Current date: 2026-08-26
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Datestamp limit: 2026-08-26 (0 days ago)
Created/updated limit: 2026-08-19 (7 days ago)
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Suggested sets: physics, physics:astro-ph, physics:gr-qc, physics:physics
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Scoring abstracts
Number of records retrieved: 821
Keyword score statistics
score 9 -- 1 abstracts
score 8 -- 1 abstracts
score 7 -- 1 abstracts
score 6 -- 2 abstracts
score 5 -- 4 abstracts
score 4 -- 4 abstracts
score 3 -- 13 abstracts
score 2 -- 21 abstracts
in total -- 47 abstracts
Articles that appeared on 2026-08-26
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[abstract 1 / 47] Wow! (score: 9)
- Title: Probing the Three-Dimensional Structure of a Jet with Faraday TomographyAuthors: Sawera Gull, Masaya Kurogi, Keitaro Takahashi,Comments: Accepted for publication in Publications of the Astronomical Society of Japan (PASJ)Subjects: astro-ph.HE astro-ph.GACreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
Magnetic fields play a fundamental role in the dynamics and radiation of JETs associated with ACTIVE GALACTIC NUCLEi (AGNs), where they accelerate and collimate the RELATIVISTIC plasma and produce the observed SYNCHROTRON emission. Faraday tomography is a powerful technique for probing the three-dimensional distribution of MAGNETic fields and SYNCHROTRON-emitting plasma along the line of sight, by reconstructing the Faraday Dispersion Function (FDF) from the observed POLARIZATION spectrum. To explore what aspects of AGN-JET structure can be revealed by Faraday tomography, we construct a simple three-dimensional model of an AGN JET that captures its essential features, and compute the resulting FDF for a range of model parameters. The JET is represented as a cylindrical region of uniform thermal-electron density threaded by a coherent helical MAGNETic field, to which a random turbulent component can optionally be added. The parameters varied include the inclination angle θ between the JET axis and the line of sight, the wavenumber of the helical field, and the amplitude of the random MAGNETic-field component. By systematically varying these parameters, we examine how the underlying MAGNETic geometry and turbulence are encoded in the observable Faraday and POLARIZATION structures. The main observational signatures identified by our model include top-bottom asymmetry across the JET, curved or double peaked FDF profiles and increasingly fragmented Faraday depth structure along longer lines of sight, providing potential diagnostics of large scale helical MAGNETic fields and small scale turbulent components. These signatures providing a physical framework for interpreting future polarimetric observations of AGN JETs from instruments such as LOFAR, MeerKAT, and the VLA.
[abstract 2 / 47] Wow! (score: 8) - Title: Spatially resolved spectral properties of M87* on event horizon scalesAuthors: Shan-Shan Zhao, Ru-Sen Lu, Rocco Lico, Yuh Tsunetoe, Sijia Peng,Comments:Subjects: astro-ph.HE astro-ph.GACreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
The supermassive BLACK HOLE at the center of the nearby RADIO GALAXy M87 (M87*) is a prime target for studying BLACK HOLE physics. Spatially resolved spectral measurements on event-horizon scales can reveal the origin of the emission and probe the plasma and gravitational environment in the immediate vicinity of the BLACK HOLE. Here, we present an analysis of spectral properties based on nearly simultaneous high-resolution images at 3.5 mm (86 GHz) and 1.3 mm (230 GHz), obtained in 2018 with the Global Millimeter VLBI Array (GMVA) including ALMA and the Greenland Telescope, and the Event Horizon Telescope (EHT). We obtain the first spatially resolved spectral-index map ($S_ν\propto ν^α$) within the compact region ($\leq 100\,μ$as). We further detect a robust radial gradient with a modest rise in the inner $\lesssim 20~μ$as (slightly inside the 1.3 mm ring), followed by a systematic decline at larger radii. The spectral index transitions from positive to negative values near $\sim 30~μ$as, close to the 3.5 mm ring radius, consistent with frequency-dependent SYNCHROTRON opacity in the innermost accretion flow. These results provide new observational constraints that can help discriminate between models of the horizon-scale emission and the launching of RELATIVISTIC JETs in M87*.
[abstract 3 / 47] Wow! (score: 7) - Title: Assessing the Credibility of Gamma-Ray QPO Candidates in 41 TeV-Selected BlazarsAuthors: Wen-Xin Yang, Yi Liu, Hong-Guang Wang, Denis Bastieri, Jun-Hui Fan,Comments: 21 pages, 9 figures, 7 tables. Accepted for publication in The Astrophysical Journal (ApJ)Subjects: astro-ph.HECreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
We analyze quasi-periodic oscillation (QPO) candidates in the 0.1-100 GeV FERMI-LAT light curves of 41 TeV BLAZARs with a conservative, multi-stage timing analysis combining FFT power spectra, red-noise Monte Carlo simulations, false-discovery-rate control, bootstrap period uncertainties, split-sample cross-validation, Lomb-Scargle and WWZ diagnostics, a detection-only sensitivity test, observingwindow checks, and injection-recovery experiments. A first-pass FFT search flags 16 sources above a raw 95% level and six strong candidates after data-quality and split-sample filtering, none satisfying a fully automated multi-method tier. Source-level significance is quantified with forward simulations that preserve the observed sampling and non-Gaussian flux distribution, treating the red-noise slope as a nuisance parameter and never assuming independence of periodogram powers. At simulation-selected reference slopes, only two of the 41 sources reach a raw source-level p < 0.05,only J1555.7+1111 reaches Benjamini-Hochberg significance, and none survives Benjamini-Yekutieli correction. No source survives the conservative slope envelope. Even J1555.7+1111, which the first-pass search flagged as significant but did not rank among its strong candidates, has a global p-value that rises to 7.5*10^-3 under the least favorable slope (~ 0.31 after the full-sample search), so it is not a robust detection. With substantial period uncertainties, a weak observing window, and limited injection-recovery sensitivity, we establish no robust gamma-ray QPO detection: a sampling-faithful red-noise treatment substantially contracts the candidate set, providing an explicit assessment of QPO credibility.
[abstract 4 / 47] Yes (score: 6) - Title: Black Hole Polarimetry: Universal Polarization of Synchrotron Radiation at the HorizonAuthors: Andrew Chael, Alexandru Lupsasca, George N. Wong, Zachary Gelles, Eliot Quataert,Comments: 24 pages, 6 figures. Accepted to ApJLSubjects: astro-ph.HE gr-qcCreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
Polarized images of a BLACK HOLE encode the direction of electroMAGNETic energy flow near its event horizon. Measuring POLARIZATION from near-horizon emission can help determine whether this energy flow is powered by the accreting plasma or the BLACK HOLE spin. Here we consider the linear POLARIZATION of SYNCHROTRON radiation emitted from the base of horizon-threading field lines in a time-stationary, axisymmetric, and degenerate Kerr MAGNETosphere with nonzero poloidal current. We show that the observed POLARIZATION pattern displays universal behavior: it is completely determined by the BLACK HOLE spin and observer inclination and is independent of the MAGNETic field geometry. We derive a simple analytic formula for this spin-dependent horizon POLARIZATION pattern. We find that this predicted pattern is also approached in time-averaged images from General Relativistic Magnetohydrodynamic simulations. Future observations with Very-Long-Baseline Interferometry at microarcsecond resolution could detect the trend of POLARIZATION toward the unique horizon value in M87*. Such observations may enable new measurements of BLACK HOLE spin and provide evidence that MAGNETic field lines thread the horizon, a necessary condition for spin-energy extraction via the Blandford--Znajek process.
[abstract 5 / 47] Yes (score: 6) - Title: Synchrotron filaments in RADIO GALAXies: rarity, stability, and environmental influences from LOFAR and ROSAT observationsAuthors: Geoffrey Ong'alo, Martin J. Hardcastle, Willice Obonyo, Marcus Brüggen, Paul Baki,Comments: 12 pages, 4 figuresSubjects: astro-ph.GACreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
We present a systematic investigation of filamentary SYNCHROTRON structures in RADIO GALAXies, using deep 144 MHz observations from the LOFAR Two-Metre Sky Survey (LoTSS) in combination with archival ROSAT X-ray data. These narrow, collimated features, linking radio lobes and often aligned with JET axes, are rare: our visual inspection of 548 cluster-associated sources identified 12 candidates (~2.2%), of which three exhibit clearly resolved filaments suitable for detailed X-ray and SYNCHROTRON minimum pressure analysis. Minimum pressures in these filaments are consistently lower than the ambient thermal pressure derived from X-ray measurements. This disparity implies a role for external confinement in filament stability, aligning with theoretical predictions of thermal pressure support and potentially toroidal MAGNETic field configurations. We discuss filament formation scenarios, including relic AGN outflows, MAGNETic draping, and plasma instabilities. Our findings highlight the utility of filamentary structures as probes of intracluster MAGNETic field topology and AGN feedback, and demonstrate the need for high-resolution, multi-frequency studies to constrain their origin and evolution.
[abstract 6 / 47] Yes (score: 5) - Title: MicroQUASAR Remnants as Pevatrons Illuminating the Galactic Cosmic Ray KneeAuthors: Bing Theodore Zhang, Shiqi Yu,Comments: 4 + 1 figures and 1 tableSubjects: astro-ph.HECreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
MicroQUASARs are primary candidates for Galactic PeVatrons, yet their collective contribution to the COSMIC RAY (CR) ``knee" remains poorly understood. We investigate this contribution by simulating anisotropic diffusive propagation through the Galactic MAGNETic field (GMF). Our results demonstrate that the GMF establishes a transport regime where MAGNETic connectivity between sources and the solar neighborhood determines the local flux. Active sources aligned with local GMF lines, such as Cygnus X-1, exhibit significant flux enhancements, while MAGNETically disconnected sources, such as V616 Mon, are strongly suppressed. By integrating source evolution with anisotropic transport, we show that the observed proton bump at the CR ``knee" is best reproduced by the cumulative contribution of microQUASAR remnants, which is often dominated by a few nearby or recent events, rather than the active ones alone. We find that a harder injection spectrum allows CRs from remnants to reproduce the PeV bump after propagation, as low-energy CRs have sufficient time to accumulate while high-energy CRs escape the Galactic plane. Our findings suggest that the integrated history of microQUASAR remnants, governed by the interplay of source age and MAGNETic connectivity, is the primary driver populating the observed CR ``knee''.
[abstract 7 / 47] Yes (score: 5) - Title: Comments on the paper "Eliminating beam-induced depolarizing effects in the hydrogen JET target for high-precision proton beam polarimetry at the Electron-Ion Collider"Authors: Andrei Poblaguev,Comments: 5 pages. Comment on arXiv:2508.01366Subjects: physics.acc-phCreated: 2026-08-24; Updated: 2026-08-26; Datestamp: 2026-08-26
A critical review of the methodology used in F. Rathmann et al., Phys. Rev. Accel. Beams 29, 021001 (2026), to evaluate beam-induced dePOLARIZATION of the Atomic Polarized Hydrogen Gas Jet (HJET) target at the Electron--Ion Collider (EIC) is presented. It is shown that several key assumptions underlying that analysis -- including the introduction of a photon emission threshold, the application of FERMI's Golden Rule to coherent hyperfine transitions, the interpretation of power broadening as a physical linewidth increase, and the treatment of spatial MAGNETic fields -- are either incorrect or internally inconsistent. As a consequence, the predicted large dePOLARIZATION effects are demonstrated to be artifacts of the adopted methodology rather than genuine physical phenomena. A consistent quantum-mechanical treatment based on the time-dependent Schrödinger equation shows that beam-induced dePOLARIZATION probabilities at the EIC are negligibly small.
[abstract 8 / 47] Yes (score: 5) - Title: An extreme case of X-ray reflection in the symbiotic V648 CarAuthors: Jherssica Freitas, Raimundo Lopes de Oliveira, Koji Mukai,Comments: Accepted for publication in ApJSubjects: astro-ph.SR astro-ph.HECreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
V648 Car is a $δ$-type symbiotic star known for its strong hard thermal X-ray emission, heavy local photoelectric absorption, and stochastic variability. We analyze NUSTAR observations, complemented by nearly contemporaneous SWIFT/XRT observations, to check for the expected presence and physical implications of Compton reflection in its X-ray spectrum. The spectra were fitted with X-ray models that accounted for thermal plasma components, different prescriptions to quantify the intrinsic absorption, the presence of the fluorescent iron line at 6.4 keV, and a reflection component. Our results reveal a strong Compton reflection contribution, accounting for approximately 37% of the total unabsorbed flux in the 3-50 keV band. The inclusion of reflection significantly improves the spectral fits and reduces the value for the maximum plasma temperature by a factor of 2 (from about 49 keV to 25 keV). If the maximum temperature is attributed to strong shock of a Keplerian flow, the inferred white dwarf mass decreases from about 20% (from $1.2$ to $0.95\,M_{\odot}$), demonstrating that neglecting reflection can lead to significant overestimates of this parameter. Reflection models yield high reflection scaling factors ($R \sim 2$), inconsistent with a simple picture of a primary X-ray source above a reflecting disk. The timing analysis reveals stochastic flickering variability with no evidence for coherent periodic modulations, thus the accreting object is likely a non-MAGNETic white dwarf. We propose a multiple-reflection model to explain the extraordinary strength of reflection features in V648 Car.
[abstract 9 / 47] Yes (score: 5) - Title: Anomalous Electric Fields in Earth's Turbulent Magnetosheath: Insights From 3D Hybrid SimulationsAuthors: Jeffersson A. Agudelo Rueda, Julia E. Stawarz, Luca Franci, Nobumitsu Yokoi, Camille Granier, Silvio S. Cerri,Comments: 28 Pages, 8 Figures, one tableSubjects: physics.plasm-ph astro-ph.SR physics.space-phCreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
In both collisional and collisionless plasmas the presence of a broad range of electroMAGNETic and plasma fluctuations provides anomalous electric fields that can be important for the dynamical evolution of the system as it is the case of MAGNETic RECONNECTion, plasma turbulence and dynamo theory. In the context of plasma turbulence at scales larger than the ion's inertial length, the plasma satisfies the frozen-in condition, and the anomalous electric fields are produced by correlations between turbulent velocity and MAGNETic fields. Conversely, for collisionless plasmas and at kinetic scales, the total electric field has additional contributions that arise from kinetic phenomena, namely, charge separation, ambipolar electric fields and electron inertia, and each of these terms presents an anomalous counterpart. In this work we characterize the anomalous electric fields. We present a framework that can explain partial balance between the anomalous resistivity and anomalous transport, and we use it to study anomalous electric fields at kinetic scales. We establish how the different contributions to the anomalous electric field couple to the large-scale electric fields and show that the anomalous terms act back-reacting on MAGNETic-field organization and they may contribute to effective turbulent MAGNETic diffusion or shielding. Finally, we test two Sub-Grid-Scale models including anisotropic transport coefficients and show that although these models partially recover the spectral information, the phase coherence is not entirely recovered by these models suggesting a more complex non-linear contribution of the anomalous terms to the resolved scales.
[abstract 10 / 47] Yes (score: 4) - Title: Studying the mirror acceleration via kinetic simulations of RELATIVISTIC plasma turbulenceAuthors: Saikat Das, Siyao Xu, Joonas Nättilä,Comments: 15 pages, 11 figures, accepted for publication in ApJSubjects: astro-ph.HE physics.plasm-phCreated: 2026-08-24; Updated: 2026-08-26; Datestamp: 2026-08-26
Efficient RELATIVISTIC turbulent acceleration of particles is indicated by recent astrophysical observations. The acceleration mechanism due to temporal variations of MAGNETic field strengths (``Type II mechanism") remains underexplored. The mirror acceleration has recently been proposed as an efficient Type II mechanism for particle energization in turbulence-compressed MAGNETic fields. We perform a 3D particle-in-cell (PIC) simulation of pair plasma to extend its study to RELATIVISTIC turbulence. By tracking individual particles, we see that the particles interacting with transverse MAGNETic mirrors can have a significant energy gain during one mirror interaction and within one gyro-orbit. As expected for the mirror acceleration, we statistically find that the momentum gain is preferentially in the direction perpendicular to the local MAGNETic field and positively correlated with the local MAGNETic field strengthening. As a result, the particle pitch angle distribution becomes increasingly anisotropic toward higher energies, with a concentration at large pitch angles. The mirror acceleration facilitates a spatial confinement of particles by stochastically increasing their pitch angles, which further enhances the mirror acceleration.
[abstract 11 / 47] Yes (score: 4) - Title: Signatures of Compact Object Mergers Inside Stars in AGN DisksAuthors: Matteo Cantiello, Alexander J. Dittmann, Saavik Ford, Barry McKernan, Carlos Palenzuela, Rosalba Perna, Taeho Ryu,Comments: 22 pages, 9 figures, Submitted to ApJSubjects: astro-ph.HE astro-ph.GA astro-ph.SRCreated: 2026-08-24; Updated: 2026-08-26; Datestamp: 2026-08-26
Disks of gas accreting onto supermassive BLACK HOLEs, powering ACTIVE GALACTIC NUCLEi (AGN), can capture stars from nuclear star clusters or form stars in situ via gravitational instability. The dense, hot disk environment can drive rapid accretion onto embedded stars, dramatically altering their evolution. Models predict that, for sufficiently rapid accretion, fresh gas replenishes hydrogen in stellar cores as quickly as it is burned, and the stars reach a quasi-steady state. Here we study encounters of such massive, long-lived (''immortal'') stars with compact objects in AGN disks. We estimate the encounter rate and the timescale for a single compact remnant to spiral into an AGN star; depending on how strongly feedback regulates the ensuing accretion, the star is either consumed in a collapsar-like, engine-driven transient or converted into a long-lived, quasi-star-like object hosting a central BLACK HOLE. We then study the merger of a binary BLACK HOLE (BBH) inside the AGN star, and show that gas drag hardens the binary to merger far faster than gravitational-wave emission alone. The resulting merger is a loud LIGO-Virgo-KAGRA (LVK) source, but the characteristic imprint of the dense environment -a strong suppression and dephasing of the inspiral relative to vacuum- falls in the deci-Hz band rather than the milli-Hz LISA band, and is best resolved by next-generation detectors such as DECIGO. We estimate that this channel could contribute a BBH merger rate of up to $\sim8\,{\rm Gpc^{-3}\,yr^{-1}}$ in favorable scenarios, and discuss the model uncertainties and directions for future work.
[abstract 12 / 47] Yes (score: 4) - Title: A Broadband X-ray Analysis and Optical Counterpart Search of IC5052 ULXAuthors: Nabil Brice, Dominic J. Walton, Felix Fürst, Daniel Stern, Amy H. Knight, Matteo Bachetti, Matthew J. Middleton, Alistair Pagan, Tim P. Roberts, Murray Brightman, Hannah P. Earnshaw, Fiona A. Harrison, Sean N. Pike,Comments: 17 pages, 8 figures, accepted for publication in MNRASSubjects: astro-ph.HECreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
We present broadband X-ray spectral and timing analysis of the Ultra-luminous X-ray source (ULX) in IC5052 using simultaneous XMM-Newton and NUSTAR observations from 2022, supplemented by archival 2013 XMM-Newton data. A two-thermal component model, often interpreted as radially-segregated emission from a super-Eddington inner disc and its associated wind, provides a statistically acceptable fit but yields an implausibly high inner disc temperature of $k T_\mathrm{in} \approx 6.4$ keV, inconsistent with even super-Eddington disc models. Including an additional continuum component from either an accretion column or a Comptonizing corona, as motivated by high S/N observations from other ULXs, provides comparable goodness of fit while allowing plausible inner disc temperatures. The accretion column model yields $k T_\mathrm{in} \approx 1.2$ keV with the column contributing $F_\mathrm{col} \approx 62\%$ of total flux, while the Comptonizing corona model yields $k T_\mathrm{in} \approx 3.0$ keV with a scattered fraction $\sim 1$, assuming the hotter disc provides the seed photons. Timing analysis initially challenges both scenarios: the accretion column model places IC5052 ULX where prior results suggest pulsations may be detectable ($F_\mathrm{col} \sim 62\%$), yet none were detected, while the corona model appears inconsistent with its lack of observed short-timescale variability. However, incorporating spectral information relaxes these constraints, allowing both models to remain physically plausible for IC5052 ULX. Finally, using improved Chandra astrometry, we identified a candidate optical counterpart consistent with an evolved high mass donor. A discrepancy between the optical extinction and X-ray fitted absorption suggests localised X-ray absorption.
[abstract 13 / 47] Yes (score: 4) - Title: Calculation of Field Line Slippage Rates in Coronal SimulationsAuthors: Valentin Aslanyan, David MacTaggart, Roger B. Scott, Chloe P. Wilkins, David I. Pontin, Anthony R. Yeates, Peter F. Wyper, Karen A. Meyer, Spiro K. Antiochos,Comments:Subjects: astro-ph.SR physics.plasm-phCreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
We present the Universal Slippage calculator (\texttt{USlip}), an extension of the Universal Fieldline Tracer (\texttt{UFiT}), that computes MAGNETic field line slippage rates from an input MAGNETic field defined on a structured grid. The slippage rate provides a local, physically grounded diagnostic of non-ideal evolution, directly quantifying departures from ideal frozen-in motion. We outline the theoretical formulation and describe an efficient numerical implementation. The method is validated against analytical solutions and applied to simulations using three coronal codes treating varying spatial scales, all of which are standard inputs for \texttt{USlip}. In all the examples considered, the slippage rate not only identifies where MAGNETic connectivity changes occur, but also accurately reproduces the observed direction of field-line slippage. The consistency of the results across analytical tests and multiple simulation platforms demonstrates that \texttt{USlip} is a robust and versatile tool for diagnosing three-dimensional RECONNECTion in dynamically evolving systems.
[abstract 14 / 47] (score: 3) - Title: Long-Integration Magnetar Burst Observatory (LIMBO): Instrument Summary and Early FRB Rate ConstraintsAuthors: Darby McCauley, Aaron Parsons, Wei Liu, Wenbin Lu, Dirk Wright, Dan Werthimer,Comments: 17 pages, 15 figures, 3 tables, accepted to RASTISubjects: astro-ph.IM astro-ph.HECreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
The Long-Integration Magnetar Burst Observatory (LIMBO) is a real-time radio transient detection pipeline designed to search for dispersed fast radio bursts (FRBs) from Galactic MAGNETars. Deployed at the University of California, Berkeley's Leuschner Radio Observatory, LIMBO employs a $4.3~\mathrm{m}$ dish with a dual-POLARIZATION feed to continuously monitor a $125~\mathrm{MHz}$ band centred at $1460~\mathrm{MHz}$. A real-time processing pipeline performs a search for dispersed transients on the summed POLARIZATIONs, with detections triggering dumps of buffered voltage data to disk. Based on calibrated sensitivity measurements, synthetic signal-injection and recovery tests, and successful detection of pulses from the Crab Pulsar, we determine that LIMBO is sensitive to radio transients with fluences $\geq 43~\mathrm{Jy \cdot ms}$. Between May and August 2023, LIMBO conducted 833 hours of follow-up observations of the Galactic MAGNETar SGR 1935+2154, yielding 12 candidate FRB detections. If these events are true, we measure FRB-like event rates from SGR 1935+2154 of $R(\geq 65~\mathrm{Jy \cdot ms}) = 112.3^{+81.3}_{-54.5}~\mathrm{yr}^{-1}$ and $R(\geq 130~\mathrm{Jy \cdot ms}) = 17.7^{+40.8}_{-15.1}~\mathrm{yr}^{-1}$. Combining these results with previously reported FRBs from SGR 1935+2154, we infer a cumulative rate-fluence power-law slope of $α=-0.60^{+0.24}_{-0.28}$ in the fluence range between $10$ and $10^6\rm\, Jy \cdot ms$. These observations demonstrate the capability of continuous, real-time monitoring of Galactic MAGNETars and establish LIMBO as an effective instrument for detecting Galactic FRBs.
[abstract 15 / 47] (score: 3) - Title: Probing past mergers of supermassive BLACK HOLEs with pulsar timing arrays: The role of pulsar termsAuthors: Hippolyte Quelquejay Leclere,Comments: 12 pages, 5 figures. Published in PRD. Revised version incorporating the referee' commentsSubjects: astro-ph.HE gr-qcCreated: 2026-08-24; Updated: 2026-08-26; Datestamp: 2026-08-26
By monitoring the times of arrival of radio pulses from millisecond pulsars, Pulsar Timing Arrays (PTAs) serve as unique gravitational wave (GW) laboratories in the nanohertz band. To date, the primary astrophysical sources of GWs targeted in this frequency range have been inspiraling supermassive BLACK HOLE binaries (SMBHBs) on circular and eccentric orbits. In this work, we demonstrate that, thanks to the so-called pulsar term in the timing residual waveform of GW signals, PTAs can probe individual SMBHBs that merged before timing observations began. We refer to the latter as zombie binaries. Using SMBHB population models consistent with current PTA constraints, we find that while the probability of detecting such systems in existing PTA datasets remains low, the Square Kilometer Array observatory is expected to achieve sufficient sensitivity to have a few zombie binaries with optimal matched filter signal-to-noise ratios exceeding 3 in its data. Although their confident identification might be challenging, this new class of PTA sources opens a novel window for studying the most massive SMBHBs in our local universe.
[abstract 16 / 47] (score: 3) - Title: Wind Acceleration as a Driver of Detached Blueshifted Absorption in Quasar Disk WindsAuthors: Randall C. Dannen, Daniel Proga, Paola Rodríguez Hidalgo, Kara Smith, Anna Ritchie, Liliana Flores, Morrigan Kalet,Comments: 1 Table, 4 FiguresSubjects: astro-ph.GACreated: 2026-08-24; Updated: 2026-08-26; Datestamp: 2026-08-26
Active galactic nuclei (AGN) unification models often emphasize the viewing angle, $i$, but $i$ alone does not determine QUASAR properties. This is crucial for QUASAR outflows: UV absorption in Extremely High Velocity Outflow (EHVO) QUASARs can reach blueshifted velocities of $\sim0.2~c$. In disk-wind models, both $i$ and internal wind structure shape the emergent spectrum. We test their interplay using biconical QUASAR disk-wind models with different acceleration lengths, $R_v$, and generate synthetic spectra over a range of $i$. We use Monte Carlo radiative transfer to account for finite continuum sources, wind attenuation, scattering, reprocessing, and emission. Changing $R_v$ greatly alters the ionization structure, continuum shape, and absorption-line profiles. At intermediate viewing angles, sightlines pass through the fastest wind. Even there, highly detached and blueshifted \CIV\ absorption like that observed in EHVO QUASARs appears only in models with small $R_v$. In these models, the gas reaches high velocity before attaining the ionization and density conditions favorable for \CIV. Models with larger $R_v$ instead produce broader, less detached troughs, even when the terminal velocity is very high. Thus, highly detached and blueshifted absorption requires both a high terminal velocity and small $R_v$, making such features diagnostics of disk-wind acceleration and structure. EHVO QUASARs provide a clear example, but the same principle applies more broadly to highly detached and blueshifted absorption in QUASAR outflows. Our results support an extended disk-wind view of AGN unification: $i$ selects the observed wind region, while $R_v$ shapes the emergent spectrum and absorption morphology.
[abstract 17 / 47] (score: 3) - Title: Effect of Neutron Star Jets on Common Envelope EvolutionAuthors: Deepanshu Gurjar, Luke Chamandy, Eric G. Blackman, Yangyuxin Zou, Baowei Liu, Jason Nordhaus,Comments: 13 pages, 9 figures, 1 table, accepted for publication in ApJSubjects: astro-ph.SR astro-ph.HECreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
The common envelope (CE) phase is a key stage in binary star evolution that is still not very well understood. Once engulfed by the giant star, the binary companion may accrete envelope material. For neutron star (NS) companions, such accretion may in principle occur at mass rates several orders of magnitude above the Eddington limit and may result in outflows dominated by powerful bi-polar JETs with mass-loss rates similar to the accretion rates. Such JETs would impact the morphology of the system and the rate of envelope unbinding, which affect the duration and outcome of the CE event. Employing 3D global hydrodynamic simulations, we study the role of such NS JETs in a CE event involving a red giant branch star. The JETs eventually drill through and break out of the envelope, producing prominent low-density bi-polar lobes. The JETs cause about twice as much envelope mass to be unbound ($\sim20\%$ of the envelope) as compared to simulations of the same duration without NS JETs ($\sim10\%$). However, the rate of mass unbinding due to the JETs decreases towards the ends of the simulations as the JETs break out and energetically decouple from the envelope. Moreover, JET activity leads to slightly reduced drag on the binary, decreasing the rate of orbital energy transfer to the envelope. Hence, while such powerful JETs can play an important role, negative feedback effects tend to prevent them from dominating envelope unbinding and dictating CE outcomes.
[abstract 18 / 47] (score: 3) - Title: High-mass binary BLACK HOLE mergers from detailed binary evolution modelsAuthors: Max M. Briel, Olcay Bıyıklı, Tassos Fragos, Anarya Ray, Zepei Xing, Monica Gallegos-Garcia, Abhishek Chattaraj, Jeff J. Andrews, Michael Zevin, Vicky Kalogera, Seth Gossage, Philipp M. Srivastava, Elizabeth Teng,Comments: Submitted to ApJ. Comments welcomeSubjects: astro-ph.HE astro-ph.SRCreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
Gravitational-wave observations reveal a population of binary BLACK HOLE (BBH) mergers with primary masses above ${\sim}40\,\mathrm{M}_\odot$, extending into and potentially beyond the pair-instability mass gap, with a possibly flat mass-ratio and broader χ_\mathrm{eff} distribution. We investigate whether super-Eddington accretion during stable mass transfer in isolated binary evolution can produce BBH mergers consistent with these properties across primary BH mass, mass-ratio, and χ_\mathrm{eff} distributions. Using POSYDON, we simulate BBH merger populations with primary BH masses above ${\sim}40\,\mathrm{M}_\odot$, under three BH accretion efficiencies: Eddington-limited, GRRMHD-informed, and fully conservative. We additionally vary the natal kick strength, including strong kicks at high BH masses. We find that super-Eddington accretion does not suppress BBH mergers in the high-mass regime. Fully-conservative accretion leads to an increase of BBH mergers in POSYDON with a strong kick-independent peak at $χ_\mathrm{eff}=0.6$ and a sharp mass-ratio peak at $q\sim0.5$, whereas observations favor $χ_\mathrm{eff}=0.0$ and a flatter mass-ratio distribution. The GRRMHD-informed and Eddington-limited accretion are compatible with the observed primary BH mass and mass ratio distribution, but require natal kicks to populate negative χ_\mathrm{eff}. A joint analysis of the primary BH mass, mass ratio, and χ_\mathrm{eff} distributions provides strong constraints on binary evolution physics, and disfavor fully-conservative BH accretion as the dominant formation mechanism for high-mass BBH mergers. The Eddington-limited and GRRMHD-informed prescriptions with modest kicks can explain part of the high-mass population, but an additional formation channel is still needed to account for the high fraction of negative χ_\mathrm{eff} systems and high secondary BH spins.
[abstract 19 / 47] (score: 3) - Title: A simulation-based quality-control framework for the broad-line region radius-luminosity relationAuthors: Juri Wladimir Seib, Francisco Pozo Nuñez, Sarah Elena Ivana Bosman,Comments: Accepted for publication in A&ASubjects: astro-ph.GACreated: 2026-08-24; Updated: 2026-08-26; Datestamp: 2026-08-26
The broad-line region (BLR) radius-luminosity (R-L) relation underpins single-epoch BLACK HOLE mass estimates in ACTIVE GALACTIC NUCLEi (AGN). The published Hβsample is heterogeneous in observational quality, and it remains unclear how much of its scatter is intrinsic rather than caused by systematics in lag recovery. We quantify the contribution of unreliable lag recovery to the observed scatter of the HβR-L relation and provide tools for quality control. We compile a publicly available database of reverberation mapping measurements for ~1200 AGN from 32 campaigns spanning more than three decades, including lags, luminosities, line widths, BLACK HOLE masses, and observational metadata. We develop a simulation-based consistency framework in which damped random walk light curves are sampled according to each campaign's baseline, cadence, and signal-to-noise ratio, and lags are recovered with the interpolated cross-correlation function (ICCF). Comparing expected, reported, and simulation-retrieved lags defines a four-tier flagging scheme. We refit the R-L relation with UltraNest for progressively cleaner samples and construct consensus samples across three reference slopes to reduce model dependence. Of 248 Hβsources, ~40% show discrepancies between reported and simulation-retrieved lags, while ~5% show direct inconsistencies between expected and retrieved lags. Excluding flagged sources and correcting for model bias reduces the inferred intrinsic scatter from σ= 0.26^{+0.02}_{-0.01} dex to 0.11\pm0.01 dex, with a corrected slope of α= 0.48\pm0.02. Our results indicate that a substantial fraction of the observed HβR-L scatter arises from observational limitations and lag-recovery biases rather than intrinsic AGN diversity. The database, simulation code, and RM-Scout campaign-planning tool are publicly available.
[abstract 20 / 47] (score: 3) - Title: Sub-Millisecond Pulsars: Missing or Impossible?Authors: T. M. Tauris, V. Venkatraman Krishnan, R. Senzel, P. C. C. Freire, S. M. Ransom, A. Papitto, C. A. N. Biscio, N. Langer, E. P. J. van den Heuvel, M. Kramer,Comments: Accepted for publication in Living Reviews in Relativity. Accepted author manuscript (116 pages, including appendices and references, 27 figures, 6 tables)Subjects: astro-ph.HE astro-ph.SRCreated: 2026-08-24; Updated: 2026-08-26; Datestamp: 2026-08-26
The minimum spin period attainable by a neutron star has been debated since the discovery of the first millisecond pulsar in 1982. A neutron star rotating faster than 1 ms would have far-reaching implications for the dense-matter equation of state, gravitational-wave emission, and the physics of accretion and spin-up. Yet despite the discovery of over 700 millisecond pulsars with spin periods between 1.4 and 10 ms, no sub-millisecond pulsar has been identified. Here we review the physical and observational constraints governing the formation, survival, and detectability of ultra-fast neutron stars. We discuss physical constraints imposed by the neutron star equation of state and their implications for the minimum attainable spin period, and we summarise gravitational-wave emission from both accreting and rotation-powered millisecond pulsars. We argue that sub-millisecond spins are not primarily excluded by equilibrium spin limits, MAGNETospheric physics, or selection effects, but instead by a combination of inefficient recycling, short mass-transfer lifetimes in the most favourable binaries, and rapid post-formation spin-down unless MAGNETic fields are exceptionally weak. Together, these effects make sub-millisecond pulsars intrinsically rare. If they exist at all, they are most likely to be detected transiently during accretion, rather than as long-lived radio pulsars. Finally, we show that stellar-mass BLACK HOLEs can attain sub-millisecond horizon spin periods, reflecting fundamentally different spin constraints.
[abstract 21 / 47] (score: 3) - Title: Searching for Solar-Basin Axionlike-Particle Decay with XMM-Newton Blank-Sky ObservationsAuthors: Bo Zhang, Chi Zhang, Lei Lei, Yang Yu, Guan-Shen Wang, Bing-Yu Su, Lei Feng,Comments: 15 pages, 5 figuresSubjects: hep-ph astro-ph.HECreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
Axion-like particles (ALPs) bound in the solar gravitational field form the so-called ALP solar-basin. Since the two-photon decay of non-RELATIVISTIC particles is approximately isotropic, this population can be searched for using observations in the anti-solar direction. In this work, we propose a search strategy for narrow decay-line signals from the ALP solar basin using \textit{XMM-Newton} blank-sky observations (XMM-BSOs) stacked spectra data taken in directions opposite to the Sun. By jointly fitting the signal and background model, we obtain limits on $g_{aγγ}^{95}$ in the mass range $m_a=1.4\text{--}16~{\rm keV}$, with typical sensitivities of $g_{aγγ}\sim10^{-10}\text{--}10^{-11}~{\rm GeV}^{-1}$. We have implemented the first anti-solar search for the solar basin, demonstrating that this strategy can exploit the stacked exposure of a large number of X-ray observations and provide a scalable analysis framework for future searches.
[abstract 22 / 47] (score: 3) - Title: Observations of ionized carbon towards the $γ$-ray-bright SUPERNOVA remnant RX J1713.7-3946Authors: A. R. Thakur, G. P. Rowell, R. Higgins, M. Burton, Y. Fukui, S. Einecke, H. Sano, G. Wong, M. D. Filipović, C. Braiding,Comments: 22 pages, 29 figuresSubjects: astro-ph.HECreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
The origin of Galactic Cosmic Rays (CRs), particularly at sub-GeV energies, remains uncertain due to their difficulty in being traced. One possible tracer of low-energy CRs is ionised carbon ([C II]), which may be enhanced in regions affected by CR-induced ionisation. We present observations of [C II] 158 $μ$m line emission across the $γ$-ray-bright SUPERNOVA remnant (SNR) RX J1713.7-3946 obtained with SOFIA. These data are compared with molecular and atomic gas from Mopra ($^{12}$CO), Nanten ($^{12}$CO) and SGPS (HI), and high-energy emission from TeV $γ$-ray H.E.S.S. and X-ray XMM-Newton. We find [C II] emission follows the atomic gas more closely than molecular gas, particularly in regions near the SNR shock front. Ratios of [C II] intensity to gas column density vary across the remnant, with peak values coinciding with regions of enhanced TeV $γ$-ray emission. To put the [C II] in a wider context, we examined pointings from the Herschel GOT C+ survey. Our analysis of the GOT C+ data shows no significant difference in the I[C II]/I[$^{12}$CO] ratio for observations towards STAR FORMATION regions, HII regions and SNRs. To assess the origin of carbon ionisation, we model [C II] emissivity using the photoionisation code CLOUDY. We find UV photons and CRs can produce comparable levels of [C II] emission, assuming low-energy CRs (< 1 GeV) are accelerated and trapped within the SNR shock. These results highlight the potential of [C II] as a tracer of CR ionisation and the importance of combining multi-wavelength observations to probe CR interactions in SNRs.
[abstract 23 / 47] (score: 3) - Title: The First X-Ray Polarimetry of the Typical Accretion Disk Corona Source 4U 1822-37Authors: WanYun Wu, Fei Xie, YuShan Ling,Comments: 10 pages, 8 figures, 5 tables. Accepted for publication in MNRASSubjects: astro-ph.HECreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
We report the first Imaging X-ray Polarimetry Explorer (IXPE) observations of the typical accretion disk corona (ADC) source 4U 1822-37, covering 44 orbital cycles, together with simultaneous SWIFT-XRT data. The POLARIZATION degree (PD) of this source is found to be higher than typical low-mass X-ray binary (LMXB) values and exhibits a significant energy dependence. Within the 2--5~keV and 5--8~keV bands, PD remains constant, with average values of \(5.6\pm0.8\%\) and \(11.6\pm1.7\%\), respectively, and the difference is significant (\(>3σ\)). Orbital phase-resolved analysis reveals that during the companion eclipse, the PD in the 2--5~keV band drops from a significantly non-zero value to a level consistent with zero, while the POLARIZATION angle (PA) remains unchanged. In contrast, the PD in the 5--8~keV band shows a marginal rising trend, reaching \(21.3\pm6.1\%\), and the PA exhibits a periodic rotation of \(30^\circ\) before the eclipse. In addition, the PA rotates by \(40^\circ\) with increasing neutral absorption on a three-day timescale. These results suggest that the soft and hard emission in the 2--8~keV band may originate from regions with different spatial distributions, with the high PD implying a scattering contribution. The PA rotation is likely linked to scattering geometry asymmetries caused by a bulge or clumps.
[abstract 24 / 47] (score: 3) - Title: A "MeerKAT-meets-LOFAR" Study of 2A 0335+096: Discovery of a Complex 500 kpc Radio Halo in a Disturbed Cool-Core ClusterAuthors: C. J. Riseley, R. J. van Weeren, L. Lovisari, R. Timmerman, A. Botteon, A. Bonafede, A. Ignesti, N. Biava, G. Brunetti, B. Colquhoun, Y. Perrott, T. Vernstrom,Comments: Accepted for publication in A&A. Main article is 13 pages, appendix 3 pagesSubjects: astro-ph.COCreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
The emerging picture of radio haloes and mini-haloes in galaxy clusters is more blurred and far less distinct than once thought. While both trace COSMIC RAY electrons and MAGNETic fields in the intracluster medium (ICM), our knowledge of the mechanisms powering these sources, their properties and their connection to cluster dynamics, is incomplete. We present new deep MeerKAT L-band (856$-$1712\,MHz) observations of the sloshing cool-core cluster 2A~0335+096, performed as part of the ``MeerKAT-meets-LOFAR'' mini-halo census, as well as reprocessed LOFAR 120$-$168\,MHz LOFAR Two-metre Sky Survey data. We present highly sensitive radio continuum images, from which we perform a spectral analysis and a comparison of the thermal and non-thermal properties using reprocessed archival \textit{XMM-Newton} data. Our MeerKAT data reveal that the known mini-halo is embedded in a large-scale radio halo spanning up to 510\,kpc in this sloshing cluster, although only the inner mini-halo is detected by LOFAR. We find a typical steep spectrum of $α= -1.20 \pm 0.09$ for the mini-halo; the non-detection of the larger-scale halo by LOFAR indicates a spectral index no steeper than $-1.2$. Our results are broadly consistent with an interpretation of turbulent (re-)acceleration powered by sloshing within the cluster potential well. This work emphasises the need for using deep, high-dynamic multi-frequency radio observations in conjunction with high-quality X-ray observations to complete our understanding of the connection between radio halo properties and cluster dynamics.
[abstract 25 / 47] (score: 3) - Title: Supernova 1987A was a "failed SUPERNOVA" twenty thousand years before its JET-driven explosionAuthors: Noam Soker,Comments: It will be submitted in two days to allow for comments (including missing references)Subjects: astro-ph.HECreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
I show that the progenitor of SUPERNOVA (SN) 1987A faded substantially and became red for hundreds of years to observers in and near the plane of the equatorial ring, because the equatorial ring, which was formed by a binary interaction between the SN 1987A progenitor and a main-sequence companion that ejected material about 20,000 years before the explosion, obscured the progenitor. For a few hundred years, the luminosity for such hypothetical observers was mainly light scattered by the two outer rings, which amounted to ~5% of the progenitor luminosity. In present terms, this event would have been classified as a "failed SUPERNOVA" by these observers, although there was no core collapse, no BLACK HOLE formation, and nothing failed. Rather, this event was a type II ILOT (intermediate-luminosity optical transient), in which equatorial ejecta temporarily obscured the central source. After a few hundred years, the outer rings became transparent, the inner ring became more transparent, and the SN 1987A progenitor brightened over a few thousand years to its normal luminosity for equatorial observers. This finding strengthens the claim that "failed SUPERNOVA" candidates are likely to be type II ILOTs. Although the binary interaction also spun up the core, the bipolar morphology of SN 1987A (its Keyhole) is misaligned with the triple-ring system. I use the jittering JETs explosion mechanism (JJEM) to speculate on a scenario that might explain this misalignment. This study adds small but unique support to the claim that the JJEM is the primary explosion mechanism of CCSNe.
[abstract 26 / 47] (score: 3) - Title: Thermal Stability of Radiation-Pressure-Dominated Accretion Disks Threaded by Net Vertical Magnetic FluxAuthors: Shahram Abbassi, Armin Memarian, Samik Mitra,Comments: 12 pages, 5 figures, Accepted for publication in ApJSubjects: astro-ph.HECreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
The classical radiation-pressure instability predicts strong thermal variability in luminous black-hole accretion disks, whereas most disk-dominated X-ray binary soft states remain comparatively stable. We examine whether net vertical MAGNETic flux can weaken this instability through its contribution to the radial stress. The stability depends not only on the equilibrium MAGNETic stress but also on how that stress changes during a thermal perturbation. We write the local stability condition in terms of the logarithmic heating response, $q_+
[abstract 27 / 47] (score: 2) - Title: Full calibration of the tomographic redshift distribution from the HSC PDR3 Shape Catalog with DESIAuthors: J. Choppin de Janvry, S. Gontcho A Gontcho, U. Seljak, A. Baleato Lizancos, E. Chaussidon, W. d'Assignies, J. DeRose, S. Heydenreich, E. Paillas, D. Valcin, T. Zhang, J. Aguilar, S. Ahlen, D. Bianchi, D. Brooks, F. J. Castander, T. Claybaugh, A. Cuceu, A. de la Macorra, P. Doel, S. Ferraro, A. Font-Ribera, J. E. Forero-Romero, E. Gaztañaga, G. Gutierrez, H. K. Herrera-Alcantar, K. Honscheid, M. Ishak, R. Joyce, S. Juneau, R. Kehoe, D. Kirkby, T. Kisner, A. Kremin, O. Lahav, C. Lamman, M. Landriau, L. Le Guillou, M. Manera, A. Meisner, R. Miquel, S. Nadathur, N. Palanque-Delabrouille, W. J. Percival, C. Poppett, F. Prada, I. Pérez-Ràfols, G. Rossi, E. Sanchez, D. Schlegel, M. Schubnell, J. Silber, D. Sprayberry, G. Tarlé, B. A. Weaver, R. Zhou,Comments: 42 pages, 11 figures, 5 tablesSubjects: astro-ph.COCreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
The calibration of tomographic redshift distributions is essential for cosmological analysis of weak lensing data. In this work, we calibrate all four tomographic bins of the Hyper Suprime Camera (HSC) weak lensing catalog with the Dark Energy Spectroscopic Instrument (DESI) Data Release 1 and 2 using the clustering redshifts technique. We include z > 1.2 redshift sources such as emission line galaxies (ELG) and QUASARs (QSO) sources in our calibration, which were not available in the previous HSC calibration (Rau et al. 2022), allowing a complete calibration of all the redshift bins. We find the first tomographic bin exhibits a small shift towards low redshifts. The second bin is in good agreement with the photometric calibration, while third and fourth bin exhibit a shift towards higher redshifts. However, these shifts are considerably smaller than the shifts obtained in the HSC Year 3 cosmic shear analyses. We evaluate the impact of galaxy bias and magnification effects from all the samples on the measurements, finding them to be small, and we propose corrections to reduce them further. Specifically, we relax the assumption of linear bias and only assume no redshift evolution of the cross-correlation coefficient, allowing us to leverage smaller clustering scales. We model the redshift distributions with splines and compare our results to previous analyses as well as to other parameterizations found in literature. For the two high-redshift tomographic bins, we find the shifts to higher redshifts with respect to the measurements performed in Rau+2022 to be $Δz_3=-0.043^{+0.022}_{-0.020}$ and $Δz_4=-0.050^{+0.012}_{-0.012}$.
[abstract 28 / 47] (score: 2) - Title: Discovery of Weak O VI Absorption in Underdense Regions of the Low-Redshift Intergalactic MediumAuthors: Sapna Mishra, Vikram Khaire, Romeo Pallikkara, Anand Narayanan, Andrew J. Fox,Comments: Accepted for publication in ApJSubjects: astro-ph.GACreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
We search for weak O VI absorption in the low-redshift intergalactic medium (IGM) using 82 high signal-to-noise QUASAR spectra from the Cosmic Origins Spectrograph on the Hubble Space Telescope. From this dataset we compile a clean sample of 396 intervening Lyman-alpha (Lya) lines with H I column densities log N (HI))< 14.5 and no individual O VI detections. Stacking at the location of the O VI doublet reveals absorption at $>5σ$ significance, with equivalent width of 1.7 $\pm$ 0.3 mA, corresponding to log N (O VI) = 12.14 $\pm$ 0.08. The stacked O VI signal associated with strong Lya (13.5 <= log N (HI) < 14.5) absorbers is significantly stronger than that associated with weaker Lya (12.5 <= log N (HI) < 13.5) absorbers. For the subset of 81 broad Lya absorbers (BLAs; b(HI) > 45 km/s), we obtain a marginal $\sim4σ$ O VI detection. Other than Si III, detected at 5$σ$, no metal lines are found. Cross-correlation with galaxies shows that 93% of Lya absorbers lack an associated bright galaxy ($>3L^\ast$) within 1~Mpc. A more complete low-redshift ($z<0.25$) search shows 66% Lya lack galaxies down to $L^\ast$. This suggests the O VI arises mainly from the diffuse IGM, not the circumgalactic medium. The stacked O VI signal suggests characteristic metallicities of $\approx 0.01Z_\odot$ under photoionisation and $\approx 0.001Z_\odot$ under collisional ionisation, though these estimates are model-dependent and assume O VI and H I trace the same phase. This study provides the first observational evidence for metal absorption in low-column-density Lya systems that individually show no detectable metals, placing important constraints on metal enrichment of the underdense IGM.
[abstract 29 / 47] (score: 2) - Title: Enhancing the sensitivity to FCNC top decays $t\to cH $ and $t\to cS $ in the boosted regime at CLICAuthors: Shuo Yang, Peng-Bo Zhao, Ji-Chong Yang,Comments: 27 pages, 11 figures, Accepted by PRDSubjects: hep-phCreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
The top QUARK, having the largest Yukawa coupling to the Higgs sector, provides a unique window into electroweak symmetry breaking and possible new physics beyond the Standard Model. Searches for rare top-QUARK processes are thus powerful probes of new physics. In this work, we investigate the flavor-changing neutral-current (FCNC) top-QUARK decays $t\to cH$ and $t\to cS$, where $S$ denotes a light scalar, at the Compact Linear Collider (CLIC) with a center-of-mass energy of $\sqrt{s}=1.5~\mathrm{TeV}$. Our analysis focuses on a kinematic regime distinct from most previous studies, in which the top QUARKs are typically highly boosted. To enhance signal discrimination in the boosted regime, we construct multi-channel JET images and employ a convolutional neural network (CNN) classifier to capture JET-substructure patterns relevant to the FCNC signals. Assuming an integrated luminosity of $4~\mathrm{ab}^{-1}$, we obtain the expected $95\%$ C.L. upper limit $\mathrm{BR}(t\to cH)\times \mathrm{BR}(H\to b\bar b)<5.27\times10^{-5}$. For the exotic scalar singlet, expected $95\%$ C.L. upper limits between $3.25\times10^{-5}$ and $5.26\times10^{-5}$ are obtained for $\mathrm{BR}(t\to cS)\times \mathrm{BR}(S\to b\bar b)$, for scalar masses between $30$ and $80~\mathrm{GeV}$.
[abstract 30 / 47] (score: 2) - Title: Assessing the large-scale angular clustering of UNIONS Lyman Break Galaxies via cross-correlationsAuthors: Constantin Payerne, Christophe Yèche, William d'Assignies Doumerg, Hendrik Hildebrandt, Martin Kilbinger, Calum Murray, Thomas de Boer, Kenneth C. Chambers, Scott Chapman, Michael J. Hudson, Alan W. McConnachie,Comments: 20 pages, 19 figures, to be submitted to The Open Journal of AstrophysicsSubjects: astro-ph.COCreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
Lyman-break galaxies (LBGs), selected via the strong spectral break blueward of the Lyman limit, are powerful tracers of large-scale structure at redshifts $z>2$. In this work, we assess the feasibility of using LBGs selected from the Ultraviolet Near Infrared Optical Northern Survey (UNIONS) multi-band photometric catalog as cosmological probes of the high-redshift Universe using two-point statistics. We demonstrate that spatially varying imaging systematics, driven by variations in PSF depth, seeing across the UNIONS footprint, limit robust measurements of the LBG auto-angular power spectrum on large scales, even after correcting the LBG field with linear or non-linear mitigation techniques. This study shows that clustering analyses of faint galaxy samples close to survey depth are challenging. We therefore turn to cross-correlation measurements with external tracers, in particular the \textit{Planck} CMB lensing convergence and QUASARs from DESI DR1 and \textit{Quaia}, which are less sensitive to the angular imaging systematics. Using both data and mock catalogues, we demonstrate that the LBG--CMB lensing cross-power spectrum can be measured more robustly than the auto-spectrum, with an amplitude consistent with theoretical predictions. Residual systematics primarily manifest as excess variance at large angular scales, without introducing a significant bias in the recovered signal. Taken together, these results establish UNIONS-selected LBGs as reliable tracers for cross-correlation cosmology at $z\sim 2.5$, and highlight cross-correlation techniques as a powerful and robust avenue for extracting cosmological information from photometric high-redshift galaxy samples in the presence of complex imaging systematics.
[abstract 31 / 47] (score: 2) - Title: Inferring 3D Coronal Magnetic Fields through Seismology-assisted Inversions of $IQU$-only Spectropolarimetric ObservationsAuthors: Alin Razvan Paraschiv,Comments: 16 pages. Published in The Astrophysical JournalSubjects: astro-ph.SRCreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
The routine measurement of the Stokes $IQUV$ signals of emission lines in the solar corona is still a challenging endeavor, particularly for observations using small-aperture instruments. Therefore, recent studies have explored the use of coronal seismology and propagating Alfvénic waves as alternative diagnostics of the coronal MAGNETic field. In particular, Z. Yang et al. showed that plane-of-sky (POS) phase-speed measurements provide a direct and consistent diagnostic of the POS MAGNETic-field component (B$_{\text{POS}}$). Building on recent theoretical advances in solar coronal POLARIZATION, we devise a novel inversion scheme and extended the CLEDB software package to exploit Stokes $IQU$ observations of two coronal emission lines combined with coronal seismology-derived B$_{\text{POS}}$ estimations. Using this framework, we perform a comprehensive statistical analysis demonstrating that this combination of diagnostics allows us to infer both MAGNETic-field orientation and strength with an accuracy comparable to that of Stokes $IQUV$ spectropolarimetry. This type of diagnostics is particularly suited for the Fe xiii 1074.7 and 1079.8 nm line pair routinely observed by new-generation instruments such as DKIST Cryo-NIRSP, DL-NIRSP, MLSO CoMP/UCoMP, and targeted by the future COSMO and CORSAIR efforts.
[abstract 32 / 47] (score: 2) - Title: An exact dyonic BLACK HOLE at the integrable locus of quadratic nonlinear electrodynamicsAuthors: Faizuddin Ahmed, Ahmad Al-Badawi, Izzet Sakalli,Comments:Subjects: gr-qcCreated: 2026-08-22; Updated: 2026-08-26; Datestamp: 2026-08-26
We obtain an exact dyonic black-hole solution in quadratic nonlinear electrodynamics defined by $-F+aF^{2}+bG^{2}$ on the special locus $b=a/2$. At this locus, the radial dependence in the electric constitutive relation cancels and the MAGNETic charge decouples, allowing the field equations to be integrated exactly. Using the field strength as the independent variable, we construct the solution in parametric closed form, with the radial quadrature expressed through Gauss hypergeometric functions and the cosmological constant retained. The solution recovers dyonic Reissner--Nordström--(anti-)de Sitter in the Maxwell limit, the known MAGNETic solution for vanishing electric charge, and the Euler--Heisenberg electric branch for vanishing MAGNETic charge. Its perturbative expansion agrees with the known dyonic result at first order and extends it to all orders. We find a three-horizon window requiring both electric and MAGNETic charges, while the corresponding Smarr integral is also expressed in closed hypergeometric form. The energy density and pressures are obtained analytically, showing that the electric charge enlarges the region satisfying the dominant energy condition relative to the purely MAGNETic case. Three distinct central curvature behaviors are identified, including a tuned self-energy singularity. We further develop the extended thermodynamics, treating the nonlinear coupling and pressure as thermodynamic variables, and find that the critical ratio decreases below the Maxwell value $3/8$ and disappears above a threshold coupling. Finally, birefringent photon propagation produces a split shadow doublet with a splitting of about $0.5\%$, whereas the geometric light ring and scalar ringdown are nearly insensitive to the nonlinear coupling, indicating that the main observable imprint of the nonlinearity lies in POLARIZATION-dependent photon propagation.
[abstract 33 / 47] (score: 2) - Title: More Numerous and Bluer: Companions of the Brightest Little Red Dots Differ from Control Galaxies at $>3σ$, Hinting at Synchronized Black Hole Seed FormationAuthors: Fabio Pacucci, C. Megan Urry,Comments: Submitted for publication in The Astrophysical Journal Letters. 10 pages, 4 figuresSubjects: astro-ph.GA astro-ph.CO astro-ph.HECreated: 2026-08-24; Updated: 2026-08-26; Datestamp: 2026-08-26
The Little Red Dots (LRDs) are a population of compact, red sources, detected abundantly at $4 \lesssim z \lesssim 9$. While their nature is still debated, many models suggest they are powered by accreting massive BLACK HOLEs. Multiple studies have detected blue companions in their vicinity, motivating our analysis: we compare $253$ LRDs uniformly selected across several JWST deep fields against $>7000$ matched controls in the same mosaics. We find that $27.7\%$ of the brightest LRD quartile host a blue ($β<-1$) companion at $0.5-2$ kpc, versus $11.6\%$ of redshift-matched controls: a $\times 2.39$ excess, significant at $3.3σ$. This phenomenon is limited to the brightest LRDs, as the full LRD sample pairs at a rate indistinguishable from controls. Moreover, the excess is confined to the close-pair window ($< 2$ kpc), outside which LRD environments are ordinary. The companions of the brightest LRDs are overwhelmingly ($92\%$) blue, and significantly bluer, with a median $β\approx-2.32$, versus $β\approx-1.92$ for those of controls, rejecting a common parent distribution at $3.4σ$. The signal is thus directional in three independent ways: luminosity, separation, and companion color, all expected for synchronized-pair seed formation. Therefore, we conclude that the association between the brightest LRDs and their close blue companions is physical, i.e., the two phenomena are causally connected: either one drives the other, or both emerge from the same synchronized formation event. A natural explanation for why the most luminous LRDs have nearby, young, star-forming neighbors is that the radiation from these neighbors enabled the direct collapse of the massive BLACK HOLEs powering the LRDs themselves.
[abstract 34 / 47] (score: 2) - Title: Spin inference with the Black Hole Explorer. I. Fisher information matrix forecastAuthors: Joseph R. Farah, Daniel C. M. Palumbo, Michael D. Johnson, Dominic O. Chang,Comments: 9 pages, 4 figuresSubjects: astro-ph.GA astro-ph.HECreated: 2026-08-24; Updated: 2026-08-26; Datestamp: 2026-08-26
General relativity predicts the presence of a thin, bright ring of light superimposed on the image of a BLACK HOLE (the ``photon ring''), whose geometry is sensitive to the spin of the BLACK HOLE. Detecting this photon ring in observations of nuclear supermassive BLACK HOLEs would yield insight into gravity in the strong-field regime as well as their growth histories. The Black Hole Explorer (BHEX) is a mission being developed to detect the photon ring for the first time, raising the question of how precisely we can constrain spin from its observations. We use the method of Fisher information matrices (FIMs) along with a simple dual-cone semi-analytic emission model to forecast BHEX spin posterior widths for the primary science targets (M87* and Sgr~A*) in a variety of configurations. We find that BHEX can constrain the dimensionless spin of its targets to a precision of $σ_{a_*} \ll 0.1$ after 30 orbits, even in the presence of significant systematic errors. We validate our results via numerical checks for stability and robustness, as well as synthetic data cross-validation to assess handling of covariances and prior information in the FIM against a full posterior exploration.
[abstract 35 / 47] (score: 2) - Title: Cows, Tasmanian Devils, and Other Mysteries: Diversity and Origins of Luminous Fast Blue Optical TransientsAuthors: Anna Y. Q. Ho, Wenbin Lu,Comments: Invited review submitted to Reports on Progress in Physics. 70 pages, 22 figures, 3 tables. Comments welcomeSubjects: astro-ph.HECreated: 2026-08-24; Updated: 2026-08-26; Datestamp: 2026-08-26
By repeatedly mapping the sky, optical telescopes have unveiled a diverse landscape of transients, ephemeral celestial events arising from the destruction of stars and stellar remnants. In this review, we focus on a recently identified phenomenon referred to as luminous fast blue optical transients (LFBOTs) and typified by the transient AT2018cow ("The Cow"). AT2018cow was distinguished by luminous emission at X-ray and radio wavelengths in addition to luminous, rapidly evolving, and blue optical emission. Certain LFBOTs have properties that have not been seen in any other class of transients, such as minutes-duration optical flaring in AT2022tsd ("The Tasmanian Devil"). Determining the physical origin of LFBOTs is likely important for understanding stellar evolution and the formation and growth of compact objects such as BLACK HOLEs. We describe how LFBOTs were discovered, their basic observational properties, and the models that have been proposed to explain them. We conclude by highlighting promising avenues for resolving the mystery of their origins.
[abstract 36 / 47] (score: 2) - Title: Amplification of metric perturbations by extremal horizonsAuthors: Samuel E. Gralla, Sepehr Salamat,Comments: 24 pages, 6 figures, 2 tablesSubjects: gr-qcCreated: 2026-08-24; Updated: 2026-08-26; Datestamp: 2026-08-26
Under normal circumstances, an observer falling into a BLACK HOLE feels nothing special upon crossing the horizon. In this paper we find an intriguing exception: For most of the parameter range of the extremal Kerr-Newman (KN) spacetime, horizon co-rotating perturbations are enhanced near the horizon, such that an infalling observer experiences an anomalously large tidal deformation as they enter the BLACK HOLE. Such perturbations arise when there is a persistent source outside the BLACK HOLE that is either co-rotating itself or has discrete Fourier support at the associated frequencies $ω=mΩ_H$ (where $m$ is the azimuthal number and $Ω_H$ is the horizon frequency). The enhancement is formally infinite at precise co-rotation, and we work with a nearly co-rotating mode to keep perturbation theory under control. The underlying physics is the emergence of discrete self-similarity in the extremal limit, with complex scaling weights of the form $-1/2\pm iα$ for real $α$. It is analogous to the BLACK HOLE Meissner effect, except that the near-horizon field is enhanced rather than screened. We numerically calculate the scaling exponents for coupled gravitoelectroMAGNETic (GEM) perturbations of extremal KN BLACK HOLEs and show that the complex exponents arise in the parameter range $Q < Q_*$ with $Q_*\approx.93M$. These exponents also predict the decay and growth rates (Aretakis effect) of generic GEM perturbations of the KN spacetime, both on and off the horizon. The enhancement of co-rotating perturbations can be viewed as a driven Aretakis instability.
[abstract 37 / 47] (score: 2) - Title: An Inverse Grad-Shafranov Neural Network Approach to Tokamak Magnetic ControlAuthors: Allen M. Wang, Adriano Mele, Cosmas Heiß, Cristian Galperti, Zander Keith, Alessandro Pau, Antoine Merle, Olivier Sauter, Daniel Gonzalez Castiñeiras, Francesco Carpanese, Federico Felici, Mark Dan Boyer, Cristina Rea, TCV Team, EUROfusion Tokamak Exploitation Team,Comments:Subjects: physics.plasm-phCreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
A new approach to tokamak MAGNETic control enabling high-precision plasma shaping and novel real-time adaptability is experimentally demonstrated on the Tokamak a Configuration Variable (TCV). The method is motivated by the insight that, under appropriate assumptions, a real-time inverse Grad-Shafranov solver approximates an optimal control policy for plasma boundary regulation. Building on this, a control architecture is developed in which classical controllers enforce operational constraints while a fast surrogate model provides a real-time inverse mapping from the desired plasma boundary to Poloidal Field Coil currents. Experimental results on TCV demonstrate improved plasma shaping with respect to the standard discharge preparation procedure --- albeit without explicit real-time shape feedback --- while enabling flexible response to asynchronous events. It is shown that a single network provides satisfactory performance across a range of plasma MAGNETic configurations. Real-time adaptivity is demonstrated in simulation, and partially in experiment, through adaptive strike point motion and early termination in response to a real-time trigger. These results suggest a viable path toward MAGNETic control architectures that reduce reliance on dense diagnostic coverage while maintaining high-accuracy plasma shaping, with potential relevance for future fusion power plant operation.
[abstract 38 / 47] (score: 2) - Title: First-Principles Simulation of Electron-Ion Collisional Transport in Magnetized and UnMAGNETized PlasmasAuthors: Keheng Zhu, Jian Liu, Chaozhou Mou, Senran Lin, Wei Zhang,Comments: 36 pages, 15 figures, 1 table. Submitted to Computer Physics CommunicationsSubjects: physics.plasm-ph physics.comp-phCreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
Accurate electron-ion collision models are central to predicting transport in fusion and space plasmas, yet most practical formulations rely on binary-collision assumptions and impact-parameter cutoffs whose quantitative accuracy is difficult to assess directly. We develop a first-principles simulation framework for collisional transport by solving the Newton-Lorentz equations for test electrons in the many-body electric field of a Debye-screened ion background, without imposing binary-collision closures or artificial lower cutoffs. The method combines explicit force summation within a Debye sphere, a volume-preserving particle pusher, and adaptive time stepping, enabling stable and scalable simulations in both unMAGNETized and MAGNETized plasmas. Using simulation-based measures of momentum relaxation and cross-field diffusion, we recover the classical scalings for the electron-ion collision frequency and perpendicular diffusion coefficient, namely $ν_{ei} \propto v_{th}^{-3}$ and $D_\perp \propto B^{-2}$. Within the parameter range studied, both simulated coefficients are lower than their corresponding classical estimates by approximately 15-25%. These regime-specific benchmark results indicate that classical transport theory captures the leading scaling behavior, but that the corresponding quantitative prefactors can remain sensitive to many-body and near-field effects in the simulated regime. The framework therefore provides a computational benchmark for testing and improving reduced collision operators and transport models.
[abstract 39 / 47] (score: 2) - Title: Interplay of Compaction, Quenching, and Black Hole Growth in the Most Massive Galaxies since $z\sim5$: Insights from JWST and Chandra DataAuthors: Novan Saputra Haryana, Masayuki Akiyama, Abdurro'uf, Suchetha Cooray, Itsna Khoirul Fitriana, Dian P. Triani, Bovornpratch Vijarnwannaluk, Juan Pablo Alfonzo, Irham Taufik Andika, Muhammad Nur Ihsan Effendi, Ibnu Nurul Huda, Takumi Kakimoto, Anton Timur Jaelani, Ronaldo Laishram, Naoki Matsumoto, Abdurrahman Naufal, Lucky Puspitarini, Ryo Albert Sutanto, Hesti Retno Tri Wulandari,Comments: Accepted for publication in ApJSubjects: astro-ph.GACreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
The buildup of dense stellar cores is expected to mark an important transition in the star-formation and black-hole growth of massive galaxies. Using spatially resolved spectral energy distribution (SED) fitting of James Webb Space Telescope near-infrared imaging, combined with stacking analysis of Chandra X-ray data, we trace stellar mass buildup and average BLACK HOLE accretion in the most massive galaxies at $z<5$, selecting 50 most massive galaxies per redshift bin at constant number density of $\sim4.4\times10^{-5}$ cMpc$^{-3}$. To robustly constrain central stellar populations, we separate ACTIVE GALACTIC NUCLEi (AGN) components affecting the photometry using multi-band morphological decomposition and SED analysis. We find that the sample selected with constant number density exhibits evolutionary trend of rapid central compaction at $z\sim4$, during which the median central 1 kpc stellar mass increases by $\sim0.60$ dex over $\sim400$ Myr. The majority of X-ray detected AGN ($63\%\pm12\%$) are hosted by galaxies undergoing the compaction, while we find neither individually detected X-ray sources nor a significant stacked X-ray signal at $z>4$, indicating that substantial average black-hole growth emerges primarily during, rather than before, the compaction. Following the compaction, central specific STAR FORMATION rates (sSFR) decline by $\sim1.24$ dex over $\sim700$ Myr at $z\sim3$ while remaining elevated galaxy-wide, signaling the onset of inside-out quenching. Despite this central suppression, specific BLACK HOLE accretion rate remains coupled to the total sSFR. Our results suggest that dense-core formation in the most massive galaxies marks the onset of inside-out quenching and a transition toward enhanced black-hole to stellar growth ratio.
[abstract 40 / 47] (score: 2) - Title: Decoupling candidate dual AGN from chance superpositions in the GOTHIC survey via a deep-learning frameworkAuthors: Bhavesh Mukheja, Snehanshu Saha, Anwesh Bhattacharya, Mousumi Das, Françoise Combes, Sudhanshu Barway,Comments: Submitted to MNRAS. Supplementary Material merged in the main textSubjects: astro-ph.GA cs.CV cs.LG math-ph math.MP physics.data-anCreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
Dual ACTIVE GALACTIC NUCLEi (DAGN) mark a critical phase in the evolution of merging galaxies and the pairing of supermassive BLACK HOLEs, yet they remain difficult to identify in large imaging surveys because of projection effects and limited spatial resolution. Compact foreground stars and unresolved substructure can mimic dual nuclei through chance superposition, complicating automated detection. We revisit the 46,061 galaxies flagged but rejected as DAGN candidates by the GOTHIC pipeline, primarily because the two nuclei fell within the SDSS fibre aperture or exceeded its separation threshold. We train a supervised deep-learning framework based on the YOLOv11 oriented-bounding-box architecture on annotated SDSS imaging to separate genuine dual nuclei from foreground stellar contaminants and other spurious alignments. The final model attains a validation precision of 0.919, recall of 0.905, and $F_1$ of 0.912 for the dual-nuclei class, and yields 29,605 dual-nucleus candidates after removing star-dominated and blended detections. Structured visual inspection indicates that $54.5$--$62\%$ are consistent with genuine dual nuclei, implying $\sim(1.4$--$1.8)\times10^{4}$ plausible systems. Cross-calibrating the YOLO separation against the deterministic GOTHIC centroid measurement and restricting to the compact regime ($d \le 6.87''$) gives a conservative subset of $\sim 13{,}672$ candidates, reaching calibrated separations of $\sim 0.56''$. Spectroscopy of the most compact ($\le 1$~kpc) systems shows they are dominated by passive, absorption-line galaxies with no resolved double-peaked emission, so confirmation requires higher-resolution follow-up. The catalogue is a statistically refined list of candidates, not confirmed DAGN. Nonetheless, deep-learning detection substantially reduces contamination and expands the plausible DAGN census.
[abstract 41 / 47] (score: 2) - Title: X-ray Polarization of Inverse Compton Scattering by Thermal and Nonthermal ElectronsAuthors: Boting Wang, Jirong Mao, Jieying Liu, Fei Xie,Comments: 14 pages, 12 figures, accepted for publication in MNRASSubjects: astro-ph.HECreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
X-ray emission from accretion-powered astrophysical systems is widely interpreted as inverse Compton (IC) scattering between energetic electrons and soft photons. Besides the emitted intensity, the POLARIZATION of this radiation provides important information about the physical properties of the electrons involved. We investigate how different electron populations shape both the spectrum and POLARIZATION of IC emission in the X-ray band. We consider three electron populations: purely thermal, purely nonthermal power-law, and a hybrid population combining both components. We take both numerical simulations and semi-analytic calculations. We first attempt the cases for thermal and nonthermal electrons, respectively. We then focus on the hybrid population, which is expected to be realistic in high-energy object environments. For the case of hybrid electrons, the scattered emission separates into three energy regimes. At low energies ($\lesssim 0.1$ keV), it is dominated by thermal electrons; at high energies ($\gtrsim 4$ keV), it is governed by the nonthermal component. Between these limits, a transition band ($\sim 0.1$-$4$ keV) appears in which both components contribute. The degree of POLARIZATION varies smoothly across these regimes, and the behavior in the transition band directly traces the relative importance of thermal and nonthermal electrons. We further show that for partially polarized seed photons, the scattered POLARIZATION scales linearly with the incident POLARIZATION while its frequency dependence remains unchanged. These results show that X-ray polarimetry provides a powerful diagnostic of the electron energy distribution in accretion-powered systems.
[abstract 42 / 47] (score: 2) - Title: Fingerprints of thermal Comptonization in accreting neutron stars. Plasma-vacuum interplay in cyclotron lines and polarisationAuthors: E. Sokolova-Lapa, D. K. Maniadakis, J. J. R. Stierhof, E. Ambrosi, A. D'Aì, C. Ferrigno, N. Schettino, M. Middleton, A. Gúrpide, V. Grinberg, G. Lipunova, I. El Mellah, P. Kretschmar, J. Wilms,Comments: Submitted to Astronomy & AstrophysicsSubjects: astro-ph.HE astro-ph.SRCreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
X-ray emission from accreting, strongly MAGNETised neutron stars and its pulse-phase variability probe their MAGNETic-field geometry, spin orientation, and emission processes. Whether the radiation emerges mainly from a hot spot or column, and whether its properties are shaped by bulk or thermal Comptonization, remain debated across luminosity regimes. We aim to disentangle intrinsic emission from visibility effects and identify observables characteristic of thermal Comptonization in hot spots and columns. We therefore derived energy-dependent beam patterns and observable signatures without assigning the model to a luminosity regime, focusing on cyclotron-resonance and polarisation effects as tracers of anisotropy. To do so, we computed angle-dependent polarised broadband spectra, including the fundamental cyclotron line, for a homogeneous, self-emitting, MAGNETised Comptonizing plasma over a broad parameter range. Accounting for light bending and projection, we obtained phase-dependent fluxes for different geometries and, for hot spots, observed linear polarisation. The beam patterns evolve with energy, driving pulse-profile changes. Near the cyclotron resonance, plasma-vacuum interplay produces a narrow central beam and side petals. Their visibility creates geometry-dependent dips, bumps, and M- and W-shaped structures in hot-spot pulsed fraction spectra, but only dips and bumps for columns. Thermally Comptonized cyclotron lines do not reliably trace plasma temperature; plasma-induced ellipticity and band averaging reduce observed soft-X-ray linear polarisation to 0-30%. Under typical X-ray pulsar accretion-channel conditions, thermal Comptonization leaves robust energy-dependent anisotropic signatures. Energy-resolved pulse profiles, pulsed fraction spectra, and polarisation thus provide complementary diagnostics of neutron star geometry, emission-region shape, and spectral formation.
[abstract 43 / 47] (score: 2) - Title: Global uniqueness of Kerr BLACK HOLE spin and inclination from a segment of the critical curveAuthors: Kenta Hioki,Comments: 29 pagesSubjects: gr-qc astro-ph.HECreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
High-resolution observations are expected to probe the photon-ring structure of BLACK HOLE images. The critical curve is the geometrically defined limiting locus on the observer's screen toward which successive higher-order photon subrings accumulate. For a Kerr BLACK HOLE, the shape of this limiting curve depends on the dimensionless spin parameter $a$ and the inclination angle $i$. We investigate whether these parameters can be determined uniquely from a connected positive-length segment of the critical curve when the segment's position and orientation on the screen are unknown. For rotating non-extremal Kerr BLACK HOLEs with $0
[abstract 44 / 47] (score: 2) - Title: Spatially resolved molecular gas conditions in the circumnuclear disc of 3C 84Authors: Bin Jia, Tom Oosterloo, Serena Viti, Raffaella Morganti,Comments:Subjects: astro-ph.GACreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
The brightest cluster galaxy NGC 1275, at the centre of the Perseus cluster, hosts the radio-loud AGN 3C 84 and a circumnuclear disc (CND) of cold molecular gas onto which large-scale CO filaments accrete, yet the physical and chemical conditions of the gas in the CND remain poorly constrained. We present a spatially resolved analysis of ALMA CO(2-1), HCN(3-2), and HCO$^+$(3-2) observations at 72 pc. The data are partitioned into beam-sized hexagonal regions and modelled with a Bayesian framework that couples a neural network emulator of time-dependent chemistry (UCLCHEM) with non-LTE radiative transfer (SpectralRadex) to infer the gas density, kinetic temperature, and COSMIC RAY ionisation rate in each region. All three line ratios peak in the inner disc and decline with radius. The inference shows radial gradients in density ($\log_{10} n({\rm H_2}) \approx 6.3$ to $\sim 5$), kinetic temperature (~200 K to ~160 K), and COSMIC RAY ionisation rate ($\log_{10}(ζ/ζ_0) \approx 4.9$ to $\sim 3$). Despite the powerful radio AGN, the observed HCN(3-2)/HCO$^+$(3-2) ratio remains $\lesssim 1$ across the disc. Our modelling attributes this to optical depth saturation of HCN(3-2) ($τ\sim 1$-3), which suppresses the intensity ratio even when the HCN abundance exceeds that of HCO$^+$ by a factor of three or more. The HCN/HCO$^+$ intensity ratio therefore cannot be used as an abundance diagnostic without accounting for optical depth, and a low ratio does not necessarily imply weak AGN influence on the chemistry. Azimuthally resolved profiles suggest a localised HCO$^+$/CO enhancement at the western disc boundary, coinciding with the filament-disc accretion interface and consistent with shock processing by velocity shear between the infalling filaments and the rotating disc. These results indicate that the CND is shaped by accretion from its filamentary environment.
[abstract 45 / 47] (score: 2) - Title: The impact of the IGM thermal state on the Ly$α$ flux 3D power spectrum from linear to highly non-linear scalesAuthors: Tomáš Šoltinský, Gabriele Autieri, Vid Iršič, Matteo Viel,Comments: 32+21 pages, 14+7 figures, 1+6 tables, Comments welcomeSubjects: astro-ph.COCreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
Recently initiated and upcoming spectroscopic surveys, such as DESI and WST, will provide more than $10^6$ high-$z$ QUASAR spectra, enabling dense sky coverage by the Ly$α$ forest. This is expected to establish the three-dimensional (3D) Ly$α$ forest power spectrum, $P_{\rm 3D,α}$, as a probe of the thermal and ionization history of the intergalactic medium (IGM). To exploit this opportunity, we quantify the imprints of reionization on the post-reionization IGM using high-fidelity numerical models. We use the Sherwood and Sherwood-Relics cosmological hydrodynamical simulations with box sizes up to $160\,h^{-1}\,\rm cMpc$ to investigate the impact of box size, mass resolution, and extracted grid resolution on $P_{\rm 3D,α}$ over $2.4\leq z\leq4.8$. After applying a Zel'dovich control variate correction, simulation volume has a modest impact over most scales and orientations, whereas degrading the mass resolution produces differences of up to $\sim13\%$. Insufficient resolution of the grid used for the optical-depth calculation can artificially enhance small-scale power by up to $\sim35\%$. The timing of $\mathrm{H\,I}$ reionization leaves only a percent-level imprint on $P_{\rm 3D,α}$ at $z=2.4$, whereas varying the photoheating rate by a factor of two changes the large-scale power by $\sim4-8\%$. Our results demonstrate that numerical effects can be comparable to, or exceed, the relic astrophysical signatures encoded in $P_{\rm 3D,α}$, making numerical convergence essential for interpreting precise Ly$α$ forest measurements. The strongest astrophysical imprint arises from spatially inhomogeneous $\mathrm{H\,I}$ reionization, which enhances the large-scale power by up to $\sim70\%$ at $z=4.2$. This highlights the potential of post-reionization Ly$α$ forest measurements as a probe of the thermal history and spatial morphology of cosmic reionization.
[abstract 46 / 47] (score: 2) - Title: Dynamical Friction as Environmental Gravitational Self-ForceAuthors: Sayak Datta,Comments:Subjects: gr-qc astro-ph.HECreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
Dynamical friction (DF) and gravitational-wave radiation reaction are conventionally treated as distinct dissipative mechanisms acting on a compact object inspiraling through a matter environment. We show that DF is not an additional force but a term at order $q^2ε$ in a covariant multiparameter expansion of the MiSaTaQuWa force equation that vanishes identically in the absence of a particle-induced perturbation of the environment's matter fields, where $q$ and $ε$ are respectively the mass ratio and environmental parameter. As a test of this identification, we evaluate it in weak and adiabatic field limit, solving the polar density-perturbation equation sourced by the particle's own order-$q$ vacuum metric perturbation. The reduction reproduces the Chandrasekhar-Ostriker drag force and predicts two features in strong gravity. An $\ell$-dependent splitting of the wake that only recombines into the Ostriker source in the weak-field limit, and a purely RELATIVISTIC axial contribution with no Newtonian counterpart. This establishes dynamical friction as an intrinsic piece of self-force theory, extending to strong field, generic orbits, and generic environments, with direct consequences for extreme-mass-ratio inspiral waveform modeling for LISA.
[abstract 47 / 47] (score: 2) - Title: The GPSP Atlas: High-resolution Galactic Photon Survival Probability Atlas for Very-High- and Ultra-High-Energy Gamma-Ray AstronomyAuthors: Ekrem Oğuzhan Angüner,Comments: 29 pages, 15 figures. Published in The Astrophysical Journal (ApJ). Public release of the GPSP and GPSP-LIV atlases, including FITS data products and Python helper modules. Data available via Zenodo: https://zenodo.org/records/21403524. Documentation and example notebooks available at https://gpsp-atlas.readthedocs.ioSubjects: astro-ph.HECreated: 2026-08-25; Updated: 2026-08-26; Datestamp: 2026-08-26
The emergence of Galactic PeV astronomy makes photon--photon ($γγ$) absorption an increasingly important component of gamma-ray data analysis. In this work, the Galactic Photon Survival Probability (GPSP) atlas is presented as the first Galactic framework describing gamma-ray survival probabilities over the full parameter space $P(l,b,d,E_γ)$ between 1 TeV and 10 PeV. The atlas is constructed using two independent GALPROP-based interstellar radiation field (ISRF) models, allowing direct assessment of ISRF-related systematics, and is released in a FITS format compatible with standard analysis frameworks. A novel gamma-ray survival phase space representation is introduced, extending 1D survival profiles into a 2D energy--distance framework that visualizes Galactic transparency and gamma-ray horizons. Using the full atlas, Galactic transparency and Galactic plane survival maps are constructed. These reveal that Galactic opacity is highly structured, with enhanced attenuation along spiral-arm tangent directions in the $\sim$100--300 TeV regime, while attenuation becomes nearly isotropic and cosmic microwave background (CMB) dominated near PeV energies. The framework naturally accommodates attenuation calculations for extended and diffuse sources. The atlas is further extended to subluminal Lorentz invariance violation (LIV) scenarios through the GPSP-LIV atlas, incorporating LIV-modified pair production kinematics and cross sections. Sources emitting in the 2--3 PeV regime beyond gamma-ray horizons are identified as promising targets for probing LIV effects. Finally, practical applications are presented for the Galactic Center PeVatron and the Cygnus X-3 regions. The GPSP and GPSP-LIV atlases establish a publicly available foundation for studies of Galactic PeVatrons, diffuse gamma-ray emission, and fundamental physics searches in the emerging era of Galactic PeV astronomy.
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