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Physics Astrophysics High Energy Astrophysical Phenomena

astro-ph.HE Watch High Energy Astrophysical Phenomena

Friday 9 October

High Energy Astrophysical Phenomena

TeV Gamma-Ray Emission in the DA 495 Region from HAWC Observations of J1952+2924, J1954+2837, and J1958+2848

R. Alfaro, C. Alvarez, E. Anita-Rangel et al. (+82 more)

Previous observations of the DA 495 region, which contains the pulsar wind nebula (PWN) DA 495 and other very-high-energy (VHE; $>100~\textrm{GeV}$) gamma-ray emitters, showed inconsistent results across different VHE experiments, including differences in the measured flux of DA 495 and in the number of reported sources. Our new dedicated analysis using 3071 days of HAWC data resolves these discrepancies. We identify three extended sources, HAWC J1952+2924 (DA 495), HAWC J1954+2837, and HAWC J1958+2848, all with curved spectra, and find a hint of a fourth source. For DA 495, a multi-wavelength analysis, including our results, radio, X-ray, and other gamma-ray data, reveals that its extended emission is best described by leptonic interactions with an inferred magnetic field of $B\sim10~\mu\textrm{G}$ and that hadronic components are not required. On the other hand, we interpret the other two sources, which have no confirmed counterparts, as TeV halos associated with nearby pulsars, PSR J1954+2836 and PSR J1958+2846, respectively. These results reinforce the interpretation of DA 495 as a leptonic-dominated PWN and add two candidates to the growing population of TeV halos.
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All authors R. Alfaro, C. Alvarez, E. Anita-Rangel, M. Araya, J. C. Arteaga-Velázquez, D. Avila Rojas, H. A. Ayala Solares, R. Babu, P. Bangale, A. Bernal, T. Capistrán, A. Carramiñana, S. Casanova, U. Cotti, J. Cotzomi, S. Coutiño de León, E. De la Fuente, N. Di Lalla, R. Diaz Hernandez, M. A. DuVernois, J. C. Díaz-Vélez, C. Espinoza, N. Fraija, S. Fraija, A. Galván-Gámez, J. A. García-González, F. Garfias, N. Ghosh, A. Gonzalez Muñoz, M. M. González, J. A. González, J. A. Goodman, J. Gyeong, J. P. Harding, I. Herzog, D. Huang, F. Hueyotl-Zahuantitla, P. Hüntemeyer, A. Iriarte, S. Kaufmann, D. Kieda, K. Leavitt, W. H. Lee, H. León Vargas, A. L. Longinotti, G. Luis-Raya, K. Malone, O. Martinez, J. Martínez-Castro, J. A. Matthews, P. Miranda-Romagnoli, P. E. Mirón-Enriquez, J. A. Morales-Soto, E. Moreno, M. Mostafá, M. Najafi, L. Nellen, M. U. Nisa, R. Noriega-Papaqui, M. Osorio-Archila, E. Ponce, Y. Pérez Araujo, E. G. Pérez-Pérez, C. D. Rho, D. Rosa-González, M. Roth, A. Sandoval, J. Serna-Franco, M. Shin, A. J. Smith, Y. Son, R. W. Springer, O. Tibolla, I. Torres, R. Torres-Escobedo, L. Villaseñor, X. Wang, Z. Wang, I. J. Watson, H. Wu, S. Yu, S. Yun-Cárcamo, X. Zhang, H. Zhou, C. de León

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

The School on Gravity: from motion to commotion

Vitor Cardoso, Jose María Ezquiaga, Julio Parra-Martinez et al. (+3 more)

Understanding the gravitational interaction is one of the great scientific endeavors of the 21st century. The Nobel Prize-winning discovery of gravitational waves in 2015, and subsequent detections by the LIGO-Virgo-KAGRA Collaboration, have marked a revolutionary step forward in physics and astrophysics by opening an entirely new window for exploring the Universe. Future upgrades to these detectors, along with upcoming facilities such as LISA, the Einstein Telescope, and radio and optical instruments, promise other breakthrough discoveries that the next generation of scientists will need to interpret. The School on Gravity (22–26 June 2026, Copenhagen) aimed to introduce junior scientists–graduate students and advanced undergraduates with a background in general relativity–to a wide range of foundational topics in the exciting new field of gravitational-wave physics. Topics spanned from the theory of motion, to new challenges introduced by quantum physics, to the astrophysics of black holes and source modeling for gravitational-wave detectors. The School on Gravity took place at the legendary Auditorium A of the Niels Bohr Institute, inviting students and lecturers to challenge current paradigms in gravitational physics in the spirit of the quantum revolution that unfolded in this very room. These lecture notes aim at opening up those new ideas presented in Auditorium A to the rest of the scientific community.
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All authors Vitor Cardoso, Jose María Ezquiaga, Julio Parra-Martinez, Laura Sberna, Gustavo J. Turiaci, Lieke van Son

High Energy Astrophysical Phenomena

Flip-Flop Shocks and Tori in Bondi-Hoyle-Lyttleton Accretion onto Rotating Kerr-Weyl Black Holes and Their Quasi-Periodic Variability

Orhan Donmez, Imtiaz Khan and G. Mustafa

We present GRHD simulations of Bondi-Hoyle-Lyttleton accretion onto a rotating black hole in Weyl conformal gravity, described by the Kerr-Weyl metric. The equatorial flow is evolved for spins a=0.9M and a=0.5M and several Weyl coefficients, which enter through an effective curvature parameter k, and is compared with Kerr runs sharing the same setup. For the k considered, the horizon, ISCO and test-particle frequencies differ from Kerr by at most ~2%. However, the curvature term grows as kr^2 and acts at the accretion radius R_acc. The flow is controlled by one quantity, eta=|k|R_acc^3/M, the ratio of curvature-induced to Newtonian acceleration at R_acc. For eta<~0.03 a stable shock cone forms, indistinguishable from Kerr. For eta~0.2-0.3 the anti-de Sitter-like term traps shocked gas behind the black hole and drives persistent flip-flop oscillations. For eta>~1.6 the cone is destroyed and an oscillating torus forms. Spin modifies only the inner few gravitational radii and does not change the regime. In strongly deviating models the mean accretion rate is 1.7-3 times the Kerr value and varies by 20-60% rms, versus 0.1-1% in Kerr-like flows. The power spectra show global QPOs with fundamentals at 2.9-4.8 Hz for a 10 Msun black hole, with harmonic ladders whose 3:2 and 2:1 ratios come from one non-sinusoidal oscillation, not resonances. These lie in the low-frequency QPO band and are unrelated to test-particle frequencies (~70-200 Hz). They scale as f_0=xi f_K(R_acc), with xi~0.7-1.1 for stable cones and xi~0.23-0.38 for flip-flop and torus regimes. Strong oscillations would be detectable within seconds for a bright Galactic source. The required |k| exceeds galactic-rotation-curve values by 18-36 orders of magnitude, so a detected shock-driven QPO would measure a local deviation from Kerr, and its absence would constrain |k|.
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High Energy Astrophysical Phenomena

Extreme mass ratio inspirals from the Hills mechanism, The eccentricity distribution of Hills EMRIs in LISA

Biancamaria Sersante, Davide Mancieri, Kevin Leopoldo Muñoz Zavala et al. (+4 more)

Extreme mass ratio inspirals (EMRIs) are promising sources for future space-based gravitational-wave detectors. We investigate EMRIs produced through the Hills mechanism, in which a stellar-mass black-hole binary (BBH) is tidally separated by a massive black hole (MBH), leaving one component bound to it. We present the first self-consistent modelling of this channel, combining an orbit-averaged Fokker-Planck treatment of the nuclear star cluster (NSC), three-body modelling of the binary-MBH encounter, Monte Carlo evolution of captured black holes (BHs), and fully relativistic EMRI trajectories to follow the evolution from binary supply down to final plunge. We find that Hills EMRIs are substantially more circular than classical EMRIs formed through two-body relaxation. For an MBH of $4 \times 10^6 M_\odot$ and circular, equal-mass BBHs of $20 M_\odot$ with initial separation of $0.1$ AU, EMRI mean eccentricities are approximately $0.097$ at our adopted LISA-band entry threshold and $0.034$ at plunge, compared with $0.478$ and $0.228$, respectively, for classical EMRIs. Of the initial BBHs, approximately $0.4$ per cent become EMRIs, whereas approximately $60$ per cent of captured BHs do. For comparable NSC initial compact-object mass, we find approximately $1.6 \times 10^{-8}$ Hills EMRIs per year per galaxy, approximately $12$ per cent of the classical EMRI yield. The Hills channel contribution to the overall eccentricity distribution depends strongly on the binary mass fraction in NSCs. We discuss implications for identifying EMRI formation channels with LISA and for quasi-periodic eruptions.
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All authors Biancamaria Sersante, Davide Mancieri, Kevin Leopoldo Muñoz Zavala, Luca Broggi, Zephyr Penoyre, Elena Maria Rossi, Alberto Sesana

High Energy Astrophysical Phenomena

Resistive alignment of a black-hole magnetosphere

Ruben Lier and Oliver Porth

Recent numerical simulations have shown that black-hole magnetospheres evolve rapidly toward alignment between the magnetic axis and spin axis but the physical origin of this process has remained unclear. We develop an analytic theory of this alignment within resistive relativistic magnetohydrodynamics. Taking the slow-spin Blandford-Znajek monopole solution as the exterior magnetic field, we reduce the induction equation to a relaxation equation for the current-sheet inclination angle. Our analysis shows that alignment results from second-order spin effects in the Blandford-Znajek solution combined with explicit resistive dissipation. We test this prediction using resistive-GRMHD simulations at several spins and resistivities and find a regime in which the measured late-time secular decay agrees quantitatively with the analytic prediction.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Binary Ellis-Bronnikov wormholes in 3+1 numerical relativity: mergers, fly-bys and gravitational waves

Nikita M. Shirokov and Ilya Nachevsky

We present what are, to our knowledge, the first 3D numerical-relativity evolutions of wormhole binaries: pairs of massive Ellis-Bronnikov drainholes held open by a ghost scalar field. Each throat is an unstable fixed point whose e-fold time matches the González-Guzmán-Sarbach linear rate to within 1.9%. Two throats obey a charge-sign rule: like scalar charges repel and opposite charges attract, with a measured attraction-to-repulsion ratio of $1.462\pm0.022$ against the predicted 3/2, so only opposite-signed pairs merge. A head-on collision forms a common MOTS around both still-open throats, born with about their combined area. The horizon then loses 28% of its area as it swallows the phantom field, and by $t=100$ lies within 1.4% of the Schwarzschild radius of the pair's mass, still shrinking. Fly-by pairs form no horizon and both mouths inflate, the one nearest capture radiating the most gravitational-wave energy measured. A lone collapsing throat sheds its seeded quadrupole as a burst ringing at the Schwarzschild frequency of the black hole it becomes, and every encounter radiates its own burst of gravitational waves and a scalar dipole of comparable energy and negative sign. A throat survives at most a few orbital periods for any plausible perturbation, and the negative-energy dipole would pump rather than drain the orbit, so these binaries have no inspiral.
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High Energy Astrophysical Phenomena

Simulation Study of Reconstruction of Cosmic Ray Extensive Air Shower with Thermal Neutron Detected by ENDA

Fan-Ping Li, Xin-Hua Ma, Hu Liu et al. (+25 more)

In the investigation of the "knee" region within the cosmic ray energy spectrum, extensive air shower (EAS) reconstruction by using different EAS secondary particles are of paramount importance for energy determination and composition separation and finally measurement of energy spectrum of different cosmic ray composition. The Electron-Neutron Detector Array (ENDA) is designed to detect thermal neutrons generated in the ground by high energy hadrons which constitute the "backbone" of EAS and carry vital information regarding the primary cosmic rays. At present, ENDA-64, consisting of 64 detectors, is employed inside the Large High Altitude Air Shower Observatory (LHAASO). This work simulates the response of ENDA and investigates the lateral distributions of thermal neutrons. A comparison of the NKG and double-exponential functions for describing this distribution using MC simulation data shows that the double-exponential function is more accurate. The mean difference between fitted and measured thermal neutron density is within ~ 6%. Meanwhile, the thermal neutron density at 10 m from the shower axis, $\rho_n$, depends mainly on the sum of all hadrons energy or the number of high-energy hadrons. The relationship between $\rho_n$ and EAS hadron energy or the number of high-energy hadrons can be well fitted by a linear function on a log scale. This work is fundamental for energy determination and composition separation with hybrid detection by using ENDA in the near future.
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All authors Fan-Ping Li, Xin-Hua Ma, Hu Liu, Tian-Lu Chen, Shu-Wang Cui, Danzengluobu, Xin-Rui Gao, Wei Gao, Wen-Chao Gao, Hai-Bing Hu, Denis Kuleshov, Kirill Kurinov, Bing-Bing Li, Mao-Yuan Liu, Ye Liu, Igor Maliy, Da-Yu Peng, Yao-Hui Qi, Jia-Bo Qin, Dong Qu, Oleg Shchegolev, Yuri Stenkin, Yu-Sen Wang, Tian-Shuang Yang, Li-Qiao Yin, Hui-Qian Zhang, Liang-Wei Zhang, Shi-Yuan Zhang

High Energy Astrophysical Phenomena

Flux Evolution of PSR B0540–69 and the Spectral Energy Distribution of its Pulsar Wind Nebula

Juan Zhang, Xuezhi Liu, Junyang Zhang et al. (+12 more)

The young Crab-like pulsar PSR B0540–69, located in the Large Magellanic Cloud, underwent a spin-down rate transition (SRT) in 2011 December, after which its pulsar wind nebula (PWN) was reported to brighten up to 2018. In this work, we extend the study of its X-ray and $\gamma$-ray flux evolution through 2026 by combining observations from multiple X-ray instruments with data from the Fermi Large Area Telescope, thereby constructing a flux history of the PSR$+$PWN system spanning more than two decades. We find that the enhanced X-ray luminosity of the PSR$+$PWN system has persisted for more than 14 yr after the SRT, up to early 2026, whereas the pulsed X-ray flux remains unchanged across all epochs. This confirms that the brightening originates from the PWN. In the $\gamma$-ray band, neither the pulsed nor the non-pulsed flux shows any detectable long-term variation between 2008 and 2025. Together, these results imply that the additional spin-down energy released at the SRT has been continuously injected into the PWN over decades, placing strong constraints on the energy budget and physical mechanism of the transition. Combining the non-pulsed X-ray and $\gamma$-ray fluxes measured here with previously published radio-to-UV data, we further construct a broadband spectral energy distribution of the PWN, which shows properties markedly different from those of the Crab Nebula.
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All authors Juan Zhang, Xuezhi Liu, Junyang Zhang, Hanlong Peng, Mingyu Ge, Songzhan Chen, Shanshan Weng, Shijie Zheng, Shumei Jia, Chengkui Li, Haisheng Zhao, Ju Guan, Yong Chen, Liming Song, Fangjun Lu

High Energy Astrophysical Phenomena

ASKAP Monitoring of the Rubin Deep Drilling Fields

Dougal Dobie, James Freeburn, Iris de Ruiter et al. (+5 more)

In the past decade, time domain astronomy surveys across the multi-messenger spectrum have developed "alert streams" which circulate observational information in real-time to the wider astronomical community. Despite this being standard practice for optical, gamma-ray and gravitational wave time domain astronomy for several years now, this kind of infrastructure has not yet been deployed at-scale for radio telescopes. We are conducting a long-term monitoring program that targets the Rubin Deep Drilling Fields using the Australian SKA Pathfinder (ASKAP). The primary goal of this program is to provide serendipitous radio observations of all objects of interest in these fields, and circulate that information in as close to real-time as possible. In this manuscript we outline the survey plans and status, the infrastructure we have developed to disseminate this information and an initial data release comprising 5 months of ASKAP observations of each field (although only 3 months overlaps with Rubin) conducted on an approximately 10 day cadence with a noise level of $\sim 60\,\mu$Jy. As part of this data release, we present updated high-cadence radio light curves to the tidal disruption event AT2018hyz and the supernova SN2024abfo along with the discovery of two new radio variables, a possible tidal disruption event ASKAP J095711.5+051205 and an in-progress extreme scattering event ASKAP J005026.4-422958. The scientific results from this program along with the infrastructure developed to acquire them will lay the foundation for the integration of future radio imaging surveys into the broader multi-messenger alert stream, leading the way for major facilities such as the Schmidt Observatory System and the SKA.
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All authors Dougal Dobie, James Freeburn, Iris de Ruiter, Katie Auchettl, James Coulson, Brent Miszalski, Anais Möller, Nikhil Sarin

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

In-flight Timing Calibration of the Follow-up X-Ray Telescope on Board the Einstein Probe

Juan Zhang, Xiaofan Zhao, Dawei Han et al. (+18 more)

After the launch of Einstein Probe (EP), pulsars are observed to calibrate the timing system of the onboard Follow-up X-ray Telescope (FXT) by measuring the times of arrival (TOAs). FXT has two independently operating modules, namely FXTA and FXTB, each equipped with the Wolter-I optics and the pnCCD camera. For scientific observations, each pnCCD has three distinct readout modes that differ in frame cycles, the full frame mode (FF, 50 ms per frame), the partial windowed mode (PW, 2.2 ms per frame), and the timing mode (TM, 23.68 $\mu$s per row, 9.4352 ms per frame). Thus, 1RXS J170849.0–400910 with the spin period of 11 s is observed in FF, PSR B1509–58 (150 ms) in PW, and Crab pulsar (33 ms) in TM as well as PSR B1821–24 (3.05 ms) and PSR B1937+21 (1.56 ms). The TOAs of these pulsars measured by FXTA and FXTB are compared with the results of NICER, and for Crab pulsar with the Jodrell Bank Monthly Ephemeris (JBE). Results verify that the timing system of FXTA and FXTB in FF, PW, and TM modes are consistent with each other, and are in good alignment with NICER. The measured advance of the Crab pulsar's main peak relative to JBE is $357^{\pm14(stat)}_{\pm54(sys)} \mu$s in FXTA and $394^{\pm14(stat)}_{\pm67(sys)} \mu$s in FXTB. Based on measurements of PSR B1821–24 and PSR B1937+21, the preliminary absolute timing accuracy is estimated to be 6 $\mu$s for FXTA and 31 $\mu$s for FXTB in TM mode. Additionally, the systematic delay of FXTA timing results relative to FXTB is found to be $20^{\pm19(stat)}_{\pm21(sys)} \mu$s.
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All authors Juan Zhang, Xiaofan Zhao, Dawei Han, Hao Wang, Yong Chen, Mingyu Ge, Shijie Zheng, Shumei Jia, Haisheng Zhao, Weiwei Cui, Hanlong Peng, Wentao Ye, Yaoming Duan, Youli Tuo, Zhen Ji, Fuli Ma, Chengkui Li, Ju Guan, Jingjing Xu, Jin Wang, Liming Song

Thursday 8 October

High Energy Astrophysical Phenomena

Disk Structure May Determine AGN Variability and Explain the Accretion Disk Size Problem: No Broad Line Region Required

Amy Secunda, Yan-Fei Jiang and Jenny E. Greene

Variability is a crucial probe of active galactic nuclei (AGN) disks, but the impact of the structure and internal physics of the disk on this variability is poorly understood. We perform 3D multi-frequency radiation magnetohydrodynamic simulations of the $1300-5940~\rm{\AA}$ emitting region of an AGN disk. This turbulent disk simulation happens to stochastically have different disk thickness above and below the midplane. Light curves emitted from the thin top of the disk are broadly consistent with traditional variability models, where the X-ray irradiation emitted from the corona is the main driver of variability in UV-optical light curves. Conversely, the UV-optical light curves emitted from the thicker bottom of the disk are not strongly correlated with the X-ray light curve and have disk continuum reverberation mapping lags that are $3-5\times$ longer than the light travel time. While these features are inconsistent with traditional variability models, they are in good agreement with numerous recent observations. Our simulations allow us to interpret these recent observations with a new model for AGN disks, where the thicker disk leads to greater X-ray absorption, less X-ray reprocessing at larger disk radii, and a stronger signal from intrinsic variability driven by fluctuations in the AGN disk. In our simulations, we can measure the inflow timescale of these fluctuations as a long lag between light curves emitted from different disk radii. Understanding how disk structure impacts AGN variability and reverberation mapping can allow us to predict the thickness of AGN disks using UV-optical AGN light curves.
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High Energy Astrophysical Phenomena

Discovery of Hidden Extragalactic Pulsars in the Parkes Archival Data

Rahul Sengar, Laila Vleeschower, Matthew Bailes et al. (+3 more)

Just over 1% of the known radio pulsar population resides in the Large and Small Magellanic Clouds (MCs), the satellite galaxies that are 50-62 kpc distant from the Milky Way. These pulsars are important for constraining the peak of the pulsar luminosity function, and may give insights into neutron star populations formed from stars of different metallicities than the Milky Way. Using search techniques that have proven highly effective at discovering a large number of pulsars in archival data by folding candidates near the noise floor at high harmonic folds, we reprocessed the original Parkes Multibeam MC surveys and discovered six pulsars. Five of these pulsars are located in the Large Magellanic Cloud (LMC), including one with a spin period of 3.8s, making it the slowest pulsar known in the MCs. The remaining pulsar was detected toward the Small Magellanic Cloud (SMC), and is associated with the Milky Way foreground. Four of the newly discovered pulsars exhibit scintillation, with one showing clear nulling and others showing possible nulling behavior. These discoveries bring the total number of radio pulsars known in the LMC to 49. A luminosity function and duty cycle analysis of all current MC pulsars shows that they are consistent with Galactic canonical pulsars. Population synthesis simulations suggest that deeper surveys would reveal many more pulsars in the MCs, including up to handful of millisecond pulsars, based on the adopted upper limits for their parent populations. Finally, this reprocessing demonstrates the continued importance of reanalyzing archival data, both to improve the completeness of pulsar surveys and detect scientifically valuable objects.
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All authors Rahul Sengar, Laila Vleeschower, Matthew Bailes, Fronefield Crawford, Duncan R. Lorimer, Joshua P. Ridley

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

Listening to the Horizon: Probing Near-Horizon Reflectivity with GW250114

R. Prasad, Subhodeep Sarkar and Sudipta Sarkar

Testing the horizon properties of astrophysical black holes is a central goal of gravitational-wave astronomy. The recently identified Direct Wave (DW), a prompt non-quasinormal component of GW250114, provides a new probe of near-horizon physics. While it remains unclear whether the DW itself carries horizon information, we show that it enables a novel null test of horizon reflectivity. If the remnant is an exotic compact object (ECO) with a partially reflecting surface, inward plunge radiation is reflected and leaks back through the gravitational potential barrier, producing a delayed DW echo whose amplitude is set by the surface reflectivity ($|\mathcal{R}_s|$). We construct the corresponding echo template, normalized by the observed DW, and search for it in quasinormal-mode-filtered data. We find no evidence for an echo ($\ln\mathcal{B}=-2.9$) and obtain the 90% credible bound $|\mathcal{R}_s|<0.06$, corresponding to a reflected energy fraction below $0.4\%$, for surfaces from $0.1\, M_f$ to a Planck length from the would-be horizon. Our method thus turns the prompt ringdown signal into a direct test of horizon reflectivity.
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High Energy Astrophysical Phenomena · Cross-listed from astro-ph.GA

ACORN I. Massive Black Hole Seeding and Tidal Disruption Events from Star Clusters in Cosmological Simulations

Yihao Zhou, Tiziana Di Matteo, Claire E. Williams et al. (+6 more)

JWST has revealed massive star clusters at $z\gtrsim 6$, which provide promising environments for massive black hole (MBH) seed formation. We introduce a new MBH seeding model for cosmological simulations, physically motivated by the runaway collisions in star clusters. Subgrid star clusters are generated according to the local ISM and evolved through stellar evolution and two-body relaxation. The masses of MBH seeds formed through runaway collisions are determined by the properties of their host clusters, including the effects of metallicity-dependent stellar winds. We further follow tidal disruption events (TDEs) with the evolving clusters, which can be enhanced in MBH binaries, and account for gravitational-wave (GW) recoil following MBH mergers. We implement this model in a constrained simulation of a 5$\sigma$ overdense region, where seeds of $10^{3}-10^{5.6}\,M_\odot$ form in clusters with $10^{4}\leq m_{\rm SC}\leq 10^{8}\,M_\odot$. Because both the seed abundance and mass are directly connected to the local environment, we have a more physical $M_{\rm BH}\!-\!M_{\rm galaxy}$ scaling for low-mass galaxies ($M_{\rm galaxy}\sim10^{6-9}\,M_\odot$), a regime poorly described by previous seeding models. Multiple MBHs are naturally allowed to form in-situ within individual halos, producing a spatially clustered population. This increases the MBH merger rate by $\sim100$ relative to other seeding models, significantly enhancing the expected LISA event rate. TDEs can dominate the growth of $10^{3-4}\,M_\odot$ MBHs and produce luminous flares of $L_{\rm peak}\sim 10^{42-43}\,{\rm erg\,s^{-1}}$, increasing the observability of low-mass seeds. This seeding prescription accelerates early MBH growth at $z\gtrsim 8$, while subsequent self-regulated gas accretion drives the central MBH toward similar masses $\sim10^{8.6}\, M_\odot$ by $z=6$ across different seeding models.
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All authors Yihao Zhou, Tiziana Di Matteo, Claire E. Williams, Aklant Kumar Bhowmick, Marta Reina-Campos, Carl L. Rodriguez, Elena González Prieto, Laura Blecha, Rupert Croft

High Energy Astrophysical Phenomena

Funnel Leakage of the Wien Fireball in the Early Nebula after a Binary Neutron Star Merger

Shao-Ze Li, Yun-Wei Yu, He Gao et al. (+2 more)

A newborn neutron star (NS) that survives after a binary NS merger can inject its rotational energy into the surrounding ejecta while the ejecta are still optically thick. The injected energy is redistributed by the pair cascade, and the nebula becomes a radiation-dominated plasma composed of photons and e^+- pairs. Compton scattering then governs the energy exchange while the photon number is conserved in scattering. This nebula is evolved with a one-zone model that includes pair creation, annihilation, photon injection, diffusion, and in particular the leakage through the jet-induced polar funnel. For typical parameters, we find that the Compton parameter y is much larger than unity at early times. The nebula therefore remains in saturated Comptonization for 100 s to a few thousand seconds, depending on the magnetic field strength of the post-merger NS. The radiation field takes a Wien spectrum with a Compton equilibrium temperature. The nebula is then a so-called Wien fireball. The Compton temperature decreases from tens of keV to a few keV at early times. As long as the ejecta are optically thick, the funnel leakage is comparable to or exceeds the adiabatic loss. The funnel emission is quasi-thermal, and its isotropic-equivalent luminosity is much higher than the spin-down luminosity. We suggest that the quasi-thermal components observed in the extended emission of short gamma-ray bursts could come from the funnel leakage of the nebula fireball.
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All authors Shao-Ze Li, Yun-Wei Yu, He Gao, Peng-Cheng Yang, Yu Qu

High Energy Astrophysical Phenomena

A morphological search for stable year-scale modulation in gamma-ray blazars

Adithiya Dinesh, Alberto Domínguez, Alba Rico et al. (+3 more)

Year-scale quasi-periodic oscillations (QPOs) in blazar gamma-ray light curves have been proposed as signatures of supermassive binary black holes and precessing jets. Red noise can mimic periodicity, and detection alone does not establish persistence or period stability. We develop and calibrate a morphological framework to characterize year-scale modulation and constrain the incidence of stable modulation in blazars. We analyze 120 Fermi-LAT light curves spanning 18.1 yr. Singular spectrum analysis selects the oscillatory mode and period, while weighted wavelet Z-transform ridge tracking measures persistence, period drift, and cycle-to-cycle volatility. Flux randomization, 10,000 red-noise simulations, and about 20,000 injections calibrate the classification. Of 97 quality-selected sources, two show persistent, coherent modulation consistent with a stationary period (Rank I: PG 1553+113 and B2 1215+30), six show coherent modulation whose stationarity cannot be established (Rank II), and 89 form Rank III. Neither Rank I nor Rank II significantly exceeds red-noise expectations. Stationary 1-3 yr injections reach Rank I in 63-97% of trials at signal-to-noise ratio (SNR) = 1, depending on period, and 100% at SNR = 2; 92% of drifting injections reach Rank II. These results limit stable, approximately sinusoidal 1-3 yr modulation to at most 7% of the sample at SNR >= 1 and 5% at SNR >= 2 (95% confidence). PG 1553+113 has the lowest false-alarm probability, 4.7% after trials. Stable year-scale modulation is uncommon, and no source is established as periodic. The framework distinguishes persistent, stationary modulation from coherent variability whose period may evolve or fluctuate, but not the physical mechanism. PG 1553+113 and B2 1215+30 are candidates for monitoring and continuous gravitational-wave searches, although their stability does not establish a binary origin.
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All authors Adithiya Dinesh, Alberto Domínguez, Alba Rico, Pablo Peñil, Marco Ajello, Sara Buson

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

Quantum Co-Design of Inhomogeneous Many-Body Neutrino Fast Flavor Transformation

Zoha Laraib, Sherwood Richers, Alessandro Baroni et al. (+2 more)

Dense-neutrino flavor evolution is a quantum many-body problem whose fully correlated treatment becomes rapidly more expensive with increasing particle number and spatial structure. We develop a QCNO quantum simulation code that maps a inhomogeneous forward-scattering neutrino Hamiltonian with advection and finite-range interactions to TEBD2 product-formula quantum circuits, and connects ideal many-body simulation, backend-aware execution, and fault-tolerant resource estimation within the same physical model. We reproduce the exact many-body evolution of the suppressed mean-field-like transverse fast flavor instability through $N=30$ and show that even a single open-boundary interaction generates Rënyi entanglement and non-stabilizer magic, although noisy backends still produce polarization RMSEs of order $0.1$–$0.3$. The restricted active interaction graph of this problem allows us to estimate the circuit depth and $T$ gate cost through $N=50$ for both NISQ and fault-tolerant approaches. The measured TEBD2 error in our fiducial ideal simulation of order $10^{-3}$ motivates a synthesis tolerance $\varepsilon_{\rm syn}\sim10^{-7}$, corresponding to about $70$ $T$ gates per $R_Z$ rotation. The generated circuit contains $1.4\times10^4$ $T$ gates per qubit for open boundaries (twice that for closed boundaries), requiring an application-level logical-$T$ error target of order $10^{-7}$ for early fault-tolerant architectures.
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All authors Zoha Laraib, Sherwood Richers, Alessandro Baroni, Kathleen Hamilton, In-Saeng Suh

High Energy Astrophysical Phenomena

Evidence for orbital eccentricity supports a hierarchical origin for GW231123

Baoxiang Wang, Tao Yang, Zhoujian Cao et al. (+3 more)

GW231123 is the most massive binary black hole merger observed to date and one of the most intriguing hierarchical merger candidates in the pair-instability mass gap. Its exceptionally large inferred component spins and remarkably short in-band duration make the source highly sensitive to waveform physics near merger. Here we show that GW231123 is better described as an eccentric binary black-hole merger. We analyse data over 11–448 Hz using the eccentric, spin-precessing effective-one-body waveform model TEOBResumS–Dalí, accounting for detector calibration uncertainty. We measure $e_{5.5\,\mathrm{Hz}}=0.34^{+0.12}_{-0.23}$ at 90% credibility and obtain a Bayes factor of 10.2 in favour of the eccentric model over its quasi-circular counterpart. GW231123-like injection–recovery studies further show that analyses starting at 20 Hz, as in previous studies, can obscure this eccentricity. Including eccentricity substantially changes the spin inference, weakening the preference for a near-extremal secondary spin and lowering its posterior median to $a_2\simeq0.7$, close to the characteristic spin expected for a black-hole merger remnant. These results provide a coherent dynamical interpretation of GW231123, in which residual eccentricity, a mass-gap black hole, and a remnant-like spin arise naturally from a hierarchical merger channel in a dense environment.
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All authors Baoxiang Wang, Tao Yang, Zhoujian Cao, Bin Hu, Xikai Shan, Rong-Gen Cai

High Energy Astrophysical Phenomena

Autocorrelation in black hole flare movies: Departures from Kerr

Fang-Stars Wei, Zelin Zhang, Zhenyu Zhang et al. (+1 more)

Autocorrelation in black hole movies encodes the time delays and angular separations between gravitationally lensed images, offering a means of testing the spacetime geometry. Using an orbiting hot spot in the parametrized Johannsen-Psaltis metric with a single deformation parameter, we investigate the ability of lensing-induced correlations to distinguish departures from Kerr. From ray-traced movies, we extract the slope (k) and intercept (b) of an approximately linear secondary ridge in the time-angle autocorrelation map as potential future observables. Variations in the spin and the metric deformation parameter produce distinctive trajectories in the (k,b) plane, allowing the two observables to jointly constrain both parameters when the orbital radius, observer inclination, and orbital angular velocity are specified. By varying the orbital angular velocity, we construct a Kerr reference region in the (k,b) plane, and we find that, for some low-spin configurations with negative deformation parameters, the measured slope-intercept pairs of the secondary peaks lie outside this reference region. This feature appears for sub-Keplerian, Keplerian, and super-Keplerian motion, indicating that secondary-ridge measurements from black hole flare movies have the potential to distinguish non-Kerr signatures.
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All authors Fang-Stars Wei, Zelin Zhang, Zhenyu Zhang, Bin Chen

High Energy Astrophysical Phenomena

Discovery of the Slowest Radio Pulsar in the Small Magellanic Cloud

Weiyu Wang and Rahul Sengar

We report the discovery of a new radio pulsar PSR J0103$-$72 in the Small Magellanic Cloud (SMC) through a reanalysis of Parkes/Murriyang archival observations targeting supernova remnants and pulsar-wind nebulae in the SMC. Previously two pulsars were discovered in these observations, and PSR J0103$-$72 is the third which we independently detected in two observations of its target field. It has a spin period of 1.327 sec and a dispersion measure (DM) of $272\pm13~\mathrm{pc\,cm^{-3}}$, making it the slowest known radio pulsar in the SMC with the second-highest DM. We did not identify any plausible supernova remnant or pulsar-wind nebula associated with the pulsar. Subtracting the predicted Galactic foreground leaves a DM contribution of $\sim 230$–$242~\mathrm{pc\,cm^{-3}}$, which may suggest a long path through the ionized medium of the SMC, enhanced ionized gas along the sightline, or both. Although these data had previously been searched using both FFT and fast folding algorithms, our FFT-based reprocessing found PSR J0103$-$72 through search techniques which have previously been highly effective in discovering a large number of pulsars in other surveys. This discovery shows that candidates with weak Fourier-domain significance can reveal faint, narrow-duty cycle pulsars missed in earlier extragalactic pulsar searches.
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High Energy Astrophysical Phenomena

An updated model of neutrino emission from proto-neutron stars

Matteo Ballelli, Federica Pompa, Christoph Ternes et al. (+2 more)

We present an improved parametric model for neutrino emission from core-collapse supernovae that directly connects neutrino luminosity and average energy to stellar properties during emission. Our model incorporates two critical physical processes: convection within the proto-neutron star and the evolution of the neutrinosphere radius during the early emission phase. Using simulated datasets of supernova neutrino events in the Super-Kamiokande detector, we assess the sensitivity to astrophysical properties in the event of a future detection. We show that the neutrino mass ordering plays a crucial role in determining which parameters can be constrained by the observed neutrino data.
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All authors Matteo Ballelli, Federica Pompa, Christoph Ternes, Marco Drago, Giulia Pagliaroli

High Energy Astrophysical Phenomena

From GeV to PeV: Orbital Modulation and Wind-Regulated Ultrahigh-energy Emission in Cygnus~X-3

Su-Yu Wan, Ruo-Yu Liu, Xing-Fu Zhang et al. (+1 more)

Recent LHAASO observations reveal ultrahigh-energy (UHE) gamma-ray emission from Cygnus~X-3 with evidence for orbital modulation, providing a rare opportunity to study particle acceleration and transport on binary scales. We develop a common binary–jet model that jointly explains the contemporaneous GeV–PeV spectra and orbital light curves. The GeV emission is produced by anisotropic inverse-Compton scattering of stellar photons by relativistic electrons, while multi-PeV protons escaping from the inner region produce TeV–PeV gamma rays through photohadronic and hadronuclear interactions. The GeV orbital modulation constrains the binary–jet geometry, allowing the UHE observations to probe the escaping proton population and its interaction with the circum-binary environment. We find that the UHE emission is strongly regulated by the accretion-driven wind structure. In the present state, a fast disk wind displaces much of the denser Wolf–Rayet (WR) wind from the escaping-proton trajectories, suppressing hadronuclear emission. Changes in the strength, collimation, or orientation of the disk wind can expose the escaping protons to a much denser WR wind and enhance the PeV gamma-ray luminosity by orders of magnitude. This provides a possible connection to the much brighter, though unconfirmed, PeV activity reported in the 1980s, and links UHE gamma-ray activity to the accretion and outflow state of the binary.
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All authors Su-Yu Wan, Ruo-Yu Liu, Xing-Fu Zhang, Dmitriy Khangulyan

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

Testing Extra-Dimensional Gravitational-Wave Polarizations with Compact-Binary Observations

Hai-Tian Wang, Dicong Liang, Lijing Shao et al. (+1 more)

Extra spatial dimensions arise naturally in theories beyond four-dimensional general relativity (GR), but direct observational evidence remains elusive. Gravitational waves offer a distinctive probe: geometric projection onto the observable three-dimensional spatial subspace can produce apparent tensor, vector, and scalar polarizations. We consider one additional spatial dimension and a two-mode tensor-wave ansatz for which the projected polarization components are fixed linear combinations of the same two underlying GR tensor waveforms. These components enter the measured strain through the standard detector antenna patterns. A frequency-domain Bayesian analysis of five compact-binary events constrains two rotation angles for two noncommuting orderings of rotations that preserve propagation within the observed subspace. Two events are further analyzed for four orderings that allow propagation to tilt into the extra dimension. For GW250114, the maximum GR quantiles among the tested rotation orderings are $Q_{\mathrm{GR}}\simeq0.6\%$ for the two-angle fits and $Q^{\mathrm{marg}}_{\mathrm{GR}}\simeq4.6\%$ for the three-angle fits after marginalizing over the third angle. Across the full event sample, the GR reference point lies inside the estimated 90% highest-posterior-density region in every case.
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All authors Hai-Tian Wang, Dicong Liang, Lijing Shao, Yu-Xiao Liu

High Energy Astrophysical Phenomena

Investigating the nature of magnetic turbulence in Tycho's SNR using X-ray observation

Ashwin Aravindaraj, Hui Zhu, Adrien Picquenot et al. (+1 more)

Supernova remnants (SNRs) are widely regarded as the primary sources of Galactic cosmic ray acceleration and the particles are energized at the shock front of SNRs through the diffusive shock acceleration (DSA) mechanism, gaining energy by repeatedly crossing the shock. Magnetic turbulence plays a crucial role in scattering these particles back and forth, making the investigation of turbulence essential to understanding the acceleration process. In this study, we apply the two-point correlation method to derive the magnetic energy spectrum from the non-thermal X-ray flux image of Tycho's SNR. This image was obtained using Poissonian-based Generalized Morphological Component Analysis (pGMCA). The turbulence length scale observed in the resulting spectrum is shorter than the turbulence scale derived from previous studies of radio observations of Tycho's SNR. Additionally, we use the X-ray rim thickness measured across Tycho which is an indicator of magnetic field strength to estimate the magnetic energy spectrum. The turbulence scale inferred from this method is consistent with that obtained from the non-thermal X-ray flux analysis.
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All authors Ashwin Aravindaraj, Hui Zhu, Adrien Picquenot, Hsiang-Kuang Chang

High Energy Astrophysical Phenomena

The Hand of God Revisited: Revealing the Shell Structure and Jet-Supernova Remnant Interaction in MSH 15-52

Lingxiao Dang, Isabel Sander, Samar Safi-Harb et al. (+1 more)

We present an X-ray analysis of the supernova remnant (SNR) MSH 15-52 associated with the young rotation-powered pulsar PSR B1509-58, using Chandra, XMM-Newton, and eROSITA, complemented by MeerKAT radio data. We report the discovery of the missing southern counterpart to the bright northern RCW 89 region and identify a foreground X-ray source that may be a previously unidentified SNR candidate. Imaging and spectroscopy with XMM-Newton and eROSITA reveal the shell properties of MSH 15-52 and suggest that both the southern and northern shell-like structures are consistent with shocked interstellar medium associated with the forward shock, while their low ionization timescales and possible hard power-law components indicate possible influence from particle injection or additional heating by the pulsar wind nebula (PWN) jets. New Chandra spectral maps of the southern jet reveal a region of hard non-thermal emission, with a photon index of approximately 1.6, suggesting interaction between the PWN and the reverse shock and possible re-acceleration of the pulsar outflow. Spatially resolved spectroscopy of the RCW 89 northern clumps reveals high-velocity, metal-rich ejecta with enhanced Ne and Mg abundances. Comparison with core-collapse nucleosynthesis models favors a massive progenitor with an initial mass of approximately 29 solar masses in one-dimensional yield models, while asymmetric explosion models show that lower-mass progenitors can also reproduce the observed abundance ratios. Our study supports a picture in which RCW 89 is part of a larger asymmetric SNR shell interacting with energetic pulsar jets, making the system a valuable laboratory for probing pulsar-PWN-SNR interaction.
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All authors Lingxiao Dang, Isabel Sander, Samar Safi-Harb, Christopher Fryer

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

A Coherent Harmonic Summing Pulsar Search Code

Scott M. Ransom

Pulsars have narrow pulses, so their signals spread over many harmonics in a Fourier transform. Standard pulsar searches add the powers of those harmonics and discard their phases, which throws away the pulse shape and some of the signal. Folding the time series at each trial period keeps both, but is expensive even with the Fast Folding Algorithm (FFA). We describe CoherentSearch.jl, an open-source Julia code that reconstructs the pulse profile at every trial spin frequency directly from the Fourier transform. It interpolates the complex amplitudes of typically 60 harmonics, inverse transforms them into a profile, and tests that profile against boxcar templates of many widths. Because the input spectrum is normalized, the noise in every profile is known in closed form, so one threshold gives one false-alarm rate across the whole search. In an injection study of over 860,000 simulated pulsars at a matched false-alarm rate, the new search recovers 76% of the pulsars in white noise, against 64% for riptide's FFA in its recommended configuration and 42% for PRESTO's accelsearch, and its threshold does not move under red noise. On one CPU core it is 1.4-2.2 times faster than riptide at matched frequency coverage, it scales to 27 times faster on 48 cores, and modern GPUs run it up to nine times faster than a 20-core workstation.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Nonreciprocal black holes with primary hair in beyond Horndeski gravity: Exact solutions and stability

Sebastian Bahamonde, Theodoros Nakas and Simon Iteanu

We develop a novel systematic method for constructing exact, static, and asymptotically flat black-hole solutions in shift-symmetric and $Z_2$-symmetric beyond Horndeski theories. In contrast to previous studies, our approach does not rely on the restrictive reciprocal condition $g_{tt}g_{rr}=-1$, allowing for more general geometries characterized by two independent metric functions. The resulting solution space contains two qualitatively distinct types of hair originating from different branches of the theory. One branch is characterized by khronometric hair, while the other by genuine scalar hair. In both, the scalar profile defines a nontrivial preferred foliation, but the shift-symmetry Noether current and the associated propagating degree of freedom are trivial for the former and nonvanishing for the latter. Focusing mainly on the second branch, we derive several distinct families of exact black-hole solutions. In general, these solutions are singular and exhibit primary scalar hair associated with an independent scalar charge. Nevertheless, we demonstrate that they can be regularized to yield regular black-hole or solitonic configurations, for which the scalar hair becomes secondary. We further investigate the stability properties of these solutions under linear perturbations by analyzing the axial sector and the monopole $(\ell=0)$ mode of the even-parity sector. For representative solutions with scalar hair, the perturbative analysis provides evidence for linear stability under the modes considered.
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High Energy Astrophysical Phenomena

Radio Continuum Study of One of the Brightest Large Magellanic Cloud Supernova Remnants N 132D

Rami Z. E. Alsaberi, Zachary J. Smeaton, Miroslav D. Filipovic et al. (+5 more)

We present a new radio continuum study of the Large Magellanic Cloud supernova remnant N 132D using observations from the Australia Telescope Compact Array (ATCA) and MeerKAT. The radio morphology shows a clear spatial correlation with the X-ray emission in the central and left regions of the remnant, as well as in the right portion of the shell, indicating a close connection between the thermal and non-thermal plasma components. Polarisation measurements reveal predominantly radial magnetic fields, with mean fractional polarisations of 1.2 per cent, 3.0 per cent, and 4.0 per cent at 2100, 5500, and 9000 MHz, respectively. There is also a complex structure in the Faraday Depth spectrum, showing a double-peaked profile that indicates regions with differing magnetisation properties or varying magnetic field geometry. The rotation measure derived from ATCA data has an average value of ~2 rad m^-2, with a maximum of ~338 rad m^-2. We estimate a constant partition magnetic field of ~90 microG and a minimum energy of 3 x 10^50 erg, which is in a constant partition between the energy density of electrons and the energy density of the magnetic field. The integrated radio spectrum follows a power law with a spectral index of -0.74 +- 0.01. These results provide new constraints on the magnetic field structure and energetic properties of N 132D and offer insight into particle acceleration and shock evolution in young supernova remnants.
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All authors Rami Z. E. Alsaberi, Zachary J. Smeaton, Miroslav D. Filipovic, Roland Kothes, Hidetoshi Sano, Ahmed H. Abdullah, Dejan Urosevic, Sanja Lazarevic

High Energy Astrophysical Phenomena

Neutron star cooling with $\Delta$ dUrca processes

Yogeesh N, Monika Sinha and Vishal Parmar

The cooling of neutron stars (NSs) provides insight into their composition and equation of state. However, a complete understanding of this phenomenon is still an open question. The early stage of NS cooling is dominated by neutrino emission from the core, which rapidly cools the star. Urca processes are one such mechanism where neutrinos escape from the core, carrying away most of the heat. Nucleonic and hyperonic direct Urca processes are known rapid cooling mechanisms. The possible appearance of $\Delta$ baryons in dense matter introduces additional weak-interaction channels, including $\Delta$ direct Urca processes. Although such processes have been discussed in the context of $\Delta$-admixed NS matter, their neutrino emissivities and impact on NS cooling have not been systematically investigated. In this work, for the first time we incorporate the neutrino emissivities of the relevant $\Delta$ direct Urca processes into NS cooling simulations. We investigate the thermal evolution of $\Delta$-admixed NSs and assess the impact of these additional neutrino emission channels on their cooling behavior. We find that $\Delta$ direct Urca processes can provide an efficient neutrino-cooling mechanism and significantly accelerate the thermal evolution of NSs. Our results demonstrate that $\Delta$ baryons and their associated weak-interaction processes can play an important role in explaining NSs with unusually low surface temperatures and provide a new connection between the composition of dense matter and NS cooling observations.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph

Analysis of p-Wave Sommerfeld Resonance Behavior in Finite-Size Dark Matter

Wu-Long Xu, Jin Min Yang and Rui Zhu

Different stages of cosmic evolution impose different requirements on the dark matter annihilation cross section. Sommerfeld enhancement provides a possible way to accommodate them. However, in the point-like dark matter scenario, satisfying these requirements with either $s$-wave or $p$-wave Sommerfeld enhancement can strongly constrain the dark matter and mediator masses and their coupling. A finite dark matter size introduces an additional parameter and may relax these constraints. Motivated by this possibility, in this work we study the $p$-wave Sommerfeld resonances of finite-size dark matter (like proton or neutron) without specifying its internal structure. We find that the $p$-wave contribution can exceed the $s$-wave contribution. Nevertheless, the finite-size $p$-wave resonances are weaker than those in the point-like case. Despite this suppression, their velocity dependence remains similar to that of point-like dark matter. We then extend our analysis to nugget dark matter composed of a small number of constituents. In this case, the $p$-wave Sommerfeld enhancement exhibits behavior similar to that of point-like dark matter.
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