High Energy Astrophysical Phenomena

arXiv:astro-ph.HE

Cosmic ray production, acceleration, propagation, supernovae and supernova remnants, neutron stars, pulsars, black holes.

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Hadronic Origin of Sub-PeV Gamma-Ray Emission from LHAASO J0621+3755

Very High Energy (VHE) gamma rays are primarily estimated to arise from high-energy electromagnetic interactions in pulsars and their halo through electron inverse Compton (IC) scattering. Hadronic channels like neutral pion decay have also been proposed to produce TeV-PeV gamma rays from the Pulsar halo. The neutral pions are expected to be generated from cosmic ray (CR) protons interacting with the ambient/cloud. The recent observations of sub-PeV gamma rays from the halo of pulsar PSR J0622+3749 by the Large High Altitude Air Shower Observatory Kilometre-Square Array (LHAASO-KM2A) detector provide a platform to explore different channels of their production. Previous studies support consistency with the leptonic modeling of the halo, which attributes its origin to slow diffusion in the interstellar medium. In this work, we investigated the possibility of proton-proton channel as the origin of these photons. To explain the observed gamma rays with energy $\sim 4$ TeV by the High-Altitude Water Cherenkov (HAWC) telescope till 200 TeV by the LHAASO observatory, one requires the CR proton luminosity to be $η_p\sim 0.1$ of the pulsar PSR J0622+3749 spin-down luminosity. In this case, we have considered the protons propagating in a one-zone superdiffusion environment, specifically $α= 1$ in a cloud of gas density 1 per cm$^{3}$.

2601.00692

Jan 2026High Energy Astrophysical Phenomena

Readdressing the contribution of photonuclear reactions to the muon content of extensive air showers: a heuristic approach

The indirect ground-based observations of cosmic rays through extensive air showers in modern experiments typically involve the use of Monte Carlo simulations to determine the characteristics of the primary particles. These simulations necessitate assumptions about particle interactions at energies that have not yet been experimentally probed, which introduces systematic uncertainties in key observables, particularly the number of muons. Current research on this uncertainty primarily focuses on hadronic interaction models, the dominant source of muon production. This study presents an approach that takes into account another significant mechanism for muon generation: photonuclear reactions. A robust heuristic technique has been developed to estimate the contribution of these interactions to the total number of muons over a wide range of extensive air shower parameters (including primary particle type, energy, and slant atmospheric depth) and photonuclear interaction models, with an absolute percentage error on the order of $10\%$ in the estimated number of muons. Furthermore, several potential applications of the suggested method in relation to modern challenges in extensive air shower physics are discussed.

2512.12481

Dec 2025High Energy Astrophysical Phenomena

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Cosmology and Nongalactic Astrophysics Earth and Planetary Astrophysics Astrophysics of Galaxies Instrumentation and Methods for Astrophysics Solar and Stellar Astrophysics

869 papers

GRB 180728A and SN 2018fip: the nearest high-energy cosmological gamma-ray burst with an associated supernova

The long GRB 180728A, at a redshift of $z = 0.1171$, stands out due to its high isotropic energy of $E_{γ,iso} \sim 2.5 \times 10^{51}$ erg, in contrast with most events at redshift $z<0.2$. We analyze the properties of GRB 180728A's prompt emission, afterglow, and associated supernova SN 2018fip, comparing them with other GRB-SN events. This study employs a dense photometric and spectroscopic follow-up of the afterglow and the SN up to 80 days after the burst, supported by image subtraction to remove the presence of a nearby bright star, and modelling of both the afterglow and the supernova. GRB 180728A lies on the $E_{p,i}-E_{γ,iso}$ plane occupied by classical collapsar events, and the prompt emission is one of the most energetic at $z < 0.2$ after GRB 030329 and GRB 221009A. The afterglow of GRB 180728A is less luminous than that of most long GRBs, showing a shallow early phase that steepens around 5 hours (0.2 days). The GRB exploded in an irregular, low-mass, blue, star-forming galaxy, typical of low-z collapsar events. Because of the relatively faint afterglow, the light curve bump of SN 2018fip dominates the optical emission already after $\sim$3 days and is one of the best sampled to date. The strong suppression below $\sim$ 4000 angstrom and a largely featureless continuum in the early 6--9 days spectra favor aspherical two-component ejecta with a high-velocity collimated component ($> 20,000 km s^{-1}$), dominant early-on, and a more massive, low-velocity component, which dominates at much later epochs. Our findings indicate that asymmetries need to be considered in order to better understand GRB-SNe. In any case, SN 2018fip shares many characteristics with typical GRB-SNe. Its kinetic energy is below the common range of $10^{52}-10^{53}$ erg and does not correlate with the high energy of the GRB, highlighting the diversity of the GRB-SN energy budget partition.

2601.04179Jan 2026

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A spectroscopically confirmed, strongly lensed, metal-poor Type II supernova at z = 5.13

Observing supernovae (SNe) in the early Universe (z > 3) provides a window into how both galaxies and individual stars have evolved over cosmic time, yet a detailed study of high-redshift stars and SNe has remained difficult due to their extreme distances and cosmological redshifting. To overcome the former, searches for gravitationally lensed sources allow for the discovery of magnified SNe that appear as multiple images - further providing the opportunity for efficient follow-up. Here we present the discovery of "SN Eos": a strongly lensed, multiply-imaged, SN II at a spectroscopic redshift of z = 5.133 +/- 0.001. SN Eos exploded in a Lyman-α emitting galaxy when the Universe was only ~1 billion years old, shortly after it reionized and became transparent to ultraviolet radiation. A year prior to our discovery in JWST data, archival HST imaging of SN Eos reveals rest-frame far ultraviolet (~1,300Å) emission, indicative of shock breakout or interaction with circumstellar material in the first few (rest-frame) days after explosion. The JWST spectroscopy of SN Eos, now the farthest spectroscopically confirmed SN ever discovered, shows that SN Eos's progenitor star likely formed in a metal-poor environment (<= 0.1 Z_{\odot}), providing the first direct evidence of massive star formation in the metal-poor, early Universe. SN Eos would not have been detectable without the extreme lensing magnification of the system, highlighting the potential of such discoveries to eventually place constraints on the faint end of the cosmic star-formation rate density in the very early Universe.

2601.04156Jan 2026

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Implications of Non-equatorial Relativistic Accretion Flows for Ultra-Fast Inflows in AGNs

Motivated by a number of X-ray observations of active galactic nuclei (AGNs) that exhibit a potential signature of ultra-fast inflows (UFIs), we consider in this work a scenario that UFIs can be physically identified as weakly-magnetized hydrodynamic accretion flows that is guided and channeled by poloidal magnetic field into low-to-mid latitude above the equatorial disk. In the context of general relativistic hydrodynamics (GRHD) under a weak-field limit in Kerr spacetime, we present a set of preliminary results by numerically calculating the physical property of GRHD flows (e.g. kinematics and density distribution) in an effort to simulate redshifted absorption line spectra. Our model demonstrates that such GRHD accretion off the equatorial plane (i.e. $v \gsim 0.1c$ where $c$ is the speed of light in the vicinity of AGN closer than $\sim 100$ \sw radii) can manifest itself as UFIs in the form of redshifted absorption signature assuming the observed characteristics such as column density of $N_H \sim 10^{23}$ cm$^{-2}$ and ionization parameter of $\log (ξ\rm{[erg~cm~s^{-1}])} \sim 3$ as also seen in recent multi-epoch {\it NuSTAR} observations among other data.

2601.04141Jan 2026

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Satellite-borne γ-ray astrophysics from coherent interactions in oriented crystals

High-density and high-Z crystals are a key element of most space-borne $γ$-ray telescopes operating at GeV energies (such as Fermi-LAT). The lattice structure is usually neglected in the development of a crystalline detector, although its effects on the energy deposit development should be taken into account, since the interactions of a high energy ($\sim$~GeV) photon or e$^\pm$ impinging along the axis of an oriented crystal are different than the ones observed in a fully isotropic medium. Specifically, if the angle between a photon (e$^\pm$) trajectory and the crystal axis is smaller than $\sim$ 0.1$^\circ$, a large enhancement of the pair production (bremsstrahlung) cross-section is observed. Consequently, a photon-induced shower inside an oriented crystal develops within a much more compact region than in an amorphous medium. Moreover, for photon energies above a few GeV and incidence angles up to several degrees, the pair-production cross-section exhibits a pronounced dependence on the angle between the crystal axis and the photon polarization vector. \\ In this work we show that these effects could be exploited to develop a novel class of light-weight pointing space-borne $γ$-ray telescopes, capable of achieving an improved sensitivity and resolution, thanks to a better shower containment in a smaller volume with respect to non-oriented crystalline detectors. We also show that an oriented tracker-converter system could be used to measure the polarization of a $γ$-ray source above few GeV, in a regime that remains unexplorable through any other detection technique. This novel detector concept could open new pathways in the study of the physics of extreme astrophysical environments and potentially improve the detector sensitivity for indirect Dark Matter searches in space.

2601.04129Jan 2026

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Exploring the potential for ultra-relativistic jets in Scorpius X-1 with low angular resolution radio observations

Scorpius X-1 (Sco X-1) is a neutron star X-ray binary in which the neutron star is accreting rapidly from a low mass stellar companion. At radio frequencies, Sco X-1 is highly luminous and has been observed to have jet ejecta moving at mildly relativistic velocities away from a radio core, which corresponds to the binary position. In this Letter, we present new radio observations of Sco X-1 taken with the Karl G. Jansky Very Large Array. Using a fast imaging method, we find that the 10 and 15GHz data show a number of flares. We interpret these flares as the possible launching of fast jets ($βΓ$>2), previously observed in Sco X-1 and called ultra-relativistic flows, and their interaction with slower moving jet ejecta. Using the period between successive flares, we find that it is possible for the fast jets to remain undetected, as a result of the fast jet velocity being sufficiently high to cause the jet emission to be beamed in the direction of the motion and out of our line of sight. Our findings demonstrate that the ultra-relativistic flows could be explained by the presence of fast jets in the Sco X-1 system.

2601.03962Jan 2026

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Evidence for a Damped Millisecond Quasi-Periodic Structure in a Fast Radio Burst

Fast radio bursts (FRBs) are millisecond-duration transients of unknown origin, likely associated with compact astrophysical objects. We report evidence for a damped millisecond quasi-periodic structure in a non-repeat FRB~20190122C. The burst consists of eight closely spaced radio pulses separated by $\sim$1 ms, with pulse amplitudes exhibiting an exponential decay starting from the brightest component. Combined Gaussian fitting and time-series analysis reveal a quasi-periodic oscillation (QPO) at $\sim$1 kHz. The observed QPO is consistent with damped magnetospheric oscillations. Assuming an Alfvén wave origin, we estimate a surface magnetic field of $\sim 10^{12}$ G and a characteristic spin period of $\sim$1 s, favoring a low-field magnetar or young neutron star scenario. The absence of frequency drift and the presence of exponential damping disfavor a merger-driven origin. These results suggest the first detection of an exponentially decaying QPO in any FRB, marking a rare detection of coherent oscillatory behavior in FRBs.

2601.03950Jan 2026

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Search for gamma-ray variability around Fermi-LAT pulsar glitches

Pulsars are the most numerous class of Galactic gamma-ray sources detected by the Fermi Large Area Telescope (LAT). Young pulsars occasionally experience sudden timing discontinuities called glitches, characterized by rapid changes in rotational parameters, usually followed by a return to regular rotation. PSR J2021+4026 is unique among Fermi-LAT pulsars, exhibiting quasiperiodic switches between two states with varying spin-down rates approximately every 3-4 years, correlated with sudden changes in gamma-ray emission features. This study searched for gamma-ray emission variability in pulsars correlated with glitch occurrence. We introduced a novel approach to analyzing LAT gamma-ray pulsars through systematic examination of variability associated with spin-down rate changes. We tracked rotation and gamma-ray emission changes for seven promising glitches selected based on observed spin-down rate variations. Using 14 years of Fermi-LAT data, we conducted binned likelihood spectral analysis of data windows around selected glitch epochs. We improved best-fit parameter precision by incorporating likelihood weights calculated from diffuse background models, accounting for systematic error contributions. The phase-averaged flux and spectral parameters of analyzed pulsars showed no significant variation across investigated glitches. The 95% upper limits on relative flux change indicate the Vela pulsar flux is unchanging, with a 0.5% upper limit on relative change, making it promising for further searches. The connection between glitch dynamics and gamma-ray emission remains unclear, and PSR J2021+4026 remains unique in its gamma-ray variability properties. We conclude that comprehensive investigation of glitches is warranted to further unravel their underlying mechanisms.

2601.03939Jan 2026

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First detection of VHE gamma-ray signal from the FSRQ TON 0599

TON 0599 (z=0.7247) belongs to the few flat spectrum radio quasars (FSRQs) detected in the very high energy (VHE, $E > 100$ GeV) gamma-ray band. Its redshift makes it currently one of the farthest VHE gamma-ray sources. It was detected for the first time with the MAGIC telescopes on 2017 December 15, and observed until December 29. The flux reached a maximum of about 50 per cent of the Crab Nebula flux above 80 GeV on the second night of observation, after which we witnessed a gradual decrease of the flux. The VHE gamma-ray spectrum connects smoothly to the one in the high energy ($E > 100$ MeV) band obtained from simultaneous observations with Fermi-LAT. It features a cut-off at energies around 50 GeV, indicating the location of the gamma-ray emission zone beyond the broad line region. In addition, we were able to follow the spectral evolution during the fading phase of the flare. Multiwavelength analysis based on observations in optical, near-infrared, and radio bands acquired by the Whole Earth Blazar Telescope (WEBT) Collaboration from November to March, as well as observations in X-ray and optical$-$UV bands with instruments on board the Swift satellite, shows strong correlation between different bands. We model the broadband emission with a simple one-zone leptonic model, where the high-energy peak is predominantly produced by external Compton (EC) scattering of photons from the dusty torus.

2601.03873Jan 2026

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Short gamma-ray burst progenitors have short delay times

Short gamma-ray bursts (SGRBs) are thought to be primarily associated with binary neutron star (BNS) mergers. The SGRB population can therefore be scrutinized to look for signatures of the delay time between the formation of the progenitor massive star binary and the eventual merger, which could produce an evolution of the cosmic rate density of such events whose shape departs from that of the cosmic star formation history (CSFH). To that purpose, we study a large sample of SGRBs within a hierarchical Bayesian framework, with a particular focus on the delay time distribution (DTD) of the population. Following previous studies, we model the DTD either as a power-law with a minimum time delay or as a log-normal function. We consider two models for the intrinsic SGRB luminosity distribution: an empirical luminosity function (ELF) with a doubly broken power-law shape, and one based on a quasi-universal structured jet (QUSJ) model. Regardless of the chosen parametrization, we find average time delays $10\lesssim \langle τ_\mathrm{d}\mathrm\rangle/\mathrm{Myr}\lesssim 800$ and a minimum delay time $τ_\mathrm{d,min}\lesssim 350\,\mathrm{Myr}$, in contrast with previous studies that found long delay times of few Gyr. We demonstrate that the cause of the longer inferred time delays in past studies most likely resides in an incorrect treatment of selection effects.

2601.03861Jan 2026

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Characteristics of the High-frequency Humps in the Black hole X-ray Binary Swift J1727.8--1613

We present a detailed timing analysis of the two high-frequency humps observed in the power density spectrum of Swift J1727.8--1613 up to 100 keV, using data from the Hard X-ray Modulation Telescope (Insight-HXMT). Our analysis reveals that the characteristic frequencies of the humps increase with energy up to $\sim30$ keV, followed by a plateau at higher energies. The fractional rms amplitudes of the humps increase with energy, reaching approximately 15\% in the 50-100 keV band. The lag spectrum of the hump is characterized primarily by a soft lag that varies with energy. Our results suggest that the high-frequency humps originate from a corona close to the black hole. Additionally, by applying the relativistic precession model, we constrain the mass of Swift J1727.8--1613 to $2.84 < M / M_{\odot} < 120.01$ and the spin to $0.14 < a < 0.43$ from the full-energy band dataset, using triplets composed of a type-C quasi-periodic oscillation and two high-frequency humps. When considering only the high-energy bands with stable characteristic frequencies, we derive additional constraints of $2.84 < M/M_{\odot} < 13.98$ and $0.14 < a < 0.40$.

2601.03696Jan 2026

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Late-Time Infrared Cooling in Magnetar-Driven Supernovae

A central magnetar engine is commonly invoked to explain energetic supernovae, which should have multiple signals in multiwavelength emission. Photoionization from the pulsar wind nebula (PWN) can create distinct spectroscopic signals in the nebular phase. Recent models suggest infrared emission, particularly from Ne II, can be prominent at late times. This work examines the cooling power of optical and infrared transitions to determine which lines contribute strongly to cooling and on what timescale. The models show infrared cooling becomes strong at $\sim$ 3 years post-explosion and dominates by 6 years, with [Ne II] 12.8$μ$m being the strongest coolant. The fraction of total cooling in the infrared increases sharply once the PWN luminosity decreases below 10$^{40}$ erg s$^{-1}$, and this fraction also increases with increasing ejecta mass and decreasing average PWN photon energy. However, the emission from [Ne II] 12.8$μ$m increases with increasing PWN luminosity and increasing ejecta mass. Cooling at 1 year is dominated by optical O and S lines, with infrared Ar, Ni, and Ne lines becoming strong at 3 years. Optical cooling is almost negligible at 6 years, with the supernova cooling almost entirely through mid- and far-infrared transitions. JWST spectroscopy with MIRI should be able to detect these lines out to $z \sim 0.1$. Supernovae with higher magnetic fields transition to infrared cooling on earlier timescales, while infrared-dominated supernovae should have strong emission from neutral atoms and emit strongly in radio at sub-decade timescales.

2601.03373Jan 2026

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Multiwavelength Modeling of the Luminous Fast Blue Optical Transient AT2024wpp

Luminous fast blue optical transients (LFBOTs) are a growing class of enigmatic energetic transients. They show fast rises and declines, high temperatures throughout their evolution, and non-thermal emission in radio and X-rays. Their power source is currently unknown, but proposed models include engine-driven supernovae, interaction-powered supernovae, shock cooling emission, intermediate mass black hole tidal disruption events (IMBH TDEs), and Wolf-Rayet/black hole mergers, among others. AT2024wpp is the most optically luminous LFBOT to date and has been observed extensively at multiple wavelengths, including radio, optical, UV, and X-rays. We take models from multiple scenarios and fit them to the AT2024wpp optical, radio, and X-ray light curves to determine if which of these scenarios can best describe all aspects of the data. We show that none of the multiwavelength light curve models can reasonably explain the data, although other physical arguments favour a stellar mass/IMBH TDE of a low mass star and a synchrotron blast wave. We discuss how this scenario can be tested with late-time observations, and what other scenarios could possibly explain the broadband data.

2601.03372Jan 2026

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Simulation-Based Prediction of Black Hole Spectra: From $10M_\odot$ to $10^8 M_\odot$

It has long been thought that black hole accretion flows are driven by magnetohydrodynamic (MHD) turbulence, and there are now many general relativistic global simulations illustrating the dynamics of this process. However, many challenges must be overcome in order to predict observed spectra from luminous systems. Ensuring energy conservation, local thermal balance, and local ionization equilibrium, our post-processing method incorporates all the most relevant radiation mechanisms: relativistic Compton scattering, bremsstrahlung, and lines and edges for 30 elements and all their ions. Previous work with this method was restricted to black holes of $10 M_\odot$; here, for the first time, we extend it to $10^8 M_\odot$ and present results for two sub-Eddington accretion rates and black hole spin parameter 0.9. The spectral shape predicted for stellar-mass black holes matches the low-hard state for the lower accretion rate and the steep power law state for the higher accretion rate. For high black hole mass, both accretion rates yield power-law continua from $\sim 0.5 - 50$~keV whose X-ray slopes agree well with observations. For intermediate mass black holes, we find a soft X-ray excess created by inverse Compton scattering of low-energy photons produced in the thermal part of the disk; this mechanism may be relevant to the soft X-ray excess commonly seen in massive black holes. Thus, our results show that standard radiation physics applied to GRMHD simulation data can yield spectra reproducing a number of the observed properties of accreting black holes across the mass spectrum.

2601.03349Jan 2026

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AT2024wpp: An Extremely Luminous Fast Ultraviolet Transient Powered by Accretion onto a Black Hole

We present the discovery of AT 2024wpp ("Whippet"), a fast and luminous 18cow-like transient. At a redshift of z=0.0868, revealed by Keck Cosmic Web Imager spectroscopy of its faint and diffuse star-forming host, it is the fourth-nearest example of its class to date. Rapid identification of the source in the Zwicky Transient Facility data stream permitted ultraviolet-through-optical observations to be obtained prior to peak, allowing the first determination of the peak bolometric luminosity (2x10^45 erg/s), maximum photospheric radius (10^15 cm), and total radiated energy (10^51 erg) of an 18cow-like object. We present results from a comprehensive multiwavelength observing campaign, including a far-UV spectrum from the Cosmic Origins Spectrograph on the Hubble Space Telescope and deep imaging extending >100 days post-explosion from the Very Large Telescope, Hubble Space Telescope, Very Large Array, and Atacama Large Millimetre Array. We interpret the observations under a model in which a powerful rapidly-accreting central engine blows a fast (~0.15c) wind into the surrounding medium and irradiates it with X-rays. The high Doppler velocities and intense ionization within this wind prevent any identifiable features from appearing in the ejecta or in the surrounding circumstellar material, even in the far-ultraviolet. Weak H and He signatures do emerge in the spectra after 35 days in the form of double-peaked narrow lines. Each peak is individually narrow (full width ~3000 km/s) but the two components are separated by ~6600 km/s, indicating stable structures of denser material, possibly representing streams of tidal ejecta or an ablated companion star.

2601.03337Jan 2026

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Large-scale radio bubbles around the black hole transient V4641 Sgr

Black holes (BHs) in microquasars can launch powerful relativistic jets that have the capacity to travel up to several parsecs from the compact object and interact with the interstellar medium. Recently, the detection of large-scale very-high-energy (VHE) gamma-ray emission around the black hole transient V4641 Sgr and other BH-jet systems suggested that jets from microquasars may play an important role in the production of galactic cosmic rays. V4641 Sgr is known for its superluminal radio jet discovered in 1999, but no radio counterpart of a large-scale jet has been observed. The goal of this work is to search for a radio counterpart of the extended VHE source. We observed V4641 Sgr with the MeerKAT radio telescope at the L and UHF bands and produced deep maps of the field using high dynamic range techniques. We report the discovery of a large-scale (35 pc), bow-tie-shaped, diffuse, radio structure around V4641 Sgr, with similar angular size to the extended X-ray emission discovered by XRISM. However, it is not spatially coincident with the extended VHE emission. After discussing the association of the structure with V4641 Sgr, we investigate the nature of the emission mechanism. We suggest that the bow-tie structure arose from the long-term action of large-scale jets or disk winds from V4641 Sgr. If the emission mechanism is of synchrotron origin, the radio/X-ray extended structure implies acceleration of electrons up to more than 100 TeV as far as tens of parsecs from the black hole.

2601.03140Jan 2026

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Transient Large-Scale Anisotropy in TeV Cosmic Rays due to an Interplanetary Coronal Mass Ejection

Large- or medium-scale cosmic ray anisotropy at TeV energies has not previously been confirmed to vary with time. Transient anisotropy changes have been observed below 150 GeV, especially near the passage of an interplanetary shock and coronal mass ejection containing a magnetic flux rope ejected by a solar storm, which can trigger a geomagnetic storm with practical consequences. In such events, cosmic rays provide remote sensing of the magnetic field properties. Here we report the observation of transient large-scale anisotropy in TeV cosmic ray ions using data from the Large High Altitude Air Shower Observatory (LHAASO). We analyze hourly skymaps of the transient cosmic ray intensity excess or deficit, the gradient of which indicates the direction and magnitude of transient large-scale anisotropy across the field of view. We observe enhanced anisotropy above typical hourly fluctuations with $>$5$σ$ significance during some hours of November 4, 2021, in separate data sets for four primary cosmic ray energy ranges of median energy from $E$=0.7 to 3.1 TeV. The gradient varies with energy as $E^γ$, where $γ\approx-0.5$. At a median energy $\leq$1.0 TeV, this gradient corresponds to a dipole anisotropy of at least 1\%, or possibly a weaker anisotropy of higher order. This new type of observation opens the opportunity to study interplanetary magnetic structures using air shower arrays around the world, complementing existing in situ and remote measurements of plasma properties.

2601.02801Jan 2026

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Super-Orbital Variations in Magnetar Rotation Measure Arising from the Precession of Companion Star: Implications for FRB 20220529

Recent observations of FRB 20220529 reveal significant variation and a partial reversal in its rotation measure (RM), suggesting the presence of a dynamically evolving magnetized environment, which could be caused by the orbital motion of the magnetar within the binary system. Here we develop the binary model by suggesting that the spin and magnetic axis of the companion star could undergo precession around the orbital axis. It is then investigated how the precession period and the inclination of the magnetic axis, as well as a possible disc wind, can influence the evolution behaviors of the RM and dispersion measure (DM) of FRB emission. As the foremost consequence, the RM variation can be significantly altered on timescales longer than the orbital period, producing super-orbital evolution and complex patterns. Applying this model to FRB 20220529, we find that its RM evolution could be reproduced with a precession period of 182 days and an inclination angle of approximately $19^{\circ}$, while the other binary parameters are fixed at their typical values. Meanwhile, the absence of significant variation of the DM argues against the presence of a dense equatorial disc around the companion star, which would be constrained by future long-term observations.

2601.02734Jan 2026

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SN 2024abfl: A Flat-Plateau, Low-Luminosity Type IIP Supernova with Early CSM Interaction

We present photometric and spectroscopic observations of SN 2024abfl, a low-luminosity Type IIP supernova (LLSN) discovered shortly after explosion. The transient reached a peak absolute magnitude of $M_V = -14.9$ and exhibited an extended, flat plateau lasting $\sim$125 days. From the late-time bolometric light curve, we estimate a $^{56}$Ni mass of $\sim0.01~M_\odot$, consistent with other LLSNe. Analytical shock-cooling models fail to reproduce the rapid early rise, indicating that circumstellar material (CSM) interaction contributed to the initial emission. The spectroscopic evolution is typical of LLSNe, with relatively narrow metal lines and low expansion velocities ($\lesssim 3000$ km s$^{-1}$) that decline slowly over time. We detect a broad ``ledge'' feature around 4600 Åwithin three days of explosion, which we interpret as a blend of high-ionization shock-accelerated CSM lines. Multi-peaked H$α$ profiles develop during the plateau phase, consistent with complex ejecta-CSM interactions. As one of the best-observed examples of LLSNe, SN 2024abfl exhibits a weak explosion and signatures of nearby CSM, offering new insights into progenitor properties, pre-explosion mass loss, and the diversity of LLSNe.

2601.02638Jan 2026

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Exploring Composition Mixing in Kilonova Ejecta with Ray-by-ray Simulations

Binary neutron star merger (BNSM) ejecta are considered a primary repository of $r$-process nucleosynthesis and a source of the observed heavy-element abundances. We implement composition mixing into ray-by-ray radiation-hydrodynamic simulations of BNSM ejecta, coupled with an online nuclear network (NN). We model mixing via a gradient-based mixing approximation that evolves simultaneously with the hydrodynamics. We find that mixing occurs in regions where the electron fraction changes rapidly. While mixing smooths composition gradients in transition regions, it has a negligible impact on the heavy-element yields. This is because the primary $r$-process site (the equatorial ejecta) is initially homogeneous in free neutrons, leaving no strong gradients for mixing to act upon. In each angular ray, the abundances of the most produced elements are robust under mixing, while the less abundant ones are more affected. The total global abundances change only slightly from mixing, since each angular ray contributes its most abundant elements. Furthermore, the predicted kilonova light curves show only minor reddening, with differences below the detectability of state-of-the-art telescopes. In general, we do not observe significant effects from mixing in the time span of the $r$-process. Consequently, mixing only leads to minor variations in abundances and light curves in ray-by-ray simulations.

2601.02600Jan 2026

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Thick Disks, Thin Hopes: Suppressed Capture and Merger Rates in AGN

Multiple models have been suggested over the years to explain the structure and support of accretion disks around supermassive black holes, from the standard thin thermal-pressure-dominated $α$-disk model to more recent models that describe geometrically thicker radiation or magnetic or turbulence-dominated disks. In any case, objects embedded in the disk (e.g. compact objects, stars, gas, dust) can undergo gravitational and hydrodynamic interactions with each other leading to interesting processes such as binary interaction/capture, gravitational wave merger events, dynamical friction, accretion, gap opening, etc. It has long been argued that disks of active galactic nuclei (AGN) can enhance the rates for many of these events; however, almost all of that analysis has assumed specific thin-disk models (with aspect ratios $H/R \lesssim 0.01$). We show here that the rates for processes such as these that are mediated by gravitational cross-sections has a very strong inverse dependence on the thickness $H/R$ (scaling as steeply as $(H/R)^{-8}$), and $H/R$ can vary in the outer disk (where these processes are often invoked) by factors $\gtrsim 1000$ depending on the assumed source of pressure support in the disk. This predicts rates that can be lower by tens of orders-of-magnitude in some models, demonstrating that it is critical to account for disk parameters such as aspect ratio and different sources of disk pressure when computing any meaningful predictions for these rates. For instance, if magnetic pressure is important in the outer disk, as suggested in recent work, capture rates would be suppressed by factors $\sim 10^{10}-10^{20}$ compared to previous studies where magnetic pressure was ignored.

2601.02487Jan 2026

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