Current date: 2026-04-21

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Datestamp limit: 2026-04-21 (0 days ago)

Created/updated limit: 2026-04-14 (7 days ago)

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OAI-PMH request: http://export.arxiv.org/oai2?verb=ListRecords&from=2026-04-21&until=2026-04-21&set=physics&metadataPrefix=arXiv

Scoring abstracts

Number of records retrieved: 234

Keyword score statistics

score 10 -- 1 abstracts

score 8 -- 1 abstracts

score 7 -- 1 abstracts

score 6 -- 3 abstracts

score 4 -- 4 abstracts

score 3 -- 2 abstracts

score 2 -- 4 abstracts

in total -- 16 abstracts

Articles that appeared on 2026-04-21

[abstract 1 / 16] Wow! (score: 10)
arXiv:2604.16688 [pdf, ps, other]

Title: Persistence of the Millihertz X-ray Quasi-Periodic Oscillation in the Active Galactic Nucleus 1ES 1927+654

Authors: Megan Masterson, Erin Kara, William N. Alston, Riccardo Arcodia, Mitchell Begelman, Joheen Chakraborty, Andrew C. Fabian, Margherita Giustini, Adam Ingram, Peter Kosec, Sibasish Laha, Giovanni Miniutti, Christos Panagiotou, Ciro Pinto, Claudio Ricci, Dev R. Sadaula, Onic I. Shuvo, Benny Trakhtenbrot,

Comments: Submitted to ApJ, 21 pages, 11 figures

Subjects: astro-ph.HE

Created: 2026-04-17; Updated: 2026-04-21; Datestamp: 2026-04-21

1ES 1927+654 is an extreme ACTIVE GALACTIC NUCLEus (AGN) that has defied our canonical expectations for how AGN appear across the electroMAGNETic spectrum and how they vary on short timescales. In 2022, this source began showing a X-ray quasi-periodic oscillation (QPO) at mHz frequencies, along with a newly launched radio JET. Unlike the handful of other known AGN QPOs, the QPO in 1ES 1927+654 showed a significant frequency evolution, spanning from 0.9-2.4 mHz from 2022-2024. In this work, we present the last 1.5 years of monitoring with XMM-Newton (250 ks) up to January 2026, which reveals that the QPO persists but has plateaued at a constant frequency of approximately 2.5 mHz. We perform detailed spectral-timing analyses on this exquisite dataset, consisting of over 900 QPO cycles, more than any AGN QPO to date. Our main findings are: (1) the stacked XMM-Newton power spectra shows no significant second harmonic, (2) a soft (reverberation-like) lag is observed at all frequencies and remains remarkably stable even as the QPO frequency evolved from 2022-2024, and (3) extreme X-ray jumps on the QPO period (up to ~80% baseline flux) persist to present day with a remarkably stable dip-rise-fall pattern. Finally, we also detect the first AGN QPO in NUSTAR observations, which is present from 2023 to 2026 at frequencies consistent with the XMM-Newton detections. While we explore models for eclipses and coupled disk-corona behavior to simultaneously explain the lags, dips, and QPO, these new observations strain such models.

[abstract 2 / 16] Wow! (score: 8)
arXiv:2601.21411 [pdf, ps, other]

Title: TeV Gamma-Rays from the Low-Luminosity Active Galactic Nucleus NGC 4278: Implications for the Diffuse Neutrino Background

Authors: Chengchao Yuan, Ruo-Yu Liu,

Comments: 11 pages, 4 figures, 2 tables. Updated the diffuse neutrino intensity. Accepted for publication in ApJ

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

Created: 2026-04-18; Updated: 2026-04-21; Datestamp: 2026-04-21

This work investigates the origin of the TeV emission detected by the Large High Altitude Air Shower Observatory (LHAASO) from NGC~4278, a galaxy hosting a low-luminosity ACTIVE GALACTIC NUCLEus (LLAGN). Considering two plausible scenarios, AGN JETs and winds, we model the X-ray, GeV, and TeV emission during both TeV-low (quasi-quiet) and TeV-high (active) states. The spectral energy distributions can be explained either by single-zone leptonic emission from moderately RELATIVISTIC JETs or by lepto-hadronic emission from sub-RELATIVISTIC winds. The best-fit parameters suggest that the transition from the quasi-quiet to the active state may be driven jointly by an enhanced accretion rate and the JET deceleration or wind expansion. We further show that future MeV and very-high-energy $γ$-ray observations can discriminate between the leptonic and lepto-hadronic scenarios. Although the neutrino flux from NGC 4278 predicted by the wind model is too low to be detected with current neutrino observatories, a lepto-hadronic wind scenario can account for the PeV diffuse neutrino background when adopting a local LLAGN density ($n_{\rm L,0}$) corrected for the TeV duty cycle ($ΔT_{\rm TeV}/T$, the fraction of a LLAGN's lifetime spent in a TeV-emitting phase), $n_{\rm L,0}(ΔT_{\rm TeV}/T) \sim 10^{-5}~\rm Mpc^{-3}$, as inferred from the LHAASO detection.

[abstract 3 / 16] Wow! (score: 7)
arXiv:2507.13436 [pdf, ps, other]

Title: The role of three-dimensional effects on ion injection and acceleration in perpendicular shocks

Authors: Luca Orusa, Damiano Caprioli, Lorenzo Sironi, Anatoly Spitkovsky,

Comments: 12 pages, 8 figures. Few comments and clarifications added, results unchanged. Matches version published by ApJ

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

Created: 2026-04-17; Updated: 2026-04-21; Datestamp: 2026-04-21

Understanding the conditions that enable particle acceleration at non-RELATIVISTIC collisionless shocks is essential to unveil the origin of COSMIC RAYs. We employ 2D and 3D hybrid simulations (with kinetic ions and fluid electrons) to explore particle acceleration and MAGNETic field amplification in non-RELATIVISTIC perpendicular shocks, focusing on the role of shock drift acceleration and its dependence on the shock Mach number. We perform an analysis of the ion injection process and demonstrate why efficient acceleration is only observed in 3D. In particular, we show that ion injection critically depends on the "porosity" of the MAGNETic turbulence in the downstream region near the shock, a property describing how easily the post-shock region allows particles to traverse it and return upstream without being trapped. This effect can only be properly captured in 3D. Additionally, we explore the impact of numerical resolution on ion energization, highlighting how resolving small-scale turbulence -- on scales below the thermal ion gyroradius -- is essential for accurately modeling particle injection. Overall, our results emphasize the necessity of high-resolution 3D simulations to capture the fundamental microphysics driving particle acceleration at perpendicular shocks.

[abstract 4 / 16] Yes (score: 6)
arXiv:2405.11028 [pdf, ps, other]

Title: Simulations of Interacting Binary Systems -- Pathways to Radio Bright GRB Progenitors

Authors: Angel Hernandez, Roseanne M. Cheng, Nicole M. Lloyd-Ronning, Carl E. Fields,

Comments: Accepted to ApJ, significantly updated from original version

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

Created: 2026-04-17; Updated: 2026-04-21; Datestamp: 2026-04-21

Although the association of GAMMA-RAY BURSTs with massive stellar death is on firm footing, the nature of the progenitor system and the key ingredients required for a massive star to produce a GAMMA-RAY BURST remain open questions. Here, we investigate the evolution of a $15-25M_\odot$ massive star with a $10-15 M_\odot$ BLACK HOLE using the MESA stellar evolution code. We quantify companion-influenced angular momentum evolution over stellar lifetime for orbital periods where tides are significant, varying stellar and BLACK HOLE masses, initial stellar spin, and accretion and dynamo prescriptions while tracking mass loss and angular momentum. Final spin is set by tidal torques versus stellar winds. For binaries that initially avoid Roche lobe overflow, tides can spin up the star, but late stage expansion can drive tidal stripping; associated mass and angular momentum loss can suppress spin up. We find that massive star BLACK HOLE binaries at comparable mass ratios may be potential GRB progenitors for short orbital periods ($\sim 20 - 5\times10^2$ days) and long orbital periods ($\sim 2\times10^3 - 4\times10^3$ days), where our suite of lifetime simulations reveals a favored parameter space with negligible mass loss and enough spin angular momentum to power a GRB JET. For initially non-rotating stars, this provides a lower limit on final spin above a threshold estimate consistent with forming a post collapse BLACK HOLE mass of $5-10M_\odot$ with spin parameter $\geq 0.5$. For initially rapidly rotating stars, tidal interactions may sustain high spin when mass loss is negligible because the binary is not tidally synchronized.

[abstract 5 / 16] Yes (score: 6)
arXiv:2604.16605 [pdf, ps, other]

Title: Possible fractal nature of accretion flows in MAD and SANE simulations: Implications to GRS 1915+105

Authors: Srishty Aggarwal, Rohan Raha, Mayank Pathak, Banibrata Mukhopadhyay,

Comments: 18 pages, 10 figures. Comments are welcome

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

Created: 2026-04-17; Updated: 2026-04-21; Datestamp: 2026-04-21

The general RELATIVISTIC MAGNETohydrodynamic (GRMHD) simulations are widely used to study accretion disk and JET dynamics around a BLACK HOLE. Despite strong observational evidences for intrinsically nonlinear behavior, the interpretations of GRMHD simulation results, more precisely the underlying timeseries, have not been well-explored by nonlinear timeseries analysis. In this work, we characterize the JET and disk dynamics of different GRMHD simulated flows using the nonlinear timeseries analysis. As diagnostic tools, we consider Higuchi fractal dimension (HFD), Hurst Index (H) and spectral slope. We implement them for two model disk frameworks: MAGNETically arrested disk (MAD) and standard and normal evolution (SANE), across a range of BLACK HOLE spins with the Kerr parameter spanning from -0.9375 to 0.9375. We simulate the disk/JET systems by two well-documented codes: HARMPI and BHAC, and obtain, respectively, low and high temporally resolved timeseries data. For both JET and disk dynamics, MADs are characterized by higher HFD, lower H and flatter spectral slopes than SANEs. High HFD in MAD could be due to its intermittent variability and indicates that it has lesser long-range temporal correlations than SANE. Moreover, HFD in MAD decreases with spin magnitude owing to increase in collimated, hence ordered, JETs. However, in SANE, it increases with spin for positive ones due to interplay of winds and JETs. Extending our analysis to observations, we attempt to segregate the classes of BLACK HOLE: GRS 1915+105, into MAD- and SANE-like clusters based on their spectral properties extracted from X-ray data. The mean HFD of MAD-like cluster is higher than SANE-like cluster, thus, corroborating with the simulation results. Our work highlights the role of nonlinear timeseries analysis to understand the underlying dynamics of accretion flows and their connection to MAGNETic regulation.

[abstract 6 / 16] Yes (score: 6)
arXiv:2604.16768 [pdf, ps, other]

Title: GeV emission in the region of Vela: a new view of the SUPERNOVA remnant

Authors: Miguel Araya, Santiago Ramírez, Diego Bueso, Braulio J. Solano-Rojas,

Comments: 9 pages, 3 figures. To appear in A&A. Comments welcome!

Subjects: astro-ph.HE

Created: 2026-04-18; Updated: 2026-04-21; Datestamp: 2026-04-21

The Vela SUPERNOVA remnant (SNR), G263.9-3.3, and its pulsar wind nebula (PWN), Vela X, is one of the closest such systems, and it has been studied using observations across the electroMAGNETic spectrum. SNRs are known sources of gamma rays with energies from GeV to the TeV range. In the GeV band, a cluster of cataloged unidentified FERMI-LAT point sources are found across the large angular extension of the Vela SNR. We aim to search for a high-energy signature associated to the SNR. We applied two independent machine learning algorithms to classify unidentified point sources in the Vela region by comparing their properties to those of known populations of FERMI pulsars and ACTIVE GALACTIC NUCLEi. We analyzed LAT data and modeled the spectrum of any emission attributable to Vela using leptonic and hadronic processes typical of SNRs. We find that most of the "point sources" cataloged within the extent of Vela do not share characteristics with those of the two most common FERMI point-like source populations and that even after the emission attributed to these "point sources" is subtracted, considerable residual emission is seen throughout Vela. Morphologically, most of the GeV emission is found within the shell of the SNR. We conclude that the majority of the cataloged point sources are likely spurious, and the GeV gamma rays come from an extended source, which we argue is the counterpart of the Vela SNR. Adopting a simple morphology given by a uniform disk for the emission the resulting extension is 6.5 deg. The northeastern portion of G263.9-3.3, where the ambient density is thought to be higher, is brighter in gamma rays than the south and west. The spectrum of the emission is best fit with a hadronic model. These facts make the hadronic origin for the gamma rays more likely.

[abstract 7 / 16] Yes (score: 4)
arXiv:2510.21104 [pdf, ps, other]

Title: Observation of In-ice Askaryan Radiation from High-Energy Cosmic Rays

Authors: ARA Collaboration, N. Alden, S. Ali, P. Allison, S. Archambault, J. J. Beatty, D. Z. Besson, A. Bishop, P. Chen, Y. C. Chen, Y. -C. Chen, S. Chiche, B. A. Clark, A. Connolly, K. Couberly, L. Cremonesi, A. Cummings, P. Dasgupta, R. Debolt, S. de Kockere, K. D. de Vries, C. Deaconu, M. A. DuVernois, J. Flaherty, E. Friedman, R. Gaior, P. Giri, J. Hanson, N. Harty, K. D. Hoffman, M. -H. Huang, K. Hughes, A. Ishihara, A. Karle, J. L. Kelley, K. -C. Kim, M. -C. Kim, I. Kravchenko, R. Krebs, C. Y. Kuo, K. Kurusu, U. A. Latif, C. H. Liu, T. C. Liu, W. Luszczak, A. Machtay, K. Mase, M. S. Muzio, J. Nam, R. J. Nichol, A. Novikov, A. Nozdrina, E. Oberla, C. W. Pai, Y. Pan, C. Pfendner, N. Punsuebsay, J. Roth, A. Salcedo-Gomez, D. Seckel, M. F. H. Seikh, Y. -S. Shiao, J. Stethem, S. C. Su, S. Toscano, J. Torres, J. Touart, N. van Eijndhoven, A. Vieregg, M. Vilarino Fostier, M. -Z. Wang, S. -H. Wang, P. Windischhofer, S. A. Wissel, C. Xie, S. Yoshida, R. Young,

Comments:

Subjects: astro-ph.HE

Created: 2026-04-17; Updated: 2026-04-21; Datestamp: 2026-04-21

We present the first experimental evidence for in-ice Askaryan radiation -- coherent charge-excess radio emission -- from high-energy particle cascades developing in the Antarctic ice sheet. In 208 days of data recorded with the phased-array instrument of the Askaryan Radio Array, a previous analysis has incidentally identified 13 events with impulsive radiofrequency signals originating from below the ice surface. We here present a detailed reanalysis of these events. The observed event rate, radiation arrival directions, signal shape, spectral content, and electric field POLARIZATION are consistent with in-ice Askaryan radiation from COSMIC RAY air shower cores impacting the ice sheet. For the brightest events, the angular radiation pattern favors an extended cascade-like emitter over a pointlike source. An origin from the geoMAGNETic separation of charges in COSMIC RAY air showers is disfavored by the arrival directions and POLARIZATION. Considering the arrival angles, timing properties, and the impulsive nature of the passing events, the event rate is inconsistent with the estimation of the combined background from thermal noise events and on-surface events at the level of $5.1\,σ$.

[abstract 8 / 16] Yes (score: 4)
arXiv:2602.24255 [pdf, ps, other]

Title: Direct VLBI Detection of Interstellar Turbulence Imprint on a Quasar: TXS 2005+403

Authors: Alexander Plavin, Alexander Pushkarev, Yuri Kovalev,

Comments: 5 pages, 3 figures, 1 table; accepted to ApJL

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

Created: 2026-04-17; Updated: 2026-04-21; Datestamp: 2026-04-21

We report the first unambiguous detection of refractive substructure in an ACTIVE GALACTIC NUCLEus (AGN) using ground-based Very Long Baseline Interferometry (VLBI). Our analysis of TXS 2005+403 - observed at 1-5 GHz along a line of sight through the Cygnus region - reveals clear signatures of turbulence-induced substructure on long baselines that cannot be explained by the smooth scatter-broadened profile from diffractive effects alone. This signal persists across multiple observations spanning 2010-2019, demonstrating stable scattering properties along this line of sight. The combination of high flux density, compact intrinsic structure, and strong scattering establishes TXS 2005+403 as an exceptional laboratory for probing Galactic turbulence. This detection demonstrates that AGNs can serve as cosmic lighthouses illuminating interstellar plasma across the sky, complementing pulsar scintillation studies and informing scattering mitigation for millimeter-wavelength imaging of Sagittarius A*.

[abstract 9 / 16] Yes (score: 4)
arXiv:2603.20663 [pdf, ps, other]

Title: FAST Polarization Catalog of FRB 20240114A

Authors: Tian-Cong Wang, Jun-Shuo Zhang, Xiao-Hui Liu, Wei-Yang Wang, Pei Wang, He Gao, Di Li, Bing Zhang, Wei-Wei Zhu, Jin-Lin Han, Ke-Jia Lee, Ye Li, Dengke Zhou, Wan-Jin Lu, Jintao Xie, Jianhua Fang, Jin-Huang Cao, Chen-Chen Miao, Yu-Hao Zhu, Yunchuan Chen, Si-Lu Xu, Huaxi Chen, Xiao-Feng Cheng, Qin Wu, Shuo Cao, Long-Xuan Zhang, Shi-Yan Tian, Yong-Kun Zhang, Yi Feng, De-Jiang Zhou, Jia-Rui Niu, Heng Xu, Xuelei Chen, Yuan-Pei Yang, Dong-Zi Li, Fa-Yin Wang, Chao-Wei Tsai, Wen-Fei Yu, Chen-Hui Niu, Jia-Wei Luo, Rui Luo, E. Gugercinoglu, Zi-Wei Wu, Chun-Feng Zhang, Xiang-Lei Chen, Shuai Feng, Xiang-Han Cui, Qing-Yue Qu, Yuan-Hong Qu, Bo-Jun Wang, Yi-Dan Wang, Lin Lin, Ai-Yuan Yang, Yuan-Chuan Zou, Yu-Xiang Huang, Wei-Cong Jing, Jian Li, Yong-Feng Huang, Su-Ming Weng, Shi-Han Yew, Xue-Feng Wu, Lei Zhang, Ru-Shuang Zhao,

Comments:

Subjects: astro-ph.HE

Created: 2026-04-18; Updated: 2026-04-21; Datestamp: 2026-04-21

Polarization measurements of fast radio bursts (FRBs) probe the MAGNETized plasma surrounding their central engines. FRB~20240114A is an exceptionally active repeating source, with 17,356 bursts detected between 2024 January 28 and 2025 May 30 by FAST, enabling time-resolved polarimetric studies. In this work, we present a polarimetric catalog of 6,131 bright bursts (with a signal-to-noise ratio S/N $\geq$ 20, 35.3% of the total sample), including arrival time (MJD$_{\text{topo}}$), dispersion measure (DM), burst width (W$_{\text{eff}}$), bandwidth, Faraday rotation measure (RM), linear and circular POLARIZATION degrees (DOL, DOC), and intrinsic POLARIZATION angle (PA$_0$). We detect a clear temporal evolution of RM: after an initial stable phase, it decreases linearly by $\sim$200 $\rm rad\ m^{-2}$ over 200 days, forming a bimodal distribution, whereas DM remains stable at 528.9 $\rm pc\ cm^{-3}$. The linear POLARIZATION fraction is generally high, with the 3$σ$ lower bound around 76%, while circular POLARIZATION is low, with 1,157 of 17,356 bursts (6.67%) having DOC $\geq$10%. We perform a power-law fit between $|\textrm{V}|$/I and $|\textrm{RM}|$, which yields an index of $-2.98 \pm 0.80$. It is found that the combined 2D distribution of L/I versus V/I remains stable, implying that the emission mechanism is largely invariant. Our PA$_0$ measurements show a broad, non-uniform distribution, implying a complex emission geometry. These results suggest that FRB~20240114A resides in a dynamically evolving MAGNETo-ionic environment. This catalog provides a foundation for studies of repeating FRB progenitors and their environments.

[abstract 10 / 16] Yes (score: 4)
arXiv:2604.16595 [pdf, ps, other]

Title: On the Gamma-ray Efficiency of Superluminous Supernovae: Potential Detections and Population-Level Constraints

Authors: Milena Crnogorčević, Tim Linden, Ariel Goobar, Brian D. Metzger,

Comments: 18 pages (excl. references and appendix), 8 figures, 2 tables. Comments welcome!

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

Created: 2026-04-17; Updated: 2026-04-21; Datestamp: 2026-04-21

Superluminous SUPERNOVAe (SLSNe) are among the most energetic stellar explosions, yet their central power source remains uncertain. Models invoking MAGNETar spin-down or circumstellar interaction predict GeV gamma-ray emission once the ejecta becomes transparent to high-energy photons. We search for such emission from 223 hydrogen-poor SLSNe using 17 years of FERMI-LAT data, defining source-specific search windows based on the Bethe--Heitler transparency time. We find no significant ($\geq5σ$) GeV emission. A joint-likelihood analysis constrains the GeV-to-optical efficiency to $η< 1.3\times10^{-3}$, two orders of magnitude below the predictions for weakly MAGNETized MAGNETar nebulae. A hierarchical population analysis shows that fewer than $0.7\%$ of SLSNe-I can have $η> 10^{-2}$. SN 2017egm, however, shows a suggestive excess ($\sim$4 $σ$). In the 0.1--500 GeV band, the observed $L_γ/L_{\rm opt} \sim 0.68$ for SN 2017egm exceeds hadronic expectations by over an order of magnitude, favoring a MAGNETar origin. The non-detection of the similarly nearby SN 2018bsz disfavors simple uniform-efficiency scenarios, or potentially points to diversity in the underlying powering mechanisms. We also note a possible excess from SN 2024jlc, though continued FERMI-LAT monitoring is needed because the source may still be within its transparency window.

[abstract 11 / 16] (score: 3)
arXiv:2512.09036 [pdf, ps, other]

Title: Probing the origin of the kilonova candidate GRB 230307A: analysis of host galaxy and offset

Authors: Clecio R. Bom, Davi C. Rodrigues, Arianna Cortesi, Amanda E. Araujo-Carvalho, Daniel Ruschel-Dutra, Giuliano Iorio, Luidhy Santana-Silva, Charles D. Kilpatrick, Fabricio Ferrari, Luis Lomeli-Nuñez, Thomas Harvey, Duncan Austin, Christopher J. Conselice, Nathan Adams, Roberto Cid Fernandes,

Comments: v2. 9 pages, 5 figures. Accepted in ApJL

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

Created: 2026-04-17; Updated: 2026-04-21; Datestamp: 2026-04-21

We investigate the host galaxy of the long GAMMA-RAY BURST GRB 230307A, which is associated with a kilonova candidate likely produced by a binary neutron-star (BNS) merger. The transient occurred at a projected offset of ~40 kpc from its host. We consider two explanations for this large distance: (i) NSs that merge inside a remote globular cluster, or (ii) a BNS that formed in the disk whose orbit was strongly modified by the NS natal kicks. Using JWST data and comparisons with known globular clusters, we show that a globular-cluster origin is unlikely. Using JWST and MUSE data, we derive the host galaxy morphology, stellar mass, estimate the atomic gas (HI+He) contribution, and the host rotation curve. Assuming an NFW halo and applying Bayesian inference, we obtain a mass model for the host. From this model, we compute the time required for a disk-formed BNS, with a given natal kick, to reach the observed offset while marginalizing over uncertainties and over the initial position in the disk. We compare these results with BNS-merger simulations from a population-synthesis code combined with stellar evolutionary tracks, which provide the coalescence time and kick velocity for each realization. The two approaches have an overlap in the kick-time diagram, but only 0.1% of the simulated systems is compatible with the galaxy-mass model. This indicates that a disk origin is possible, but requires fine-tuned conditions for the kilonova to occur at such a large distance from the host galaxy.

[abstract 12 / 16] (score: 3)
arXiv:2604.16920 [pdf, ps, other]

Title: Testing Weak Equivalence Principle with IceCube Event and Blazar

Authors: Tian-Cong Wang, Aleksandra Piorkowska - Kurpas, Marek Biesiada, He Gao,

Comments:

Subjects: astro-ph.HE

Created: 2026-04-18; Updated: 2026-04-21; Datestamp: 2026-04-21

Einstein's Weak Equivalence Principle (WEP), the universality of free fall, is a fundamental component of general relativity and other metric theories of gravity. Its validity can be tested through the post-Newtonian parameter gamma, which quantifies the amount of spacetime curvature due to the presence of unit rest mass. In this paper, we use high-energy neutrino events detected by IceCube and associated with the gamma-ray BLAZARs TXS 0506+056 and PKS 0735+178 to test the WEP via the Shapiro delay induced by the gravitational potential of Laniakea. We find that violation of the equivalence principle for neutrinos and photons is limited to an accuracy of 10^-6, 10^-7 and 10^-8, representing improvements of one, two, and three orders of magnitude, respectively, over previous constraints obtained from other high-energy neutrino-BLAZAR associations and up to six orders of magnitude tighter compared to the constraints obtained with MeV neutrinos from SN1987A.

[abstract 13 / 16] (score: 2)
arXiv:2510.01317 [pdf, ps, other]

Title: Expectations for the first supermassive black-hole binary resolved by PTAs I: Model efficacy

Authors: Levi Schult, Polina Petrov, Stephen R. Taylor, Nihan Pol, Nima Laal, Maria Charisi, Chung-Pei Ma,

Comments: 26 pages, 7 figures, 3 tables. Accepted for publication in Physical Review D

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

Created: 2026-04-17; Updated: 2026-04-21; Datestamp: 2026-04-21

One of the most promising targets for Pulsar Timing Arrays (PTAs) is identifying an individual supermassive BLACK HOLE binary (SMBHB) out of the population of binaries theorized to produce a gravitational wave background (GWB). In this work, we emulate realistic PTA datasets, complete with an increasing number of pulsars and timing baseline, in which we inject a single binary on top of a Gaussian GWB. We vary the binary's source parameters, including sky position and frequency, and create ten noise realizations for each source/PTA combination to synthesize an ensemble of datasets to assess current Bayesian binary search techniques. We develop a novel, cross-correlation based model, Spike Pixel (SP), tuned for the frequency-specific anisotropy induced by an individual SMBHB and compare its binary detection and characterization capabilities to two waveform-based template models. We find that a template-based search including the full gravitational-wave signal structure (i.e., both the Earth and pulsar effects of an incident GW) returns the highest Bayes Factors (BF) and the most robust parameter estimation. SP attains a realization-median BF>10 at source strengths (S/N)~7-15. Interestingly, despite being a deterministic model, the Earth-term template struggles to identify and characterize low-frequency binaries (i.e., 5 nHz). These binaries require higher source strengths (S/N)~16-19 to reach the same BF threshold. This is likely due to neglected confusion effects between the pulsar and Earth terms. By contrast, SP shows promise for parameter estimation despite treating a binary's GW signal as excess directional GW power without phase modeling. Sky location and frequency parameter constraints returned by SP are only surpassed by the Earth term template model at (S/N)~12-13. Milestones for a first detection using the full-signal GW model are included in a companion paper Petrov et al. 2026.

[abstract 14 / 16] (score: 2)
arXiv:2604.16551 [pdf, ps, other]

Title: Photon rings and shadows of BLACK HOLEs with non-minimal couplings between curvature and electroMAGNETic field

Authors: Zhixiang Yin, Changjun Gao, Yun-Long Zhang,

Comments: 14 pages, 40 figures. Manuscript under revision; comments are welcome

Subjects: gr-qc

Created: 2026-04-17; Updated: 2026-04-21; Datestamp: 2026-04-21

We investigate BLACK HOLEs with non-minimal couplings between the electroMAGNETic field and spacetime curvature, focusing on their event horizons, shadows, and photon rings. Such couplings can naturally arise from both classical effective field theories of gravity and quantum effects in curved spacetime. Starting from a general action with three independent coupling terms, we derive static and spherically symmetric BLACK HOLE solutions using a series expansion method. We find that all couplings enlarge the event horizon and photon sphere, while their observational consequences differ. The coupling $F^μ_{\ ν}F_{μρ}R^{νρ}$ slightly increases the shadow size and the separation between the zeroth- and first-order photon rings, leaving higher-order spacings nearly unchanged. The coupling $F_{μν}F_{σρ}R^{μνσρ}$ significantly enlarges the shadow and the zeroth-first ring separation, but rapidly suppresses the spacing between higher-order rings. In contrast, the $F^2R$ coupling reduces the shadow size and causes the zeroth- and first-order rings to nearly coincide, leading to an enhanced brightness, while increasing the separation of higher-order rings and leaving them easier to resolve observationally. We further generate BLACK HOLE images via backward ray tracing and confirm these features within the observationally resolvable regime. These findings can make observational constraints on the non-minimal couplings or might provide new evidence for the modifications to gravity caused by classical or quantum effects.

[abstract 15 / 16] (score: 2)
arXiv:2604.16650 [pdf, ps, other]

Title: Neutron star atmospheres composed of fusion ashes

Authors: Valery F. Suleimanov, Juri Poutanen, Klaus Werner,

Comments: 16 pages, 21 figures, 6 tables, submitted to A&A, revised after the second referee report

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

Created: 2026-04-17; Updated: 2026-04-21; Datestamp: 2026-04-21

Here we present models of hot neutron star (NS) atmospheres consisting of thermonuclear ashes of various chemical compositions. These models are essential for studying thermonuclear flashes in X-ray bursting NSs in which nuclear-burning ashes are transported to the stellar surface. We consider four different mixtures, each dominated by helium, chromium, iron, or nickel. In addition to the opacity sources previously used in NS atmosphere modeling, we include photoionization from excited ionic states as well as approximately 5000 spectral lines. We also develop a method that enables the simultaneous treatment of Compton scattering and a large number of spectral lines. A key feature of the modeled NS atmospheres is the presence of a layer in the transition region between the optically thin and optically thick parts of the atmosphere where the radiation-pressure force increases significantly. This enhanced force sets an upper limit on the maximum attainable bolometric flux for a given surface gravity and chemical composition. The emergent spectra from the computed atmospheres display pronounced absorption edges, whose energies are determined by the dominant chemical species. We fit the model spectra using a diluted blackbody modified by a single absorption edge, and we investigate how the fit parameters depend on both the relative bolometric flux and the chemical composition of the atmosphere. Finally, we discuss constraints on these models imposed by the properties of X-ray bursts that exhibit absorption edges in their spectra, as observed in the systems HETE~J1900.1$-$2455 and GRS~1747$-$312.

[abstract 16 / 16] (score: 2)
arXiv:2604.16751 [pdf, ps, other]

Title: The Qz5 Survey (II): Metallicity Evolution of Damped Lyα Systems Out to z$\sim$5

Authors: Marie Wisz, Marc Rafelski, Grecco Oyarzun, Regina Jorgenson, Michele Fumagalli, Marcel Neeleman, Xavier Prochaska, Lise Christensen, Eldon Fobbs, George Becker, Joseph Hennawi, Gabor Worseck, Sebastian Lopez,

Comments: 32 pages, 10 figures, 1 table, 3 appendices; accepted to ApJ 16 April 2026

Subjects: astro-ph.GA

Created: 2026-04-17; Updated: 2026-04-21; Datestamp: 2026-04-21

Damped Ly$α$ absorbers (DLAs) are the highest \HI\ column density (\NHI) absorption line systems detected in the spectra of background QUASARs. DLAs dominate the neutral gas content of the Universe ($Ω_{\rm HI}$) and are used to measure the metallicity evolution of \HI\ gas. In this work, we introduce a sample of five recently detected DLAs at $z > 4.7$, found in mid to high-resolution spectroscopy from VLT/X-shooter and Keck/HIRES. These DLAs were not pre-selected based on metallicity, enabling an unbiased study of the metallicity of HI gas at $z \sim 5$. We also search for DLAs unbiased in metallicity at $0