$-$021 have recently been discovered with an 18-year monitoring programme at the Owens Valley Radio Observatory, making these systems strong supermassive BLACK HOLE binary (SMBHB) candidates. The sinusoidal variations in PKS 2131$-$021 dominate its light curves from 2.7 GHz to optical frequencies. We report sinusoidal variations observed in both objects with the Atacama Cosmology Telescope (ACT) at 95, 147 and 225 GHz consistent with the radio light curves. The ACT 95 GHz light curve of PKS 2131$-$021 agrees well with the contemporaneous 91.5 GHz ALMA light curve and is comparable in quality, while the ACT light curves of PKS J0805$-$0111, for which there are no ALMA or other millimetre light curves, show that PKS 2131$-$021 is not an isolated case, and that this class of AGN exhibits the following properties: (a) the sinusoidal pattern dominates over a broad range of frequencies; (b) the amplitude of the sine wave compared to its mean value is monochromatic (i.e., nearly constant across frequencies); (c) the phase of the sinusoid phase changes monotonically as a function of frequency; (d) the sinusoidal variations are intermittent. We describe a physical model for SMBHB systems, the modified Kinetic Orbital model, that explains all four of these phenomena. Monitoring of ${\sim}8000$ BLAZARs by the Simons Observatory over the next decade should provide a large number of SMBHB candidates that will shed light on the nature of the nanohertz gravitational-wave background.
[abstract 7 / 37] Wow! (score: 7) - Title: Dissecting the radiation mechanism of short GRB~160821B through multi-wavelength modellingAuthors: Ankur Ghosh, Monica Barnard, Jagdish C. Joshi, Soebur Razzaque,Comments: 9 pages, 5 figuresSubjects: astro-ph.HECreated: 2025-10-01; Updated: 2025-10-02; Datestamp: 2025-10-02
GRB~160821B is the only short GRB detected to date at very high energy (VHE, $\gtrsim 100$ GeV). At a redshift $z=0.161$, it was detected by MAGIC telescopes approximately four hours since the trigger. VHE dataset was complied with the datasets of other wavelengths in between the timescale of 1.7 to 4 hours to construct the broadband spectral energy distribution (SED). In previous studies of GRB~160821B, SYNCHROTRON and external Compton (EC) model could explain the VHE emission better than the SYNCHROTRON and SYNCHROTRON self-Compton (SSC) model. Although, these fits were mostly eyeballing data without any optimisation. Our model includes the combination of SYNCHROTRON, SSC, and EC models with Markov Chain Monte Carlo (MCMC) techniques. Our analysis reveals that the EC contribution is negligible in comparison with the SSC and our model explains the VHE data well for the wind medium. We found that GRB~160821B is the least energetic VHE GRB and it occurred in high density wind medium which is quiet unusual for a short GRB. But like other long-duration VHE GRBs, GRB~160821B occurred in a poorly MAGNETised medium. As there is no statistical study on afterglow modelling of short GRB sample, we compare the inferred properties of GRB~160821B with other VHE GRBs. It stands out distinctively in the $E_{k, \rm iso}$ - $ε_B$ parameter space and lies outside the 3-$σ$ region of the correlation. In future, more VHE detections of short GRBs, in the CTA era, will provide crucial insights into the emission sites, radiation mechanisms, and particle acceleration, as well as their connection to long GRBs.
[abstract 8 / 37] Wow! (score: 7) - Title: Quasar Main Sequence unfolded by 2.5D FRADO (Natural expression of Eddington ratio, BLACK HOLE mass, and inclination)Authors: M. H. Naddaf, M. L. Martínez-Aldama, P. Marziani, B. Czerny, D. Hutsemékers,Comments: 4 pages plus 2 pages of appendices, 3 figures, originally accepted for publication in A&A LettersSubjects: astro-ph.GA astro-ph.HECreated: 2025-10-01; Updated: 2025-10-02; Datestamp: 2025-10-02
The QUASAR main sequence (QMS), characterized by the Eigenvector 1 (EV1), serves as a unifying framework for classifying type-1 ACTIVE GALACTIC NUCLEi (AGNs) based on their diverse spectral properties. Although a fully self-consistent physical interpretation has long been lacking, our physically motivated 2.5D FRADO (Failed Radiatively Accelerated Dusty Outflow) model naturally predicts that the Eddington ratio ($\dot{m}$) is the primary physical driver of the QMS, with BLACK HOLE mass ($M_{\rm BH}$) and inclination ($i$) acting as secondary contributors. We employed a dense grid of FRADO simulations of the geometry and dynamics of the broad-line region (BLR), covering a representative range of $M_{\rm BH}$ and $\dot{m}$. For each simulation, we computed the full width at half maximum (FWHM) of the H$β$ line under different $i$. The resulting FWHM--$\dot{m}$ diagram closely resembles the characteristic trend observed in the EV1 parameter space. This establishes the role of $\dot{m}$ as the true proxy for the Fe II strength parameter ($R_{\rm Fe}$), and vice versa. Our results suggest that $\dot{m}$ can be regarded as the sole underlying physical tracer of $R_{\rm Fe}$ and should therefore scale directly with it. The $M_{\rm BH}$ accounts for the virial mass-related scatter in FWHM, while $i$ acts as a secondary driver modulating $R_{\rm Fe}$ and FWHM for a given $\dot{m}$ and $M_{\rm BH}$.
[abstract 9 / 37] Yes (score: 6) - Title: Accelerating SED Modeling of Astrophysical Objects Using Neural NetworksAuthors: Federico Testagrossa, Georgios Vasilopoulos, Despina Karavola, Stamatios Ilias Stathopoulos, Maria Petropoulou, Chengchao Yuan, Walter Winter,Comments: 4 pages, 2 figures. Proceedings of the "IAUS 397: Exploring the Universe with Artificial Intelligence (UniversAI)" conferenceSubjects: astro-ph.HE astro-ph.IMCreated: 2025-09-30; Updated: 2025-10-02; Datestamp: 2025-10-02
Interpreting the spectral energy distributions (SEDs) of astrophysical objects with physically motivated models is computationally expensive. These models require solving coupled differential equations in high-dimensional parameter spaces, making traditional fitting techniques such as Markov Chain Monte Carlo or nested sampling prohibitive. A key example is modeling non-thermal emission from BLAZAR JETs - RELATIVISTIC outflows from supermassive BLACK HOLEs in Active Galactic Nuclei that are among the most powerful emitters in the Universe. To address this challenge, we employ machine learning to accelerate SED evaluations, enabling efficient Bayesian inference. We generate a large sample of lepto-hadronic BLAZAR emission models and train a neural network (NN) to predict the photon spectrum with strongly reduced run time while preserving accuracy. As a proof of concept, we present an NN-based tool for BLAZAR SED modeling, laying the groundwork for future extensions and for providing an open-access resource for the astrophysics community.
[abstract 10 / 37] Yes (score: 5) - Title: Ultra-long Gamma-ray Bursts from Micro-Tidal Disruption Events: The Case of GRB 250702BAuthors: Paz Beniamini, Hagai B. Perets, Jonathan Granot,Comments: 12 pages, 1 figure. SubmittedSubjects: astro-ph.HECreated: 2025-09-30; Updated: 2025-10-02; Datestamp: 2025-10-02
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 precursor $\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 precursor-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 11 / 37] Yes (score: 5) - Title: Search for UHE neutrinos from GRBs with the Pierre Auger ObservatoryAuthors: Yago Lema-Capeans,Comments: Presented at the 39th International Cosmic Ray Conference (ICRC 2025). 12 pages, 4 figuresSubjects: astro-ph.HECreated: 2025-09-30; Updated: 2025-10-02; Datestamp: 2025-10-02
We report on the search for ultra-high-energy neutrinos from the prompt emission of GAMMA-RAY BURSTs (GRBs) using Surface Detector (SD) data from Phase I of the Pierre Auger Observatory (2004-2021). A total of 570 GRBs occur within the most neutrino-sensitive field of view of the SD, considering both Earth-skimming and downward-going detection channels. For this purpose, GRB neutrino emission has been modeled using the numerical software NeuCosmA, incorporating gamma-ray measurements and inferred parameters such as the JET Lorentz factor and the minimum variability time scale. No neutrino candidates were found, and upper limits were obtained by stacking the individual GRB neutrino fluences. These limits are complementary to those of IceCube and ANTARES and provide the strongest constraints on prompt GRB neutrino fluence above $10^{18}$ eV. Additionally, limits on GRB fluence in alternative models of neutrino production have been derived using Auger data.
[abstract 12 / 37] Yes (score: 5) - Title: Late-afterglow Emission from a Quasi-spherical Outflow in a stratified environmentAuthors: Nissim Fraija, Boris Betancourt-Kamenetskaia, Antonio Galván, Alvaro Montalvo, A. C. Caligula Do E. S. Pedreira, Peter Veres, Rosa Leticia Becerra, Maria G. Dainotti, Simone Dichiara, Hermes León Vargas,Comments: 26 pages, 9 figures, 5 tables, Accepted in MNRASSubjects: astro-ph.HECreated: 2025-09-30; Updated: 2025-10-02; Datestamp: 2025-10-02
Gamma-ray bursts (GRBs) are cosmic events occurring at large distances beyond our galaxy. They provide a unique opportunity to study electroMAGNETic patterns not seen elsewhere. When the collimated GRB outflow interacts with the outer layers of a star or the wind generated by a binary neutron star merger, it releases energy, forming a quasi-spherical outflow around it. This broad outflow begins to radiate once it has transferred enough energy to the surrounding medium. We have developed a new analytical model that describes the SYNCHROTRON afterglow scenario of the quasi-spherical outflow, including factors such as stratified density, self-absorption regime, and the fraction of electrons accelerated by the shock front. We also successfully describe the multiwavelength observations of a sample of llGRB afterglows (GRB 980425, 031203, 060218, 100316D, 130603B, 150101B and 171205A) that exhibited a late component, analyzed in both stellar wind and constant-density environments. Our analysis shows that a constant-density environment is favored. Additionally, we consider the multiwavelength upper limits of the short bursts reported in the SWIFT-BAT database.
[abstract 13 / 37] Yes (score: 5) - Title: Addressing Selected Gamma-Ray Burst Science Topics with Future Space InstrumentsAuthors: Nicolas De Angelis,Comments: 12 pages, PoS paper from the Frontier Research in Astrophysics - IV (FRAPWS2024) workshopSubjects: astro-ph.HE astro-ph.IMCreated: 2025-10-01; Updated: 2025-10-02; Datestamp: 2025-10-02
Gamma-ray bursts (GRBs) are among the most energetic events in the universe, offering insights into stellar collapse, extreme matter behavior, and cosmic evolution. The advent of multi-messenger astronomy, combining electroMAGNETic, gravitational wave, and neutrino observations, alongside advances in high-energy polarimetry, is revolutionizing GRB research, enabling deeper exploration of their physical mechanisms. This manuscript summarizes how upcoming and proposed space-based missions will tackle key challenges in GRB science, focusing on four areas: (i) identifying high-redshift GRBs to probe the early universe, (ii) enhancing multi-messenger detection and localization, (iii) improving multi-wavelength follow-up of GRB afterglows, and (iv) studying prompt emission POLARIZATION to understand JET dynamics and MAGNETic fields. Highlighting planned missions and their advancements, this work provides a snapshot of current GRB research frontiers, with updates on the evolving status of these missions.
[abstract 14 / 37] Yes (score: 5) - Title: Do plasmoids induce fast MAGNETic RECONNECTion in well-resolved current sheets in 2D MHD simulations?Authors: G. H. Vicentin, G. Kowal, E. M. de Gouveia Dal Pino, A. Lazarian,Comments: 21 pages, 12 figuresSubjects: physics.plasm-ph astro-ph.HE hep-thCreated: 2025-10-01; Updated: 2025-10-02; Datestamp: 2025-10-02
We investigate the development of tearing-mode instability using the highest resolution two-dimensional MAGNETohydrodynamic simulations of RECONNECTing current sheets on a uniform grid, for Lundquist numbers $10^3 \le S \le 2 \times 10^5$. Although the tearing-mode instability is commonly thought to trigger a plasmoid cascade that enables fast RECONNECTion - i.e., independent of $S$ - our results, in broad agreement with the recent findings of Morillo \& Alexakis (2025), challenge this belief. We demonstrate a Sweet-Parker scaling of the RECONNECTion rate $V_{\text{rec}} \sim S^{-1/2}$ up to Lundquist numbers $S \sim 10^4$. For larger values, plasmoid formation sets in leading to a slight enhancement of the RECONNECTion rate, $V_{\text{rec}} \sim S^{-1/3}$, consistent with the prediction from linear tearing mode induced RECONNECTion, indicating that RECONNECTion remains resistivity dependent, and therefore slow. In our simulations, the plasmoids do not form a cascade of mergers, as they are rapidly advected out of the RECONNECTion layer. Our findings call for the revision of the role of plasmoid formation in 2D high Lundquist number MAGNETic RECONNECTion. Even if future studies demonstrate that 2D plasmoid-RECONNECTion becomes resistivity-independent at sufficiently large $S$, directly extending those results to 3D astrophysical environments is not justified, as in realistic circumstances, the increase of $S$ also raises the Reynolds number of the outflows, making it essential to account for the dominant role of turbulence.
[abstract 15 / 37] Yes (score: 4) - Title: Kinetic Simulations of Particle Acceleration in Relativistic Perpendicular Electron-positron Shocks with Proton AdmixtureAuthors: Huan Yu, Qi Xia, Jun Fang,Comments: 8 pages, 10 figuresSubjects: astro-ph.HECreated: 2025-10-01; Updated: 2025-10-02; Datestamp: 2025-10-02
Particle acceleration in RELATIVISTIC shocks of electron-positron plasmas with proton admixture is investigated through two-dimensional (2D) particle-in-cell (PIC) simulations. The upstream plasma, with a bulk Lorentz factor of $10$ and a MAGNETization parameter of 0.02, includes a small fraction of protons ($\sim 5\%$ by number). A RELATIVISTIC perpendicular shock is formed by reflecting the flow off a conducting wall. The shock structure, electroMAGNETic fields, and particle energy spectra are analyzed. The particle density and the MAGNETic field have fluctuations. In the far-downstream region of the shock, positrons are accelerated to energies comparable to protons and develop a hard nonthermal component with a spectral index of $\sim 2$ in their energy spectrum, while electrons remain confined to lower energies. This asymmetry is attributed to the POLARIZATION properties of proton-driven electroMAGNETic waves, which favor positron acceleration. The results highlight the importance of plasma composition in shaping particle acceleration and nonthermal emission in RELATIVISTIC shocks. These findings provide new insights into the microphysics of particle acceleration in astrophysical sources containing RELATIVISTIC shocks.
[abstract 16 / 37] (score: 3) - Title: The Evolution of Pop III.1 Protostars Powered by Dark Matter Annihilation. II. Dependence on WIMP PropertiesAuthors: Konstantinos Topalakis, Devesh Nandal, Jonathan C. Tan,Comments: Submitted to A&A, 11 pages, 7 figures, comments are welcomeSubjects: astro-ph.GA astro-ph.CO astro-ph.HE astro-ph.SR hep-phCreated: 2025-09-30; Updated: 2025-10-02; Datestamp: 2025-10-02
The rapid appearance of supermassive BLACK HOLEs (SMBHs) at $z\gtrsim7$ requires efficient pathways to form massive BLACK HOLE seeds. We investigate whether annihilation of weakly interacting massive particles (WIMPs) can alter primordial (Pop III.1) protostellar evolution sufficiently to enable formation of such `heavy'' seeds. Using the one-dimensional Geneva stellar-evolution code (GENEC) with an implemented Gould single-scatter capture module, we compute a grid of protostellar evolution models covering ambient WIMP mass densities $ρ_χ=10^{12}$-$10^{16}\ \mathrm{GeV\,cm^{-3}}$, WIMP masses $m_χ=30$-$3000\ \mathrm{GeV}$, spin-dependent cross sections $σ_{\rm SD}=10^{-42}$-$10^{-40}\ \mathrm{cm^2}$, and baryonic accretion rates $\dot{M_*}=(1-3)\times10^{-3}\, M_\odot \,{\rm yr}^{-1}$. We find a robust bifurcation of outcomes. For sufficiently high ambient DARK MATTER density ($ρ_χ\gtrsim5\times10^{14}\ \mathrm{GeV\,cm^{-3}}$) and capture efficiency ($σ_{\rm SD}\gtrsim10^{-41}\ \mathrm{cm^2}$) WIMP annihilation supplies enough energy to inflate protostars onto extended, cool (Hayashi-track) configurations that dramatically suppress ionizing feedback and permit uninterrupted growth to $\sim10^{5}\,M_\odot$. Lighter WIMPs and larger $σ_{\rm SD}$ favour earlier and stronger annihilation support; heavier WIMPs delay the effect. For our fiducial case, WIMP masses $<$3 TeV are essential for allowing growth to the supermassive regime, otherwise the protostar evolves to the compact, feedback-limited regime that results in `light'' seeds. These results indicate that, under plausible halo conditions, DM annihilation provides a viable channel for forming heavy BLACK HOLE seeds.
[abstract 17 / 37] (score: 3) - Title: Redshifted civilizations, galactic empires, and the FERMI paradoxAuthors: Chris Reiss, Justin C. Feng,Comments: 18 pages, 7 figuresSubjects: gr-qc physics.pop-phCreated: 2025-10-01; Updated: 2025-10-02; Datestamp: 2025-10-02
Given the vast distances between stars in the Milky way and the long timescales required for interstellar travel, we consider how a civilization might overcome the constraints arising from finite lifespans and the speed of light without invoking exotic or novel physics. We consider several scenarios in which a civilization can migrate to a time-dilated frame within the scope of classical general relativity and without incurring a biologically intolerable level of acceleration. Remarkably, the power requirements are lower than one might expect; biologically tolerable orbits near the photon radius of Sgr A* can be maintained by a civilization well below the Type II threshold, and a single Type II civilization can establish a galaxy-spanning civilization with a time dilation factor of $10^4$, enabling trips spanning the diameter of the Milky way within a human lifetime in the civilizational reference frame. We also find that isotropic monochromatic signals from orbits near the photon radius of a BLACK HOLE exhibit a downward frequency drift. The vulnerability of ultraRELATIVISTIC vessels to destruction, combined with the relatively short timescales on which adversarial civilizations can arise, provides a strong motivating element for the ``dark forest'' hypothesis.
[abstract 18 / 37] (score: 3) - Title: Faraday DePOLARIZATION Study of a Radio Galaxy Using LOFAR Two-metre Sky Survey: Data Release 2Authors: Samantha Sneha Paul, Abhik Ghosh,Comments: 12 pages, 7 figures, SubmittedSubjects: astro-ph.COCreated: 2025-10-01; Updated: 2025-10-02; Datestamp: 2025-10-02
We present a detailed dePOLARIZATION analysis of a RADIO GALAXy ILTJ012215.21+254334.8, utilizing polarimetric data from the LOFAR Two-metre Sky Survey (LoTSS) Data Release 2 (DR2) catalogue. The selected source exhibits a rotation measure (RM) of ~ - 47 rad/m^2 and a projected linear size of 335 kpc at a redshift z ~ 0.05. DePOLARIZATION model fitting was performed on LOFAR High Band Antenna data (120 - 168 MHz), with fractional POLARIZATION detected at 3.0%. Five dePOLARIZATION models were tested, and Bayesian qu-fitting revealed that the three-component model (1T+2ED) best describes the data, with a reduced chi-squared value of 2.12 and a logarithmic Bayesian evidence of 1384.82. This model includes a Faraday-thin component at RM ~ - 0.3 rad/m^2 (instrumental leakage) and two external Faraday dispersion astrophysical emission at RM ~ - 47 rad/m^2. The results demonstrate that dePOLARIZATION in low-frequency RADIO GALAXies requires multi-component modelling and is driven by turbulence and inhomogeneity in the MAGNETo-ionic medium. Our findings highlight the potential of LOFAR POLARIZATION studies for probing galactic and intergalactic MAGNETic fields with high precision.
[abstract 19 / 37] (score: 3) - Title: Understanding the evolution of BLACK HOLE spin in X-ray binary systems: Case study of XTE~J1550-564Authors: L. Bartolomeo Koninckx, M. A. De Vito, O. G. Benvenuto,Comments: Accepted for publication in A&ASubjects: astro-ph.HE astro-ph.SRCreated: 2025-10-01; Updated: 2025-10-02; Datestamp: 2025-10-02
We present a comprehensive study of the X-ray binary system XTE~J1550-564, with the primary objective of analyzing the evolution of the BLACK HOLE's spin parameter. To achieve this objective, we embarked on the necessary step of identifying a plausible progenitor for the system. Using a set of models covering various parameter combinations, we were able to replicate the system's observed characteristics within acceptable error margins, including fundamental parameters such as component masses, orbital period, donor luminosity, and effective temperature. The model results indicate the possibility of diverse evolutionary pathways for the system, highlighting the significant role played by the initial mass of the donor star and the efficiency of mass transfer episodes. While some models are well-aligned with estimates of the mass transfer rate, they all fall short of explaining the BLACK HOLE's observed moderate spin ($a^* = 0.49$). We also explored alternative MAGNETic braking prescriptions, finding that only an extreme and fully conservative scenario, based on the convection and rotation boosted prescription, can reproduce the observed spin and only in a marginal way. Our study attempts to shed light on the complex dynamics of BLACK HOLE X-ray binaries and the challenges of explaining their observed properties with theoretical models.
[abstract 20 / 37] (score: 3) - Title: Machine Learning Approaches for Classifying Star-Forming Galaxies and Active Galactic Nuclei from MIGHTEE-Detected Radio Sources in the COSMOS FieldAuthors: Walter Silima, Fangxia An, Mattia Vaccari, Eslam A. Hussein, S. Randriamampandry,Comments: Accepted for publication in Monthly Notices of the Royal Astronomical SocietySubjects: astro-ph.GACreated: 2025-10-01; Updated: 2025-10-02; Datestamp: 2025-10-02
Radio SYNCHROTRON emission originates from both massive STAR FORMATION and BLACK HOLE accretion, two processes that drive galaxy evolution. Efficient classification of sources dominated by either process is therefore essential for fully exploiting deep, wide-field extragalactic radio continuum surveys. In this study, we implement, optimize, and compare five widely used supervised machine-learning (ML) algorithms to classify radio sources detected in the MeerKAT International GHz Tiered Extragalactic Exploration (MIGHTEE)-COSMOS survey as star-forming galaxies (SFGs) and ACTIVE GALACTIC NUCLEi (AGN). Training and test sets are constructed from conventionally classified MIGHTEE-COSMOS sources, and 18 physical parameters of the MIGHTEE-detected sources are evaluated as input features. As anticipated, our feature analyses rank the five parameters used in conventional classification as the most effective: the infrared-radio correlation parameter ($q_\mathrm{IR}$), the optical compactness morphology parameter (class$\_$star), stellar mass, and two combined mid-infrared colors. By optimizing the ML models with these selected features and testing classifiers across various feature combinations, we find that model performance generally improves as additional features are incorporated. Overall, all five algorithms yield an $F1$-score (the harmonic mean of precision and recall) $>90\%$ even when trained on only $20\%$ of the dataset. Among them, the distance-based $k$-nearest neighbors classifier demonstrates the highest accuracy and stability, establishing it as a robust and effective method for classifying SFGs and AGN in upcoming large radio continuum surveys.
[abstract 21 / 37] (score: 2) - Title: Neutron star evolution by combining discontinuous Galerkin and finite volume methodsAuthors: Ananya Adhikari, Wolfgang Tichy, Liwei Ji, Amit Poudel,Comments: 35 pages, 20 figuresSubjects: gr-qc astro-ph.HECreated: 2025-10-01; Updated: 2025-10-02; Datestamp: 2025-10-02
We present here a new hybrid scheme that combines a discontinuous Galerkin (DG) method with compact finite volume (FV) and finite difference (FD) methods. The computational mesh is divided into smaller elements that touch but do not overlap. Like a pure DG method, our new hybrid scheme requires information exchange only at the surface of neighboring elements. This avoids the need for ghost zones that are usually many points deep in traditional FV implementations. Furthermore, unlike traditional FV implementations, that need information exchange between each element and its 26 surrounding neighbors on noncuboid meshes, our new hybrid method exchanges information only between each element and its six nearest neighbors. With this reduced communication, we aim to retain the high scalability of DG when using large supercomputers. In addition, the information exchange between adjacent elements is much simpler than in a traditional FV implementation, because we always have grid points at the interface, so that only surface interpolation is required. As a result it is much easier to implement adaptive mesh refinement. The goal is to use DG in elements with smooth matter fields and to fall back onto the more robust FV/FD method in elements that contain nonsmooth shocks or star surfaces. For this we devise trouble criteria to decide whether an element should be evolved with DG or FV/FD. We use the Nmesh program to implement and test the new scheme. We successfully evolve various single neutron star cases. These include the challenging cases of a neutron star initially in an unstable equilibrium migrating to a stable configuration and a boosted neutron star. These cases are simulated for the first time here in full 3D with general RELATIVISTIC hydrodynamics using DG methods. We also describe additional numerical methods, such as the limiters and the atmosphere treatment we need for our simulations.
[abstract 22 / 37] (score: 2) - Title: A Multispacecraft Analysis and Modeling of Type III Radio Burst Exciter Deceleration in Inhomogeneous Heliospheric PlasmaAuthors: Francesco Azzollini, Eduard P. Kontar,Comments:Subjects: astro-ph.SR physics.plasm-ph physics.space-phCreated: 2025-10-01; Updated: 2025-10-02; Datestamp: 2025-10-02
Electron beams accelerated in solar flares and escaping from the Sun along open MAGNETic field lines can trigger intense radio emissions known as type III solar radio bursts. Utilizing observations by Parker Solar Probe (PSP), STEREO-A (STA), Solar Orbiter (SolO), and Wind spacecrafts, the speeds and accelerations of type III exciters are derived for simple and isolated type III solar bursts. For the first time, simultaneous four spacecraft observations allow to determine positions, and correct the resulting velocities and accelerations for the location between the spacecraft and the apparent source. We observe velocities and acceleration to change as $u(r) \propto r^{-0.37 \pm 0.14}$ and $a(r) \propto r^{-1.71 \pm 0.20}$ with radial distance from the Sun $r$. To explain the electron beam deceleration, we develop a simple gas-dynamic description of the electron beam moving through plasma with monotonically decreasing density. The model predicts that the beam velocity decreases as $u(f)\propto f^{1/4}(r)$, so the acceleration changes $\propto r^{-1.58}$ (and speed as $\propto r^{-0.29}$) for the plasma density profile $n(r)\propto r^{-2.3}$. The deceleration is consistent with the average observation values corrected for the type III source locations. Intriguingly, the observations also show differences in velocity and acceleration of the same type III observed by different spacecrafts. We suggest the difference could be related to the additional time delay caused by radio-wave scattering between the spacecraft and the source.
[abstract 23 / 37] (score: 2) - Title: Updated predictions for gravitational wave emission from TDEs for next generation observatoriesAuthors: Martina Toscani, Luca Broggi, Alberto Sesana, Elena Maria Rossi,Comments: Main body: 10 figures, 10 pages. Appendix: 2 figures, 2 pages. Accepted for publication on A&ASubjects: astro-ph.HECreated: 2025-10-01; Updated: 2025-10-02; Datestamp: 2025-10-02
In this paper, we investigate the gravitational wave (GW) emission from stars tidally disrupted by BLACK HOLEs (TDEs), using a semi-analytical approach. Contrary to previous works where this signal is modeled as a monochromatic burst, we here take into account all its harmonic components. On top of this, we also extend the analysis to a population of repeated-partial TDEs, where the star undergoes multiple passages around the BLACK HOLE before complete disruption. For both populations, we estimate the rate of individual GW-detections considering future observatories like LISA and a potential deci-Hertz (dHz) mission, and derive the GW background from these sources. Our conclusions, even if more conservative, are consistent with previous results presented in literature. In fact, full disruptions of stars will not be seen by LISA but will be important targets for dHz observatories. In contrast, GWs from repeated disruptions will not be detectable in the near future.
[abstract 24 / 37] (score: 2) - Title: X-ray Polarimetry of Accreting White Dwarfs: A Case Study of EX HydraeAuthors: Sean J. Gunderson, Swati Ravi, Herman L. Marshall, Dustin K. Swarm, Richard Ignace, Yael Naze, David P. Huenemoerder, Pragati Pradhan,Comments: 8 pages, 3 figures. Submitted to ApJSubjects: astro-ph.SR astro-ph.HECreated: 2025-09-30; Updated: 2025-10-02; Datestamp: 2025-10-02
We present the first first X-ray POLARIZATION measurements of a white dwarf, the intermediate polar EX Hya. We measured significant POLARIZATION only in the 2 -- 3 keV energy band with a POLARIZATION degree of 8 percent at a $3σ$ significance. No significant POLARIZATION was detected above 3 keV, which we attribute to the higher energy bands having lower signal-to-noise. We found that the scattering surface detected by the IXPE is nearly perpendicular to the optical scattering plane, showing that the X-ray scattering surface is the WD and close to the base of the accretion column. Finally, we show how the POLARIZATION can be used to estimate the height of the accretion shock above the white dwarf's surface.
[abstract 25 / 37] (score: 2) - Title: Towards a few percent measurement of the Hubble constant with the current network of gravitational wave detectors without using electroMAGNETic informationAuthors: Tom Bertheas, Vasco Gennari, Nicola Tamanini,Comments: 11 pages, 4 figures, 4 tablesSubjects: gr-qcCreated: 2025-10-01; Updated: 2025-10-02; Datestamp: 2025-10-02
Gravitational waves provide a novel and independent measurement of cosmological parameters, offering a promising avenue to address the Hubble tension alongside traditional electroMAGNETic observations. In the absence of electroMAGNETic counterparts or complete host galaxy catalogs, current measurements rely on population-based methods that statistically combine BLACK HOLE merger events. Building on recent models that incorporate additional structure in the primary BLACK HOLE mass distribution, using public data from the LIGO-Virgo-KAGRA (LVK) collaboration third observing run (O3), we obtain a 30% accuracy improvement on the measurement of the Hubble constant with respect to the result reported by LVK with the third GW transient catalog (GWTC-3). Employing a realistic simulation that includes full Bayesian single-event inference, we present forecasts for the upcoming LVK observational runs, O4 and O5. Using a three power-law mass model, we project a measurement of the Hubble constant with 20% accuracy at O4 sensitivity, improving to 2.7% accuracy at O5 sensitivity. Our findings demonstrate the potential for gravitational waves to provide a substantial contribution to solving the Hubble tension within the next decade of observations.
[abstract 26 / 37] (score: 2) - Title: Rare-event detection in a backward-facing-step flow using live optical-flow velocimetry: observation of an upstream JET burstAuthors: Juan Pimienta, Jean-Luc Aider,Comments:Subjects: physics.flu-dynCreated: 2025-10-01; Updated: 2025-10-02; Datestamp: 2025-10-02
Rare and extreme events in turbulent flows play a critical role in transport, mixing and transition, yet are notoriously difficult to capture experimentally. Here we report, to our knowledge, the first direct experimental detection of an upstream-directed JET burst in a backward-facing step (BFS) flow at $Re_h=2100$, using long-duration Live Optical Flow Velocimetry (L-OFV). Continuous monitoring over 1.5 h enabled a data-driven definition of extremes as rare velocity probes excursions deep into the observed distribution's tails; in practice, large negative events ($u: Z < -6$, $v: Z < -5$ at $(x,y) = (2h,h / 2)$, where $|Z| > > 0$ stands for large deviations from the mean value) triggered the live capture of surrounding velocity fields. The recording is triggered when the probes surpass the defined threshold, using live analysis of the velocity fields. The detected event features a JET-like intrusion into the recirculation region initiated by the collapse of a merged Kelvin-Helmholtz vortex and sustained by counter-rotating vortices, and is accompanied with heavy-tailed probe statistics and simultaneous amplification of fluctuating kinetic energy and enstrophy. While a single event was recorded, underscoring its rarity, the results establish L-OFV as a viable platform for rare-event detection in separated shear layers and document a previously unreported mechanism of upstream JET bursting in BFS flow.
[abstract 27 / 37] (score: 2) - Title: Testing the nature of GW200105 by probing the frequency evolution of eccentricityAuthors: Avinash Tiwari, Sajad A. Bhat, Md Arif Shaikh, Shasvath J. Kapadia,Comments:Subjects: astro-ph.HE gr-qcCreated: 2025-10-01; Updated: 2025-10-02; Datestamp: 2025-10-02
GW200105 is a compact binary coalescence (CBC) event, consisting of a neutron star and a BLACK HOLE, observed in LIGO-Virgo-KAGRA's (LVK's) third observing run (O3). Recent reanalyses of the event using state-of-the-art waveform models have claimed observation of signatures of an eccentric orbit. It has nevertheless been pointed out in the literature that certain physical or modified gravity effects could mimic eccentricity by producing a spurious non-zero eccentricity value, at a given reference frequency, when recovered with an eccentric waveform model. We recently developed a model-independent Eccentricity Evolution Consistency Test (EECT, S. A. Bhat et al. 2025) to identify such mimickers, by comparing the measured frequency $\textit{evolution}$ of eccentricity, $e(f)$, with that expected from General Relativity (GR). In this $\textit{Letter}$, we apply EECT to GW200105 and find that it satisfies EECT within 68% confidence. Our analysis therefore lends complementary support in favour of the eccentricity hypothesis, while also providing a novel test of the consistency of $e(f)$ with GR.
[abstract 28 / 37] (score: 2) - Title: Irony at z=6.68: a bright AGN with forbidden Fe emission and multi-component Balmer absorptionAuthors: Francesco D'Eugenio, Erica Nelson, Xihan Ji, Josephine Baggen, Jenny Greene, Ivo Labbé, Gabriele Pezzulli, Vanessa Brown, Roberto Maiolino, Jorryt Matthee, Elena Terlevich, Roberto Terlevich, Alberto Torralba, Stefano Carniani,Comments: 28 pages, 15 figures, 2 tables. Submitted to ApJSubjects: astro-ph.GACreated: 2025-09-30; Updated: 2025-10-02; Datestamp: 2025-10-02
We present the deepest medium-resolution JWST/NIRSpec spectroscopy to date of a bright Little Red Dot (LRD) AGN, Irony at z=6.68. The data reveal broad Balmer emission from H$α$-H$δ$ and Balmer absorption in H$α$-H$ε$. The absorption lines are kinematically split: H$α$ is blueshifted while higher-order lines are redshifted suggesting complex gas kinematics; their relative ratios are inconsistent with a single, passive absorbing screen. The line depths require absorption of both the BLR and the continuum, ruling out a stellar origin, consistent with the smooth Balmer break. We fit the broad H$γ$-H$α$ lines and find the data favor a double-Gaussian effective profile, although exponential wings are evident. Depending on the adopted profile, single-epoch virial estimates give log(M$_\bullet$/M$_\odot$)=7.86-8.39 and $λ_{\rm Edd}$=1.7-0.4. The dynamical mass implied by the narrow lines is low log(Mdyn/M$_\odot$)=9.1, suggesting an overmassive BLACK HOLE. The narrow lines display little attenuation, A$_V<0.5$ mag; while broad H$α$/H$β\sim9$ and the broad Balmer decrements are inconsistent with standard dust attenuation curves, suggesting collisional processes. The forbidden-line spectrum includes auroral [S II] and [N II], and a forest of [Fe II] lines. Line ratios and kinematics indicate a stratified narrow-line region with both low (n$_{\rm e}$=420 cm$^{-3}$) and high densities (n$_{\rm e}\gtrsim 6.3\times10^5$ cm$^{-3}$). We detect metal absorption lines in both the optical (Ca II and Na I) and UV range (Fe II UV1-UV3). Our results support a picture of a compact AGN embedded in a dense, high covering-factor and stratified cocoon, with complex neutral-gas kinematics. While the choice of broad-line profile affects the virial estimates of M$_\bullet$, we find the effect to be of order 0.6 dex between the different approaches.
[abstract 29 / 37] (score: 2) - Title: JWST-discovered AGN: evidence for heavy obscuration in the type-2 sample from the first stacked X-ray detectionAuthors: Andrea Comastri, Giorgio Lanzuisi, Fabio Vito, Stefano Marchesi, Marcella Brusa, Roberto Gilli, Ignas Juodzbalis, Roberto Maiolino, Giovanni Mazzolari, Guido Risaliti, Jan Scholtz, Cristian Vignali,Comments: Submitted to A&ASubjects: astro-ph.GA astro-ph.HECreated: 2025-09-30; Updated: 2025-10-02; Datestamp: 2025-10-02
One of the most puzzling properties of the high-redshift AGN population recently discovered by JWST, including both broad-line and narrow-line sources, is their X-ray weakness. With very few exceptions, and regardless of the optical classification, they are undetected at the limits of the deepest Chandra fields, even when stacking signals from tens of sources in standard observed-frame energy intervals (soft, hard, and full bands). It has been proposed that their elusive nature in the X-ray band is due to heavy absorption by dust-free gas or intrinsic weakness, possibly due to high, super-Eddington accretion. In this work, we perform X-ray stacking in three customized rest-frame energy ranges (1-4, 4-7.25, and 10-30 keV) of a sample of 50 Type 1 and 38 Type 2 AGN identified by JWST in the CDFS and CDFN fields. For the Type 2 sub-sample, we reach a total of about 210 Ms exposure, and we report a significant ($\sim 3σ$) detection in the hardest (10-30 keV rest frame) band, along with relatively tight upper limits in the rest frame softer energy bands. The most straightforward interpretation is in terms of heavy obscuration due to gas column densities well within the Compton thick regime ($> 2 \times 10^{24} $cm$^{-2}$) with a large covering factor, approaching 4$π$. The same procedure applied to the Type 1 sub-sample returns no evidence for a significant signal in about 140 Ms stacked data in any of the adopted bands, confirming their surprisingly elusive nature in the X-ray band obtained with previous stacking experiments. A brief comparison with the current observations and the implications for the evolution of AGN are discussed.
[abstract 30 / 37] (score: 2) - Title: Chase Orbits, not Time: A Scalable Paradigm for Long-Duration Eccentric Gravitational-Wave SurrogatesAuthors: Akash Maurya, Prayush Kumar, Scott E. Field, Chandra Kant Mishra, Peter James Nee, Kaushik Paul, Harald P. Pfeiffer, Adhrit Ravichandran, Vijay Varma,Comments: 12 pages, 7 figuresSubjects: gr-qc astro-ph.HE physics.comp-phCreated: 2025-09-30; Updated: 2025-10-02; Datestamp: 2025-10-02
Surrogate modeling of eccentric binary BLACK HOLE waveforms has remained challenging. The complicated morphology of these waveforms due to the eccentric orbital timescale variations makes it difficult to construct accurate and efficient surrogate models, especially for waveforms long enough to cover the sensitivity band of the current ground-based gravitational wave detectors. We present a novel and scalable surrogate building technique which makes surrogate modeling of long-duration eccentric binary BLACK HOLE waveforms both feasible and highly efficient. The technique aims to simplify the harmonic content of the intermediate eccentric surrogate data pieces by modeling them in terms of an angular orbital element called the mean anomaly, instead of time. We show that this novel parameterization yields an order of magnitude fewer surrogate basis functions than using the contemporary parameterization in terms of time. We show that variations in surrogate data-pieces across parameter space become much more regular when expressed in terms of the instantaneous waveform eccentricity and mean anomaly, greatly easing their parameter-space fitting. The methods presented in this work make it feasible to build long-duration eccentric surrogates for the current as well as future third-generation gravitational wave detectors.
[abstract 31 / 37] (score: 2) - Title: Electron neural closure for turbulent MAGNETosheath simulations: energy channelsAuthors: George Miloshevich, Luka Vranckx, Felipe Nathan de Oliveira Lopes, Pietro Dazzi, Giuseppe Arrò, Giovanni Lapenta,Comments: 16 pages, 9 figures, 4 tablesSubjects: physics.plasm-ph cs.LG physics.comp-phCreated: 2025-09-30; Updated: 2025-10-02; Datestamp: 2025-10-02
In this work, we introduce a non-local five-moment electron pressure tensor closure parametrized by a Fully Convolutional Neural Network (FCNN). Electron pressure plays an important role in generalized Ohm's law, competing with electron inertia. This model is used in the development of a surrogate model for a fully kinetic energy-conserving semi-implicit Particle-in-Cell simulation of decaying MAGNETosheath turbulence. We achieve this by training FCNN on a representative set of simulations with a smaller number of particles per cell and showing that our results generalise to a simulation with a large number of particles per cell. We evaluate the statistical properties of the learned equation of state, with a focus on pressure-strain interaction, which is crucial for understanding energy channels in turbulent plasmas. The resulting equation of state learned via FCNN significantly outperforms local closures, such as those learned by Multi-Layer Perceptron (MLP) or double adiabatic expressions. We report that the overall spatial distribution of pressure-strain and its conditional averages are reconstructed well. However, some small-scale features are missed, especially for the off-diagonal components of the pressure tensor. Nevertheless, the results are substantially improved with more training data, indicating favorable scaling and potential for improvement, which will be addressed in future work.
[abstract 32 / 37] (score: 2) - Title: Serendipitous Discovery of an Optically-Dark Ultra-Luminous Infrared Galaxy at $z$ = 3.4Authors: N. H. Hayatsu, Zhi-Yu Zhang, R. J. Ivison, Chao-Wei Tsai, Ping Zhou, Katsuya Okoshi, Chentao Yang, Yuri Nishimura, Kotaro Kohno, Nobunari Kashikawa, Masahiro Nagashima, Junfeng Wang, Denis Burgarella,Comments: Accepted to MNRAS. 9 pages, 3 figuresSubjects: astro-ph.GACreated: 2025-10-01; Updated: 2025-10-02; Datestamp: 2025-10-02
Dusty, submillimeter-selected galaxies without optical counterparts contribute a non-negligible fraction of the STAR FORMATION in the early universe. However, such a population is difficult to detect through classical optical/UV-based surveys. We report the serendipitous discovery of such an optically dark galaxy, behind the quadruply-lensed $z=2.56$ QUASAR, H1413+117, offset to the north by 6\arcsec. From $^{12}$CO $J=4$--3, $J=6$--5, and part of the $J=13$--12 transitions, which all spatially coincide with a compact submillimeter continuum emission, we determine an unambiguous spectroscopic redshift, $z=3.386\pm 0.005$. This galaxy has a molecular mass $M_{\rm mol} \sim 10^{11}$ M$_\odot$ and a BLACK HOLE mass $M_{\rm BH} \sim 10^{8}$ M$_\odot$, estimated from $^{12}$CO $J=4$--3 and archival {\it Chandra} X-ray data ($L_{\rm 2-10,keV} \sim 4 \times 10^{44}$\,erg\,s$^{-1}$), respectively. We also estimate a total infrared luminosity of $L_{\rm FIR} = (2.8\pm{2.3}) \times 10^{12}$ L$_\odot$ and a stellar mass of $M_* \lesssim 10^{11}$ M$_{\odot}$, from spectral energy distribution fitting. According to these simple mass estimations, this gas-rich and X-ray bright galaxy might be in a transition phase from starburst to QUASAR offering a unique case for studying galaxy-BLACK HOLE co-evolution under extremely dusty conditions.
[abstract 33 / 37] (score: 2) - Title: Evaluating solar wind forecast using MAGNETic maps that include helioseismic far-side informationAuthors: Stephan G. Heinemann, Dan Yang, Shaela I. Jones, Jens Pomoell, Eleanna Asvestari, Carl J. Henney, Charles N. Arge, Laurent Gizon,Comments: accepted in Solar PhysicsSubjects: astro-ph.SRCreated: 2025-10-01; Updated: 2025-10-02; Datestamp: 2025-10-02
To model the structure and dynamics of the heliosphere well enough for high-quality forecasting, it is essential to accurately estimate the global solar MAGNETic field used as inner boundary condition in solar wind models. However, our understanding of the photospheric MAGNETic field topology is inherently constrained by the limitation of systematically observing the Sun from only one vantage point, Earth. To address this challenge, we introduce global MAGNETic field maps that assimilate far-side active regions derived from helioseismology into solar wind modeling. Through a comparative analysis between the combined surface flux transport and helioseismic Far-side Active Region Model (FARM) MAGNETic maps and the base surface flux transport model without far-side active regions (SFTM), we assess the feasibility and efficacy of incorporating helio-seismic far-side information in space weather forecasting. We are employing the Wang-Sheeley-Arge Solar Wind (WSA) model for statistical evaluation and leveraging the three-dimensional heliospheric MHD model, EUHFORIA, to analyze a case study. Using the WSA model, we show that including far-side MAGNETic data improves solar wind forecasts for 2013-2014 by up to 50% in correlation and 3% in Root Mean Square Error and Mean Absolute Error, especially near Earth and STEREO-A. Additionally, our 3D modeling shows significant localized differences in heliospheric structure that can be attributed to the presence or absence of active regions in the MAGNETic maps used as input boundaries. This highlights the importance of including far-side information to more accurately model and predict space weather effects caused by solar wind, solar transients, and geoMAGNETic disturbances.
[abstract 34 / 37] (score: 2) - Title: The gas streamer G1-2-3 in the Galactic CenterAuthors: S. Gillessen, F. Eisenhauer, J. Cuadra, R. Genzel, D. Calderon, S. Joharle, T. Piran, D. C. Ribeiro, C. M. P. Russell, M. Sadun Bordoni, A. Burkert, G. Bourdarot, A. Drescher, F. Mang, T. Ott, G. Agapito, A. Agudo Berbel, A. Baruffolo, M. Bonaglia, M. Black, R. Briguglio, Y. Cao, L. Carbonaro, G. Cresci, Y. Dallilar, R. Davies, M. Deysenroth, I. Di Antonio, A. Di Cianno, G. Di Rico, D. Doelman, M. Dolci, S. Esposito, D. Fantinel, D. Ferruzzi, H. Feuchtgruber, N. M. Förster Schreiber, A. M. Glauser, P. Grani, M. Hartl, D. Henry, H. Huber, C. Keller, M. Kenworthy, K. Kravchenko, J. Lightfoot, D. Lunney, D. Lutz, M. Macintosh, F. Mannucci, D. Pearson, A. Puglisi, S. Rabien, C. Rau, A. Riccardi, B. Salasnich, T. Shimizu, F. Snik, E. Sturm, L. J. Tacconi, W. Taylor, A. Valentini, C. Waring, M. Xompero,Comments: 7 pages, 5 figures, under review at A&ASubjects: astro-ph.GACreated: 2025-10-01; Updated: 2025-10-02; Datestamp: 2025-10-02
The BLACK HOLE in the Galactic Center, Sgr A*, is prototypical for ultra-low-fed galactic nuclei. The discovery of a hand-full of gas clumps in the realm of a few Earth masses in its immediate vicinity provides a gas reservoir sufficient to power Sgr A*. In particular, the gas cloud G2 is of interest due to its extreme orbit, on which it passed at a pericenter distance of around 100 AU and notably lost kinetic energy during the fly-by due to the interaction with the BLACK HOLE accretion flow. 13 years prior to G2, a resembling gas cloud called G1, passed Sgr A* on a similar orbit. The origin of G2 remained a topic of discussion, with models including a central (stellar) source still proposed as alternatives to pure gaseous clouds. Here, we report the orbit of a third gas clump moving again along (almost) the same orbital trace. Since the probability of finding three stars on close orbits is very small, this strongly argues against stellar-based source models. Instead, we show that the gas streamer G1-2-3 plausibly originates from the stellar wind of the massive binary star IRS16SW. This claim is substantiated by the fact that the small differences between the three orbits - the orientations of the orbital ellipses in their common plane as a function of time - are consistent with the orbital motion of IRS 16SW.
[abstract 35 / 37] (score: 2) - Title: Novel very-high-frequency quasi-periodic oscillations of compact, non-singular objectsAuthors: Jens Boos, Felix Wunsch,Comments: 11 pages, 8 figures, comments welcome!Subjects: gr-qc astro-ph.HECreated: 2025-10-01; Updated: 2025-10-02; Datestamp: 2025-10-02
We report on a novel set of very-high-frequency quasi-periodic oscillations (VHFQPO's) in the context of compact, non-singular horizonless objects. Focussing on the static, spherically symmetric case we utilize metrics of non-singular BLACK HOLEs that are accompanied by a regulator length scale $L > 0$. The choice $L \gtrsim GM$ generically removes the horizon from these metrics leading to compact, horizonless but non-singular objects. This generically guarantees the existence of a stable orbit at small radii $r \ll r_\text{ISCO}$, independent of the angular momentum of the massive particle. Crucially, the absence of a horizon allows the resulting VHFQPO's to escape to infinity, spanning the range from 1kHz ($M = 10M_\odot$) to 25 kHz ($M = 2M_\odot$). Within the paradigm of non-singular spacetime geometries, the absence of such VHFQPO's from X-ray binary spectra implies the presence of a horizon around the central, compact object.
[abstract 36 / 37] (score: 2) - Title: The Clustering of Active Galactic Nuclei and Star Forming Galaxies in the LoTSS DeepFieldsAuthors: C. L. Hale, P. N. Best, K. J. Duncan, R. Kondapally, M. J. Jarvis, M. Magliocchetti, H. J. A. Röttgering, D. J. Schwarz, D. J. B. Smith, J. Zheng,Comments: 24 pages, 11 figures (main text), 5 figures (appendices), Accepted to MNRASSubjects: astro-ph.CO astro-ph.GACreated: 2025-10-01; Updated: 2025-10-02; Datestamp: 2025-10-02
Using deep observations across three of the LOFAR Two-metre Sky Survey Deep Fields, this work measures the angular clustering of star forming galaxies (SFGs) and low-excitation RADIO GALAXies (LERGs) to $z$$\lesssim$1.5 for faint sources, $S_{\textrm{144 MHz}}$$\geq$200 $μ$Jy. We measure the angular auto-correlation of LOFAR sources in redshift bins and their cross-correlation with multi-wavelength sources {to} measure the evolving galaxy bias for SFGs and LERGs. Our work shows the bias of the radio-selected SFGs increases from $b=0.90^{+0.11}_{-0.10}$ at $z \sim 0.2$ to $b = 2.94^{+0.36}_{-0.36}$ at $z \sim 1.2$; faster than the assumed $b(z)$$\propto$$1/D(z)$ models adopted in previous LOFAR cosmology studies (at sensitivities where AGN dominate), but in broad agreement with previous work. We further study the luminosity dependence of bias for SFGs and find little evidence for any luminosity dependence at fixed redshift, although uncertainties remain large for the sample sizes available. The LERG population instead shows a weaker redshift evolution with $b=2.33^{+0.28}_{-0.27}$ at $z \sim 0.7$ to $b=2.65^{+0.57}_{-0.55}$ at $z \sim 1.2$, though it is also consistent with the assumed bias evolution model ($b(z)$$\propto$$1/D(z)$) within the measured uncertainties. For those LERGs which reside in quiescent galaxies (QLERGs), there is weak evidence that they are more biased than the general LERG population and evolve from $b = 2.62^{+0.33}_{-0.33}$ at $z \sim 0.7$ to $b = 3.08^{+0.85}_{-0.84}$ at $z \sim 1.2$. This suggests the halo environment of radio sources may be related to their properties. These measurements can help constrain models for the bias evolution of these source populations, and can help inform multi-tracer analyses.
[abstract 37 / 37] (score: 2) - Title: First-Order Axial Perturbation of the Reissner-Nordström Metric In a Possible Chern-Simons Gravity BackgroundAuthors: Abhishek Rout, Brett Altschul,Comments: 24 pagesSubjects: gr-qcCreated: 2025-10-01; Updated: 2025-10-02; Datestamp: 2025-10-02
We axial perturbations of Reissner-Nordström BLACK HOLEs within the framework of Chern-Simons modified gravity, a theory with includes parity violation. We derive the governing equations for the perturbations, focusing on the radial function $R(r)$ and its behavior across distinct regions: near the singularity ($r \rightarrow 0$), between the inner and outer Reissner-Nordström horizons ($r_-< r< r_+$), and in the asymptotic regime ($r \rightarrow \infty$). Using a combination of analytical and numerical methods, we analyze the solutions for varying BLACK HOLE charge-to-mass ratios ($Q/M$) and angular momentum parameters ($l$). Key findings include the suppression of perturbations by the electroMAGNETic field for higher $Q/M$; the emergence of radial resonance-like behavior for specific $l$ values; and a high degree of symmetry for solutions in the extremal limit ($Q/M \sim 1$), attributed to the AdS$_2 \times S^2$ near-horizon geometry. The WKB approximation is employed to study high-$l$ regimes, revealing quantized radial modes and singular behavior in the extremal limit. Additionally, we explore the role of boundary conditions and the Chern-Simons scalar field $Θ$, showing that consistency demands a constant field (and thus no actually observable Chern-Simons effects) in this perturbative framework. These results provide insights into the stability and dynamical properties of charged BLACK HOLEs under axial perturbations.
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