Current date: 2026-04-07

Setting default datestamp limit: 0

Datestamp limit: 2026-04-07 (0 days ago)

Created/updated limit: 2026-03-31 (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=2026-04-07&until=2026-04-07&set=physics&metadataPrefix=arXiv

Scoring abstracts

Number of records retrieved: 883

Keyword score statistics

score 11 -- 1 abstracts

score 10 -- 1 abstracts

score 8 -- 1 abstracts

score 7 -- 1 abstracts

score 5 -- 5 abstracts

score 4 -- 4 abstracts

score 3 -- 5 abstracts

score 2 -- 22 abstracts

in total -- 40 abstracts

Articles that appeared on 2026-04-07

[abstract 1 / 40] Wow! (score: 11)
arXiv:2603.25331 [pdf, ps, other]

Title: Jet Power Estimates of FSRQs PKS 1441+25 and Ton 599 from Broadband SED Modeling

Authors: Hritwik Bora, Ranjeev Misra, Rukaiya Khatoon, Rupjyoti Gogoi,

Comments:

Subjects: astro-ph.HE

Created: 2026-04-06; Updated: 2026-04-07; Datestamp: 2026-04-07

Flat-Spectrum Radio Quasars (FSRQs) are among the most energetic and powerful ACTIVE GALACTIC NUCLEi, often exhibiting JET powers comparable to or exceeding the Eddington luminosity. In this work, we performed broadband spectral energy distribution (SED) modeling of two FSRQs PKS 1441+25 and Ton 599, using SWIFT-XRT/UVOT, NUSTAR, FERMI-LAT and VERITAS observations during 2015 and 2021, respectively. We considered four particle distribution models: a broken power law, a log-parabola, and two energy-dependent models in which either the diffusion or acceleration timescale depends on energy. Our results show that the JET power estimates derived from models with intrinsic curvature, such as the log-parabola and energy-dependent models, are of the same order as those obtained with a broken power-law distribution. This contrasts with the case of High Synchrotron Peaked Blazars (HBLs), where the power estimates can differ by nearly two orders of magnitude between models. We attribute this difference to the lower electron break energies typically observed in FSRQs. Consequently, our findings suggest that, unlike in HBLs, the estimated JET powers in FSRQs are relatively insensitive to the assumed particle energy distribution, reflecting the dominance of external Compton processes and weaker dependence on spectral curvature.

[abstract 2 / 40] Wow! (score: 10)
arXiv:2604.03847 [pdf, ps, other]

Title: Characterizing Gamma-Radio Delayed Flaring Activity from Blazars

Authors: Alina Kochocki, Emma Kun, Sam Hori,

Comments: 15 pages, 4 figures

Subjects: astro-ph.HE

Created: 2026-04-04; Updated: 2026-04-07; Datestamp: 2026-04-07

Flaring activity from the JETs of ACTIVE GALACTIC NUCLEi has been studied for several decades, closely related to the loading and evolution of the JET. In this work, we focus on the sub-hundred parsec JET region, well traced by non-thermal radio and gamma-ray emission. Only in recent years have light curves capturing the decade-long behavior of such sources become available for a large ensemble of objects. While previous studies have focused on a direct correlation or few-month lag between gamma-ray and radio activity, recent neutrino-bright BLAZARs observed by the IceCube Neutrino Observatory present multi-year delays between initial gamma-ray activity and subsequent radio flares. In this work, we search for similar-timescale correlations between FERMI-LAT gamma-ray data and RATAN-600 radio data from ~100 BLAZARs. We consider two gamma-ray bands, 100 MeV-1 GeV and 1 GeV-500 GeV, as well as the integral band, to compare correlations between potential opaque and unabsorbed regions of the JET. Gaussian process modeling is used for smooth light curve function prediction. We also analyze morphological AGN core data from the MOJAVE survey, forming a sub-selection to better illustrate potential dependence on location. In the broader selection, several sources exhibit delayed flares on the order of 1-3 years. In the stacked analysis, we find the highest correlation for a radio delay on the order of 180 days. The stacked correlation resulting from the MOJAVE sub-selection corresponds to a slightly smaller time lag. Delayed radio flares or extended radio emission appear to be notable features within the general BLAZAR population.

[abstract 3 / 40] Wow! (score: 8)
arXiv:2604.03368 [pdf, ps, other]

Title: Multimessenger Signatures of Tilted, Self-Gravitating, Black Hole Disks

Authors: Milton Ruiz, Antonios Tsokaros, Stuart L. Shapiro,

Comments: 9 pages, 11 figures

Subjects: gr-qc astro-ph.HE

Created: 2026-04-03; Updated: 2026-04-07; Datestamp: 2026-04-07

We perform fully RELATIVISTIC GRMHD simulations of MAGNETized, self-gravitating BLACK HOLE-disk (BHD) systems in which the BLACK HOLE spin is misaligned with the disk angular momentum. Massive disks (disk to BH mass ratios of $16-28\%$) around rapidly rotating BLACK HOLEs ($χ\lesssim 0.97$) develop a nonaxisymmetric instability for tilt angles from $0^\circ$ to $180^\circ$. Magnetic stresses damp, but do not completely suppress, the nonaxisymmetric instability, and corresponding gravitational wave (GW) emission, in aligned systems, while they enhance it in antialigned BHDs: MRI-driven turbulence enhances angular momentum transport and accelerates nonlinear instability evolution in misaligned configurations. All models launch MAGNETically driven JETs consistent with the Blandford-Znajek (BZ) mechanism, with collimation depending on spin orientation. The GWs reflect strong nonaxisymmetric structure from a persistent $m=1$ mode. The coupling between fast MRI and the slower nonaxisymmetric instability growth governs the outcome, with tilt controlling how MRI modifies the global mode. These simulations provide the first self-consistent GRMHD treatment of tilted, self-gravitating BHD systems and support their role as multimessenger sources.

[abstract 4 / 40] Wow! (score: 7)
arXiv:2604.04768 [pdf, ps, other]

Title: Constraining the PeV gamma-ray emission zone of Cygnus X-3 with contemporaneous GeV timing and spectral observations

Authors: Xing-Fu Zhang, Ruo-Yu Liu, Dmitriy Khangulyan, Cui-Yuan Dai, Xiang-Yu Wang,

Comments: 11 pages, 7 figures, 1 table

Subjects: astro-ph.HE

Created: 2026-04-06; Updated: 2026-04-07; Datestamp: 2026-04-07

Cygnus X-3 has recently been established as a variable ultra-high-energy(UHE) gamma-ray source with photons detected up to 3.7~PeV. The temporal correlation between its PeV activity and GeV flares, together with the possible orbital modulation, suggests that the emission is produced within or close to the binary system. In this work, we test whether the contemporaneous GeV emission zone can also host the acceleration of the parent protons responsible for the multi-PeV photons. We jointly model the contemporaneous \textit{FERMI}-LAT spectrum and orbital light curve with a one-zone leptonic scenario dominated by anisotropic external inverse-Compton scattering. The fit places the GeV emission region at $H\sim2.8\times10^{11}\,$cm and constrains the MAGNETic field--size product to $BH\lesssim10^{13.3}\,$G\,cm at the $3σ$ level. This implies a maximum proton energy of only $\sim0.3$~PeV from the Hillas criterion, far below that required by the observed PeV emission. We therefore conclude that the GeV zone cannot be the main PeV acceleration site. Instead, the PeV emission should originate from a more compact inner region, and the JET MAGNETic field must dissipate rapidly between the PeV and GeV emitting zones.

[abstract 5 / 40] Yes (score: 5)
arXiv:2602.00257 [pdf, ps, other]

Title: Fireballs' Whispers of Their Central Engine: Relativistic Filtering of Afterglow QPOs

Authors: Noémie Globus,

Comments: 7 pages, 1 figure, accepted for publication in The Astrophysical Journal Letters

Subjects: astro-ph.HE

Created: 2026-04-04; Updated: 2026-04-07; Datestamp: 2026-04-07

Quasi-periodic oscillations (QPOs) in GAMMA-RAY BURSTs (GRBs) afterglows have been suggested as probes of the central engine. Such interpretations generally assume that the observed modulation frequency directly corresponds to an intrinsic oscillation frequency of the source. We show that this assumption is not generally valid and that interpreting such features without accounting for RELATIVISTIC propagation may lead to misleading inferences about the engine nature. We show that RELATIVISTIC propagation effects - most importantly integration over equal-arrival-time surfaces - act as a frequency-dependent filter that can significantly modify or suppress intrinsic variability. In the constant-$Γ$ case, the angular kernel acts as a stationary low-pass filter that suppresses high-frequency variability without altering its frequency, whereas Blandford-McKee deceleration renders the filter time-dependent and manifests observationally as an apparent frequency drift.

[abstract 6 / 40] Yes (score: 5)
arXiv:2603.01880 [pdf, ps, other]

Title: Estimating the peak energy of SWIFT GAMMA-RAY BURSTs using supervised machine learning

Authors: Wan-Peng Sun, Si-Yuan Zhu, Da-Ling Ma, Fu-Wen Zhang,

Comments: 12 pages, 16 figures, 5 tables

Subjects: astro-ph.HE

Created: 2026-04-05; Updated: 2026-04-07; Datestamp: 2026-04-07

Gamma-ray bursts (GRBs) are among the most energetic explosive phenomena in the Universe, and their peak energy ($E_{\rm p}$) is a key physical quantity for understanding the prompt emission mechanism. However, due to the limited energy coverage of the SWIFT satellite, a large fraction of SWIFT GRBs lack reliable peak energy measurements. Therefore, developing an accurate and efficient method for estimating $E_{\rm p}$ is of great importance. In this work, we propose a method based on the SuperLearner framework that integrates multiple supervised machine learning algorithms to estimate the $E_{\rm p}$ of SWIFT/BAT GRBs. We used the SWIFT/BAT observational data from December 2004 to September 2022 as training features, and adopted the peak energies of 516 GRBs jointly detected by SWIFT and either FERMI/GBM or Konus-Wind as training labels. After training and testing multiple supervised models, the final SuperLearner ensemble yields a more robust and reliable predictive model. In 100 iterations of five-fold cross-validation, the estimated $E'_{\rm p}$ values show a tight correlation with the observed $E_{\rm p}$, with an average Pearson correlation coefficient of $r = 0.72$. Compared with previous Bayesian estimates, our model provides estimations that are likely closer to the true values. Based on the trained model, we further estimated the peak energies of 650 SWIFT GRBs, significantly increasing the number of GRBs with estimated peak energies and providing new statistical support for constraining GRB emission mechanisms and energy origins.

[abstract 7 / 40] Yes (score: 5)
arXiv:2603.25949 [pdf, ps, other]

Title: General-RELATIVISTIC radiative cooling in neutron star MAGNETospheres

Authors: João Joaquim, Francisco Assunção, Pablo J. Bilbao, Luis O. Silva,

Comments: 11 pages, 5 figures

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

Created: 2026-04-05; Updated: 2026-04-07; Datestamp: 2026-04-07

Radiation reaction cooling plays an important role in describing the extreme plasma conditions found in the MAGNETospheres of astrophysical compact objects. Strong electroMAGNETic fields, characteristic of these environments, can trigger the development of anisotropic ring-shaped plasma distributions with inverted Landau populations in momentum space. In this work, we present the first systematic investigation of this mechanism in realistic astrophysical configurations, by accounting for how non-uniform electroMAGNETic field geometries and general-RELATIVISTIC effects modify the phase-space dynamics of radiatively cooled plasmas. We demonstrate analytically that drift velocities favour the formation of spiral-shaped momentum distributions that still display inverted Landau populations, and estimate the minimum and maximum plasma injection distances required for inverted momentum distributions to be able to power the emission of coherent radiation through kinetic instabilities. From numerical simulations, we conclude that curved spacetime increases the gradient of the distribution function responsible for the development of kinetic instabilities, and prolongs the persistence of the inverted momentum structure relative to flat spacetime, confirming that realistic astrophysical conditions preserve and enhance the conditions necessary for SYNCHROTRON-powered emission of coherent radiation to occur.

[abstract 8 / 40] Yes (score: 5)
arXiv:2604.04085 [pdf, ps, other]

Title: Revisiting the X-ray Variability Plane of AGNs: The Significant Role of the Photon Index

Authors: Ruisong Xia, Hao Liu, Yongquan Xue, Jialai Wang, Guowei Ren, Mouyuan Sun, Shifu Zhu, Mengqiu Huang, Qingwen Wu, Xian-Liang Lu, Zhen-Bo Su, Shuying Zhou,

Comments: 13 pages,3 figures,accepted for publication in ApJ

Subjects: astro-ph.HE

Created: 2026-04-05; Updated: 2026-04-07; Datestamp: 2026-04-07

X-ray variability provides a powerful probe of the innermost regions of ACTIVE GALACTIC NUCLEi (AGNs), offering valuable insights into the accretion process and the structure of the corona. Previous studies have established a correlation between the X-ray variability timescale, BLACK HOLE mass, and luminosity, forming the AGN X-ray variability plane. A possible link between the X-ray spectral photon index and X-ray variability was noted in early studies but has rarely been incorporated into subsequent analyses of the variability plane. Moreover, the limited sample sizes in earlier works have limited the robustness and universality of the X-ray variability plane. In this work, we compile a sample of 112 AGNs with 399 exposures from the 4XMM-DR14 catalog and constrain the correlations between X-ray variability timescale, BLACK HOLE mass, luminosity, and photon index using the recently developed fitting method, BADDAT {(Baseline-Aware Dependence fitting for DAmping Timescales)}, which enables a robust exploration of an extended parameter space. Our analysis confirms the dependence of the rest-frame variability timescale ($τ_{\rm rest}$) on BLACK HOLE mass ($M_{\rm BH}$) and further incorporates the photon index ($Γ$) into the variability plane, yielding a best-fit relation of $\log (τ_{\rm rest}/{\rm s}) = 1.22\log (M_{\rm BH}/M_\odot) - 0.24Γ- 3.53$, which is strongly favored over the model with $M_{\rm BH}$ alone. In contrast, the inclusion of luminosity does not produce a comparable improvement. The correlation with $Γ$ likely reflects the effects of Comptonization and the geometry of the corona.

[abstract 9 / 40] Yes (score: 5)
arXiv:2604.04276 [pdf, ps, other]

Title: Fast Magnetosonic Turbulence in Two-Dimensional Relativistic Plasmas

Authors: Petr Ugarov, Vladimir Zhdankin, Giuseppe Arrò,

Comments: 6 pages, 4 figures in the main paper. Supplemental Material has 4 pages, 2 figures

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

Created: 2026-04-05; Updated: 2026-04-07; Datestamp: 2026-04-07

We present fully kinetic simulations of driven 2D turbulence in a RELATIVISTIC plasma, designed for the first time to induce a fast MAGNETosonic cascade. As the driving strength increases, turbulence transitions from a weak wave-dominated regime to strong shock-driven dynamics. Using spatiotemporal Fourier analysis, we identify fast modes, finding that the weak turbulence regime exhibits spectral properties that are in excellent agreement with theoretical expectations. Our results are relevant for the modeling of turbulence in high-energy astrophysical plasmas.

[abstract 10 / 40] Yes (score: 4)
arXiv:2410.11692 [pdf, ps, other]

Title: Simulations of Protostar-Driven Photoionization in Herbig-Haro Jets

Authors: Z. Ahmane, A. Mignone, C. Zanni, S. Massaglia, A. Bouldjderi,

Comments: Revised version. Major improvements in language, clarity, and presentation. All scientific results unchanged. Published version: Astrophys. Space Sci. 365, 94 (2020)

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

Created: 2026-04-04; Updated: 2026-04-07; Datestamp: 2026-04-07

Recent studies showed that observations of line emission from shocks in YSO JETs require a substantial amount of ionization of the pre-shock matter. Photoionization from X-ray emitted close to the central source may be responsible for the initial ionization fraction. The aim of our work is to study the effect of X-ray photoionization, coming from the vicinity of the central star, on the ionization fraction inside the JET that can be advected at large distances. For this purpose we have performed axisymmetric MHD JET launching simulations including photoionization and optically thin losses using PLUTO. For typical X-ray luminosities in classical T-Tauri stars, we see that the photoionization is responsible for ionizing to 10 % -20 % the JET close to the star.

[abstract 11 / 40] Yes (score: 4)
arXiv:2505.09676 [pdf, ps, other]

Title: Homogeneous measurements of proximity zone sizes for 59 QUASARs in the Epoch of Reionization

Authors: Silvia Onorato, Joseph F. Hennawi, Elia Pizzati, Bram P. Venemans, Anna-Christina Eilers,

Comments: 33 pages, 15 figures, published on MNRAS

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

Created: 2026-04-03; Updated: 2026-04-07; Datestamp: 2026-04-07

The overionized regions surrounding high-redshift QUASARs, known as proximity zones, provide a window into the interaction between supermassive BLACK HOLEs (SMBHs) and the intergalactic medium (IGM) during the epoch of reionization (EoR). We present new homogeneous measurements of proximity zone sizes ($R_{\mathrm{p}}$) for a sample of $59$ QUASARs spanning redshifts $5.77 \leq z \leq 7.54$ (median $z = 6.59$). For $15$ of these sources, we measure $R_{\mathrm{p}}$ for the first time. The QUASARs in our catalog have absolute magnitudes at rest-frame $1450$ Å in the range $-29.13 \leq M_{1450} \leq -25.20$ (median $M_{1450} \simeq -26.49$), providing one of the most extensive data sets for exploring $R_{\mathrm{p}}$ at these epochs. The distribution of $R_{\mathrm{p}}$ values shows a large scatter at fixed redshift and luminosity, likely reflecting variations in QUASAR lifetimes ($t_{\mathrm{Q}}$), IGM density fluctuations, and IGM neutral fraction. We fit a bivariate power-law model to a large sample of $100$ objects to study the dependence of $R_{\mathrm{p}}$ with both $M_{1450}$ and $z$: we find that the evolution of $R_{\mathrm{p}}$ with luminosity is in agreement with the models ($R_{\mathrm{p}} \propto 10^{-0.4 M_{1450}/2.87}$), while the evolution of $R_{\mathrm{p}}$ with $z$ is steeper than previous works ($R_{\mathrm{p}} \propto (1+z)^{-2.44}$). We identify $13$ QUASARs with small proximity zone size, defined using the residuals of our fit. In all cases, except for J2211$-$6320, we rule out the presence of associated dense absorbers that prematurely truncate $R_{\mathrm{p}}$, and suggest a short $t_{\mathrm{Q}}$ ($\lesssim 10^4$ yr) as a possible explanation for their small proximity zone sizes.

[abstract 12 / 40] Yes (score: 4)
arXiv:2604.03945 [pdf, ps, other]

Title: Photon Propagation through Magnetar-Hosted Axion Clouds: Time Delays and Polarimetric Constraint

Authors: M. M. Chaichian, B. A. Couto e Silva, B. L. Sánchez-Vega,

Comments: 34 pages and 1 figure

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

Created: 2026-04-05; Updated: 2026-04-07; Datestamp: 2026-04-07

Temporal offsets between Gamma-Ray Bursts (GRBs) and high-energy neutrinos provide a useful probe of propagation effects in extreme astrophysical environments. We investigate whether such offsets can be generated by photon propagation through dense axion clouds gravitationally bound to MAGNETars. Working within the Euler-Heisenberg effective theory extended by the axion sector, we derive the modified photon dispersion relations in the presence of a strong MAGNETic background and an oscillating axion field. We show that axion-photon mixing turns the MAGNETized vacuum into an anisotropic birefringent medium, leading to geometry-dependent deviations from luminal propagation and kinematic time delays that reach $Δt_{\perp}\simeq1.33\times10^{-12}\,\mathrm{s}$ for orthogonal propagation. Although this effect is many orders of magnitude larger than the delays expected in diffuse astrophysical backgrounds, it remains far too small to account for the macroscopic offsets discussed in current multimessenger candidates. We further show that the same birefringent medium constrains the survival of the intrinsic linear POLARIZATION of prompt GRB emission, yielding the environmental bound $g_{aγγ}\lesssim6.02\times10^{-14}\,\mathrm{GeV}^{-1}$ for benchmark MAGNETar-scale parameters and axion masses near $m_a\sim10^{-4}\,\mathrm{eV}$. Magnetar-hosted axion clouds thus emerge as complementary environments in which dispersive transport and polarimetric observables jointly probe axion electrodynamics.

[abstract 13 / 40] Yes (score: 4)
arXiv:2604.04814 [pdf, ps, other]

Title: Diffusion of PeV Cosmic Rays in the Turbulent and Multiphase Interstellar Medium

Authors: Yue Hu,

Comments: 22 pages,8 figures, accepted for the publication in MDPI-Galaxies

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

Created: 2026-04-06; Updated: 2026-04-07; Datestamp: 2026-04-07

Galactic COSMIC RAYs (CRs) are a fundamental non-thermal component of the interstellar medium (ISM). Understanding the transport of super-high-energy particles is essential for interpreting observations of Galactic PeVatrons. Classical diffusion models assuming a homogeneous and isothermal medium oversimplify the multiphase ISM. We utilize high-resolution 3D MHD simulations to self-consistently generate a multiphase ISM, comprising the warm (WNM), unstable (UNM), and cold neutral medium (CNM), and investigate 1.5-15 PeV particle transport using a test-particle approach. We find that thermal phase transitions induce steep MAGNETic field strength gradients at phase boundaries, creating localized MAGNETic fluctuations that act as efficient sites for adiabatic mirror reflections and non-adiabatic pitch-angle scattering, strongly enhancing cross-field transport at these interfaces. However, because phase boundaries occupy only a small volume fraction and particles spend most of their trajectory in the weakly scattering WNM and UNM, the global pitch-angle scattering coefficient in the multiphase ISM is smaller than in an equivalent isothermal medium. This locally strong scattering nevertheless drives both parallel and perpendicular spatial diffusion coefficients to $\sim10^{30} {\rm cm^2 s^{-1}$ at 1.5~PeV, with the perpendicular component exceeding its isothermal counterpart ($\sim 10^{28}{\rm cm^2 s^{-1}$) by two orders of magnitude. Using a phase--phase diffusion matrix decomposition, we show that global CR transport is governed by the volume-filling, trans-Alfvénic WNM and UNM, where particles stream along stochastically wandering field lines. Cross-phase displacement correlations are universally positive, indicating cooperative transport between thermal phases. In contrast, the super-Alfvénic CNM acts as an efficient confinement that substantially suppresses local diffusion.

[abstract 14 / 40] (score: 3)
arXiv:1110.0483 [pdf, ps, other]

Title: An effect of abrupt current disruption

Authors: Andis Dembovskis,

Comments: 32 pages, 53 figures. While there was not enough of time & finance dedicated to finish the work, the current accomplishment is still considered to be of value for reporting as is

Subjects: physics.plasm-ph

Created: 2026-04-06; Updated: 2026-04-07; Datestamp: 2026-04-07

Every engine, let it internal combustion engine in car or turbine of airplane, needs a high quality fuel igniter. During last decades there have been some minor changes made in ignition systems, like invention of Capacitive Discharge Ignition, Multiple Discharge Ignition, Ignition with Direct Current Discharge, but all based on the same principle of High Voltage spark path creation. This work contains description, schematics and photographs of a new spark creation approach, providing high robustness through high power, big volume, long duration plasma. The system uses less or the same amount of energy as would CDI ignition, JET providing many times more efficient energy output. The solution is a highly applicable innovation, being able to significantly improve spark robustness in all current HV spark ignition systems. Despite a simplicity of setup, it is still unclear why the effect persists, thus calling for additional research input.

[abstract 15 / 40] (score: 3)
arXiv:2512.05194 [pdf, ps, other]

Title: Lagrangian versus Eulerian Methods for Toroidally-Magnetized Isothermal Disks

Authors: Yashvardhan Tomar, Philip F. Hopkins,

Comments: 5 pages, 2 figures. Updated with version accepted to The Open Journal of Astrophysics

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

Created: 2026-04-04; Updated: 2026-04-07; Datestamp: 2026-04-07

A number of simulations have seen the emergence of strongly-toroidally-MAGNETized accretion disks from interstellar medium inflows. Recently, Guo et al. 2025 (G25) studied an idealized test problem of toroidally-MAGNETized disks in isothermal ideal MHD with an Eulerian static-mesh method, and argued the midplane behavior changes qualitatively (with a significant loss of toroidal MAGNETic flux) when the the thermal scale-length is resolved ($Δx < H_{\rm thermal}$). We rerun the G25 test problem with two Lagrangian methods: meshless finite-mass, and meshless finite-volume. We show that Lagrangian methods reproduce the high-resolution ($Δx \ll H_{\rm thermal}$) Eulerian G25 results. At low resolution ($Δx \gg H_{\rm thermal}$), behaviors differ: Lagrangian methods still lose flux and evolve 'as close as possible' to the converged solution, while Eulerian methods show no evolution. We argue this difference in convergence behavior is related to the ability of Lagrangian codes to follow flows to an arbitrarily thin midplane layer, analogous to the well-studied difference in Jeans fragmentation problems. This and results from other higher-resolution simulations and different codes suggest that the sustained midplane toroidal fields seen in recent Lagrangian multi-scale, multi-physics simulations cannot be a numerical resolution effect, and some physical difference between those simulations and the G25 test problem explains their different behaviors.

[abstract 16 / 40] (score: 3)
arXiv:2601.11784 [pdf, ps, other]

Title: Einstein Probe discovery of EP J171159.4-333253: an eclipsing neutron star low-mass X-ray binary with clocked bursts

Authors: Y. L. Wang, F. Coti Zelati, E. Parent, A. Marino, N. Rea, V. S. Dhillon, J. Blanco-Pozo, I. Ribas, S. P. Littlefair, Z. H. Yang, G. B. Zhang, S. Guillot, K. R. Ni, J. H. Wu, A. Patruno, Y. Cavecchi, G. Illiano, A. Papitto, F. Ambrosino, B. F. Liu, H. Q. Cheng, H. Feng, J. W. Hu, C. C. Jin, H. Sun, L. Tao, Y. J. Xu, H. N. Yang, W. Yuan, Q. C. Zhao,

Comments: 28 pages, 15 figures; accepted for publication in ApJ

Subjects: astro-ph.HE

Created: 2026-04-06; Updated: 2026-04-07; Datestamp: 2026-04-07

EP J171159.4-333253 is a new neutron-star low-mass X-ray binary discovered in outburst by the Einstein Probe (EP) on 2025 June 23, exhibiting clocked type-I X-ray bursts, eclipses and dips. In this paper, we report on the results of the X-ray spectral and timing analyses for EP J171159.4-333253 using data collected by EP and NUSTAR during the first 21 days of the outburst. The X-ray burst recurrence time can be characterized over a subset of nine bursts spanning 1.6 days around the NUSTAR observation, and the result is $t_{\rm rec}=8196 \pm 177\,$s with indications of a possible decreasing trend. From the X-ray eclipse events, the binary orbital period and the eclipse duration are estimated to be $P_{\rm orb}=6.48301 \pm 0.00003\,$hr and $D_{\star,X} = 1245.5^{+6.9}_{-6.5}\,$s, respectively. These enable an estimate of the mass and radius of the companion star and the binary inclination, which are $M_2\approx0.6-0.8\,M_\odot$, $R_2\approx0.7-0.8\,R_\odot$ and $i\approx73-75^\circ$, respectively. We also report on joint ULTRACAM and EP observations on 2025 July 21--22, detecting the source optical counterpart and covering an eclipse in both X-ray and optical bands. The optical eclipse is wavelength-dependent and broader than in X-rays, indicating that part of the optical emission arises from an extended region in the accretion flow. Despite a moderate variation in the source flux, the properties of the persistent X-ray emission are typical of a hard spectral state. We further evaluated the ratio of the accretion energy to the thermonuclear energy to be 120--130, implying helium bursts with the accreted hydrogen being depleted in-between bursts.

[abstract 17 / 40] (score: 3)
arXiv:2604.03429 [pdf, ps, other]

Title: The VLBI spectrum of the persistent radio source associated with FRB 20190417A

Authors: G. Bruni, L. Piro, Y. -P. Yang, L. Nicastro, A. Rossi, E. Palazzi, E. Maiorano, S. Savaglio, B. Zhang,

Comments: Submitted to A&A

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

Created: 2026-04-03; Updated: 2026-04-07; Datestamp: 2026-04-07

We aim to confirm the compact nature and constrain the radio spectra of candidate persistent radio sources (PRSs) associated with repeating fast radio bursts (FRBs). We performed European VLBI Network (EVN) observations at 5 and 8 GHz targeting two candidates identified in a recent VLA survey. We measured flux densities and upper limits at milliarcsecond resolution and combined them with published VLBI data at lower frequencies to derive spectral constraints. We detect a compact source associated with FRB 20190417A at 5 GHz with a flux density of $150\pm45$ uJy, while no detection is obtained at 8 GHz. The source is unresolved and has a brightness temperature $T_{\rm b} \gtrsim 10^{6-7}$ K, confirming its non-thermal nature. Combining our measurement with VLBI data at 1.4 GHz, we derive a spectral index $α= -0.19 \pm 0.29$, consistent with a nearly flat spectrum. This makes FRB 20190417A only the second PRS with a spectral index constrained using VLBI data. The inferred luminosity places the source on the proposed $L_ν$-|RM| relation. Including this source yields a scatter of $σ_Δ= 0.65$, corresponding to $\hatα|ε| = 1.5 \pm 0.7$, consistent with forward shocks in the free-expansion phase or young pulsar wind nebulae. For the candidate PRS associated with FRB 20181030A, we report upper limits of 80 uJy at 5 GHz and 150 uJy at 8 GHz, corresponding to $L_{5\,\mathrm{GHz}} \lesssim 3.8 \times 10^{25}\ {\rm erg\ s^{-1}\ Hz^{-1}}$, and implying a steep spectral index ($α\lesssim -1.2$) if the VLA emission arises from a compact component. Our results highlight the importance of VLBI in isolating compact emission from FRB engines and provide one of the few spectral constraints for PRSs at milliarcsecond resolution. The consistency of FRB 20190417A with the $L_ν$-|RM| relation supports a nebular origin for the persistent emission.

[abstract 18 / 40] (score: 3)
arXiv:2604.04014 [pdf, ps, other]

Title: Extraction method for response functions from X-ray light curves of AGN by optimization algorithm

Authors: Sanhanat Deesamutara, Tirawut Worrakitpoonpon, Poemwai Chainakun, Wasutep Luangtip, Jiachen Jiang, Francisco Pozo Nuñez, Andrew J. Young,

Comments: accepted in ApJ, 16 pages, 7 figures

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

Created: 2026-04-05; Updated: 2026-04-07; Datestamp: 2026-04-07

We introduce a numerical optimization method to extract the X-ray reverberation response functions from the multi-band light curves of the ACTIVE GALACTIC NUCLEi. This approach does not require prior assumptions about the accretion disc and corona geometry, provided that the light curves result from the superposition of direct and singly-convolved signals, consistently across all bands. By reformulating the light curve equations into the matrix form, the optimal response matrix is derived by minimizing the squared difference between the observed and reconstructed light curves using a gradient-based optimization algorithm. We demonstrate that the method can robustly accommodate up to two convolution processes, such as the reverberation and the propagation, simultaneously. When tested on the synthesized light curves, the method demonstrates robustness of the solutions to variations in the relative contributions of each light curve component as the recovered response kernel remains acceptably close to the ground truth, as evaluated by both the response geometry and the reconstructed light curves. The method's tolerance to random noise was also assessed. With appropriate denoising, the response kernel can be reliably recovered when the signal-to-noise ratio is at least $100$. We show, as a proof of concept, that the proposed method is geometrical-model independent and has the potential to offer a flexible complement to traditional approaches.

[abstract 19 / 40] (score: 2)
arXiv:2110.15351 [pdf, ps, other]

Title: Action-angle variables of a binary BLACK HOLE with arbitrary eccentricity, spins, and masses at 1.5 post-Newtonian order

Authors: Sashwat Tanay, Leo C. Stein, Gihyuk Cho,

Comments: 28 pages, 6 figures. Includes Erratum: Phys. Rev. D 113, 089901 (2026), DOI: 10.1103/q488-83rh. The original article follows the erratum

Subjects: gr-qc astro-ph.HE

Created: 2026-04-04; Updated: 2026-04-07; Datestamp: 2026-04-07

Accurate and efficient modeling of the dynamics of binary BLACK HOLEs (BBHs) is crucial to their detection through gravitational waves (GWs), with LIGO/Virgo/KAGRA, and LISA in the future. Solving the dynamics of a BBH system with arbitrary parameters without simplifications (like orbit- or precession-averaging) in closed form is one of the most challenging problems for the GW community. One potential approach is using canonical perturbation theory which constructs perturbed action-angle variables from the unperturbed ones of an integrable Hamiltonian system. Having action-angle variables of the integrable 1.5 post-Newtonian (PN) BBH system is therefore imperative. In this paper, we continue the work initiated by two of us in arXiv:2012.06586, where we presented four out of five actions of a BBH system with arbitrary eccentricity, masses, and spins, at 1.5PN order. Here we compute the remaining fifth action using a novel method of extending the phase space by introducing unmeasurable phase space coordinates. We detail how to compute all the frequencies, and sketch how to explicitly transform from the action-angle variables to the usual positions and momenta. This analytically solves the dynamics at 1.5PN. This lays the groundwork to analytically solve the conservative dynamics of the BBH system with arbitrary masses, spins, and eccentricity, at higher PN order, by using canonical perturbation theory.

[abstract 20 / 40] (score: 2)
arXiv:2505.06654 [pdf, ps, other]

Title: A G_2G2-Holonomy Model for Late-Time Cosmic Acceleration in M-theory: Alleviating the Hubble Tension through Geometric Vacuum Energy

Authors: Moustafa Amin M. Radwan,

Comments: This version is withdrawn due to a fundamental revision of the geometric moduli stabilization parameters. The author has developed a more rigorous first-principles derivation from G2-holonomy manifolds that renders the phenomenological assumptions in this early version obsolete

Subjects: astro-ph.CO

Created: 2026-04-03; Updated: 2026-04-07; Datestamp: 2026-04-07

A framework is developed within an eleven-dimensional M-theory scenario where dynamical geometric moduli, originating from a $G_{\mathrm{2}}$-holonomy compactification, generate an evolving cosmological term, $Λ(z)$. This ``Geometric Vacuum Energy'' (GVE) is shown to be consistent across both cosmological and astrophysical scales. We demonstrate that a natural attractor solution alleviates the Hubble tension, yielding an inferred $H_0 \approx 69.4\ \mathrm{km}\,\mathrm{s}^{-1}\,\mathrm{Mpc}^{-1}$ and a suppressed structure growth parameter $S_8 \approx 0.67$, while remaining in excellent agreement with cosmic chronometer data ($χ^2/N \approx 0.44$). Its predictions in the strong-gravity regime profoundly strengthen the framework's self-consistency. We show that this model supports stable, hairy BLACK HOLE solutions whose existence conditions are congruent with the cosmological attractor ($Φ_{\text{horizon}} \leftrightarrow Φ_{\text{cosmology}}$). Furthermore, these objects exhibit a rich, falsifiable phenomenology, including (i) the definitive breaking of isospectrality in their gravitational-wave quasi-normal modes, (ii) a suppressed Integrated Sachs-Wolfe effect, and (iii) unique thermodynamic and electroMAGNETic accretion signatures. These interconnected findings highlight a pathway where a single, theoretically-motivated framework can naturally reconcile multiple observational puzzles.

[abstract 21 / 40] (score: 2)
arXiv:2507.07183 [pdf, ps, other]

Title: Mass Distribution of Binary Black Hole Mergers from Young and Old Dense Star Clusters

Authors: Claire S. Ye, Maya Fishbach, Kyle Kremer, Marta Reina-Campos,

Comments: 12 pages, 6 figures, 1 table. Published on ApJ. Data behind figures 3-6 can be found at https://doi.org/10.5281/zenodo.15832905

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

Created: 2026-04-06; Updated: 2026-04-07; Datestamp: 2026-04-07

Dense star clusters are thought to contribute significantly to the merger rates of stellar-mass binary BLACK HOLEs (BBHs) detected by the LIGO-Virgo-KAGRA collaboration. We combine $N$-body dynamic models of realistic dense star clusters with cluster formation histories to estimate the merger rate distribution as a function of primary mass for merging BBHs formed in these environments. It has been argued that dense star clusters -- most notably old globular clusters -- predominantly produce BBH mergers with primary masses $M_p\approx30\,M_{\odot}$. We show that dense star clusters forming at lower redshifts -- and thus having higher metallicities -- naturally produce lower-mass BBH mergers. We find that cluster BBH mergers span a wide range of primary mass, from about $6\,M_{\odot}$ to above $100\,M_{\odot}$, with a peak near $8\,M_{\odot}$, reproducing the overall merger rate distribution inferred from gravitational wave detections. Our results show that most low-mass BBH mergers (about $95\%$ with $M_p\lesssim 20\,M_{\odot}$) originate in metal-rich ($Z \sim Z_{\odot}$) dense star clusters, while more massive BBH mergers form predominately in metal-poor globular clusters. We also discuss the role of hierarchical mergers in shaping the BBH mass distribution. Gravitational wave detection of dynamically-formed low-mass BBH mergers -- potentially identifiable by features such as isotropic spin distributions -- may serve as probes of cluster formation histories in metal-rich environments at low redshifts.

[abstract 22 / 40] (score: 2)
arXiv:2510.04703 [pdf, ps, other]

Title: Testing BLACK HOLE metrics with binary BLACK HOLE inspirals

Authors: Zhe Zhao, Swarnim Shashank, Debtroy Das, Cosimo Bambi,

Comments: 28 pages, 1 figure. v2: refereed version

Subjects: gr-qc astro-ph.HE

Created: 2026-04-06; Updated: 2026-04-07; Datestamp: 2026-04-07

Gravitational wave astronomy has opened an unprecedented window onto tests of gravity and fundamental physics in the strong-field regime. In this study, we examine a series of well-motivated deviations from the classical Kerr solution of General Relativity and employ gravitational wave data to place constraints on possible deviations from the Kerr geometry. The method involves calculating the phase of gravitational waves using the effective one-body formalism and then applying the parameterized post-Einsteinian framework to constrain the parameters appearing in these scenarios beyond General Relativity. The effective one-body method, known for its capability to model complex gravitational waveforms, is used to compute the wave phase, and the post-Einsteinian framework allows for a flexible, model-independent approach to parameter estimation. We demonstrate that gravitational wave data provide evidence supporting the Kerr nature of BLACK HOLEs, showing no significant deviations from General Relativity, thereby affirming its validity within the current observational limits. We further assess the potential impact of orbital eccentricity and find that, within observationally allowed ranges, its contribution to the inferred deviations is subdominant. This work bridges theoretical waveform modeling with observational constraints, providing a pathway to test the no-hair theorem and probe the astrophysical viability of modified BLACK HOLEs.

[abstract 23 / 40] (score: 2)
arXiv:2511.21808 [pdf, ps, other]

Title: A Comprehensive Study of WIMP Models Explaining the FERMI-LAT Galactic Center Excess

Authors: Chuiyang Kong, Mattia Di Mauro,

Comments: 19 pages and 11 figures. Accepted by PRD. This version matches the published one

Subjects: hep-ph astro-ph.HE

Created: 2026-04-04; Updated: 2026-04-07; Datestamp: 2026-04-07

The Galactic Center excess (GCE) of GeV $γ$ rays may hint at DARK MATTER (DM), yet its origin remains debated. Motivated by this, we survey weakly interacting massive particle (WIMP) models that can fit the GCE while satisfying relic-density, direct-detection (DD), and indirect-detection (ID) bounds. We group candidates into hadronic (Higgs portals; simplified scalar/vector mediators), leptonic ($U(1)_{L_i-L_j}$), and mixed ($U(1)_{B-L}$, $Z$-portal) classes. Across all cases, present DD and dwarf-spheroidal $γ$-ray limits exclude wide regions, leaving mainly narrow resonant funnels with $m_{\rm DM}\!\simeq\! m_{\rm med}/2$ and portal couplings $\ll 1$. In hadronic setups, scalar and vector Higgs portals survive only in a thin strip near $m_h/2\simeq62.5$ GeV with portal couplings $\sim 10^{-4}$, while the Dirac Higgs and $Z$ portals are essentially excluded. The UV-complete vector Higgs portal retains resonant bands whose viable portal strength depends on the mixing angle. Simplified scalars allow small windows for complex-scalar or vector DM; Dirac DM is strongly disfavored, whereas a pseudoscalar with Dirac DM remains viable over a broader parameter range. For a simplified $Z'$ mediator, a pure vector coupling leaves only a marginal region, while pure axial is excluded by DD/ID bounds. In leptonic scenarios, inverse-Compton emission is essential: $L_μ-L_e$ (and, to a lesser extent, $B\!-\!L$) fits the GCE with near-thermal cross sections, while $L_μ-L_τ$ is disfavored. Overall, viable WIMP explanations are constrained to finely tuned resonant regime, with leptophilic vectors and pseudoscalar portals emerging as the most robust options.

[abstract 24 / 40] (score: 2)
arXiv:2511.23117 [pdf, ps, other]

Title: Probing Observable Features of Lorentz violation in Low-Energy Hořava Gravity with Accretion Disk Images of Black Hole

Authors: Meng-Die Zhao, Yu-Yan Wang, Ke-Jian He, Guo-Ping Li,

Comments: Published in Eur. Phys. J. C

Subjects: gr-qc

Created: 2026-04-04; Updated: 2026-04-07; Datestamp: 2026-04-07

In this paper, we study the observable signatures of Lorentz violation (LV) in low-energy Horava gravity by simulating the images and POLARIZATION features of rotating LV BLACK HOLEs using a backward ray-tracing method. Within a thin-disk accretion model and the ZAMO framework, we numerically solve the geodesics equation of photon and simulate the corresponding thin-disk images and POLARIZATION patterns. The results show that the LV parameter l strongly affects the inner shadow, brightness asymmetry, and POLARIZATION properties of the thin disk. The decrease of l leads to a more elliptical and untilted inner shadow, while increasing l produces a pronounced leftward D-shaped structure of the critical curve. In addition, the variation of l alters the distribution of polarized intensity and POLARIZATION direction, especially near the critical curve. Moreover, it also shows that a positive l enhances the BLACK HOLE's angular velocity, while a negative one suppresses it, indicating that the sign of l determines the trend direction of the LV effect. These findings suggest that future high-resolution EHT observations combining the thin-disk images and POLARIZATION patterns could provide valuable tests of the LV effect.

[abstract 25 / 40] (score: 2)
arXiv:2512.23060 [pdf, ps, other]

Title: Finding Quasars behind the Galactic Plane. IV. Candidate Selection from Chandra with Random Forest

Authors: Xu Zhang, Yanli Ai, Yanxia Zhang, Yuming Fu, Xue-Bing Wu, Zhiying Huo, Wenfeng Wen, Jiayuan Zhou, Dexuan Kong, Linfeng Zeng, Heng Wang,

Comments: ApJ accepted (2026)

Subjects: astro-ph.GA

Created: 2026-04-05; Updated: 2026-04-07; Datestamp: 2026-04-07

Quasar samples remain severely incomplete at low Galactic latitudes because of strong extinction and source confusion. We conduct a systematic search for QUASARs behind the Galactic plane using X-ray sources from the Chandra Source Catalog (CSC 2.1), combined with optical data from Gaia DR3 and mid-infrared data from CatWISE2020. Using spectroscopically confirmed QUASARs and stellar-type objects from data sets including DESI, SDSS, and LAMOST, we apply a Random Forest classifier to identify QUASAR candidates, with stellar contaminants suppressed using Gaia proper-motion constraints. Photometric redshifts are estimated for the candidates using a Random Forest regression model. Applying this framework to previously unclassified CSC sources, we identify 7570 QUASAR candidates, including 1060 Galactic Plane Quasar (GPQ) candidates at |b|<20°, of which 551 are high-confidence candidates. Relative to the previously known GPQ sample, our selected GPQs reach lower optical and X-ray fluxes, improving sensitivity to low-flux GPQs. In addition, both the GPQ candidates and known GPQs display harder X-ray spectra than the all-sky QUASAR sample, consistent with increased absorption through the Galactic plane. Pilot spectroscopy confirms two high-confidence GPQ candidates as QUASARs at spectroscopic redshifts of z=1.2582 and z=1.1313, and further spectroscopic follow-up of the GPQ sample is underway. This work substantially improves the census of GPQs and provides a valuable target sample for future spectroscopic follow-up, enabling the use of GPQs to refine the reference frames for astrometry and probe the Milky Way interstellar and circumgalactic media with the absorption features of GPQs.

[abstract 26 / 40] (score: 2)
arXiv:2601.19616 [pdf, ps, other]

Title: On the rarity of rocket-driven Penrose extraction in Kerr spacetime

Authors: An T. Le,

Comments: 20 pages, 6 figures, 8 tables, submitted to Physical Review D

Subjects: astro-ph.HE cs.SY eess.SY gr-qc physics.comp-ph

Created: 2026-04-05; Updated: 2026-04-07; Datestamp: 2026-04-07

We study rocket-driven Penrose extraction in the test-particle limit on a fixed Kerr background for equatorial prograde flybys under explicit steering prescriptions. A spacecraft ejects exhaust inside the ergosphere; when the exhaust attains negative Killing energy, the remaining spacecraft gains energy by 4-momentum conservation. Across 320{,}000 simulated trajectories spanning black-hole spin, exhaust velocity, and orbital parameters, extraction with escape is rare in broad parameter scans (at most ${\sim}1\%$) and requires high spin ($a/M\gtrsim 0.89$), highly RELATIVISTIC exhaust ($v_e\gtrsim 0.91c$), and finely tuned initial conditions. Under optimal tuning the success rate reaches ${\sim}70\%$ at $a/M = 0.95$. For representative escape trajectories, a single periapsis impulse is more propellant-efficient than the continuous-thrust controllers studied here. All quoted thresholds are empirical and specific to the orbit family, prior, and steering protocol studied.

[abstract 27 / 40] (score: 2)
arXiv:2602.04743 [pdf, ps, other]

Title: Relativistic and Recoil Corrections to Light-FERMIon Vacuum Polarization for Bound Systems of Spin-0, Spin-1/2, and Spin-1 Particles

Authors: G. S. Adkins, U. D. Jentschura,

Comments: 18 pages; RevTeX

Subjects: hep-ph

Created: 2026-04-06; Updated: 2026-04-07; Datestamp: 2026-04-07

In bound systems whose constituent particles are heavier than the electron, the dominant radiative correction to energy levels is given by light-fermion (electronic) vacuum POLARIZATION. In consequence, RELATIVISTIC and recoil corrections to the one-loop vacuum-POLARIZATION correction are phenomenologically relevant. Here, we generalize the treatment, previously accomplished for systems with orbiting muons, to bound systems of constituents with more general spins: spin-0, spin-1/2, and spin-1. We discuss the application of our more general expressions to various systems of interest, including spinless systems (pionium), muonic hydrogen and deuterium, and devote special attention to the excited non-S states of deuteronium, the bound system of a deuteron and its antiparticle. The obtained energy corrections are of order alpha^5*m_r, where alpha is the fine-structure constant and m_r is the reduced mass.

[abstract 28 / 40] (score: 2)
arXiv:2604.03370 [pdf, ps, other]

Title: Holes in the BH$^\star$? AGN signatures in the FUV spectrum of a black-hole dominated Little Red Dot at $z=7.04$

Authors: Xihan Ji, Gabriele Pezzulli, Francesco D'Eugenio, Roberto Maiolino, Stefano Carniani, Sandro Tacchella, Gareth Jones, Aaron Smith, Joris Witstok, Andrew C. Fabian, Sophia Geris, Anishya Harshan, Yuki Isobe, Lucy R. Ivey, Ignas Juodžbalis, Robert Pascalau, Jan Scholtz, Callum Witten,

Comments: 27 pages, 21 figures, to be submitted to MNRAS

Subjects: astro-ph.GA

Created: 2026-04-03; Updated: 2026-04-07; Datestamp: 2026-04-07

It has been suggested that "Little Red Dots" (LRDs) might be accreting BLACK HOLEs enshrouded by dense gas in a nearly closed geometry, which completely covers the central BLACK HOLE, leading to an atmosphere-like structure known as the "black-hole star" ($\rm BH^\star$). We test this scenario by analysing new JWST spectroscopy in the far ultraviolet (FUV, rest-frame) of the prototypical LRD Abell2744-QSO1, at $z=7.04$. We found the presence of broad Ly$α$ emission with an FWHM of $\sim 1000$ km/s, and detections of OI, CIV, and/or FeII emission lines. The NIRCam imaging and NIRSpec slit images indicate that the low-velocity component ($v\lesssim 200$ km/s) of Ly$α$ is likely spatially extended, but the high-velocity component ($v\gtrsim 200$ km/s) of Ly$α$ remains unresolved. Based on the multi-component kinematics and flux of Ly$α$ relative to Balmer lines, we conclude that the observed line profile is unlikely to be broadened by subsequent resonant scattering through the interstellar medium. This suggests that the high-velocity component of Ly$α$ originates in the broad-line region, although resonant scattering in the dense gas likely makes Ly$α$ broader than H$α$ as observed. The nebular features of this LRD indicate that there is at least one relatively optically thin direction where Ly$α$ can escape from the broad-line region (BLR). We also found indications that photons from the BLR are powering fluorescence of FeII and OI on a larger physical scale. The FUV features thus challenge the fully-covered geometry interpretation and suggest that there are "holes" in the $\rm BH^\star$, or the absorbing medium is simply clumpy.

[abstract 29 / 40] (score: 2)
arXiv:2604.03421 [pdf, ps, other]

Title: How nonlinear spectral back transfer limits the temporal coherency of zonal modes?

Authors: Rameswar Singh, P H Diamond,

Comments:

Subjects: physics.plasm-ph

Created: 2026-04-03; Updated: 2026-04-07; Datestamp: 2026-04-07

Zonal modes are central to MAGNETic confinement because their radial shears regulate turbulence and transport. While the generation of these flows is well understood, the mechanisms limiting their persistence in collisionless regimes remain unresolved. In this Letter, we demonstrate that nonlinear spectral back-transfer of free energy from zonal modes to turbulence sets the fundamental limit on the temporal coherency of the shearing field. Using gyrokinetic GENE simulations, we show that back-transfer is highly intermittent and occurs in bursts that co-exist with the zonal flow generation process. We find that negative triangularity (NT) plasmas exhibit significantly reduced back-transfer compared to positive triangularity (PT). This suppression increases the shear auto-coherence time $τ_{E}$ and the shearing Kubo number $K_{u}$, leading to more resilient and effective turbulence regulation despite lower absolute zonal kinetic energy. These results identify back-transfer as a key nonlinear damping mechanism and suggest that it must be explicitly treated in reduced models of drift-wave zonal-flow turbulence.

[abstract 30 / 40] (score: 2)
arXiv:2604.03545 [pdf, ps, other]

Title: Relaxed MAGNETohydrodynamics with cross-field flow

Authors: Arash Tavassoli, Stuart R. Hudson, Zhisong Qu, Matthew Hole,

Comments:

Subjects: physics.plasm-ph cs.NA math.NA

Created: 2026-04-04; Updated: 2026-04-07; Datestamp: 2026-04-07

The phase-space Lagrangian model of Dewar et al. (Phys. Plasmas 27, 062507, 2020) provides a framework for incorporating cross-field flow into relaxed equilibria while retaining ideal MAGNETohydrodynamics force balance. Here, we characterize the steady-state solution space and identify a solvability condition that couples the prescribed constrained flow to the geometry through the metric tensor. Using this condition, we construct equilibria in slab, cylindrical, and toroidal geometries. In toroidal geometry, the cross-field flow strongly correlates with MAGNETic-island structure: varying the rotation frequency modifies the dominant Fourier harmonic of the radial component of the MAGNETic field and can drive a transition from a primary (m = 1) island to secondary (m = 2) islands. In slab and cylindrical geometries, flow parameters weakly affect island width but strongly modify equilibrium profiles.

[abstract 31 / 40] (score: 2)
arXiv:2604.03579 [pdf, ps, other]

Title: Preferential Appearance of H$α$ Moreton Waves along Photospheric Magnetic Network Boundaries

Authors: C. H. Zhai, Y. W. Ni, J. H. Guo, P. F. Chen,

Comments: 12 pages, 4 pages, to appear in ApJ Letters

Subjects: astro-ph.SR

Created: 2026-04-04; Updated: 2026-04-07; Datestamp: 2026-04-07

Moreton waves are rare chromospheric signatures of large-scale coronal disturbances, often associated with big flares and coronal mass ejections (CMEs). Using high-cadence, full-disk H$α$ spectroscopic observations from CHASE, together with the EUV data from SDO/AIA and MAGNETograms from SDO/HMI, we analyzed a coronal EUV wave and an H$α$ Moreton wave event associated with a filament eruption on 2024 July 29. The Moreton wave fronts are roughly cospatial with the fast-mode coronal EUV wave fronts, which propagate with a speed of $\sim$600 km s$^{-1}$. By comparing the Moreton wave fronts with photospheric features, we found that they preferentially appear along photospheric supergranule boundaries characterized by 1600 Å bright ridges, concentrated MAGNETic fields, and convective downflows. It is shown that the H$α$ line profiles at the Moreton wave fronts are systematically redshifted. Gaussian fit yields a systematic downward Doppler velocity of 1.73 km s$^{-1}$. Using the bisector method, we further derived height-dependent Doppler velocities in the chromosphere. While there is an expected tendency for the downward velocity to decrease from 4.12 km s$^{-1}$ in the upper chromosphere to 1.60 km s$^{-1}$ in the lower chromosphere, it is intriguing to see an unexpected velocity enhancement in the lower chromosphere. We conjecture that coronal fast-mode MHD waves experience mode-conversion to slow-mode waves, which propagate along MAGNETic field lines of the MAGNETic canopy, forming preferential appearance of Moreton waves at MAGNETic networks, where the convective downflow contributes to the velocity enhancement in the lower chromosphere.

[abstract 32 / 40] (score: 2)
arXiv:2604.03769 [pdf, ps, other]

Title: Dispersion Measure Distribution of Unlocalized Fast Radio Bursts as a Probe of the Hubble Constant

Authors: Yang Liu, Jun-Jie Wei, Puxun Wu, Xue-Feng Wu,

Comments: 7 pages, 2 figures, 2 tables

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

Created: 2026-04-04; Updated: 2026-04-07; Datestamp: 2026-04-07

We present constraints on the Hubble constant ($H_0$) derived from the observed dispersion measure (DM) distribution of unlocalized fast radio bursts (FRBs). While localized FRBs with redshift measurements have been used to investigate the Hubble tension, their sample remains limited. Here we demonstrate that unlocalized FRBs -- which are far more numerous -- can independently constrain $H_0$ without requiring redshift information, as cosmic expansion imprints itself on their DM distribution. Analyzing a selected sample of 2124 unlocalized FRBs from the CHIME Catalog II, we obtain $H_0 = 73.8^{+14.0}_{-12.3}~\mathrm{km\,s^{-1}\,Mpc^{-1}}$ at the $1σ$ confidence level, corresponding to an uncertainty of about 18%. Breaking the degeneracy between $H_0$ and the characteristic cutoff energy $E_*$ of the FRB isotropic energy distribution would reduce this uncertainty to 9%. This work constitutes the first $H_0$ measurement derived solely from the DM distribution of unlocalized FRBs, highlighting their potential as a new cosmological probe. Future joint analyses with localized FRBs promise even tighter constraints.

[abstract 33 / 40] (score: 2)
arXiv:2604.04002 [pdf, ps, other]

Title: Features of spherical torus p 11B burning plasmas

Authors: Y. -K. M. Peng, A. Ishida, T. Sun, W. Liu, H. Huang, Y. Shi, B. Liu, D. Guo, Z. Li, D. Luo, X. Xiao, G. Zhao, M. Liu,

Comments:

Subjects: physics.plasm-ph

Created: 2026-04-05; Updated: 2026-04-07; Datestamp: 2026-04-07

A spherical torus (ST) p B11 plasma model that satisfies multi-MAGNETofluid force balance is developed, which includes small fractions of suprathermal ions with temperatures around 0.5 MeV and suprathermal electrons in the MeV range. Alongside the primary thermal plasma with ion temperatures exceeding 100 keV and densities above 10E20 m-3, these components enhance fusion reaction rates by leveraging the p B11 double-peak fusion cross section. Suprathermal ions and strong toroidal rotation driven by neutral beam injection have been observed in devices such as START, MAST, NSTX, Globus-M2, and ST40. Central-solenoid-free plasma initiation, ramp-up, and sustainment were tested on EXL-50 and replicated on EXL-50U with partial central induction, demonstrating efficient current drive and consistent with the multi-MAGNETofluid equilibrium model. Motivated by ENN's aneutronic commercial fusion roadmap, this paper presents a rotating, thermally un-equilibrated ST p B11 plasma with unique properties: fluid components experience separate balance under centripetal, electrostatic, and Lorentz forces with common electric and MAGNETic fields, leading to large rotation speed differences between thermal boron ions and suprathermal protons; a large outboard region with MAGNETic well and omnigeneity is created, affecting neoclassical transport and gradient-driven turbulence; suprathermal charged particles can extend beyond the last closed flux surface and be limited by plasma-facing components, influencing recycling and pedestal conditions; and the superposition of these plasma components modifies sources and sinks of free energy, prompting renewed evaluation of stability, turbulence, transport, heating, current drive, and flux diffusion. Challenges and opportunities for sustained burn are discussed for a compact p B11 ST with 1.4-meter major radius, 13-MA current, and 3-T toroidal field.

[abstract 34 / 40] (score: 2)
arXiv:2604.04068 [pdf, ps, other]

Title: The Distribution of Cosmic Ray Electrons in Star-Forming Galaxies

Authors: Anvar Shukurov, Charles Jose,

Comments: 18 pages, 4 figures, submitted as research topic `The Role of Plasmas and Cosmic Magnetism in High-energy Astroparticle Physics' to Frontiers in Astronomy and Space Sciences

Subjects: astro-ph.GA

Created: 2026-04-05; Updated: 2026-04-07; Datestamp: 2026-04-07

We derive explicit, algebraic expressions for the steady-state number density of COSMIC RAY electrons as a function of position and energy using Green's function of the diffusion equation with energy losses for an axisymmetric distributions of the particle sources in the galactocentric radius $r$ and distance to the mid-plane $z$. The solution is obtained for a Gaussian distribution of the particle sources in $r$ and $z$ but we show that it can be used for an arbitrary spatial distribution of the sources. The accuracy of our results is about 10% or better in a wide ranges of $r$ and $z$ and particle energies. These solutions can be used in the interpretation of radio astronomical observations of galaxies, particularly in the studies of the radio luminosities for large galaxy samples, and represent a physically justifiable and efficient alternative to the assumption of the energy equipartition between COSMIC RAYs and interstellar MAGNETic fields.

[abstract 35 / 40] (score: 2)
arXiv:2604.04546 [pdf, ps, other]

Title: Inference of recoil kicks from binary BLACK HOLE mergers up to GWTC--4 and their astrophysical implications

Authors: Tousif Islam,

Comments: 13 pages, 8 figures

Subjects: astro-ph.HE gr-qc

Created: 2026-04-06; Updated: 2026-04-07; Datestamp: 2026-04-07

We infer recoil (kick) velocities for all binary BLACK HOLE merger events reported up to the GWTC--4 catalog, together with candidate intermediate-mass BLACK HOLE events. We obtain informative kick constraints for GW231028\_153006 ($839^{+1018}_{-681}\,\mathrm{km\,s^{-1}}$) and GW231123\_135430 ($974^{+944}_{-760}\,\mathrm{km\,s^{-1}}$). Additionally, we compute recoil velocities for recently reported events from the ongoing fourth observing run: GW241011\_233834, GW241110\_124123, and GW250114\_082203, obtaining $v_{\rm kick} = 974^{+555}_{-466}\,\mathrm{km\,s^{-1}}$, $394^{+582}_{-207}\,\mathrm{km\,s^{-1}}$, and $115^{+301}_{-95}\,\mathrm{km\,s^{-1}}$, respectively. The remnant of GW241011\_233834 is therefore inferred to have one of the largest recoil velocities among currently known events. We find that present recoil kick constraints are driven primarily by measurements of the mass ratio and spin magnitudes, while the contribution from spin orientation angles remains subdominant in most cases. We estimate typical retention probabilities of the remnant BLACK HOLEs in GWTC catalogs to be $\sim 1$--$5\%$ for globular clusters, $\sim 15$--$30\%$ for nuclear star clusters, $\sim 5$--$40\%$ for dwarf galaxies, and $\sim 70$--$100\%$ for elliptical galaxies. We further show that, even for remnants retained in globular clusters, recoil-induced spatial displacements from the cluster core are often significant, which can substantially suppress the chances of hierarchical mergers. We find that the probability for a GWTC merger remnant to participate in hierarchical mergers is $\sim 0.1$--$1\%$ in globular clusters and $\sim 1$--$15\%$ in nuclear star clusters.

[abstract 36 / 40] (score: 2)
arXiv:2604.04559 [pdf, ps, other]

Title: Cavitation-bubble Interaction with an Initially Perturbed Free Surface

Authors: Jingyu Gu, Zirui Liu, A-Man Zhang, Shuai Li,

Comments:

Subjects: physics.flu-dyn

Created: 2026-04-06; Updated: 2026-04-07; Datestamp: 2026-04-07

The interaction of a spark-generated cavitation bubble with an initially perturbed free surface is investigated experimentally, numerically, and analytically. By exploiting contact-line pinning, we accurately prescribe an initial meniscus with a thin, hydrophilic-coated rod inserted into the liquid. A pronounced surface cavity, driven by the oscillating bubble, forms and penetrates downward to a scale comparable to the bubble itself. The coupled cavity-bubble system exhibits two distinct regimes -- coalescence and non-coalescence -- separated by a critical condition governed by the non-dimensional stand-off parameter $γ$ and the initial meniscus height $h_m$. In the non-coalescence regime, the cavity evolves through inception, expansion, and rebound/JETting. The maximum cavity length $h_c$ follows a power-law scaling $h_c\proptoγ^α$ with $α=-2.7$ (experiments) and $α=-2.6$ (simulations) for $1.5\lesssimγ\lesssim3$, where inertia dominates. Deviations emerge for $γ\lesssim1.5$ (strong nonlinearity) and $γ\gtrsim3$ (surface tension and viscosity become noticeable). An analytical model based on the Rayleigh-Plesset equation combined with nonlinear Rayleigh-Taylor instability theory captures the trend and confirms that $h_m$ plays only a secondary role relative to $γ$. In the coalescence regime, atmospheric air vents into the bubble through the merged cavity, weakening the collapse intensity and reducing the associated pressure peak. We also examine air/liquid compressibility and boundary layer effects, whose significance grows as $γ$ decreases. These findings are relevant to surface-JETting technologies, cavitation-erosion mitigation, and underwater-noise suppression.

[abstract 37 / 40] (score: 2)
arXiv:2604.04568 [pdf, ps, other]

Title: Stationary Einstein-vector-Gauss-Bonnet BLACK HOLEs

Authors: Burkhard Kleihaus, Jutta Kunz,

Comments: 18 pages, 10 figures

Subjects: gr-qc

Created: 2026-04-06; Updated: 2026-04-07; Datestamp: 2026-04-07

We study spontaneously vectorized BLACK HOLEs in Einstein-vector-Gauss-Bonnet theory with a quadratic coupling function. Besides the static, spherically symmetric BLACK HOLEs carrying an electric charge, there are uncharged static, axially symmetric BLACK HOLEs that possess a MAGNETic dipole moment. Both types possess radial excitations. The MAGNETic BLACK HOLEs are prolate. They are hotter than the Schwarzschild BLACK HOLEs and possess lower free energy. The domain of existence of the rotating vectorized BLACK HOLEs is bounded by the Kerr BLACK HOLEs, the spherically and axially symmetric static BLACK HOLEs, and the critical solutions.

[abstract 38 / 40] (score: 2)
arXiv:2604.04577 [pdf, ps, other]

Title: From NVSS to RACS: Identifying truly Compact and Steep spectrum Radio sources

Authors: Rajat Shinde, Yogesh Maan, Apurba Bera,

Comments: 15 pages, 6 figures

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

Created: 2026-04-06; Updated: 2026-04-07; Datestamp: 2026-04-07

Compact, steep-spectrum radio sources are key tracers of exotic astrophysical objects such as pulsars and high-redshift RADIO GALAXies. All-sky radio surveys at different frequencies, like the TIFR-GMRT Sky Survey (TGSS) and the NRAO VLA Sky Survey (NVSS), have been usually exploited to identify such tracers. The more recent imaging survey, Rapid ASKAP Continuum Survey (RACS), with higher angular resolution and better sensitivity offers an avenue for a far better identification and characterization of compact, steep-spectrum sources. In this work, using publicly available RACS images at 887 MHz and 1.4 GHz, we present an image-domain characterization of 171 compact source candidates between declinations -40 degrees and +41 degrees, that were detected and appeared compact at 147 MHz in TGSS but not detected at 1.4 GHz in NVSS. Our detailed characterization resulted in the identification of 66 compact sources, 87 non-compact, diffuse or resolved sources, and 18 sources that are not detected in either of the RACS or NVSS images, implying spectral indices steeper than -2.0. Out of the 66 compact sources, 34 have spectral indices steeper than -1.5. We demonstrate that a large fraction of the sources in our sample were earlier not detected and resulted in incorrect spectral index limits due to poor imaging quality of NVSS in the Galactic plane. We present the spectral indices and morphological classification of all the sources in our sample and discuss their usefulness in identifying and studying interesting sources such as radio pulsars, high-redshift RADIO GALAXies, and other extragalactic sources.

[abstract 39 / 40] (score: 2)
arXiv:2604.04798 [pdf, ps, other]

Title: Flare Impulsive-phase Durations

Authors: Brian R. Dennis, Hugh Hudson, Joel Allred,

Comments:

Subjects: astro-ph.SR

Created: 2026-04-06; Updated: 2026-04-07; Datestamp: 2026-04-07

This Research Note is in response to the recent paper by S. M. Perriyil et al. (2026). They provide measurements of the time delay (delta t) between the hard X-ray and soft X-ray peak times for 96 flares observed with RHESSI and GOES. These delays are found to be dependent on the length of 9 the MAGNETic loop(s) joining the HXR footpoints seen in RHESSI images. We offer a possible explanation for this coincidence in terms of the duration of the electron beam heating, commonly inferred from the duration of the HXR emission, and the time taken for heated plasma to rise to the loop top as inferred in this paper from delta t. We suggest that the particle acceleration occurs at or near the top of the loop(s) and that it is quenched by the increase in density as the heated plasma reaches the acceleration site.

[abstract 40 / 40] (score: 2)
arXiv:2604.04867 [pdf, ps, other]

Title: Measurement of the galaxy-velocity power spectrum of DESI tracers with the kinematic Sunyaev-Zeldovich effect using DESI DR2 and ACT DR6

Authors: Edmond Chaussidon, Selim C. Hotinli, Simone Ferraro, Kendrick Smith, Xinyi Chen, J. Aguilar, S. Ahlen, D. Bianchi, D. Brooks, T. Claybaugh, A. Cuceu, A. de la Macorra, B. Dey, P. Doel, A. Font-Ribera, J. E. Forero-Romero, E. Gaztañaga, S. Gontcho A Gontcho, G. Gutierrez, J. Guy, H. K. Herrera-Alcantar, K. Honscheid, C. Howlett, D. Huterer, M. Ishak, R. Joyce, D. Kirkby, A. Kremin, O. Lahav, M. Landriau, L. Le Guillou, M. Manera, A. Meisner, R. Miquel, S. Nadathur, J. A. Newman, N. Palanque-Delabrouille, W. J. Percival, F. Prada, I. Pérez-Ràfols, G. Rossi, L. Samushia, E. Sanchez, D. Schlegel, M. Schubnell, H. Seo, J. Silber, D. Sprayberry, G. Tarlé, B. A. Weaver, C. Yèche, R. Zhou,

Comments:

Subjects: astro-ph.CO

Created: 2026-04-06; Updated: 2026-04-07; Datestamp: 2026-04-07

Joint analyses of high-resolution CMB temperature maps with galaxy surveys provide a unique way to reconstruct the radial velocity field of the underlying matter distribution via the kinematic Sunyaev-Zeldovich (kSZ) effect. Using data from the Atacama Cosmology Telescope (ACT) DR6 and the Dark Energy Spectroscopic Instrument (DESI) DR2, we present radial velocity reconstructions for luminous red galaxies (LRGs), emission-line galaxies (ELGs), and QUASARs (QSOs). Leveraging the spectroscopic data, we are able to reliably model the foreground contamination and report a negligible impact on our main observables. We detect the velocity-galaxy cross-correlation at $17.0σ$ for LRGs, and for the first time, at $8.3σ$ for ELGs and $6.8σ$ for QSOs. We further report the first detection of the velocity-velocity correlation using LRGs at $3.1σ$, as well as the highest cumulative detection of the kSZ effect to date at $20.8 σ$. Similarly to previous results, we find a lower amplitude of the kSZ signal compared to our fiducial halo model prediction and electron profile assuming a Battaglia profile. Combining these new observables, we obtain constraints on local-type primordial non-Gaussianity (PNG): $f_{\rm NL}^{\rm loc} = 15.9_{-34.4}^{+34.6}$ at 68\% confidence, which represents the tightest constraint to date derived from the velocity field. The measurements presented here already exhibit lower noise on a per-mode basis than the galaxy auto-correlation on the largest scales, $k<0.004~\rm{Mpc^{-1}}$, highlighting the key role these observables will play in the context of future CMB experiments such as the Simons Observatory.