Current date: 2026-05-20

Setting default datestamp limit: 0

Datestamp limit: 2026-05-20 (0 days ago)

Created/updated limit: 2026-05-13 (7 days ago)

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

Setting default set: physics

OAI-PMH request: http://export.arxiv.org/oai2?verb=ListRecords&from=2026-05-20&until=2026-05-20&set=physics&metadataPrefix=arXiv

Scoring abstracts

Number of records retrieved: 755

Keyword score statistics

score 9 -- 1 abstracts

score 8 -- 2 abstracts

score 7 -- 2 abstracts

score 6 -- 1 abstracts

score 5 -- 6 abstracts

score 3 -- 5 abstracts

score 2 -- 21 abstracts

in total -- 38 abstracts

Articles that appeared on 2026-05-20

[abstract 1 / 38] Wow! (score: 9)
arXiv:2605.20153 [pdf, ps, other]

Title: The exceptional 2017 gamma-ray flare of the RADIO GALAXy NGC 1275: VERITAS and Multiwavelength Observations

Authors: A. Acharyya, A. Archer, P. Bangale, J. T. Bartkoske, W. Benbow, Y. Chen, J. L. Christiansen, A. J. Chromey, A. Duerr, M. Errando, M. Escobar Godoy, A. Falcone, S. Feldman, Q. Feng, S. Filbert, L. Fortson, A. Furniss, W. Hanlon, O. Hervet, C. E. Hinrichs, J. Holder, Z. Hughes, M. Iskakova, W. Jin, M. N. Johnson, P. Kaaret, M. Kertzman, M. Kherlakian, D. Kieda, T. K. Kleiner, N. Korzoun, F. Krennrich, S. Kundu, M. J. Lang, M. Lundy, G. Maier, E. Meyer, P. Moriarty, R. Mukherjee, W. Ning, M. Ohishi, R. A. Ong, A. Pandey, J. Escudero Pedrosa, M. Pohl, E. Pueschel, J. Quinn, P. L. Rabinowitz, K. Ragan, P. T. Reynolds, D. Ribeiro, E. Roache, C. Rulten, I. Sadeh, L. Saha, M. Santander, G. H. Sembroski, R. Shang, M. Splettstoesser, D. Tak, A. K. Talluri, J. V. Tucci, J. Valverde, V. V. Vassiliev, D. A. Williams, S. L. Wong, T. Yoshikoshi, P. S. Smith, J. Kataoka,

Comments: 24 pages, 9 figures

Subjects: astro-ph.HE

Created: 2026-05-19; Updated: 2026-05-20; Datestamp: 2026-05-20

The RADIO GALAXy NGC 1275 is the Brightest Cluster Galaxy in the Perseus cluster. It is well-studied across all wavebands, including Very High Energy (VHE; E>100GeV gamma-rays, and with radio observations over the last 20 years tracking an unusual radio component, "C3". NGC 1275 was observed in an exceptional VHE flaring state between 2016 December 31 and 2017 January 3. The flare peak reached ~1.5 Crab units as measured by the MAGIC observatory. We report on the observations of NGC~1275 conducted by VERITAS and multi-wavelength data collected during this flaring state, and for context, data taken between 2009 and 2017 inclusive. VERITAS detected the declining state of the flare on 2017 January 2 (MJD 57755) and 3 (MJD 57756) at an average flux state of 0.5 Crab units. VERITAS spectra show an overall long-term trend of harder-when-brighter. During the flare, the gamma-ray spectrum obtained from the combined FERMI-LAT, MAGIC, and VERITAS observations, changes from a power law with an exponential cut-off on January 1 to a log-parabola on January 2. To study the evolution of the flare in more detail, multi-band spectral energy distributions (SEDs) were constructed for the nights of 2017 January 1 and 2 corresponding to the shift from the peak to the decline of the flare. A blob-in-JET modeling of the SEDs results in support for a two-component model with a JET angle of 10 degrees to the line of sight and the gamma-ray emission zone located in the vicinity of the C3 radio component.

[abstract 2 / 38] Wow! (score: 8)
arXiv:2508.00976 [pdf, ps, other]

Title: A Census of Variable Radio Sources at $3\,$GHz

Authors: Yjan A. Gordon, Peter S. Ferguson, Michael N. Martinez, Eric J. Hooper,

Comments: 25 pages, 20 Figures, 5 Tables. Published in OJAp. Supplementary data available at https://zenodo.org/records/18010746

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

Created: 2026-05-19; Updated: 2026-05-20; Datestamp: 2026-05-20

A wide range of phenomena, from explosive transients to ACTIVE GALACTIC NUCLEi, exhibit variability at radio wavelengths on timescales of a few years. Characterizing the rate and scale of variability in the radio sky can provide keen insights into dynamic processes in the Universe, such as accretion mechanics, JET propagation, and stellar evolution. We use data from the first two epochs of the Very Large Array Sky Survey (VLASS) to conduct a census of the variable radio sky. Approximately $3,600$ compact sources are found to significantly vary in brightness during the $\sim2.5\,$ years between observations. In this work we focus on sources that are detected in both VLASS epochs, but estimate there may be $>10,000$ additional variable radio sources in VLASS that are only detected in either the first or second epoch. For objects detected in both epochs whose mean flux density across the two epochs, $μ_{S}$, is brighter than $20\,$mJy, $5\,$% show brightness variations $>30\,$%, rising to $9\,$% at $μ_{S}>300\,$mJy. We analyze the redshift distributions, infrared colors, and $γ$-ray properties of the variable radio sources, finding that most have multiwavelength characteristics that are consistent with BLAZARs and QUASARs. Blazars in particular are found to be overrepresented among the variable radio sources, and the largest absolute changes in flux density are produced by BLAZARs. The largest fractional changes in brightness are exhibited by galactic sources. We discuss our results, including some of the more interesting and extreme examples of variable radio sources identified, as well as future research directions.

[abstract 3 / 38] Wow! (score: 8)
arXiv:2605.18955 [pdf, ps, other]

Title: Automating the detection of POLARIZATION angle rotations in BLAZARs. Re-analysis of RoboPol data reveals 27 new rotations

Authors: Anastasia Glykopoulou, Ioannis Liodakis, Dmitry Blinov,

Comments: Accepted for publication in Astronomy & Astrophysics. 10 pages, 5 figures. GitHub: https://github.com/glykanastasia/blazar-evpa-rotation-detector

Subjects: astro-ph.HE

Created: 2026-05-18; Updated: 2026-05-20; Datestamp: 2026-05-20

We present an automated pipeline for the detection of EVPA rotations in BLAZARs, integrating correction of the 180$^\circ$ ambiguity, Bayesian Blocks segmentation, and statistical validation. Applied to RoboPol monitoring data, the method identified 48 rotations across 25 sources, including multiple events in RBPLJ2232+1143, RBPLJ1751+0939, RBPLJ1800+7828, and RBPLJ2253+1608. The rotations span amplitudes from 90.8$^\circ$ to 359.7$^\circ$, durations between 7.0 and 111.3 days, and rotation rates averaging 5.0$^\circ$/day. Comparison with previous catalogs reveals systematic differences: Bayesian Blocks rotations are on average $\sim$10\% larger in amplitude, about twice as long in duration, and roughly two-thirds slower in angular velocity, reflecting systematic biases between adaptive binning and manual segmentation. In addition, we report 27 previously unreported rotations, including 11 from the final 2016--2017 season. A correlation analysis with contemporaneous FERMI--LAT $γ$-ray light curves shows that longer rotations tend to coincide with enhanced $γ$-ray activity, while rotation amplitude alone is not predictive of $γ$-ray brightness. Our pipeline minimizes subjective biases, expands the list of known EVPA rotations, and provides a reproducible framework for future multiwavelength studies of BLAZAR JET dynamics and particle acceleration.

[abstract 4 / 38] Wow! (score: 7)
arXiv:2410.13071 [pdf, ps, other]

Title: Particle Acceleration Time due to Turbulent-Induced Magnetic Reconnection

Authors: Elisabete M. de Gouveia Dal Pino, Tania E. Medina-Torrejon,

Comments: Accepted for publication in the ApJ

Subjects: astro-ph.HE hep-ph

Created: 2026-05-19; Updated: 2026-05-20; Datestamp: 2026-05-20

We numerically investigate a crucial parameter for understanding particle acceleration theory via turbulence-induced MAGNETic RECONNECTion: the particle acceleration time. We examine particles accelerated either during the JET's dynamic evolution or in a post-processing, nearly stationary regime. We derive the particle acceleration time and compare it with theoretical predictions for both the FERMI and drift regimes identified in the simulations. In the FERMI regime, the acceleration time is expected to be independent of the particles' energy, for constant RECONNECTion velocity, as energy increases exponentially with time. Conversely, we expect the RECONNECTion acceleration time to depend on the current sheet's thickness and the RECONNECTion velocity, a dependence recently revisited by xu and lazarian 2023. They identified three conditions for \(t_{acc}\). We tested these relations using statistical distributions of the current sheets' thickness and RECONNECTion velocities in the turbulent JET over time. The resulting average value of \(t_{acc}\) was found to be nearly constant with particle energy. We compared this acceleration time with the average acceleration time derived directly from 50,000 particles accelerated in situ in the same RELATIVISTIC JET. When considering a longer time interval for particle acceleration in a nearly stationary snapshot of the turbulent JET, we find that the acceleration time during the FERMI regime remains nearly independent of particle energy and aligns with the acceleration time theoretical relations up to the threshold energy, attained when the particles Larmor radius becomes as large as the thickness of the largest current sheets. Beyond this threshold, the acceleration regime shifts to the slower drift regime, showing strong energy dependence, as predicted. The results also indicate a clear dominance of the FERMI regime of acceleration.

[abstract 5 / 38] Wow! (score: 7)
arXiv:2605.19109 [pdf, ps, other]

Title: Radiative PIC simulations of RELATIVISTIC pair plasma: multiple interacting current sheets and turbulent evolution

Authors: Fulvia Pucci, Elena Amato, Dario Borgogno, Niccolo' Bucciantini, Maria Elena Innocenti, Kevin M Shoeffler, Marco Tavani, Valerio Vittorini,

Comments: 11 Pages, 6 Figures, One Table, Special Issue for the 2nd European Conference on Magnetic Reconnection in Plasmas

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

Created: 2026-05-18; Updated: 2026-05-20; Datestamp: 2026-05-20

Two-dimensional RELATIVISTIC particle-in-cell (PIC) simulations of radiative MAGNETic RECONNECTion in pair plasmas with multiple interacting current sheets are carried out to mimic the dynamics in high-energy astrophysical environments, such as particle acceleration regions in pulsar wind nebulae and RELATIVISTIC outflows, where the MAGNETic field is expected to reverse polarity multiple times. Initially, due to RECONNECTion within each isolated sheet, particles are accelerated and SYNCHROTRON emission beyond the burn-off limit is confirmed, even if the particle distribution function shows steep slopes. After this phase, plasmoids lead to cross-sheet interactions and merging, with new current sheets formed. In this regime a Kolmogorov-like spectrum for the MAGNETic energy develops over a couple of decades, followed by a dissipation range starting around 5~$d_e$ (electron inertial lengths), showing that multi-sheet RECONNECTion evolves nonlinearly into well-developed turbulence. This phase provides secondary acceleration and further cooling by SYNCHROTRON emission, with intermittent radiative bursts. We show that high energy accelerated particles by the primary current sheets are further energized during the turbulent phase, while the distribution of the most energetic particles remains steep.

[abstract 6 / 38] Yes (score: 6)
arXiv:2605.19877 [pdf, ps, other]

Title: The first IXPE view of the eclipsing ADC source 4U 1822-37

Authors: A. Anitra, A. Gnarini, T. Di Salvo, R. Iaria, A. Marino, F. Barra, L. Burderi, A. Sanna, L. Marra, S. Bianchi, G. Matt, F. Ursini, F. Capitanio, S. Fabiani, P. Kaaret, A. Tarana,

Comments: 12 pages, 8 figures. Submitted to Astronomy and Astrophysics

Subjects: astro-ph.HE

Created: 2026-05-19; Updated: 2026-05-20; Datestamp: 2026-05-20

Accretion-disc corona sources are high-inclination low-mass X-ray binaries in which the innermost regions are hidden and the observed X-ray emission is dominated by radiation scattered above the disc. 4U 1822-37 is a key binary system of this class, but its geometry is still debated. X-ray polarimetry offers a direct probe of the scattering structure. We present the first X-ray spectro-polarimetric study of 4U 1822-37 and test whether its spectrum and polarisation can be explained within the accretion-disc-corona scenario. We analysed a coordinated campaign with IXPE, XMM-Newton, NUSTAR, and SWIFT. We performed broadband spectral modelling and model-independent, energy-resolved, and orbital-phase-resolved polarimetric analyses. The broadband spectrum requires a soft thermal component, a Comptonised continuum, a hard power-law tail, and RELATIVISTICally blurred reflection. The observed 0.1-100 keV luminosity, $L_{\rm obs}\simeq6.1\times10^{36}\ {\rm erg\,s^{-1}}$, is far below the intrinsic luminosity expected from the orbital evolution, supporting a geometry in which only a small fraction of the intrinsic emission is scattered into the line of sight by an extended, optically thin corona. In the 2-8 keV band, IXPE measures ${\rm PD}=7.9\pm0.6\%$ and ${\rm PA}=-24^\circ\pm2^\circ$. The PD increases with energy, while the PA remains approximately constant. During eclipse, the PD decreases to ${\rm PD}=5.5\pm1.7\%$, with no significant PA variation. This behaviour is consistent with the companion occulting the most polarimetrically efficient part of the extended corona. The high PD, stable PA, energy-dependent polarisation, and eclipse behaviour support a picture in which 4U 1822-37 is observed in an extreme high-inclination, scattering-dominated regime. The extended corona is the main structure shaping both the observed X-ray emission and its polarisation.

[abstract 7 / 38] Yes (score: 5)
arXiv:2602.09102 [pdf, ps, other]

Title: Polarization Signatures of Inspiraling Hotspots around Kerr Black Holes

Authors: Pablo Ruales, Delilah E. A. Gates, Alejandro Cárdenas-Avendaño,

Comments: 16 pages, 8 figures v2: Updated to match published version

Subjects: astro-ph.HE gr-qc

Created: 2026-05-16; Updated: 2026-05-20; Datestamp: 2026-05-20

Polarimetric interferometry is a powerful tool for probing both BLACK HOLE accretion physics and the background spacetime. Current models aimed at explaining the observed multiwavelength flares in Sgr A* often assume hotspots moving on geodesic, Keplerian orbits. In many scenarios, though, a hotspot may instead follow an inspiraling trajectory, potentially transitioning into a plunge toward the BLACK HOLE. In this work, we present a general framework to simulate the polarized emission from generic equatorial inspiraling hotspots in Kerr spacetime using a parametric four-velocity profile. This parametrization defines a continuous family of flows, ranging from Cunningham's disk model (fixed radius orbits outside the innermost stable circular orbit and plunging motion within the innermost stable circular orbit) to purely radial motion, thereby extending the standard assumptions. Within this framework, we show that inspiral motion produces a distinctive observational signature: a precessing, unwinding evolution of the polarimetric Stokes Q-U looping pattern, in sharp contrast with the closed Q-U loops associated with stable orbits at a fixed radius. We then explore how the morphology of these signatures depends on BLACK HOLE spin, observer inclination, and MAGNETic-field configuration. The presented model can be applied to current and near-future interferometric observations of linear POLARIZATION, offering a new avenue to probe the physics of matter spiraling inward and the RELATIVISTIC velocities of plunging plasma.

[abstract 8 / 38] Yes (score: 5)
arXiv:2605.18946 [pdf, ps, other]

Title: Magnetic Prandtl number dependence of plasmoid-mediated RECONNECTion

Authors: Vinay Kumar, Axel Brandenburg,

Comments: 19 pages, 10 figures. Comments welcome!

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

Created: 2026-05-18; Updated: 2026-05-20; Datestamp: 2026-05-20

We investigate the dependence of the plasmoid-mediated MAGNETic RECONNECTion rate on the MAGNETic Prandtl number using two-dimensional MAGNETohydrodynamic simulations of two coalescing MAGNETic islands. For Lundquist numbers below the onset of the plasmoid instability, the RECONNECTion rate follows the expected Sweet-Parker scaling and decreases with increasing MAGNETic Prandtl number. However, once the current sheet becomes plasmoid unstable, the dependence on the MAGNETic Prandtl number weakens considerably. In the fully plasmoid-mediated regime, we find RECONNECTion rates that remain nearly independent of the MAGNETic Prandtl number over the explored parameter range. We show that the largest RECONNECTion rates are associated with strongly non-linear phases involving plasmoid interactions and mergers. We further compare our results with simulations of the boundary-driven Taylor problem, where previous studies reported a stronger MAGNETic Prandtl number dependence, and provide a possible explanation for the differing scalings obtained in the two setups. These results may have implications for RECONNECTion-mediated decay in MAGNETically dominated turbulence and related astrophysical systems.

[abstract 9 / 38] Yes (score: 5)
arXiv:2605.18958 [pdf, ps, other]

Title: Directly tracking the re-brightening of a supermassive BLACK HOLE accretion disk

Authors: R. Middei, E. Nardini, C. Done, E. Lusso, F. Vagnetti, G. Risaliti, E. Piconcelli, S. Bianchi, G. Matzeu, A. Trindade Falcão, D. Ł. Król, M. Perri, A. Maselli, K. Horne, J. V. Hernández Santisteban,

Comments: Accepted for publication in ApJ. 13 pages, 5 figures

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

Created: 2026-05-18; Updated: 2026-05-20; Datestamp: 2026-05-20

Accretion onto supermassive BLACK HOLEs powers the most luminous persistent sources in the Universe, the so-called ACTIVE GALACTIC NUCLEi, whose emission is characterized by two distinct spectral components: thermal optical/ultraviolet radiation from an optically thick accretion disk and a power-law X-ray tail from a corona located in the innermost regions of the accretion flow. Yet, how radiatively efficient accretion disks develop and couple to the hot corona remains poorly understood. Using six years of simultaneous ultraviolet and X-ray monitoring of the nearby active galaxy ESO 511-G030, we witness a dramatic evolution of the broadband spectral energy distribution, driven by an increase of the ultraviolet flux from the disk by more than an order of magnitude over a time scale of less than three years. The overall behavior is unlikely to track an uncovering event, and is instead compatible with a progressive recovery of the optically thick component of the accretion flow. At accretion rates higher than approximately one per cent of the Eddington limit, ultraviolet and X-ray data are tightly coupled and follow the well-defined, non-linear correlation between disk and corona found in the more luminous QUASARs. Below this threshold, the relation apparently breaks down, as expected in case of evaporation of the inner accretion disk into a geometrically thick, optically thin hot flow. This is a strong hint of an accretion-state transition analogous to those observed in stellar-mass BLACK HOLEs, and confirms the need for a paradigm change in the models of radiatively efficient accretion flows around supermassive BLACK HOLEs.

[abstract 10 / 38] Yes (score: 5)
arXiv:2605.19057 [pdf, ps, other]

Title: Magnetohydrodynamics Simulations

Authors: E. A. Huerta,

Comments: 32 pages, 1 figure. Invited chapter for the book "Machine Learning Techniques for Astrophysics and Cosmology" (Eds. C. Bambi, V. Kashyap, S. Shashank and N. Yoshida, Springer Singapore, expected in 2027)

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

Created: 2026-05-18; Updated: 2026-05-20; Datestamp: 2026-05-20

Magnetohydrodynamics (MHD) couples the Navier--Stokes and Maxwell equations into a nonlinear system of partial differential equations governing stellar interiors, astrophysical JETs, fusion plasmas, and space weather. Numerical advances, including finite-volume Godunov schemes, constrained-transport algorithms, high-order spectral-element and discontinuous-Galerkin discretisations, and adaptive mesh refinement, have made MHD a predictive tool for solar eruptions, tokamak confinement, and MAGNETised turbulence. A fundamental barrier nevertheless remains. In three-dimensional MHD turbulence, the degrees of freedom required to resolve all active scales grow as $\mathcal{O}(\mathrm{Re}^{9/4})$ or faster, where $\mathrm{Re}$ is the Reynolds number. Direct numerical simulation is therefore intractable at astrophysical and fusion-relevant parameters, particularly when the Lundquist number $S$ exceeds $10^{10}$ and both viscous and resistive dissipation ranges must be resolved. Kinetic closures, radiation transport, and uncertainty quantification further increase the cost. This chapter examines how AI may help bridge this gap. We review physics-informed neural networks, Fourier neural operators and physics-informed neural operators, which learn solution operators across families of MHD problems; and hybrid operator-diffusion frameworks that combine deterministic surrogates with score-based generative models to recover broadband turbulent spectra. These developments are set within the wider landscape of exascale high-order solvers, GPU acceleration, task-based parallelism, data-driven sub-grid closures, and prospective quantum algorithms for implicit linear systems in resistive MHD. The central claim is that physics-informed AI, integrated with conventional solvers and trained on leadership-scale simulations, offers a credible route to regimes beyond the reach of classical discretisation alone.

[abstract 11 / 38] Yes (score: 5)
arXiv:2605.19473 [pdf, ps, other]

Title: Radio-X-ray Time Lags in GX 339-4: Probing Magnetic Field Transport in Black Hole Accretion

Authors: Dizhan Du, Bei You, Zhen Yan, Yuao Ma, Xinwu Cao,

Comments: 13 pages, 7 figures, submitted to APJ

Subjects: astro-ph.HE

Created: 2026-05-19; Updated: 2026-05-20; Datestamp: 2026-05-20

We present an analysis of the time delay between the radio emission and the X-ray Compton luminosity during the 2010-2011 outburst of GX 339-4. Using the interpolated cross-correlation function (ICCF), we measure the time delay between the Compton luminosity and the radio luminosity, and find that during the rising hard state, the radio emission precedes the Compton luminosity by approximately 3 days. In contrast, in the decaying hard state, the radio emission lags behind the Compton luminosity by about 8 days. By estimating the mass accretion rate and the disk truncation radius, the calculated inner MAGNETic field can account for both the radio delay in the decaying hard state and the radio precedence in the rising hard state. The time delays observed in different outbursts across multiple sources are compared further, and the underlying physical mechanisms account for this difference are discussed. These results provide insights into the evolving coupling between the inner accretion flow and the JET in BLACK HOLE X-ray binaries.

[abstract 12 / 38] Yes (score: 5)
arXiv:2605.19507 [pdf, ps, other]

Title: The Astro2Geo Project I. Radio astrometric offsets correlated with Gamma-ray brightness

Authors: Jeffrey A. Hodgson, Hana Krasna, Aletha de Witt, Pfesesani van Zyl, Janeth Valverde,

Comments: Accepted for publication in PASA

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

Created: 2026-05-19; Updated: 2026-05-20; Datestamp: 2026-05-20

Precision geodesy relies on the stability of the International Celestial Reference Frame (ICRF), yet its reference sources, Active Galactic Nuclei (AGN), exhibit changes in source structure that can manifest as apparent shifts in their astrometric positions. The high-precision radio measurements used to maintain the ICRF therefore provide a means to investigate the astrophysical mechanisms driving these changes. In particular, the observed astrometric variability offers a unique opportunity to link positional shifts in AGN to high-energy astrophysical processes. We investigated the relationship between the astrometric positions of ICRF AGN and their Gamma-ray emission. We measured the positional offsets of radio cores relative to the ICRF3 at both S/X and K bands and compared them to FERMI-LAT Gamma-ray fluxes within +/-30 days. Out of 92 radio sources, we identified 57 that had enough overlapping data. We find a high incidence of statistically significant (p<0.05) power-law correlations, with ~90% of sources exhibiting this behaviour. The nature of this correlation is complex: we observe both positive and negative correlations, and the sign of the correlation can differ between the two frequency bands for the same source. To explain the correlations, we tested variable Gamma-ray emission locations, changes in nuclear opacity, and variations in JET position angle. Our analysis reveals no single explanation and suggests a complex interplay of multiple physical mechanisms. A search for time lags between the radio position offsets and Gamma-ray fluxes revealed tentative - and highly caveated - evidence for a time-delay in only five sources. A statistical comparison with the OCARS catalogue shows that, although our sample is biased towards optically brighter sources with better-constrained astrometric solutions, it remains representative of the broader AGN population in terms of redshift.

[abstract 13 / 38] (score: 3)
arXiv:2509.14328 [pdf, ps, other]

Title: Cosmic-ray impact on optical and mid-infrared emission line diagnostics in NGC 5728

Authors: E. Koutsoumpou, J. A. Fernández-Ontiveros, K. M. Dasyra, L. Spinoglio,

Comments: 17 pages, 10 figures, 3 tables, accepted for publication in Astronomy & Astrophysics

Subjects: astro-ph.GA

Created: 2026-05-18; Updated: 2026-05-20; Datestamp: 2026-05-20

Cosmic rays (CRs), from ACTIVE GALACTIC NUCLEi (AGN) JETs and SUPERNOVAe (SNe), serve as a significant feedback mechanism influencing emission lines in narrow line region (NLR) clouds. These highly energetic particles, propelled by shocks, heat the interstellar medium (ISM) and modify its chemical composition. This study investigates the role of CRs, particularly in their ability to excite gas and align with observed line ratios across UV and optical diagnostics. We employ CLOUDY to explore CR ionization rate, ionization parameter, and initial hydrogen density effects on optical and mid-infrared (MIR) emission. Our analysis includes high-quality optical data from the Multi Unit Spectroscopic Explorer (MUSE) on the Very Large Telescope (VLT) for NGC 5728, supplemented by infrared observations from the James Webb Space Telescope (JWST). Our previous results indicate that CRs are instrumental in heating the inner regions of gas clouds, enhancing emission of low-ionization optical lines. Mid-infrared data reveal that emission lines like [Ar II] and [Ne II] within the JWST Mid-Infrared Instrument (MIRI) field of view are sensitive to CRs. In contrast, high-ionization lines (for example, [Ne V]) serve as robust tracers of photoionization insensitive to CRs. Moreover, mixed optical and MIR diagnostics offer insight into the relative roles of CRs and shocks, which often produce similar signatures in emission lines. We find that while both mechanisms can elevate certain line ratios, their influence on MIR diagnostics diverges: shocks and CRs affect low-ionization lines differently, allowing for a better understanding when multi-wavelength data are available. Our approach not only helps to resolve the degeneracy between metallicity and CR ionization but also enables the potential differentiation of shocks and CR-driven processes in AGN.

[abstract 14 / 38] (score: 3)
arXiv:2512.04203 [pdf, ps, other]

Title: The impact of strong feedback on galaxy group scaling relations

Authors: D. Eckert, R. Seppi, J. Braspenning, A. Finoguenov, F. Gastaldello, L. Lovisari, E. O'Sullivan, S. Ettori, B. D. Oppenheimer, M. A. Bourne, D. -W. Kim, M. Sun, H. Khalil, G. Gozaliasl, Y. E. Bahar, V. Ghirardini, W. Cui, K. Kolokythas, S. McGee,

Comments: Matching the version published in A&A letters

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

Created: 2026-05-19; Updated: 2026-05-20; Datestamp: 2026-05-20

Feedback from active supermassive BLACK HOLEs alters the distribution of matter in the Universe by injecting energy in the neighbouring hot gaseous medium, which leads to ejection of gas from the halos of galaxy groups and massive galaxies. Recent cosmological simulations such as FLAMINGO calibrate their feedback model on the baryon fractions of galaxy groups to tune the efficiency of gas ejection. However, recent observational constraints from optically selected groups and the kinetic Sunyaev-Zel'dovich effect yield lower baryon fractions than previous studies, which indicates that feedback may be more ejective than previously thought. Here we show that models involving highly ejective feedback are inconsistent with the scaling relations of local galaxy groups in the mass range $10^{13}-10^{14}M_\odot$. We study the X-ray luminosity-temperature relation in a sample of 44 galaxy groups with high-quality XMM-Newton observations. We show that highly ejective models under-predict the luminosity of galaxy groups at fixed mass at high significance ($5.7σ$). This conclusion is robust against selection effects and is obtained from directly measurable and minimally correlated quantities. We point out that turning observable quantities into gas fraction estimates is challenging, especially in the context of stacking large samples of heterogeneous systems. We argue that calibrating feedback models on baryon fractions is prone to systematic uncertainties and that observable scaling relations are better suited for this task.

[abstract 15 / 38] (score: 3)
arXiv:2605.19211 [pdf, ps, other]

Title: Temporal evolution of the circumstellar disk orientation in the transient X-ray pulsar GRO J1008-57

Authors: Yongfeng Hu, Hua Xiao, Sergey S. Tsygankov, Long Ji, Juri Poutanen, Runting Huang,

Comments: 8 pages, 6 figures, 1 table; accepted for publication in Astronomy & Astrophysics (A&A)

Subjects: astro-ph.HE

Created: 2026-05-19; Updated: 2026-05-20; Datestamp: 2026-05-20

The transient X-ray pulsar GRO J1008-57 was previously found to exhibit Type I outbursts occurring at stable orbital phases before its first observed Type II outburst in 2012. In this work, we extend the study to investigate the phase evolution after several Type II outbursts using long-term SWIFT/BAT and MAXI/GSC observations. Our results reveal that the orbital phases of Type I outbursts follow a step-like evolution: they remain largely stable over many orbital periods but undergo abrupt, small-amplitude jumps coincident with each Type II outburst. Such a step-like behavior is difficult to explain with the commonly proposed mechanisms involving a highly eccentric or precessing disk around the Be star. The energetics of Type I X-ray outbursts show a systematic increase before Type II outbursts, followed by a rapid decline and a subsequent gradual recovery. This behavior suggests cycles of disk depletion and reconstruction driven by Type II outbursts. Considering the small amplitude of each phase jump, we propose that this step-like phase evolution may be related to the long orbital period of GRO J1008-57, implying infrequent neutron star-disk interactions. After disk depletion by Type II outbursts, the disk around the Be star has enough time to rebuild its density and restore a geometric structure similar to its pre-Type II outburst state. Consequently, the orbital phases of subsequent Type I outbursts not only change very slightly but can also remain stable over many orbital periods until the next Type II-driven disk reconfiguration, yielding the observed step-like evolution.

[abstract 16 / 38] (score: 3)
arXiv:2605.19226 [pdf, ps, other]

Title: Faraday Complexity and DePOLARIZATION in LOFAR Two-metre Sky Survey (LoTSS-DR2) Polarized Radio Sources

Authors: Rudra Sinha, Abhik Ghosh,

Comments: 12 pages, 5 figures, 2 tables, submitted

Subjects: astro-ph.CO

Created: 2026-05-19; Updated: 2026-05-20; Datestamp: 2026-05-20

We present a broadband spectro-polarimetric analysis of 1,565 polarized radio sources from the LOFAR Two-Metre Sky Survey Data Release 2 (LoTSS-DR2) RM Grid catalogue. This study uses frequency-dependent Stokes Q and U spectra across the 120-168 MHz LOFAR HBA band to investigate their POLARIZATION properties. The POLARIZATION behaviour of each source is modelled with multi-component Faraday dePOLARIZATION models to investigate the MAGNETo-ionic environments responsible for low-frequency dePOLARIZATION. Significant Faraday complexity is observed throughout the sample, with 43.2% of sources requiring two or three Faraday components. External Faraday dispersion dominates the dePOLARIZATION behaviour, with 54.1% of sources classified as external-screen dominated and approximately 60% showing statistically significant evidence for turbulent external Faraday-active media, while only 10.3% are consistent with pure internal differential Faraday rotation. The intrinsic POLARIZATION angle and RM separations between fitted components are generally small, suggesting that many RM components trace physically related emission regions embedded within common MAGNETo-ionic environments. A weak but statistically significant anti-correlation is detected between the POLARIZATION spectral index, $β$, and weighted Faraday dispersion, $σ_{\rm RM,wtd}$, for two-component systems, whereas one- and three-component populations show no significant trend. The rest-frame Faraday dispersion, $σ_{\rm RM,rest}$, exhibits significant positive correlations with redshift for the external-screen dominated and mixed dePOLARIZATION populations, even after controlling for radio luminosity, indicating increasingly turbulent or strongly MAGNETized environments surrounding radio AGN at earlier cosmic epochs.

[abstract 17 / 38] (score: 3)
arXiv:2605.19608 [pdf, ps, other]

Title: Reassessment of Ionospheric Responses to GRB~221009A: Disentangling Instrumental, Illumination and Geophysical Effects

Authors: Maosheng He, Quanhan Li, Shun-Rong Zhang, Jeffrey M. Forbes, Jiuhou Lei, Libo Liu, Jiankui Shi, Chi Wang,

Comments:

Subjects: physics.space-ph

Created: 2026-05-19; Updated: 2026-05-20; Datestamp: 2026-05-20

Gamma-ray bursts (GRBs) have long been proposed to perturb Earth's ionosphere, with occasional reports of disruptions in ultra- and extremely-low-frequency radio signals. The exceptionally bright GRB~221009A was recently claimed to induce multi-altitude ionospheric responses, including perturbations in satellite electric fields, regional total electron content (TEC), and the equatorial electroJET (EEJ). These claims have renewed interest in the potential near-Earth impacts of astrophysical transients. Here we perform an independent reassessment using expanded datasets spanning multiple altitudes. We find no coherent, burst-like TEC enhancement, show that the reported electric-field anomalies recur under specific illumination conditions each orbit, and demonstrate that the EEJ fluctuations preceded the burst and coincide with solar-wind variability. Together, these results indicate that the reported GRB-induced ionospheric responses are fully attributable to other natural geophysical processes and instrumental artefacts, thereby resolving a high-profile controversy and clarifying the true limits of GRBs'ionospheric effects.

[abstract 18 / 38] (score: 2)
arXiv:2411.17811 [pdf, ps, other]

Title: Cosmic Ray Ionization of Low-Excitation Lines in Active Galactic Nuclei and Starburst Galaxies

Authors: E. Koutsoumpou, J. A. Fernández-Ontiveros, K. M. Dasyra, L. Spinoglio,

Comments: 24 pages, 16 figures, 4 tables, accepted for publication in Astronomy & Astrophysics

Subjects: astro-ph.GA

Created: 2026-05-18; Updated: 2026-05-20; Datestamp: 2026-05-20

Cosmic rays (CRs) can significantly impact dense molecular clouds in galaxies, heating the interstellar medium (ISM) and altering its chemistry, ionization, and thermal properties. Their influence is particularly relevant in environments with high CR rates, such as starburst galaxies with SUPERNOVA remnants or JETs and outflows in ACTIVE GALACTIC NUCLEi (AGN). CRs transfer energy to the ionized phase of the ISM far from the ionization source, preventing gas cooling and driving large-scale winds. In this work, we use CLOUDY to explore the effect of CRs on nebular gas, a relatively underexplored area, mainly focused on cold molecular gas. Our models cover a broad range of density ($1 - 10^4\,\rm{cm^{-3}}$), ionization parameter ($-3.5 \leq \log U \leq -1.5$), and CR ionization rate ($10^{-16}\, \rm{s^{-1}} - 10^{-12}\, \rm{s^{-1}}$). These are compared to MUSE observations of two AGN, Centaurus A and NGC 1068, and the starburst NGC 253. We find that CR rates $\gtrsim 10^{-13}\, \rm{s^{-1}}$, typical of AGN and strong starburst galaxies, can significantly alter the thermal structure of the ionized gas by forming a deep secondary low-ionization layer beyond the photoionization-dominated region. This enhances emission from low-ionization transitions, such as [\ion{N}{ii}], [\ion{S}{ii}], and [\ion{O}{i}], affecting line-ratio diagnostics, metallicity, and ionization estimates. Unlike pure photoionization models, AGN simulations with high CR ionization rates reproduce the Seyfert loci in BPT diagrams without requiring super-solar metallicities for the narrow-line region. Additionally, STAR FORMATION simulations with high CR ionization rates can explain line ratios in the LINER domain. We propose new maximum starburst boundaries for BPT diagrams to distinguish regions dominated by AGN photoionization from those that could be explained by STAR FORMATION plus high CR ionization rates.

[abstract 19 / 38] (score: 2)
arXiv:2502.10445 [pdf, ps, other]

Title: ElectroMAGNETism from RELATIVISTIC fluid dynamics

Authors: Jeongwon Ho, Hyeong-Chan Kim, Jungjai Lee, Yongjun Yun,

Comments: Last published version, 15 pages, 1 figure

Subjects: physics.gen-ph

Created: 2026-05-18; Updated: 2026-05-20; Datestamp: 2026-05-20

We reformulate classical electroMAGNETism within the matter-space framework of RELATIVISTIC fluid dynamics. The central assumption is that the relevant degrees of freedom are encoded in differential forms on a three-dimensional matter space and mapped to spacetime by pull-back. The absence of four-forms in matter space imposes nontrivial kinematical constraints on the induced spacetime fields and restricts gauge transformations to those compatible with the flow. Because of this (matter-space) gauge symmetry, the physically relevant sector is retained, and the Aharonov-Bohm phase is naturally associated with the matter-space potential. The construction admits two electroMAGNETic frames. We argue that the frame identifying the spacetime field strength directly with the intrinsic matter-space two-form is geometrically preferred. In the first frame, the homogeneous sector is fixed by the matter-space structure, while the sourced equation follows from an action-based RELATIVISTIC-fluid formulation in a first-order setting where the potential and field strength are varied independently and the matter-space constraints are imposed on shell. In the massless case and to quadratic order, locality and the (matter-space) gauge symmetry fix the leading field term in the action uniquely, so the resulting equations provide the minimal dynamical completion once charge carriers are included. We also clarify how duality controls the status of the Bianchi identity in the absence of MAGNETic charge carriers, and we briefly discuss helicity conservation and a natural nonlinear extension implied by the one-fluid constraints. In the second frame, on the other hand, the matter space 1-form is not directly related with the gauge potential.

[abstract 20 / 38] (score: 2)
arXiv:2508.15269 [pdf, ps, other]

Title: Simulation Studies of Resonant Excitation of Electron Bernstein Waves in Capacitive Discharges

Authors: Deepak Gautam, Sarveshwar Sharma, Igor Kaganovich, Bhooshan Paradkar,

Comments:

Subjects: physics.plasm-ph

Created: 2026-05-19; Updated: 2026-05-20; Datestamp: 2026-05-20

The behavior of capacitive coupled plasma (CCP) discharges is investigated in a mildly MAGNETized regime, defined by the condition 1 $\leq$ $f_{ce}/f_{rf}$ $\lt$ 2, where $f_{ce}$ and $f_{rf}$ are the cyclotron and radio-frequencies (RF), respectively. This regime exhibits complex and distinctive plasma dynamics due to the interplay between RF fields and the externally applied MAGNETic field. Two prominent phenomena are observed in this regime. First, the plasma density profile becomes asymmetric across the discharge, deviating from the typical symmetric distribution seen in unMAGNETized CCPs. Second, electron Bernstein waves (EBWs), high-frequency electrostatic waves, are excited and propagate within the bulk plasma, particularly along steep electron density gradients. As the strength of the MAGNETic field increases within this regime, the CCP discharge undergoes a transition from a symmetric configuration to an asymmetric one, and then returns to a symmetric profile at higher field strengths. Notably, the excitation and propagation of EBWs are strongly correlated with the presence of discharge asymmetry and localized density gradients. These waves play a significant role in energy transport and electron heating under mildly MAGNETized conditions. To gain deeper insight into the underlying physics, detailed numerical simulations are carried out using the particle-in-cell Monte Carlo collision (PIC-MCC) technique. These simulations capture the kinetic behavior of electrons and ions, including the collisionless effects and sheath dynamics essential to understanding the excitation of EBWs and the evolution of discharge symmetry. The study thus sheds light on the role of weak MAGNETic fields in shaping plasma behavior and highlights the importance of wave-particle interactions in MAGNETized CCPs.

[abstract 21 / 38] (score: 2)
arXiv:2508.16208 [pdf, ps, other]

Title: Resonantly Driven Electron Bernstein Waves in Magnetized Low-Pressure Capacitive Discharges

Authors: Deepak Gautam, Sarveshwar Sharma, Igor Kaganovich, Bhooshan Paradkar,

Comments:

Subjects: physics.plasm-ph

Created: 2026-05-19; Updated: 2026-05-20; Datestamp: 2026-05-20

The physics of capacitively coupled plasma (CCP) discharges is investigated in a mildly MAGNETized regime, defined by $1 \le f_{ce}/f_{rf} < 2$, where $f_{ce}$ and $f_{rf}$ denote the electron cyclotron frequency and the applied radio-frequency (RF), respectively. A distinctive feature of this regime is the excitation of electron Bernstein waves (EBWs) that propagate into the bulk plasma. As the applied MAGNETic field increases, notable changes in the discharge characteristics occur, with EBWs observed to propagate along the plasma density gradient inside the bulk. The underlying physics of CCP operation in this regime is analyzed in detail using particle-in-cell Monte Carlo collisions (PIC-MCC) simulations.

[abstract 22 / 38] (score: 2)
arXiv:2509.14895 [pdf, ps, other]

Title: Constraining GAMMA-RAY BURST parameters with the first ultra-high energy neutrino event KM3-230213A

Authors: KM3NeT Collaboration, O. Adriani, A. Albert, A. R. Alhebsi, S. Alshalloudi, M. Alshamsi, S. Alves Garre, A. Ambrosone, F. Ameli, M. Andre, L. Aphecetche, M. Ardid, S. Ardid, J. Aublin, F. Badaracco, L. Bailly-Salins, B. Baret, A. Bariego-Quintana, Y. Becherini, M. Bendahman, F. Benfenati Gualandi, M. Benhassi, D. M. Benoit, Beňušová, E. Berbee, E. Berti, V. Bertin, P. Betti, S. Biagi, M. Boettcher, D. Bonanno, S. Bottai, A. B. Bouasla, J. Boumaaza, M. Bouta, M. Bouwhuis, C. Bozza, R. M. Bozza, H. Brânzaš, F. Bretaudeau, M. Breuhaus, R. Bruijn, J. Brunner, R. Bruno, E. Buis, R. Buompane, J. Busto, B. Caiffi, D. Calvo, A. Capone, F. Carenini, V. Carretero, T. Cartraud, P. Castaldi, V. Cecchini, S. Celli, L. Cerisy, M. Chabab, A. Chen, S. Cherubini, T. Chiarusi, M. Circella, R. Clark, R. Cocimano, J. A. B. Coelho, A. Coleiro, A. Condorelli, R. Coniglione, P. Coyle, A. Creusot, G. Cuttone, R. Dallier, A. De Benedittis, G. De Wasseige, V. Decoene, P. Deguire, I. Del Rosso, L. S. Di Mauro, I. Di Palma, A. F. Díaz, D. Diego-Tortosa, C. Distefano, A. Domi, C. Donzaud, D. Dornic, E. Drakopoulou, D. Drouhin, J. -G. Ducoin, P. Duverne, R. Dvornický, T. Eberl, E. Eckerová, A. Eddymaoui, T. van Eeden, M. Eff, D. van Eijk, I. El Bojaddaini, S. El Hedri, S. El Mentawi, A. Enzenhöfer, G. Ferrara, M. D. Filipović, F. Filippini, D. Franciotti, L. A. Fusco, S. Gagliardini, T. Gal, J. García Méndez, A. Garcia Soto, C. Gatius Oliver, N. Geißelbrecht, E. Genton, H. Ghaddari, L. Gialanella, B. K. Gibson, E. Giorgio, I. Goos, P. Goswami, S. R. Gozzini, R. Gracia, B. Guillon, C. Haack, H. van Haren, A. Heijboer, L. Hennig, J. J. Hernández-Rey, A. Idrissi, W. Idrissi Ibnsalih, G. Illuminati, R. Jaimes, O. Janik, D. Joly, M. de Jong, P. de Jong, B. J. Jung, P. Kalaczyński, J. Keegans, V. Kikvadze, G. Kistauri, C. Kopper, A. Kouchner, Y. Y. Kovalev, L. Krupa, V. Kueviakoe, V. Kulikovskiy, R. Kvatadze, M. Labalme, R. Lahmann, M. Lamoureux, G. Larosa, C. Lastoria, J. Lazar, A. Lazo, G. Lehaut, V. Lemaître, E. Leonora, N. Lessing, G. Levi, M. Lindsey Clark, F. Longhitano, S. Madarapu, F. Magnani, L. Malerba, F. Mamedov, A. Manfreda, A. Manousakis, M. Marconi, A. Margiotta, A. Marinelli, C. Markou, L. Martin, M. Mastrodicasa, S. Mastroianni, J. Mauro, K. C. K. Mehta, G. Miele, P. Migliozzi, E. Migneco, M. L. Mitsou, C. M. Mollo, L. Morales-Gallegos, N. Mori, A. Moussa, I. Mozun Mateo, R. Muller, M. R. Musone, M. Musumeci, S. Navas, A. Nayerhoda, C. A. Nicolau, B. Nkosi, B. Ó Fearraigh, V. Oliviero, A. Orlando, E. Oukacha, L. Pacini, D. Paesani, J. Palacios González, G. Papalashvili, P. Papini, V. Parisi, A. Parmar, C. Pastore, A. M. Păun, G. E. Păvălaš, S. Peña Martínez, M. Perrin-Terrin, V. Pestel, M. Petropavlova, P. Piattelli, A. Plavin, C. Poirè, V. Popa, T. Pradier, J. Prado, S. Pulvirenti, C. A. Quiroz-Rangel, N. Randazzo, A. Ratnani, S. Razzaque, I. C. Rea, D. Real, G. Riccobene, J. Robinson, A. Romanov, E. Ros, A. Šaina, F. Salesa Greus, D. F. E. Samtleben, A. Sánchez Losa, S. Sanfilippo, M. Sanguineti, D. Santonocito, P. Sapienza, M. Scaringella, M. Scarnera, J. Schnabel, J. Schumann, J. Seneca, P. A. Sevle Myhr, I. Sgura, R. Shanidze, Chengyu Shao, A. Sharma, Y. Shitov, F. Šimkovic, A. Simonelli, A. Sinopoulou, B. Spisso, M. Spurio, O. Starodubtsev, D. Stavropoulos, I. Štekl, D. Stocco, M. Taiuti, G. Takadze, Y. Tayalati, H. Thiersen, S. Thoudam, I. Tosta e Melo, B. Trocmé, V. Tsourapis, E. Tzamariudaki, A. Ukleja, A. Vacheret, V. Valsecchi, V. Van Elewyck, G. Vannoye, E. Vannuccini, G. Vasileiadis, F. Vazquez de Sola, A. Veutro, S. Viola, D. Vivolo, A. van Vliet, E. de Wolf, I. Lhenry-Yvon, S. Zavatarelli, D. Zito, J. D. Zornoza, J. Zúñiga,

Comments: Accepted for publication in Astronomy & Astrophysics

Subjects: astro-ph.HE

Created: 2026-05-19; Updated: 2026-05-20; Datestamp: 2026-05-20

Context: The detection of the highest energy neutrino observed to date by KM3NeT, with an estimated energy of 220 PeV, opens up new possibilities for the study and identification of the astrophysical sources responsible for a diffuse flux of such ultra-high-energy neutrinos, among which GAMMA-RAY BURSTs are longstanding candidates. Aims: Based on the event KM3-230213A, we derive constraints on the baryon loading and density of the surrounding environment in models of blastwaves in long-duration GAMMA-RAY BURSTs. Methods: We compute the diffuse flux from GAMMA-RAY BURST blastwaves, either expanding in a constant density interstellar medium or developing in a radially decreasing density of a wind-like environment surrounding the GAMMA-RAY BURST progenitor star, by taking into account the expected neutrino spectra and luminosity function. We use a Poisson likelihood method to constrain the blastwave model parameters by calculating the expected number of neutrino events within the 90% confidence level energy range of KM3-230213A and by using the joint exposure of KM3NeT/ARCA, IceCube and Pierre Auger. Results: We constrain the baryon loading to be $\leq \{392, 131, 39, 13\}$ at 90% confidence level, which is inversely proportional to a varying interstellar medium particle density of $\{1, 3, 10, 30\}$ cm$^{-3}$. In the wind-like environment case, the baryon loading is $\leq \{20, 50, 100\}$ at 90% confidence level, which is proportional to the sixth power of a varying density parameter of $\{0.05, 0.06, 0.07\}$.

[abstract 23 / 38] (score: 2)
arXiv:2509.23490 [pdf, ps, other]

Title: The mechanism for creating "dynamical gravastar" BLACK HOLE mimickers also explains formation of "little red dots"

Authors: Stephen L. Adler,

Comments: Latex, 9 pages, 2 figures

Subjects: gr-qc

Created: 2026-05-19; Updated: 2026-05-20; Datestamp: 2026-05-20

We argue that a high pressure phase transition of RELATIVISTIC matter to a state with negative energy density, which leads to the formation of horizonless, globally unitary BLACK HOLE mimickers, also gives rise to the appearance of ``little red dots''. The energy source for the dots is the release of latent energy from the phase transition, and their excess redness is a result of this release taking place in a central region of exponentially small positive $g_{00}$, and hence very high gravitational redshift.

[abstract 24 / 38] (score: 2)
arXiv:2511.10474 [pdf, ps, other]

Title: Disk warping and BLACK HOLE X-ray binaries I. Tentative unification of low-frequency quasi-periodic oscillations

Authors: Gregoire Marcel, Samuel Turner, Benjamin Ricketts, Vanessa Lopez-Barquero, Douglas Buisson, Federico Vincentelli, Matthew Middleton, Christopher Reynolds, Mark Avara,

Comments: 18 pages, 13 figures. Accepted in A&A

Subjects: astro-ph.HE

Created: 2026-05-19; Updated: 2026-05-20; Datestamp: 2026-05-20

X-ray binaries exhibit complex variability patterns studied in the power-spectrum. These include the broad-band noise (BBN) components and various types of narrow components called quasi-periodic oscillations (QPOs). There is currently no consensus about either what determines the presence/absence of the BBN or what generates the QPOs. Many believe the latter is due to frame-dragging effects caused by Lense-Thirring torques. We wish to investigate the potential impact of those frame-dragging effects on the accretion disk itself. In particular, we focus on its impact on the observed variability and the presence (and types) of QPOs associated. We make analytical estimates to assess the potential presence of a geometric warp in the inner accretion disk during state transitions. We show that the presence of a warp can modify the spectral-timing properties in a way that matches the observed transition between QPO types during outbursts. We also discuss the peculiar case of Cyg X-1, as well as how the hard-to-soft transition could be driven by the warp itself. The (expected) emergence of a warp provides a consistent explanation for the evolution of both the BBN and the QPO properties during state transitions. This offers a first path toward unifying the variability of BLACK HOLE X-ray binary.

[abstract 25 / 38] (score: 2)
arXiv:2512.03236 [pdf, ps, other]

Title: Real-Time Adaptive Feedback Control of a Supersonic Dual-Stream Jet

Authors: Melissa Yeung, Yiyang Sun,

Comments:

Subjects: physics.flu-dyn

Created: 2026-05-18; Updated: 2026-05-20; Datestamp: 2026-05-20

Adaptive control is applied to a supersonic dual-stream JET flow comprised of Mach 1.6 core and Mach 1.0 bypass streams that mix to form a supersonic shear layer. The vortices shed are the source of a high-frequency tone that persists throughout the flow. The intricate flow dynamics motivates the need for an elaborate and efficient actuation system to suppress the tone and weaken the propagating shock train. The present work utilizes online dynamic mode decomposition, which estimates the system dynamics as a locally linear evolution. Snapshot matrices are constructed using sensor measurements, facilitating economical and real-time computations, which are continuously updated and used in a feedback control model. Adaptive control is found to efficiently target the resonant tone with little disturbance to the mean features. The framework is not sensitive to sensor placements, enabling actuator design under physically realizable spatial locations in practical implementation. To reflect physical limitations, constraints are imposed on the controller model. It is found that the restricted controller yields greater vortex suppression due to repeated transitory stabilization of the shear layer instability. Statistical analysis reveals intermittent low-pressure events are responsible for the characteristic frequency, which are largely suppressed by adaptive feedback control.

[abstract 26 / 38] (score: 2)
arXiv:2605.00125 [pdf, ps, other]

Title: High temporal resolution THz streaking of high brightness RELATIVISTIC electron beams

Authors: Maximilian Lenz, Brian Schaap, Atharva Kulkarni, Yuemei Tan, Yining Yang, Renkai Li, Pietro Musumeci,

Comments: 10 pages, 12 figures. Submitted to Phys. Rev. Accel. Beams

Subjects: physics.acc-ph

Created: 2026-05-18; Updated: 2026-05-20; Datestamp: 2026-05-20

We report a systematic experimental study of terahertz (THz) streaking structures for ultrafast characterization of RELATIVISTIC, high-brightness electron beams. Horn-coupled waveguide geometries are investigated, enabling a comparative characterization of streaking strength, dispersion, transmission, and temporal fidelity. Analytical models and electroMAGNETic simulations are used to describe the dependence of streaking power on the waveguide dimensions and the drive frequency. Experimentally, the structures are characterized using compressed electron beam from an RF photoinjector over a range of THz field strengths, beam energies, and bunch durations. These results establish general design principles and performance limits for THz streaking structures applicable to ultrafast electron beam diagnostics.

[abstract 27 / 38] (score: 2)
arXiv:2605.12973 [pdf, ps, other]

Title: A Spatially Resolved HI Survey of Seyfert Galaxies: the Role of AGN Feedback in Shaping Atomic Gas Reservoirs

Authors: Ruitian Li, Xin Wang, Daizhong Liu, Hui Shi, Yuxuan Pang, Pengfei Ren, Shengzhe Wang, Ming Zhu, Mengting Ju, Xiao-Lei Meng, Xinwen Shu, Ningyu Tang, Jing Wang, Chuan-Peng Zhang, Hong-Xin Zhang, Le Zhang, Zheng Zheng, Fujia Li, Chen Xu, Sijia Li, Yiming Yang, Hang Zhou,

Comments: 16 pages, 8 figures, 4 tables, Accepted for publication in ApJS

Subjects: astro-ph.GA

Created: 2026-05-15; Updated: 2026-05-20; Datestamp: 2026-05-20

Active galactic nucleus (AGN) feedback is a key ingredient in galaxy evolution, yet its impact on the cold atomic gas reservoir -- the neutral hydrogen (HI) phase -- remains poorly constrained. We present the most extensive spatially resolved HI 21-cm survey of Seyfert AGN hosts to date, based on observations with the Giant Metrewave Radio Telescope (GMRT). Our high-resolution HI maps of eight Seyfert galaxies reveal detailed kinematics and surface density distributions of their atomic gas disks. We find that AGN-host galaxies exhibit a slightly shallower HI mass-size relation than the canonical relation or the SIMBA simulation predictions; however, the measured slope remains consistent with the canonical value within $2σ$ uncertainties. This result suggests that AGN feedback does not significantly disrupt the global extent or large-scale structure of atomic gas reservoirs. To investigate the internal HI kinematics in greater detail, we perform a 3D kinematic forward modeling of the HI disk in UGC 4503. Our analysis reveals an elevated intrinsic velocity dispersion of $σ= 14.9^{+6.1}_{-3.8}$ km/s and a reduced level of rotational support, with $V/σ= 14.28_{-4.17}^{+4.97}$, compared to large-sample star-forming spirals. These kinematic signatures, together with localized residuals in the velocity field, indicate that AGN-driven outflows or JETs may inject or indirectly affect the turbulence in the atomic gas disk, potentially regulating the cold gas reservoir. Future GMRT observations, combined with optical integral-field spectroscopy from MaNGA, will enable quantitative constraints on the role of AGN feedback in regulating STAR FORMATION efficiency across a larger and more representative galaxy sample.

[abstract 28 / 38] (score: 2)
arXiv:2605.17983 [pdf, ps, other]

Title: Higher-order statistics of the stochastic gravitational wave background from supermassive BLACK HOLE binaries

Authors: Hinano Hisamatsu, Koutarou Kyutoku,

Comments: 15 pages, 10 figures

Subjects: astro-ph.HE astro-ph.GA gr-qc

Created: 2026-05-19; Updated: 2026-05-20; Datestamp: 2026-05-20

Recent progress in gravitational wave observations has positioned Pulsar Timing Arrays as a key tool for detecting the stochastic gravitational wave background in the nanohertz band. It is widely believed that this background is primarily attributed to the cosmic ensemble of inspiraling supermassive BLACK HOLE binaries. While traditional analyses have predominantly focused on the spectral amplitude and frequency dependence of the gravitational wave background, higher-order statistics such as variance, skewness, and kurtosis could potentially be useful for extracting further physical information. However, these statistical moments are known to diverge when the redshift integration is extended down to z=0. In this study, we propose a strategy to resolve this issue by introducing a physically motivated lower integration limit, z_min, defined by the sensitivity for detecting individual sources. Since higher-order statistics are primarily determined by local sources, we may adopt the lowest-order approximation with respect to redshift in their computations. Under this approximation, we demonstrate that all higher-order statistics beyond the expectation value depend on the mass function only through a weighted average of the chirp mass, <\mathcal{M}^{10/3}>, irrespective of the redshift evolution model. We show that the ratio of the variance to the expectation value provides information on <\mathcal{M}^{10/3}>/<\mathcal{M}^{5/3}> independently of the total number of mergers. We also find a consistency relation between the kurtosis and the squared skewness, paving the way for testing the binary-origin hypothesis of the gravitational wave background. Our findings demonstrate that higher-order statistics provide a new window for interpreting the gravitational wave background, offering a methodology to break existing degeneracies and refine our understanding of the mass function.

[abstract 29 / 38] (score: 2)
arXiv:2605.18973 [pdf, ps, other]

Title: GRB 260310A/SN 2026fgk: Photometric and Spectroscopic Evolution of a Nearby GRB-Supernova and an Exceptionally Bright Afterglow at z=0.153

Authors: Brendan O'Connor, Malte Busmann, Xander J. Hall, Kenta Taguchi, Masaomi Tanaka, Daniel Gruen, Seiji Toshikage, Ariel J. Amsellem, Ziyuan Zhu, Antonella Palmese, Dylan Green, John Banovetz, Yu-Han Yang, Eleonora Troja, Hendrik van Eerten, Julius Gassert, Mitra Maleki, Steven Bailey, Segev BenZvi, Tomas Cabrera, Keerthi Kunnumkai, Adam Myers, Christoph Ries, David Schlegel, Michael Schmidt, Silona Wilke, Muskan Yadav,

Comments: To be submitted

Subjects: astro-ph.HE

Created: 2026-05-18; Updated: 2026-05-20; Datestamp: 2026-05-20

The association of broad-lined Type Ic SUPERNOVAe with long-duration GAMMA-RAY BURSTs (GRBs) has been known for 28 years. However, only about seventy GAMMA-RAY BURST SUPERNOVAe (GRB-SNe) have been identified, of which only half have spectroscopic classifications. At $z=0.153$, GRB 260310A is the 12th spectroscopically confirmed GRB-SN discovered within 1 Gpc, offering a critical opportunity to follow one of these rare SUPERNOVAe in detail. We present optical to near-infrared imaging and spectroscopy of GRB 260310A and SN 2026fgk out to 65 d after discovery. The optical afterglow is among the brightest ever observed from a GRB. Spectra obtained more than two weeks after the explosion reveal broad absorption features that securely identify SN 2026fgk as a Type Ic-BL SUPERNOVA. Modeling of the multi-wavelength ($grizJK_s$) lightcurve shows that the SUPERNOVA is approximately half the luminosity ($k_\textrm{98bw}=0.4-0.6$) of the canonical GRB-SN 1998bw. We derive a nickel mass of $M_\textrm{Ni}=0.4-0.5$ $M_\odot$ with a total ejected mass of $M_\textrm{ej}\approx4-6 $ $M_\odot$ and kinetic energy $E_\textrm{K}=(3-8)\times10^{51}$ erg. The GRB exploded at an extremely large offset of 15 kpc from its host galaxy. Long-slit spectra reveal a ``bridge'' of nebular emission extending along the galaxy's disk to the GRB location, which has a sub-solar metallicity ($\sim$\,$0.4Z_\odot$), compared to a near solar metallicity for the host galaxy. This indicates that the large offset arises from the galaxy's extended light profile rather than an isolated environment.

[abstract 30 / 38] (score: 2)
arXiv:2605.19067 [pdf, ps, other]

Title: Kinetic theory of the Thermal Farley-Buneman Instability in the E-region ionosphere

Authors: Yakov S. Dimant, Meers M. Oppenheim,

Comments: 72 pages, 1 figure

Subjects: physics.plasm-ph

Created: 2026-05-18; Updated: 2026-05-20; Datestamp: 2026-05-20

This paper develops a fully kinetic linear theory of the thermal Farley-Buneman instability (TFBI) in the E-region ionosphere with unMAGNETized ions. The TFBI combines spatially uniform E-region plasma instabilities, such as the Farley-Buneman instability (FBI), ion thermal instability (ITI), and electron thermal instability (ETI). Similar collision-dominated plasma processes can also occur in the solar and stellar chromospheres, as well as in other planetary atmospheres. For the first time in the theory of the FBI-related processes, the kinetic description of ions includes the driving electric field, resulting in automatic inclusion of the ITI. This analytic theory has produced a comprehensive linear wave dispersion relation. It is remarkable that, similarly to the oversimplified earlier ion-kinetic studies, this much more general kinetic dispersion relation involves only elementary functions and the standard plasma dispersion function (albeit of several different arguments). This new theory is limited to plasma waves with the frequencies of the order, or larger than, the ion-neutral collision frequency. This inherently kinetic frequency range is of importance for accurate interpretation of radar signals scattered from relatively high E-region altitudes, but at altitudes where ions are unMAGNETized (mostly, below 110 km).

[abstract 31 / 38] (score: 2)
arXiv:2605.19153 [pdf, ps, other]

Title: GstLAL O4 Online Results Paper

Authors: Shomik Adhicary, Pratyusava Baral, Amanda Baylor, Becca Ewing, Yun-Jing Huang, Rachael Huxford, Prathamesh Joshi, James Kennington, Ryan Magee, Cody Messick, Wanting Niu, Cort Posnansky, Surabhi Sachdev, Shio Sakon, Urja Shah, Divya Singh, Leo Tsukada, Zach Yarbrough, Noah Zhang, Kipp Cannon, Sarah Caudill, Bryce Cousins, Jolien D. E. Creighton, Heather Fong, Richard N. George, Olivia Godwin, Reiko Harada, Soichiro Kuwahara, Alvin K. Y. Li, Duncan Meacher, Soichiro Morisaki, Debnandini Mukherjee, Alexander Pace, Anarya Ray, Stefano Schmidt, Ron Tapia, Koh Ueno, Aaron Viets, Leslie Wade, Madeline Wade, Graham Woan, Chad Hanna,

Comments:

Subjects: gr-qc astro-ph.HE astro-ph.IM

Created: 2026-05-18; Updated: 2026-05-20; Datestamp: 2026-05-20

Gravitational-wave observations of merging binary neutron stars and BLACK HOLEs are now routinely made by detectors in the Advanced LIGO-Virgo-KAGRA network. Neutron star binary systems may also produce detectable electroMAGNETic and particle emission over times scales ranging from seconds to years. Real-time gravitational-wave searches play a central role in enabling time-critical electroMAGNETic and/or neutrino follow-up observations. During the fourth observing run (O4) of the Advanced LIGO-Virgo-KAGRA network, multiple real-time searches operated continuously to identify candidate gravitational-wave events and publicly disseminate information about these discoveries. Here, the performance and results of the GstLAL real-time analysis are reported. The analysis is designed to identify candidates with low latency, high detection efficiency, and sustained operational uptime over long observing periods. Across O4, it produced initial candidate uploads with a median latency of 15.8 s while maintaining an effective uptime of 98% during the first two parts of the observing run. During the run, the analysis contributed to 250 candidates classified as astrophysically plausible, provided the first upload for 222 of these, and was the sole contributor for 75. Among Gravitational-Wave Transient Catalog events with a false-alarm rate below one per year, 88% were identified as significant in low latency and promoted for expert vetting and public dissemination. The low-latency astrophysical classifications agreed with the final catalog classifications for 93% of the events considered.

[abstract 32 / 38] (score: 2)
arXiv:2605.19315 [pdf, ps, other]

Title: Anomalous Hall effect in anisotropic type-II Weyl semimetals

Authors: R. Martínez von Dossow, A. Martín-Ruiz, Luis F. Urrutia,

Comments: Accepted for publication in Physical Review D

Subjects: hep-th

Created: 2026-05-19; Updated: 2026-05-20; Datestamp: 2026-05-20

We extend our previous analysis [Phys. Rev. D 109, 065005 (2024)] of CPT-odd electroMAGNETic response in tilted, anisotropic Weyl semimetals to the overtilted (type-II) regime, where electron and hole pockets coexist at the FERMI level. Starting from the minimal QED sector of the Standard-Model Extension matched to a lattice-motivated anisotropic Dirac Hamiltonian with tilt, we compute the zero-temperature finite-density effective action nonperturbatively from the vacuum POLARIZATION tensor, and corroborate the result using a complementary chiral kinetic theory formulation that consistently incorporates both FERMI-sea and FERMI-surface contributions. In the type-II regime the unbounded linear dispersion necessitates a physical ultraviolet regularization. Implementing a hard momentum cutoff tied to the lattice bandwidth, we show that the CPT-odd, axion-like response remains finite across the type-I to type-II Lifshitz transition, while acquiring tilt- and anisotropy-dependent renormalizations together with nonuniversal, cutoff-sensitive terms governed by the geometry of the electron and hole pockets. As a concrete application, we evaluate the anomalous Hall conductivity in the prototypical type-II Weyl semimetal WTe$_2$, using parameters extracted from first-principles calculations and experiments, and find that FERMI-sea and FERMI-surface contributions are comparable and partially cancel, yielding a finite and strongly anisotropic Hall response characteristic of the overtilted regime.

[abstract 33 / 38] (score: 2)
arXiv:2605.19348 [pdf, ps, other]

Title: Transition of vortex dipole dynamics in holographic superfluids

Authors: Yu-Kun Yan, Shanquan Lan, Yu Tian, Hongbao Zhang,

Comments: 6 pages, 4 figures

Subjects: hep-th

Created: 2026-05-19; Updated: 2026-05-20; Datestamp: 2026-05-20

Using holographic duality, we reveal a transition in vortex dipole dynamics below a critical dipole size in strongly interacting superfluids, characterized by a significant suppression of mutual friction. In the bulk, this transition is triggered by a topological RECONNECTion of vortex tubes, which disconnects the boundary vortices from the BLACK HOLE horizon and forms a \textit{U-pipe}. Consequently, the post-transition evolution is governed by the contraction of the bulk \textit{U-pipe} rather than the mutual friction associated with the horizon, revealing a scale-dependent dissipation mechanism. We further show that this RECONNECTion persists over a broad temperature range, even when the transition becomes unobservable at high temperatures. Our results provide a dissipation-based interpretation for the anomalous critical dipole scale observed in strongly interacting cold-atom experiments, and suggest the existence of distinct dissipative regimes in strongly interacting superfluids.

[abstract 34 / 38] (score: 2)
arXiv:2605.19472 [pdf, ps, other]

Title: Chromospheric resonator model for sunspot revealed by multi-height observation of umbral wave

Authors: Kartika Sangal, A. K. Srivastava, Libo Fu, Ding Yuan, Song Feng, Yuandeng Shen,

Comments: Accepted for publication in Monthly Notices of the Royal Astronomical Society

Subjects: astro-ph.SR

Created: 2026-05-19; Updated: 2026-05-20; Datestamp: 2026-05-20

Sunspots are transient, MAGNETically intense features that host oscillations linked to MAGNETohydrodynamic (MHD) waves. These waves may contribute to plasma heating and drive mass flows in the solar wind. Beyond their energetic role, they serve as diagnostic tools for probing sunspot structure. In this study, we investigated chromospheric wave propagation in a sunspot using high-resolution, multi-wavelength observations from the Goode Solar Telescope at Big Bear Solar Observatory. Spectral analysis shows that the intensity at H$α$ line core and its wings exhibited oscillatory signal at about 3 min. We performed a cross-wavelet analysis to examine the phase relationship between the wing-integrated and line-core intensity oscillations of the H$α$ line and the centroid-derived H$α$ Doppler velocity. We also analyze the phase relationships between intensity pairs from different passband combinations of the H$α$ line. The results indicate the presence of slow MAGNEToacoustic modes manifesting standing waves along with upward propagating waves. The observed phase patterns suggest that umbral waves are confined within a non-ideal acoustic resonator, providing measurable wave properties that could serve as input for sunspot seismology and refine models of sunspot atmospheric structure.

[abstract 35 / 38] (score: 2)
arXiv:2605.19476 [pdf, ps, other]

Title: Prospect of Measuring the Cosmic Dipole by Strongly Lensed Gravitational Waves Associated with Galaxy Surveys

Authors: Anson Chen, Jun Zhang,

Comments: 17 pages, 10 figures

Subjects: astro-ph.CO gr-qc

Created: 2026-05-19; Updated: 2026-05-20; Datestamp: 2026-05-20

The cosmic dipole observed in the cosmic microwave background (CMB) is traditionally interpreted as being caused by the observer's motion relative to the background. However, tensions with dipole measurements from RADIO GALAXy counts motivate the need for independent probes. This work investigates the feasibility of using strongly lensed gravitational wave (GW) events to measure the cosmic dipole. Strongly lensed GWs produce multiple time-delayed images, which can be used to infer the distances to both the lens and the source. These distances, associated with the observed redshifts of the lens and the source from galaxy catalogues, encode information about the background cosmology and cosmic dipole effects. By reconstructing a statistical sample of doubly lensed GW events based on the singular isothermal sphere lens model, the cosmic dipole can be estimated jointly with background cosmological parameters. Using realistic simulations for Einstein Telescope and Cosmic Explorer, we forecast that a dipole magnitude $g$ consistent with both the CMB and number count measurement could be detected with 10 years of observation. Furthermore, constraints on $g$ are greatly improved by combining constraints from doubly lensed events with those from triply or quadruply lensed events. In the most optimistic scenario, where we measure the number count dipole magnitude with 10 years of observation, we obtain $g = (2.45^{+1.53}_{-1.28}) \times 10^{-3}$ from the combined constraint, provided that systematic uncertainties are mitigated. Although challenging, strongly lensed GWs offer a novel approach to measuring the cosmic dipole, providing an independent consistency test with different systematics from electroMAGNETic probes.

[abstract 36 / 38] (score: 2)
arXiv:2605.19553 [pdf, ps, other]

Title: Recent Findings from the Telescope Array Experiment

Authors: Jihyun Kim,

Comments: 10 pages, 11 figures, contribution to the 2026 Very High Energy Phenomena in the Universe session of the 60th Rencontres de Moriond

Subjects: astro-ph.HE astro-ph.IM

Created: 2026-05-19; Updated: 2026-05-20; Datestamp: 2026-05-20

The Telescope Array (TA) is the largest ultra-high energy COSMIC RAY (UHECR) observatory in the Northern Hemisphere. Together with its extensions, TA Low Energy (TALE), TALE infill, and the TA$\times$4 array, it measures extensive air showers (EAS) initiated by UHECRs across an energy range spanning from $10^{15}$ eV to beyond $10^{20}$ eV. All components of the experiment employ a hybrid detection approach, combining plastic scintillator arrays that sample the EAS footprint at ground level with telescopes that record fluorescence and Cherenkov light from shower development in the atmosphere. The ongoing construction of TA$\times$4 will significantly increase statistics at the highest energies by expanding the surface detector area by a factor of four. In addition, the recently deployed TALE infill array further lowers the hybrid energy threshold of TALE. This presentation summarizes the current status of the TA experiment and highlights recent findings on the energy spectrum, mass composition, and anisotropy.

[abstract 37 / 38] (score: 2)
arXiv:2605.19653 [pdf, ps, other]

Title: Evidence for Intermediate-Mass Black Holes From Microlensing Signatures in CHIME/FRB catalog 2

Authors: Huan Zhou, Zhengxiang Li, Cheng-Gang Shao, Xi-Jing Wang, Kai Liao, He Gao, Zong-Hong Zhu,

Comments: 11 pages, 5 figures, 1 table

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

Created: 2026-05-19; Updated: 2026-05-20; Datestamp: 2026-05-20

Intermediate-mass BLACK HOLEs (IMBHs) are the missing link in the cosmic hierarchy of BLACK HOLEs, bridging the gap between stellar-mass BLACK HOLEs and supermassive ones. They also serve as unique laboratories for testing strong-field gravity and are prime targets for future multi-messenger observations. However, IMBHs are a population that has remained notoriously difficult to detect. The microlensing effect of fast radio bursts (FRBs) can serve as a clean and powerful method to probe IMBHs. In this work, we develop a pipeline to search for microlensed FRBs based on their dynamic spectra and apply it to the CHIME/FRB Catalog 2. Two microlensing signatures have been identified in two separate sources, i.e. FRB~20190131D and FRB~20211115A. The inferred lens masses for these two signatures are $\sim[539-609]~M_{\odot}$ and $\sim[1544-2571]~M_{\odot}$, respectively. Here we interpret them as evidence for IMBHs. If there are no intervening structures-such as galaxies or clusters-along the line of sights for these two sources, the two identified IMBHs might be isolated and of primordial origins. In that case, we obtain primordial BLACK HOLEs (PBHs) within these two mass ranges would constitute $\sim4\%$ of DARK MATTER. Moreover, if these two candidates are not genuine lensing signatures, the abundance of intermediate-mass PBHs with masses $>300,M_{\odot}$ is constrained to be $\sim13\%$ at $95\%$ confidence level. Therefore, more comprehensive observational information for FRBs, together with a deeper understanding of whether the intrinsic emission mechanisms of FRBs can produce lensing-like signals, will be crucial for establishing this effect as a powerful tool for probing (primordial) IMBHs.

[abstract 38 / 38] (score: 2)
arXiv:2605.20112 [pdf, ps, other]

Title: Gravitational-wave constraints on $H_0$ are robust to (putative) redshift evolution in the binary BLACK HOLE mass spectrum at current sensitivity

Authors: Alessandro Agapito, Viola De Renzis, Michele Mancarella,

Comments: 12 + 5 pages, 6 + 7 figures

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

Created: 2026-05-19; Updated: 2026-05-20; Datestamp: 2026-05-20

Spectral-siren cosmology constrains the Hubble constant $H_0$ using gravitational-wave observations of compact-binary coalescences. The method combines luminosity distances inferred from the waveform with redshift information statistically encoded in population features of the source-frame mass spectrum. Because the detector measures redshifted masses, structure in the intrinsic mass distribution acts as an internal ``ruler'', making the inference sensitive to assumptions about the population model. In particular, redshift evolution of the mass spectrum is widely discussed as a potential systematic for $H_0$ measurements. We revisit spectral-siren constraints with the GWTC-4.0 binary BLACK HOLE catalog, explicitly allowing the main mass scales of a standard parametric mass model to evolve with redshift. We find no compelling evidence for evolution at current sensitivity. Allowing evolution produces a modest, non--statistically--significant shift of the $H_0$ posterior toward lower values, which we interpret with targeted posterior and event-level diagnostics. Importantly, the associated systematic uncertainty is subdominant to that induced by alternative redshift-independent descriptions of the mass spectrum, such as the number of spectral features and the functional form used to model them. Our results indicate that, at current sensitivity, spectral-siren constraints on $H_0$ are robust to redshift evolution of the mass spectrum within the flexibility explored here. Using injection studies, we show that this mild $H_0$ shift is reproduced when a non-evolving underlying population is analyzed with an evolving model, consistent with an over-flexible population description at the present signal-to-noise. The sign and magnitude of the shift can, however, depend on detector sensitivity and redshift reach as the population features become increasingly constrained directly by the data.