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Physics Astrophysics High Energy Astrophysical Phenomena

astro-ph.HE Watch High Energy Astrophysical Phenomena

Monday 12 October

High Energy Astrophysical Phenomena

Indirect Dark Matter Detection in the Multi-Messenger Era: Experiments, Systematics, Anomalies, and Prospects for Discovery

Muad Ghaith and Khaled Obaideen

Indirect searches for dark matter (DM) span gamma rays, charged cosmic rays, neutrinos, X-rays, radio emission, the cosmic microwave background (CMB), and the 21~cm signal, but reported constraints and anomalies vary in evidential strength. This critical review synthesizes peer-reviewed literature from January 2000 through October 2026 using a structured search strategy. We assess observations through a framework linking particle interactions and halo source terms to propagation or cosmological energy deposition, instrumental response, background modeling, and statistical inference. Fermi-LAT observations of dwarf spheroidal galaxies provide robust GeV-scale benchmarks for DM annihilation, whereas Galactic-center searches offer higher expected signals but depend more on foregrounds and halo profiles. Charged-cosmic-ray measurements are precise but limited by propagation and source uncertainties, while neutrino searches offer complementary sensitivity through solar capture, directional and flavor information, and high-mass annihilation or decay. Several widely discussed signals, including the 3.5~keV line, 511~keV emission, the Galactic-center GeV excess, charged-particle features, cluster radio excesses, and candidate gamma-ray lines remain inconclusive because of limited independent confirmation, uncertain target scaling, spectral degeneracies, or background-modeling limitations. Cosmological observations provide complementary constraints from CMB energy-injection limits and 21~cm measurements of the intergalactic medium. Artificial intelligence increasingly supports reconstruction and inference but requires rigorous calibration and domain-shift validation. The strongest case for DM discovery would require statistically consistent evidence across independent targets, instruments, or messengers, under common particle-physics parameters, and with well-characterized uncertainties.
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High Energy Astrophysical Phenomena

An end-to-end experimental pipeline for automated track identification for paleo-detectors

Claudio Galelli, Alessandro Testi and Lorenzo Caccianiga

Paleo-detectors aim to exploit the damage tracks left in natural minerals by cosmic messengers over geological times to reconstruct past fluxes of energetic particles. For cosmic rays, the expected signal is abundant, and the tracks are micron-scale, so they can be revealed by etching and read out with conventional optical microscopy; what remains challenging is turning a bulk sample into a calibrated track-length spectrum that can be quantitatively confronted with theoretical predictions. In this work we present the experimental pipeline we developed for this purpose within the INFN PRImuS experiment, from sample preparation and automated multi-focus microscopy to track recognition with OptimusPrimus, a two-stage machine-learning algorithm, and to a forward-folding model that propagates geometric sectioning, etching and the measured detection response into simulated spectra. The pipeline was built and validated on chemically etched obsidian where the recovered track-length distribution is statistically compatible with expert annotation. In parallel, we developed and characterized a dry argon-plasma etching protocol for halite, an evaporite mineral of particular interest as a low-background cosmic-ray paleo-detector. Since every stage of the pipeline is mineral-agnostic, with only the trained networks and the detection response to be re-derived from annotated data, we are now applying it to plasma-etched halite with the aim of identifying cosmic-ray-induced tracks.
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High Energy Astrophysical Phenomena · Cross-listed from astro-ph.GA

A Quest for Changing-State AGNs

Kasra Mokhtarpour and Vicki Sarajedini

We use Gaia Data Release 3 (DR3) light curves to identify photometrically selected changing-state active galactic nucleus (CSAGN) candidates. We employ unsupervised deep learning and anomaly detection methods to identify unusual patterns of variability in the light curves of 872,228 AGNs with known variability. We find that 8,504 light curves show anomalous behavior. Among these, 682 sources show evidence for two-state photometric behavior during the Gaia DR3 observing baseline. These 682 CSAGN candidates were selected using an automated statistical pattern recognition approach based on Gaussian mixture models (GMMs) to identify sources whose magnitude distributions are consistent with two preferred brightness levels, substantially reducing the need for human visual inspection in selecting the CSAGN candidates. The candidates tend to have fainter absolute magnitudes and lower redshifts than the non-anomalous Gaia variable AGN sample, suggesting that some may be accreting at lower rates. Our approach builds a large candidate sample with less reliance on human visual selection. Follow-up observations of these sources can help identify what drives changing-state transitions and clarify their connection to accretion-disk physics and supermassive black hole (SMBH) fueling.
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High Energy Astrophysical Phenomena · Cross-listed from astro-ph.CO

Self-Interacting Dark Matter: From Particle Physics Theories to Structure Formation Simulations

Martin Rosenlyst, Vinh Tran, Oliver Zier et al. (+7 more)

We present a unified theory-to-simulation framework for self-interacting dark matter (SIDM), combining a self-contained introduction to its particle-physics foundations and representative benchmark models with an explicit, systematic mapping to simulation inputs and validated numerical implementations in the moving-mesh code AREPO-2. We characterize representative elementary and composite dark-sector models through their particle content, symmetries, interactions, production mechanisms, and constraints. We then establish an explicit mapping from their microscopic properties to the inputs required for structure-formation simulations, including modifications to cosmological initial conditions, internal-state mass splittings and populations, reaction networks, velocity- and angle-dependent cross sections, dissipative energy loss, and decay rates and recoil kinematics. Building on the efficient, scalable SIDM infrastructure introduced in our companion work, we implement isotropic and anisotropic self-scattering with constant or velocity-dependent cross sections, multi-state and inelastic reactions, and dissipative scattering, as well as a dedicated DM decay module. We validate the implementations through beam-lattice deflection experiments, thermalization and uniform-box decay tests, isolated-halo gravothermal core-collapse simulations, and cosmological box and zoom-in simulations. The tests reproduce analytical predictions and published inelastic and dissipative benchmarks, with agreement across numerical schemes. The resulting framework provides a common reference for researchers across disciplines and a practical route from microscopic dark-sector theories to nonlinear astrophysical predictions beyond standard isotropic, elastic SIDM.
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All authors Martin Rosenlyst, Vinh Tran, Oliver Zier, Xuejian Shen, Mark Vogelsberger, Thejs Brinckmann, Mads T. Frandsen, Jesús Zavala, Frederik Holt Dihver Christensen, Mikkel Theiss Kristensen

High Energy Astrophysical Phenomena

Double Detonations on a Moving Mesh with $\texttt{Cattails}$: Characterizing Early Reddening in SNe Ia

Dillon Hasenour, Paul Duffell and Abigail Polin

Type Ia supernovae are useful as cosmological distance indicators and are significant sources of chemical enrichment in galaxies, but much about their origins remains uncertain. The double detonation explosion mechanism is one promising model for these transients. We present a suite of thermonuclear hydrodynamic double detonation models of sub-Chandrasekhar mass white dwarfs spanning thin to thick helium shells. Thin shell models produce light curves and spectra consistent with normal Type Ia supernovae, and thicker shell models have early time luminosity bumps from radioactive ashes in the shell and early reddening in color sometimes observed in peculiar Type I supernovae. The reddening is due to line blanketing from heavy elements produced in the shell detonation encompassing the central emission. We perform the computations using $\texttt{Cattails}$, a moving mesh nuclear hydrodynamics code introduced in this work. After carrying out subsequent radiative transfer calculations using the $\texttt{Sedona}$ code, we relate the time of early reddening to the mass of the initial helium shell. We also consider how the relation changes as a function of total mass as well as how the peak brightness depends on the total mass. Finally, we provide a series of fitting functions that can be used to estimate the mass of the shell consistent with an observation of reddening in the early color evolution of a type Ia supernova.
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High Energy Astrophysical Phenomena · Cross-listed from astro-ph.GA

Evidence for Hierarchical Turbulent Scaling in Nearby Star-Forming Galaxies

Luna Maria Scipio, Fernando A. N. Santos and Jay Armas

We find recurring signatures of intermittency in molecular-gas velocities from cloud to galactic scales. In 31 selected galaxies from PHANGS-ALMA, velocity-centroid exponents through sixth order show nonlinear order dependence and nearly linear relations between consecutive exponents across galaxies. Positive estimated offsets from single-exponent scaling occur in all 52 galaxies with a valid power law fit and 99 of 100 clouds. A generalized She-Leveque hierarchy accommodates these signatures, supporting a hierarchical description of turbulent scaling in molecular gas across these environments.
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High Energy Astrophysical Phenomena

The Thousand-Pulsar-Array programme on MeerKAT - XX. Co-existing interacting periodicities and polarization modulation in PSR J1901-0906

Jui-An Hsu, Patrick Weltevrede, Geoff Wright et al. (+3 more)

We present a comprehensive analysis of the complex subpulse modulation in PSR J1901-0906 using data from the Thousand-Pulsar-Array (TPA) programme. Our analysis reveals the coexistence of three distinct periodicities in the subpulse modulation of both profile components, which obey a beat relation. We also detect additional spectral beat features caused by the modulation of these co-existing periodicities by investigating the Fourier phase correlation in two-dimensional fluctuation spectra. Moreover, the single-pulse polarization states are shown to be modulated and synchronized with the three co-existing periodicities observed in total intensity. Such synchronization has been reported for only a small number of pulsars, but this discovery marks the only one where this synchronization involves multiple co-existing periodicities. The modulation beats are similar to, yet more complex than, the beat system previously identified in PSR J1514-4834 with higher-order harmonics playing a significant role. The coexistence of the observed beat-like periodicities in PSR J1901-0906 implies that they are not independent, but rather originate from an underlying, interconnected physical system within the pulsar magnetosphere. Building upon the same geometric framework previously applied to PSR J1514-4834, we demonstrate that a feedback system with interacting rotating carousels successfully reproduces the complex subpulse modulations observed in PSR J1901-0906 and naturally explains the beat relations.
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All authors Jui-An Hsu, Patrick Weltevrede, Geoff Wright, Michael J Keith, Aris Karastergiou, Xiaoxi Song

High Energy Astrophysical Phenomena

Blackbody evolution and circumstellar medium properties of broad-lined H-rich superluminous supernovae

Tuomas Kangas, Takashi Nagao, Uliana Pylypenko et al. (+2 more)

Broad-lined H-rich superluminous supernovae (SLSNe II) tend to show signs of interaction, including a UV excess compared to a blackbody function. However, a quantitative analysis of the CSM configuration and the UV excess has so far not been performed for most of the literature sample. Additionally, SN 2023gpw showed signs of asymmetry in its peculiar blackbody and spectral evolution, raising the question of whether similar properties can be found in other SLSNe II. We aim to characterize the circumstellar environment of SLSNe II by searching for signs of asymmetry, quantifying the UV excess, and investigating any IR echoes produced by dust. Diversity among SLSNe II is also explored. We fit blackbody functions to the SEDs of SLSNe II to quantify the UV excess luminosity and its evolution. We use this to investigate mass-loss rates required to produce the excess through interaction. We also investigate the line profiles in SLSN II at late times and compare line velocities to the blackbody radius evolution. We examine public WISE IR images and place constraints on IR echoes. We find mass loss rates of $\sim10^{-4}$ to $\sim0.03\, \mathrm{M_\odot}$~yr$^{-1}$ when assuming all interaction luminosity emerges in the UV, i.e., conservative lower limits for the total mass loss rate. Radii calculated from line velocities in late-time spectra are mostly too large for a spherical interaction photosphere, only compatible with the blackbody radius evolution if the CSM is non-spherical with a low filling factor. This is in some cases supported by a mismatch between spectroscopic and blackbody expansion velocities. Considerable diversity is seen in the sample, probably as a result of different viewing angles and CSM masses. WISE images seem too shallow to observe IR echoes in SLSNe II beyond $z\sim0.1$, but in the nearest event, SN 2020jhm, a likely IR echo is detected, suggesting pre-existing dust.
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All authors Tuomas Kangas, Takashi Nagao, Uliana Pylypenko, Steve Schulze, Lin Yan

High Energy Astrophysical Phenomena

Direct Observational Constraint on Upstream Magnetic Field Amplification Reveals the Particle Acceleration Limit in a Supernova Remnant

Yuya Kawabata, Takaaki Tanaka, Hiromasa Suzuki et al. (+1 more)

The origin of Galactic cosmic rays up to the knee energy (PeV) remains a long-standing open question in astrophysics. Supernova remnant shocks are leading candidates for accelerating particles to PeV energies, yet this requires strong magnetic field amplification in the upstream region to confine the highest energy particles. Despite its importance, the upstream magnetic field strength has long lacked direct observational constraints. Here we report the observation of numerous synchrotron X-ray hotspots extending into the upstream of the supernova remnant RX J1713.7$-$3946 in archival Chandra data. These hotspots show spatial and temporal properties consistent with synchrotron emission from secondary electrons produced by hadronic interactions between accelerated protons and dense molecular clumps. Using the spatial extent of these upstream hotspots as a physical scale, we estimate the proton diffusion length to be $\sim 1~\mathrm{pc}$. This measurement provides a constraint on the upstream magnetic field strength of $\sim 10~\mu\mathrm{G}$, which is consistent with recent simulations of Bell-instability-driven magnetic field amplification. Our results indicate that the current amplification is insufficient to reach PeV energies, explaining the observed TeV gamma-ray spectral cutoff and providing a diagnostic for assessing PeVatron capability in stellar shocks.
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All authors Yuya Kawabata, Takaaki Tanaka, Hiromasa Suzuki, Tsuyoshi Inoue

High Energy Astrophysical Phenomena · Cross-listed from astro-ph.IM

Deep learning methods for gamma event selection in TAIGA-IACT image analysis in stereo-mode

E. O. Gres, A. P. Kryukov, P. A. Volchigov et al. (+6 more)

In astrophysical complex TAIGA there are four Imaging Atmospheric Cherenkov telescopes (IACTs), located at a distance of 300-500 m from each other, due to which extensive air showers (EAS) generated by cosmic and gamma radiation are recorded by a single telescope or by multiple telescopes simultaneously (stereo-mode). The analysis of EAS images from two or more Cherenkov telescopes together is of particular interest, since for this approach the reconstruction of physical parameters of the primary gamma ray is much more accurate than in mono-observations. However, the gamma-ray event reconstruction strongly depends on the quality of the hadron background suppression of the classifier, therefore, the gamma event selection stage is one of the important ones in the further analysis of IACT data. We propose and study several neural network methods for gamma event selection in joint TAIGA-IACT image analysis. Neural network methods we suggested involves a single-stage analysis of IACT images from two telescopes, while the second method considers the formation of autoencoder-derived essential features that contain the EAS physical parameters, including the type of primary particle.
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All authors E. O. Gres, A. P. Kryukov, P. A. Volchigov, A. P. Demichev, J. J. Dubenskaya, D. P. Zhurov, S. P. Polyakov, E. B. Postnikov, A. J. Razumov

High Energy Astrophysical Phenomena

Equation of State Classification of Core-Collapse Supernovae with a Network of Gravitational-Wave Detectors

A. Akhmetali, Y. S. Abylkairov, J. A. Font et al. (+2 more)

Gravitational waves from core-collapse supernovae may provide a unique probe of the equation of state (EOS) of dense nuclear matter. In previous work, we assessed the potential of machine-learning methods for EOS classification for rapidly rotating supernovae using individual gravitational-wave detectors. Here, we extend the framework to detector networks and investigate the impact of detector configuration, source distance, arrival time, and sky location on the classification. Using convolutional neural networks, we perform 10-class EOS classification directly from noisy detector data for both second- and third-generation observatories. We find that detector geometry strongly influences classification performance. For Galactic events, current detector networks can achieve promising classification performance, but the reach depends sensitively on the detector network antenna response. Adding detectors improves time-averaged performance and produces more uniform classification across the sky. Third-generation observatories extend the classification reach to 100 kpc for favorable source orientations but do not remove the dependence on detector geometry.
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All authors A. Akhmetali, Y. S. Abylkairov, J. A. Font, M. Zanolin, E. Abdikamalov

High Energy Astrophysical Phenomena

Radiation-Regulated Spherical Accretion with an Inner Accretion Disk

Cheng-Liang Jiao, Liying Zhu, Xiang-dong Shi et al. (+1 more)

We develop a theoretical model for radiation-regulated spherical accretion with an inner accretion disk. In our model, the outer accretion flow remains quasi-spherical and optically thick, while the luminosity generated by the inner disk is self-consistently coupled to the accretion rate and irradiates the inflowing gas. By solving the global transonic structure with radiative transfer treated in the diffusion approximation, we investigate how radiation regulates the flow structure and the accretion rate. We find that the luminosity is constrained by a generalized Eddington limit, leading to a saturated accretion rate typically lower than the classical Bondi prediction by orders of magnitude. At sufficiently low densities, the enthalpy flux of the spherical inflow contributes substantially to the emergent luminosity, in which case the inner disk luminosity is reduced and the accretion flow enters an unsaturated state. A criterion is derived to estimate whether the accretion flow is saturated. We further demonstrate the applicability of our model by considering fallback accretion in failed supernova systems. The predicted nearly constant emergent luminosity, constrained by the generalized Eddington limit, provides a possible explanation for the observed luminosity plateau in the failed supernova candidate M31-2014-DS1. The presence of an inner disk also provides sufficient radiation to avoid the under-luminous predictions of a purely spherical fallback model extending down to the central object. Our model provides a framework for studying radiation-regulated accretion flows in systems where low but finite angular momentum leads to the formation of an accretion disk within a larger-scale quasi-spherical inflow.
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All authors Cheng-Liang Jiao, Liying Zhu, Xiang-dong Shi, Er-gang Zhao

High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Quasinormal modes of rotating black holes with ultralight scalar fields

Leif Lui and Adrian Ka-Wai Chung

We report the first accurate computation of the leading-order shifts in the quasinormal-mode frequencies of rapidly rotating black holes surrounded by massive scalar fields with nonminimal curvature coupling. For fields with reduced Compton wavelengths no shorter than the black-hole mass scale, the numerical errors in the frequency shifts are typically $10^{-8} - 10^{-5}$ for dimensionless spins between 0 and 0.9, and at most $\mathcal{O}(10^{-3})$ next to the scalar-mass threshold. Our results open up the possibility of searching for ultralight scalar particles, prime dark-matter candidates, using existing gravitational-wave signals.
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Sunday 11 October

High Energy Astrophysical Phenomena

Rotating Vector Model predictions in millisecond pulsar magnetospheres with dipole and quadrupole field components

Anna V. Bilous

The rotating vector model (RVM) is widely used to interpret pulsar radio polarization under the assumption of a dipolar magnetic field. Motivated by tentative evidence for non-dipolar magnetic structure in millisecond pulsars provided by recent modeling of surface thermal X-ray pulsations, we examine how a global quadrupole component modifies position-angle (PA) behavior within the classical RVM framework. We numerically integrate magnetic field lines in static vacuum magnetospheres composed of a centered dipole component that is inclined with respect to the spin axis, and a centered quadrupole component aligned with it. We then compute the open field line regions (OFLRs), emission skymaps, and PA curves for a range of dipole inclinations, relative quadrupole strengths, and light cylinder radii corresponding to two trial spin periods of 1\,ms and 5\,ms. We find that quadrupole-modified magnetospheres produce a wide variety of PA behaviors and substantially alter the morphology and total area of OFLRs, with the OFLR area varying non-monotonically with quadrupole strength and, in some cases, exceeding that of the corresponding pure dipole. Depending sensitively on the field configuration and viewing geometry, three broad PA regimes can be distinguished: a) nearly dipolar PA swings that are largely insensitive to emission altitude; b) moderately distorted, altitude-dependent PA tracks that can bias dipolar RVM fits; and c) strongly dispersed PA behavior associated with emission from different OFLRs, which can remain incompatible with a single dipolar PA track even within narrow emission altitude ranges. These results demonstrate that dipole-like PA curves do not uniquely imply a purely dipolar magnetic field, while global quadrupole components alone are insufficient to reproduce the full complexity of observed millisecond pulsar PA profiles.
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High Energy Astrophysical Phenomena

Bayesian exploration of weakly interacting models of dark matter admixed neutron stars based on multi-density constraints

Payaswinee Arvikar, Prashant Thakur and Sarmistha Banik

We present a unified Bayesian analysis of Higgs-portal, neutron-decay, and axion-like-particle (ALP)-mediated dark matter in neutron stars within the single-fluid approximation. Using a common relativistic mean-field description of hadronic matter, we combine finite-nucleus and heavy-ion collision data, chiral effective field theory, NICER measurements of four pulsars, and GW170817. The individual dark-sector parameters remain weakly determined, while model-dependent shifts in nuclear skewness reveal the sensitivity of the inferred hadronic equation of state to the assumed dark-matter mechanism. The three scenarios yield substantially overlapping mass-radius and tidal-deformability predictions, with median maximum masses near $2.1\,M_\odot$. For $1.4\,M_\odot$ stars, the Higgs-portal model predicts higher $f$-mode frequencies and shorter damping times than the neutron-decay and ALP models, although their credible regions overlap. Comparison with three consistently reanalysed two-fluid models gives the largest Bayesian evidence to neutron decay: under the adopted priors, its Bayes factors relative to the Higgs-portal and two-fluid alternatives are approximately $24$-$37$, but only $2.2$ relative to ALP. This ranking concerns complete dark-matter models and does not establish a general preference for either fluid description or evidence for a dark component itself. Improved nuclear constraints and future gravitational-wave asteroseismology could provide complementary information to disentangle the hadronic and dark-sector contributions.
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High Energy Astrophysical Phenomena

Revisiting the Multiwavelength Data of GRB 240825A: Implications for a Two-Stage Central Engine and a Dusty Environment

Ren-Jie Xiong, Zi-Qi Wang, Xiao-Li Huang et al. (+1 more)

Reanalyzing the multi-wavelength data of GRB 240825A, we identify two distinct prompt-emission episodes, i.e. an early, spectrally soft plateau and a subsequent bright, spectrally hard gamma-ray pulse. We show that this signature is consistent with a two-stage central engine model, in which the early soft plateau is powered by the dipolar spin-down radiation of a transient proto-magnetar, while the later hard pulse arises from a relativistic jet launched by fallback accretion onto the nascent black hole via the Blandford-Znajek mechanism. Adopting simulation-motivated initial black hole (BH) masses ($M_{\rm BH,0}$) and spins ($a_0$), our fits to the second episode yield total masses supplied to the post-collapse disk of $M_{\rm fb}=0.45$–$0.96 M_\odot$, fallback radii of $r_{\rm fb}=16.9$–$17.6 r_g$, and characteristic fallback timescales of $t_{\rm fb}=0.13$–$0.25$ s. The corresponding maximum inner accretion rates range from $0.18$ to $0.70 M_\odot \mathrm{s}^{-1}$, which is sensitive to $a_0$. Joint spectral fits with optical-X-ray afterglow data reveal a coupled temporal evolution of dust extinction and equivalent hydrogen column density. Incorporating this extinction evolution, an external forward-reverse shock model in a wind-like medium can account for the radio-to-GeV band afterglow data. Although ambient dust and the bright host galaxy may obscure any associated supernova, late-time optical reddening remains compatible with a supernova contribution. Applying the empirical relation between the prompt spectral peak energy and the SN peak bolometric magnitude gives an illustrative estimate of $M_{\rm bol,peak}=-19.46\pm0.35$ mag for a putative associated SN. These results support a two-stage evolution of the central engine and variable dusty environment of GRB 240825A, which provides insights into the nature of its progenitor.
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All authors Ren-Jie Xiong, Zi-Qi Wang, Xiao-Li Huang, En-Wei Liang

High Energy Astrophysical Phenomena

Mapping the Contracting Corona in GS 1354-64 with Insight-HXMT and XRISM: Evolving X-ray Lags and Quenched Reflection across a Complete State Transition

Kaushik Chatterjee, Min Wei, Jie Liao et al. (+13 more)

We present a comprehensive broadband spectro-temporal analysis of the dynamically confirmed Galactic black hole transient GS 1354-64 during its 2025-26 outburst, using near-simultaneous observations from Insight-HXMT and XRISM. The high spectral resolution of the XRISM-Resolve microcalorimeter, coupled with the high-cadence broadband coverage of Insight-HXMT, reveals a dramatic evolution in the inner accretion geometry. During the early hard-intermediate state, the spectrum was dominated by a hot Comptonizing corona accompanied by relativistically broadened reflection features. As the outburst progressed, the corona cooled efficiently, the photon index steepened (Gamma >~ 2.5), and the reflection signatures, including the broad Fe K-alpha emission, were quenched, yielding a featureless, disk-dominated continuum. Concurrently, Type-C quasi-periodic oscillations (QPOs) evolved from 0.25 Hz to 6.52 Hz. Cross-spectral timing analysis revealed that the broadband X-ray time lags changed from pronounced positive (hard) delays (~160 ms) at low frequencies to near zero as the source softened. However, a statistical analysis incorporating the measurement uncertainties shows that the broadband lags lack a significant monotonic correlation with the QPO frequency, photon index, or fractional rms. Instead, the scattered lag behavior suggests a competition between positive Comptonization delays and negative thermal reverberation. While the spectral softening and QPO acceleration provide strong evidence for a geometric contraction of the corona (whether interpreted via Lense-Thirring precession or the Two-Component Advective Flow (TCAF) paradigm), the broadband timing properties underscore the turbulent and inhomogeneous nature of the inner flow as the advancing Keplerian disk drives the source into the soft state.
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All authors Kaushik Chatterjee, Min Wei, Jie Liao, Biswaraj Palit, Santanu Mondal, Honghui Liu, Chandra B. Singh, Sandeep K. Rout, Ashutosh Tripathi, Mayukh Pahari, Guobao Zhang, Zejun Jiang, Brajesh Kumar, Wei Wang, Hsiang-Kuang Chang, Xiaowei Liu

Saturday 10 October

High Energy Astrophysical Phenomena

A GeV Gamma-Ray Spectral Excess in the Fermi Blazar 4FGL J0136.5+3906

Shi-Ju Kang, Yue Yin, Yong-Gang Zheng et al. (+2 more)

We report the detection of a $\sim${{19}} GeV gamma-ray spectral excess (peak energy in observer frame) at $\sim$5.7$\sigma$ significance (3 degrees of freedom, without correction for trials and the look-elsewhere effect) in the Fermi-LAT data of the blazar 4FGL J0136.5$+$3906, based on $\sim${17} years of observations. The excess manifests as a distinct bump-like feature in the 100 MeV$-$1 TeV spectrum, with a flux of $\sim$3.6$\rm \times10^{-10}~ph~cm^{-2}~s^{-1}$. No similar feature is detected in nearby sources or background regions. The origin of this signal cannot be explained by standard blazar emission models and remains unknown. This Letter presents the observational finding without providing a definitive physical interpretation.
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All authors Shi-Ju Kang, Yue Yin, Yong-Gang Zheng, Qingwen Wu, Junhui Fan

High Energy Astrophysical Phenomena · Cross-listed from astro-ph.IM

ELISA: A Bayesian X/$\gamma$-ray Spectral Analysis Toolkit

Wang-Chen Xue, Sheng-Lun Xie, Chao Zheng et al. (+11 more)

Forward-folded X/$\gamma$-ray spectral fitting increasingly benefits from Bayesian workflows to better capture counting statistics, background uncertainties, and complex parameter degeneracies, while fully reproducible end-to-end implementations are still not always straightforward to deploy in routine analyses. We present ELISA (Efficient Library for Spectral Analysis), an open-source Python toolkit that streamlines the full spectral analysis loop for X/$\gamma$-ray astronomy: data loading, model construction, inference, and model validation and comparison. ELISA couples a JAX-accelerated forward model with a unified fitting interface, supporting both rapid optimization and modern Bayesian sampling. Built-in diagnostics make convergence checks and predictive assessment a standard part of the workflow, motivating principled model refinement when needed. Using a spectral fitting example of the Insight-HXMT Crab observation, we find substantial improvements in sampling efficiency compared with XSPEC's default MCMC implementation. ELISA is available at https://github.com/wcxve/elisa and on PyPI at https://pypi.org/project/astro-elisa.
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All authors Wang-Chen Xue, Sheng-Lun Xie, Chao Zheng, Shao-Lin Xiong, Xiao-Bo Li, Yong Chen, Peng Zhang, Yan-Qiu Zhang, Jia-Cong Liu, Chen-Wei Wang, Wen-Jun Tan, Yue Wang, Jin-Peng Zhang, Zheng-Hang Yu

High Energy Astrophysical Phenomena

Magnetar X-ray flares as elementary reconnection events in a self-organized critical magnetosphere

Sheng-Lun Xie, Yi Zhao, Wen-Long Zhang et al. (+3 more)

Magnetar bursts are commonly attributed to magnetic energy release, yet the physically relevant dissipation unit has remained uncertain. Here we argue that this unit is not the burst as conventionally defined, but the short substructures within bursts, namely magnetar X-ray flares (MXFs). Using 789 MXFs from SGR~J1935+2154, we show that their waiting times separate into two components, interpreted as reflecting clustered intra-episode events and longer inter-episode intervals, that their proxy emission measure and temperature exhibit distinct rising and declining trends, and that their energy release scale (ERS) proxy distribution has a high-end slope in the same statistical regime as solar and stellar flares. Combined with the previously measured MXF duration slope, these results identify MXFs as a three-dimensional fractal-diffusive self-organized critical (FD-SOC) system with $\beta_{\rm diff}\simeq2$, implying reconnection avalanches that expand linearly through an active magnetosphere. We infer that magnetar active episodes are global unloading states assembled from many elementary flares. Magnetar X-ray flares are therefore the physically relevant units for magnetar outburst statistics and for connecting magnetar high-energy activity to other impulsive phenomena.
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All authors Sheng-Lun Xie, Yi Zhao, Wen-Long Zhang, Chen-Wei Wang, Yun-Wei Yu, Shao-Lin Xiong

High Energy Astrophysical Phenomena

Impact of Decay-Chain Feeding by Long-Lived Heavy Nuclei on Nuclear Cosmochronology

Qiu-Hong Chen, Meng-Hua Chen, Xianlin Yang et al. (+1 more)

Nuclear cosmochronology provides an independent method for determining the ages of astrophysical objects without relying on Galactic chemical evolution models. Long-lived radioactive actinides synthesized via the rapid neutron-capture process ($r$-process) particularly thorium and uranium serve as ideal chronometric nuclei. However, predicting the initial abundances of these nuclei and their subsequent long-term evolution remains a major source of uncertainty in nuclear cosmochronology. In this work, we investigate the impact of decay-chain feeding from long-lived progenitor nuclei on nuclear cosmochronology and estimate the corresponding age corrections. We develop a self-consistent radioactive decay network that includes all relevant decay pathways and couple it to $r$-process nucleosynthesis calculations. By tracking the long-term evolution of $r$-process nucleosynthesis based on neutron star merger trajectories, the dominant long-lived nuclei shaping the evolution of the chronometric elements Th and U are identified as $^{232}$Th, $^{235}$U, $^{236}$U, $^{238}$U, and $^{244}$Pu. It is found that delayed feeding substantially modifies the long-term evolution of actinides particularly for $^{232}$Th, which receives significant late-time contributions from heavier progenitor nuclei such as $^{244}$Pu and $^{236}$U. As a consequence, the U/Th and Th/X chronometers exhibit significant sensitivity to delayed feeding from the progenitor nuclei $^{244}$Pu and $^{236}$U, with age corrections reaching $\sim5$~Gyr. These results suggest that decay-chain feeding from long-lived progenitor nuclei plays a crucial role in nuclear cosmochronology and should be properly accounted for in age determinations based on actinide chronometers.
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All authors Qiu-Hong Chen, Meng-Hua Chen, Xianlin Yang, En-Wei Liang

High Energy Astrophysical Phenomena

Reawakening of GS 1843+00: A Multiwavelength Study of its 2026 Giant X-ray Outburst

Gaurava K. Jaisawal, Georgios Vasilopoulos, Francesco Carotenuto et al. (+1 more)

GS 1843+00 (Ginga 1843+009) is a poorly studied Be/X-ray binary system that underwent a major X-ray outburst in 2026 February-May after nearly sixteen years of quiescence. We present an X-ray, optical, and radio study of GS 1843+00 during this outburst, focusing on the evolution of the neutron star emission geometry, Be-disk connection, and possible outflow activity. We analyse three NuSTAR observations obtained at different stages of the outburst, complemented by archival RXTE and Chandra data, optical spectroscopy and imaging with the Nordic Optical Telescope, and a MeerKAT radio observation. NuSTAR observations reveal coherent X-ray pulsations around 29.7 s with a spin-up rate of $(-5.1\pm0.1)\times10^{-8}$ s s$^{-1}$ during the outburst. The pulse profiles show strong evolution with energy and outburst phase, with distinct morphologies even at comparable luminosities. The pulsed fraction varies between 1 and 16% and exhibits a complex reversal in energy dependence above 7 keV, increasing with energy during the first two observations and decreasing during the third. The 3-79 keV broadband spectra are described by thermal Comptonization with a blackbody and an Fe K$\alpha$ emission line, with no evidence for a cyclotron absorption feature. Phase-resolved spectroscopy reveals variations in the Comptonization and blackbody parameters, indicating changes in the accretion-column structure. Optical spectroscopy confirms the presence of a Be-circumstellar disk through H$\alpha$ and Paschen-series emission lines. No radio counterpart is detected, with a $3\sigma$ upper limit of 36 $\mu$Jy beam$^{-1}$ at 1.28 GHz. Weaker H$\alpha$ emission compared with previous epochs indicates that the Be-circumstellar disk was in a different state during the current episode, while the radio non-detection suggests that any associated outflow activity was faint or below the detection limit.
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All authors Gaurava K. Jaisawal, Georgios Vasilopoulos, Francesco Carotenuto, Hannah C. I. Wichern

Friday 9 October

High Energy Astrophysical Phenomena

The effect of triples on the Chemically Homogeneous Evolution Channel for producing Gravitational Wave Sources

Silvia A. Popa, Selma E. de Mink, Stephen Justham et al. (+3 more)

Despite the growing number of gravitational-wave (GW) detections, the formation of merging binary black holes (BBHs) is still debated. One of the proposed formation channels is Chemically Homogeneous Evolution (CHE), which makes distinct predictions for the properties of the resulting black holes (BHs): high masses ($\gtrsim35\, M_\odot$) and large, orbitally-aligned spins. These predictions are based on studies that consider this channel only in isolated binaries. However, most massive stars reside in triples. We investigate how a tertiary affects the CHE channel. We use detailed binary models computed with MESA for the inner CHE systems coupled with analytical prescriptions for the hierarchical triple dynamics. Specifically, we study the von Zeipel-Lidov-Kozai mechanism that can accelerate the merger of the inner BBHs through high-eccentricity excitations. We show that a tertiary companion enables mergers at higher metallicities, where the classical binary CHE channel does not operate. At $Z_\odot/3$, triples produce BHs with lower masses (around $15\,M_\odot$) and lower spins (around 0.25) compared to the low-metallicity classical scenario. We further expect triple dynamics to lead to spin-orbit misalignment and potential residual eccentricities at merger. In triples at $Z_\odot/3$, half of the mergers occur within 1 Gyr. Moreover, 10% of the population leads to prompt mergers within 1 Myr (1% within 1 kyr) that are of potential interest for electromagnetic counterparts. We conclude that the triple CHE channel is promising as (i) it may contribute more substantially to the local merger rate than had been expected for the classical CHE channel due to the shorter delay times and effectiveness at higher metallicities and (ii) produces mergers with properties that more closely resemble the lower masses and lower spins inferred for most of the observed GW merger population.
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All authors Silvia A. Popa, Selma E. de Mink, Stephen Justham, Jakob Stegmann, Alejandro Vigna-Gomez, Lieke A. C. van Son

High Energy Astrophysical Phenomena · Cross-listed from hep-ph

A Comprehensive Interpretation of the LZ High-Energy Recoil Event: A Minimal $U(1)_B$ Dark Sector and Its Experimental Tests

Mattia Di Mauro

The $248$ keV nuclear-recoil candidate reported by LUX-ZEPLIN (LZ) motivates an inelastic dark matter (DM) interpretation, in which scattering converts the DM particle into a slightly heavier state. We provide a comprehensive study of this interpretation in an anomaly-free model of gauged baryon number, where a new vector boson, $Z_B$, mediates interactions between DM and quarks. Breaking the baryonic gauge symmetry generates the new particle masses and a small splitting between two DM states, while a residual symmetry keeps the lighter state stable. We identify regions compatible with the LZ candidate, the observed DM abundance, and current ATLAS and CMS dijet constraints. Within the scanned domain, these regions span DM masses $m_\chi\simeq0.19$-$4.5$ TeV, mediator masses $M_{Z_B}\simeq0.05$-$5.0$ TeV, and gauge couplings $g_B\simeq0.004$-$0.74$, with correlated values of these parameters. A representative thermal solution has $m_\chi=1$ TeV, $M_{Z_B}=1.44$ TeV, $g_B\simeq0.228$, and a mass splitting of $300$ keV. A small electroweak mixing allows the heavier DM state to decay rapidly, suppressing unwanted signals from its surviving population. This interpretation can be tested through complementary measurements: additional LZ and XENONnT data can establish whether the high-energy recoil signal persists, ATLAS and CMS Run-3 dijet searches can probe the mediator mass and coupling, and a dedicated IceCube analysis of four-quark final states can test DM capture and annihilation in the Sun. Together, these measurements can test complementary parts of the surviving region and assess whether the LZ candidate is consistent with this interpretation.
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High Energy Astrophysical Phenomena

A Pipeline for the AI-Assisted Analysis of Imaging X-ray Polarimetry Explorer Observations of Black Hole X-ray Binaries and Limits on Their Polarization Variability

B. Domine, B. Liu, H. Krawczynski et al. (+3 more)

The Imaging X-ray Polarimetry Explorer (IXPE) has opened a new window into the high-energy Universe, with the capability to measure the arrival time, arrival direction, energy, and, for the first time with the required sensitivity, the polarization of X-rays from black holes, neutron stars, and other cosmic sources of X-rays. In this paper, we discuss the use of Artificial Intelligence (AI) agents for the analysis of IXPE data. The pipeline combines an immutable code base with evolving knowledge databases. The generation of analysis projects makes use of a literature data base to judge the novelty of the proposed analysis projects. We emphasize that the analysis requires two types of expert knowledge: detailed instructions about how to reduce the X-ray data, and expert knowledge about how to interpret the results. We employ several levels of auditors that scrutinize the analysis plan, the analysis scripts, and the analysis results for data and method adequacy. The pipeline includes a staggered approach to interpret the analysis results. We present exemplary results from the pipeline applied to IXPE observations of Black Hole X-ray Binaries (BHXRBs) including comparisons of results from the analysis pipeline with published results and a systematic search for polarization degree and polarization angle variability in long IXPE observations. We critically discuss the performance of the pipeline and future avenues for improving it.
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All authors B. Domine, B. Liu, H. Krawczynski, M. Kundu, Shravan Vengalil Menon, Fang Zhou

High Energy Astrophysical Phenomena · Cross-listed from astro-ph.GA

A first view of interstellar Fe-bearing dust grains with XRISM

I. Psaradaki, L. Corrales, E. Costantini et al. (+8 more)

Understanding the reservoirs of iron (Fe) in our Galaxy is crucial for probing the mechanisms that drive dust grain growth in the interstellar medium (ISM). High-resolution X-ray absorption spectroscopy offers a powerful tool to investigate the chemistry of dust grains, particularly those containing Fe, through spectroscopic features near photoabsorption edges known as X-ray Absorption Fine Structures (XAFS). With the Resolve spectrometer aboard XRISM, we can now examine the Fe K-edge (7.1 keV) owing to its improved spectral resolution in this energy range. This enabled us to probe the dust grain chemistry in high Galactic column densities. In this work, we present a pilot study on dust grain chemistry through the Fe K-edge of the XRISM Performance Verification target GX 340+0. This source is a persistently bright low-mass X-ray binary with a hydrogen column density of 6.6x10^22 cm^-2 along the line of sight, providing sufficient optical depth at the Fe K-edge. By fitting combined dust and gas models, we find that Fe is depleted by 95% into dust along the line of sight towards the source. Moreover, we find evidence that 38% of the solid-phase Fe is in metallic iron, 47% in iron sulfides, and the remainder in silicates. The large contribution from metallic iron and iron sulfides differs from what is typically inferred from X-ray studies of diffuse ISM and may suggest that that these compounds become more significant reservoirs of Fe in higher column density Galactic sightlines.
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All authors I. Psaradaki, L. Corrales, E. Costantini, M. Mehdipour, D. Rogantini, H. Takahasi, R. Ballhausen, P. Chakraborty, T. Nakagawa, R. K. Smith, S. Zeegers

High Energy Astrophysical Phenomena · Cross-listed from cond-mat.stat-mech

IceCube data for astrophysical neutrinos exhibit q-statistical behavior

Constantino Tsallis and Ugur Tirnakli

Relevant IceCube recent data for astrophysical neutrinos are analyzed. Similarly to cosmic rays and proton-proton LHC collisions, the corresponding spectra are satisfactorily described, for the entire interval of measured energies, through q-Gaussians. This fact reinforces the already available evidence that nonadditive entropies (either of the $S_q$ class or of the $S_{delta}$ one, or even alternative ones) appear to play a crucial role in systems such as black holes and related cosmological phenomena (e.g., dark energy). The IceCube data yield sensibly high values for the momenta-distribution nonadditive index (q \simeq 1.6), in contrast with the cosmic rays values (q \simeq 1.2) and the LHC values (q \simeq 1.1). This fact neatly indicates very-long-ranged space-time correlations. The detailed associated physical mechanisms remain, at the present stage, as an instigating open issue.
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High Energy Astrophysical Phenomena

Adiabatic evolution of hadronic neutron stars

Domenico Logoteta, Francesco Zeno Constanzo, Ignazio Bombaci et al. (+3 more)

In this paper we compute several structural properties of static and rotating neutron stars, considering both rigid and differential rotation. To this end, we use a finite-temperature beta-stable equation of state (EOS) extending the zero-temperature hadronic EOS derived by Fortin et al. (2017). We account for the formation of hyperons and the presence of a neutrino-trapped component. Our goal is to provide insights into the long-term evolution of a protoneutron star (PNS) formed after a core-collapse supernova (CCSN) or a remnant resulting from a binary neutron star merger (BNSM). The EOS is derived using a relativistic mean-field quantum many-body theory within the Hartree approximation. Coupling constants are determined using experimental data on hypernuclei and hypernuclear matter to better account for uncertainties in hyperon single-particle potentials. Our EOS models reproduce the typical features of cold neutron stars and PNSs for nucleonic and hyperonic compositions. In particular, they are consistent with measured masses (2.01 M_sun and 2.14 M_sun for PSR J0348+0432 and PSR J0740+6620) and dimensionless tidal deformabilities from GW170817. Thermal contributions act differently depending on composition and rotation state. Finally, our evolutionary scheme provides a simple way to interpret the long-term evolution of BNSM remnants or PNSs from CCSNe, complementing dynamical simulations unable to cover full evolutionary timescales.
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All authors Domenico Logoteta, Francesco Zeno Constanzo, Ignazio Bombaci, Sebastiano Bernuzzi, Albino Perego, David Radice

High Energy Astrophysical Phenomena · Cross-listed from nucl-th

Impact of ab initio E1 strength on neutron capture rates along the nickel isotopic chain

Francesca Bonaiti and Joanna E. Sobczyk

Nucleosynthesis simulations of the r-process require neutron capture rates for neutron-rich nuclei, many of which lie beyond experimental reach. Predicting these rates relies on theoretical calculations of the low-energy electric dipole (E1) strength near the neutron threshold. We present the first ab initio computation of the E1 strength along the nickel isotopic chain, for $^{58}$Ni and the even-even isotopes $^{68-80}$Ni. The E1 strength is obtained with the Lorentz integral transform coupled-cluster (LIT-CC) method, extended to axially symmetric reference states to reach open-shell nuclei, using two- and three-nucleon interactions from chiral effective field theory. The approach is benchmarked against the measured photoabsorption cross section of $^{58}$Ni and the E1 strength of $^{68}$Ni. Along the chain we find low-lying E1 strength above the neutron threshold that grows with neutron number. Including it in the reaction code TALYS enhances the neutron capture rates forming $^{68-78}$Ni between 3 and 10 GK, with an effect that increases with temperature and neutron number and an uncertainty dominated by the inversion of the integral transform. For $^{80}$Ni, where strong pygmy dipole strength lies just above threshold, the enhancement sets in already around 0.5 GK. Together, these results open the way to ab initio input for neutron capture rates along isotopic chains far from stability.
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High Energy Astrophysical Phenomena

Perpendicular transport in isotropic magnetic turbulence. The role of stochastic drifts

F. Pucci, P. Blasi, O. Pezzi et al. (+2 more)

In cosmic ray propagation through turbulent magnetic fields, transport perpendicular to the mean field plays an important role in various astrophysical environments. Numerical simulations have shown that parallel and perpendicular diffusion coefficients exhibit different energy scalings, causing their ratio to increase with energy, but a comprehensive theoretical explanation remains elusive. Here, we investigate perpendicular diffusion using test particle simulations in synthetic isotropic turbulence spanning 6-7 orders of magnitude in wavenumber, together with a theoretical extension of nonlinear guiding center theory that incorporates stochastic drifts. Our approach combines field line random walk and random guiding center drifts to describe perpendicular transport. We find that parallel and perpendicular diffusion coefficients exhibit the same energy scaling only for $r_L \lesssim 10^{-2} L_c$, where $r_L$ is the particle Larmor radius and $L_c$ is the turbulence coherence length. At higher energies, perpendicular diffusion develops a stronger energy dependence, consistently across different turbulence levels. Our theoretical model suggests that this behavior arises from stochastic drifts induced by turbulent magnetic field components parallel to the mean field.
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All authors F. Pucci, P. Blasi, O. Pezzi, C. Evoli, F. Malara