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Physics Astrophysics High Energy Astrophysical Phenomena

astro-ph.HE Watch High Energy Astrophysical Phenomena

Thursday 10 September

High Energy Astrophysical Phenomena

Probing Lorentz Invariance Violation in Cosmogenic Neutrino Propagation with KM3-230213A

Rodrigo Sasse, Rodrigo Guedes Lang and Rita de Cássia dos Anjos

We investigate superluminal Lorentz invariance violation (LIV) in the neutrino sector using cosmogenic neutrino fluxes generated with ultrahigh-energy cosmic-ray propagation models. Standard fluxes are calculated with CRPropa 3.2 and subsequently modified using a prescription based on LIV-induced neutrino splitting. Superluminal LIV suppresses the flux at the highest energies while producing an enhancement at PeV - EeV energies. We use the KM3-230213A event as a benchmark to evaluate the sensitivity of current observations to these spectral modifications. Although the available statistics do not allow a formal constraint, the predicted fluxes are particularly sensitive to coefficients in the range $10^{-24} \mathrm{eV}^{-1} \lesssim \delta_{\nu,1} \lesssim 10^{-22}\,\mathrm{eV}^{-1}$, with the results strongly depending on the assumed cosmic-ray source properties. Intermediate coefficients can enhance the expected event rate within the reconstructed energy range of KM3-230213A, whereas larger coefficients may overproduce neutrinos in energy intervals constrained by IceCube and the Pierre Auger Observatory. These results identify a region of observational sensitivity to LIV and provide testable predictions for future neutrino telescopes.
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High Energy Astrophysical Phenomena

Which Type Ia supernova observables best indicate the ages of their progenitor stars?

Young-Lo Kim, Chul Chung, Young-Wook Lee et al. (+3 more)

Type Ia supernovae (SNe Ia) observables, such as the light-curve shape and the colour, are expected to contain information about the progenitor star. In this work, we explore this information, with a particular focus on the age of the SN Ia progenitor star. For this, we construct the SN Ia progenitor age distribution (SPAD) and compare it to the observed distributions of light-curve shape (x1) and the colour (c) parameters in a volume-limited SN Ia sample. We find that SPAD and the x1 distribution share a common shape: a young/high-x1 peak and an old/low-x1 bump in the tail, and this shape varies systematically with redshift. In contrast, this behaviour is not evident in the c distribution. We then examine the correlation of the local age at the SN Ia explosion site, used as a proxy for the progenitor age, with x1 and c. The local age and x1 are well correlated (the linear correlation coefficient ~ -0.71), whereas the local age and c show no significant correlation (the coefficient ~ 0.08). Furthermore, we find that the x1 distribution systematically evolves with the local age. Lastly, we demonstrate that an empirical mapping approach based on SPAD successfully reproduces the observed x1 distribution across different redshift bins. Taken together, our results suggest that the light-curve shape distribution indicates progenitor age at the population level more robustly than the colour does. In particular, younger progenitors are more likely to have higher-x1 SNe Ia. We discuss an application for creating a more homogeneous sample of SNe Ia in terms of progenitor age across a wide redshift range without the Malmquist bias, thereby improving the accuracy of cosmological constraints derived from SNe Ia.
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All authors Young-Lo Kim, Chul Chung, Young-Wook Lee, Seunghyun Park, Junhyuk Son, Suk-Jin Yoon

High Energy Astrophysical Phenomena

Long-term X-ray spectral analysis of Cygnus X-1 using AstroSat

H Lalthantluanga, Akash Garg, Ranjeev Misra et al. (+2 more)

We performed a spectral analysis of long-term observations (2016-2019) of the black hole binary Cygnus X-1 using AstroSat, covering its hard, intermediate, and soft states. During soft states, we found that a typical spectrum fitted with a single Comptonization, a thermal disc, and an iron line yields poor fits and unphysically small disk radii (R_in < 1 R_g). While adding a relativistic disk component (kerrbb) improved the fit but required high color factors (f_col ~ 3.35-5.08), indicating additional Comptonization. We therefore adopted a dual-Comptonization model with hot (optically thin) and warm (optically thick) coronae. This provided consistent good fits across all soft and hard states of Cygnus X-1. The spectral evolution reveals the critical role of dual Comptonization in shaping the broadband emission of Cygnus X-1.
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All authors H Lalthantluanga, Akash Garg, Ranjeev Misra, Vanzarmawii Chhangte, Lalthakimi Zadeng

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

Accretion onto a moving black hole for stiff equations of state

Elliott Ewell, Peter K. Harris, Thomas W. Baumgarte et al. (+1 more)

We revisit accretion of an asymptotically uniform fluid onto a moving Schwarzschild black hole, the relativistic analog of Bondi-Hoyle-Lyttleton accretion. Expanding on previous treatments, we focus on relativistic accretion of stiff fluids with adiabatic indices $\Gamma \geq 5/3$, which is particularly relevant for the treatment of primordial black holes captured by neutron stars. We perform numerical simulations to systematically explore the dependence of the steady-state accretion and drag rates on the asymptotic sound speed $a_\infty$ and relative speed $v_\infty$, and identify different regimes, both subsonic and supersonic, in which these rates either increase or decrease with respect to the spherical accretion rate for $v_\infty = 0$. We propose simple analytical approximations that capture the qualitative features observed in the dependence of the accretion and drag rates on $a_\infty$ and $v_\infty$.
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All authors Elliott Ewell, Peter K. Harris, Thomas W. Baumgarte, Stuart L. Shapiro

High Energy Astrophysical Phenomena

Time-Integrated Searches for Sub-TeV Neutrino Sources with IceCube-DeepCore

R. Abbasi, M. Ackermann, J. Adams et al. (+418 more)

We have developed techniques for a competitive sub-TeV time-integrated neutrino search and applied it to 11.1 years of IceCube-DeepCore data. The DeepCore subarray lowers the sensitivity of IceCube down to sub-TeV energies and is especially interesting for objects with soft spectra. Three studies were performed: a search for neutrino emission from AGN exhibiting high intrinsic X-ray flux, including NGC 1068, as identified by SWIFT/BAT; a search for neutrino emission from Galactic objects identified by Fermi-LAT as exhibiting a spectral shape consistent with neutral pion decay; and an all-sky search for neutrino point sources. Objects for this study were selected given their prospects for sub-TeV neutrino emission. No evidence for sub-TeV neutrino emission is found in any of the searches performed. Finally, for each catalog of objects, we use a statistical combination of the p-values via a binomial test to search for aggregated neutrino emission from a subset of the objects. Neither of the binomial tests yields significant results. For NGC 1068, assuming a power law spectrum with index 3.4, the 90% confidence level upper limit on per-flavor neutrino emission in the 30–400 GeV range is $\Phi_{\nu+\bar{\nu}}|_{\mathrm{1 TeV}} < 9.5 \times 10^{-11}$ TeV$^{-1}$ cm$^{-2}$ s$^{-1}$, a factor of two higher than the extrapolation of IceCube's measurement at higher energies. We additionally provide neutrino flux upper limits for a variety of spectra.
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All authors R. Abbasi, M. Ackermann, J. Adams, J. A. Aguilar, M. Ahlers, J.M. Alameddine, S. Ali, N. M. Amin, K. Andeen, C. Argüelles, S. Athanasiadou, S. N. Axani, R. Babu, X. Bai, A. Balagopal V., S. W. Barwick, V. Basu, R. Bay, J. J. Beatty, J. Becker Tjus, P. Behrens, J. Beise, C. Bellenghi, S. Benkel, S. BenZvi, D. Berley, E. Bernardini, D. Z. Besson, E. Blaufuss, L. Bloom, S. Blot, F. Bontempo, J. Y. Book Motzkin, C. Boscolo Meneguolo, S. Böser, O. Botner, J. Böttcher, J. Braun, B. Brinson, Z. Brisson-Tsavoussis, L. Brusa, R. T. Burley, D. Butterfield, K. Carloni, J. Carpio, N. Chau, Y. C. Chen, Z. Chen, D. Chirkin, S. Choi, A. Chubarov, B. A. Clark, D. A. Coloma Borja, A. Connolly, J. M. Conrad, D. F. Cowen, C. De Clercq, J. J. DeLaunay, D. Delgado, T. Delmeulle, S. Deng, P. Desiati, K. D. de Vries, G. de Wasseige, T. DeYoung, J. C. Díaz-Vélez, S. DiKerby, T. Ding, M. Dittmer, A. Domi, L. Draper, L. Dueser, D. Durnford, K. Dutta, M. A. DuVernois, T. Ehrhardt, L. Eidenschink, A. Eimer, C. Eldridge, P. Eller, E. Ellinger, D. Elsässer, R. Engel, H. Erpenbeck, W. Esmail, S. Eulig, J. Evans, P. A. Evenson, K. L. Fan, K. Fang, K. Farrag, A. Fattorini, A. R. Fazely, A. Fedynitch, N. Feigl, C. Finley, D. Fox, A. Franckowiak, S. Fukami, P. Fürst, J. Gallagher, E. Ganster, A. Garcia, M. Garcia, E. Genton, L. Gerhardt, A. Ghadimi, C. Glaser, T. Glüsenkamp, J. G. Gonzalez, S. Goswami, A. Granados, D. Grant, S. J. Gray, S. Griffin, S. Griswold, K. M. Groth, D. Guevel, C. Günther, P. Gutjahr, C. Ha, A. Hallgren, L. Halve, F. Halzen, L. Hamacher, M. Handt, K. Hanson, J. Hardin, A. A. Harnisch, P. Hatch, A. Haungs, J. Häußler, K. Helbing, J. Hellrung, B. Henke, L. Hennig, F. Henningsen, L. Heuermann, R. Hewett, N. Heyer, S. Hickford, A. Hidvegi, C. Hill, G. C. Hill, R. Hmaid, K. D. Hoffman, A. Hollnagel, D. Hooper, S. Hori, K. Hoshina, M. Hostert, W. Hou, M. Hrywniak, T. Huber, K. Hultqvist, K. Hymon, A. Ishihara, W. Iwakiri, M. Jacquart, S. Jain, O. Janik, M. Jansson, M. Jin, N. Kamp, D. Kang, W. Kang, A. Kappes, L. Kardum, T. Karg, A. Karle, A. Katil, M. Kauer, J. L. Kelley, M. Khanal, A. Khatee Zathul, A. Kheirandish, T. Kim, H. Kimku, F. Kirchner, J. Kiryluk, C. Klein, S. R. Klein, Y. Kobayashi, S. Koch, A. Kochocki, R. Koirala, H. Kolanoski, T. Kontrimas, L. Köpke, C. Kopper, D. J. Koskinen, P. Koundal, M. Kowalski, T. Kozynets, A. Kravka, N. Krieger, T. Krishnan, K. Kruiswijk, E. Krupczak, E. Kun, N. Kurahashi, C. Lagunas Gualda, L. Lallement Arnaud, M. J. Larson, F. Lauber, J. P. Lazar, K. Leonard DeHolton, A. Leszczyńska, C. Li, J. Liao, C. Lin, Q. R. Liu, Y. T. Liu, M. Liubarska, C. Love, L. Lu, F. Lucarelli, W. Luszczak, Y. Lyu, M. Macdonald, E. Magnus, Y. Makino, E. Manao, S. Mancina, A. Mand, I. C. Mariş, S. Marka, Z. Marka, L. Marten, I. Martinez-Soler, R. Maruyama, J. Mauro, F. Mayhew, F. McNally, K. Meagher, A. Medina, M. Meier, Y. Merckx, L. Merten, J. Mitchell, L. Molchany, S. Mondal, T. Montaruli, R. W. Moore, Y. Morii, A. Mosbrugger, D. Mousadi, E. Moyaux, T. Mukherjee, M. Nakos, U. Naumann, R. Neshat, L. Neste, M. Neumann, M. U. Nisa, K. Noda, A. Noell, A. Novikov, A. Obertacke, V. O'Dell, A. Olivas, R. Orsoe, J. Osborn, E. O'Sullivan, B. Owens, V. Palusova, H. Pandya, A. Parenti, C. Parisel, N. Park, V. Parrish, E. N. Paudel, L. Paul, C. Pérez de los Heros, T. Pernice, T. C. Petersen, J. Peterson, S. Pick, M. Plum, A. Pontén, V. Poojyam, B. Pries, R. Procter-Murphy, G. T. Przybylski, L. Pyras, C. Raab, J. Rack-Helleis, N. Rad, M. Ravn, K. Rawlins, Z. Rechav, A. Rehman, I. Reistroffer, E. Resconi, C. D. Rho, W. Rhode, L. Ricca, B. Riedel, A. Rifaie, E. J. Roberts, S. Rodan, M. Rongen, A. Rosted, C. Rott, T. Ruhe, L. Ruohan, D. Ryckbosch, J. Saffer, D. Salazar-Gallegos, P. Sampathkumar, A. Sandrock, G. Sanger-Johnson, M. Santander, S. Sarkar, M. Scarnera, M. Schaufel, H. Schieler, S. Schindler, L. Schlickmann, B. Schlüter, F. Schlüter, N. Schmeisser, T. Schmidt, F. Schmitt, A. Scholz, F. G. Schröder, S. Schwirn, S. Sclafani, D. Seckel, L. Seen, M. Seikh, S. Seunarine, P. A. Sevle Myhr, R. Shah, S. Shah, A. Sharma, S. Shefali, N. Shimizu, C. Silva, M. Shin, B. Skrzypek, R. Snihur, J. Soedingrekso, D. Soldin, P. Soldin, G. Sommani, D. Song, C. Spannfellner, G. M. Spiczak, C. Spiering, J. Stachurska, M. Stamatikos, T. Stanev, T. Stezelberger, T. Stürwald, T. Stuttard, G. W. Sullivan, I. Taboada, S. Ter-Antonyan, A. Terliuk, A. Thakuri, M. Thiesmeyer, W. G. Thompson, J. Thwaites, W. Tian, S. Tilav, K. Tollefson, J. A. Torres, S. Toscano, D. Tosi, K. Upshaw, A. Vaidyanathan, N. Valtonen-Mattila, J. Valverde, J. Vandenbroucke, T. Van Eeden, N. van Eijndhoven, L. Van Rootselaar, J. van Santen, J. Vara, F. Varsi, M. Velazquez, M. Venugopal, M. Vereecken, S. Vergara Carrasco, S. Verpoest, A. Vijai, J. Villarreal, C. Walck, A. Wang, E. H. S. Warrick, C. Weaver, P. Weigel, A. Weindl, J. Weldert, A. Y. Wen, C. Wendt, J. Werthebach, M. Weyrauch, N. Whitehorn, C. H. Wiebusch, D. R. Williams, L. Witthaus, J. Woodward, G. Wrede, X. W. Xu, J. P. Yanez, Y. Yao, E. Yildizci, S. Yoshida, F. Yu, S. Yu, T. Yuan, S. Yun-Cárcamo, A. Zander Jurowitzki, A. Zegarelli, S. Zhang, Z. Zhang, P. Zhelnin, P. Zilberman, C. Zilleruelo Cañas

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

Reconsidering the role of bright and dark gravitational-wave standard sirens for cosmology

Alberto Colombo, Sonia Triscari-Benimavò and Simone Mastrogiovanni

Gravitational-wave (GW) standard sirens have emerged as powerful probes of cosmic expansion. They are commonly divided into two classes: bright sirens, observed in coincidence with an electromagnetic (EM) counterpart, and dark sirens, detected without one. Bright sirens have often been considered the main avenue for precision cosmology; however, following the latest observing run of the LIGO-Virgo-KAGRA (LVK) collaboration, the estimates of merger rates of compact objects involving neutron stars (NSs) have decreased. In this Letter, we reconsider the role that bright and dark sirens will play in precision cosmology. We demonstrate that bright sirens, although detected in small numbers, will play a crucial role in achieving the precision needed to address the Hubble tension, primarily by breaking the degeneracy between the Hubble constant ($H_0$) and the matter density parameter ($\Omega_m$) inherent to dark sirens. Alternatively, we show that dark sirens alone can resolve the $H_0$ tension when supplemented with an external prior on $\Omega_m$. Furthermore, we present a self-consistent statistical framework for GW cosmology with bright and dark sirens, which have traditionally been treated as independent populations although they originate from the same underlying population of black holes (BHs) and NSs. Finally, we find that treating bright and dark sirens as independent populations will not significantly bias GW cosmology in the next LVK observing runs, but can lead to a biased reconstruction of the low-mass end of the mass spectrum.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Constraining Ultralight Scalars with Black Hole Binary Mergers in Galactic Nuclei

Majed Khalaf, Eric Kuflik, Alessandro Lenoci et al. (+2 more)

Ultralight scalars can form long-lived, macroscopic bound states around spinning black holes, known as superradiance clouds. These clouds provide an additional channel for energy dissipation during close encounters, enhancing the black hole binary formation and merger rates in dense environments such as galactic nuclei. We show that the rate of mergers with mass ratio below $3/10$ in the LIGO-Virgo-KAGRA GWTC-5 catalog can probe ultralight scalars in the mass range $[4\times 10^{-14},10^{-13}]$ eV, complementing existing strategies based on black hole spin measurements.
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All authors Majed Khalaf, Eric Kuflik, Alessandro Lenoci, Nicholas Chamberlain Stone, Ofri Telem

High Energy Astrophysical Phenomena

Constraining dark matter using 20-year INTEGRAL/IBIS observations I: Primordial black holes

Jordan Koechler and Pedro De la Torre Luque

Primordial black holes (PBHs) in the asteroid-mass window remain a viable dark matter candidate. In the lower part of this mass range, Hawking evaporation produces electrons and positrons that generate diffuse hard X-ray emission through inverse Compton (IC) scattering on Galactic radiation fields. We present the first search for this signal using a combined spectral and morphological analysis of the 20-year INTEGRAL/IBIS observations. We construct a physically motivated model of the Galactic hard X-ray background, including IC emission from cosmic-ray electrons and unresolved accreting white dwarfs, and consistently incorporate the IC contribution from PBH evaporation. By exploiting both spatial and spectral information, we improve the separation between a possible PBH signal and astrophysical backgrounds compared to analyses based only on spectral data. We derive constraints on the PBH dark matter fraction over a broad mass range, including extended PBH mass functions and rotating PBHs. We assess the impact of uncertainties in cosmic-ray propagation and the Galactic dark matter density profile, finding that the propagation of low-energy electrons and positrons represents the main source of uncertainty in the predicted signal. Despite these limitations, our results provide competitive constraints over a wide range of PBH masses, highlighting the potential of hard X-ray observations as a complementary probe of evaporating PBHs.
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High Energy Astrophysical Phenomena · Cross-listed from astro-ph.SR

Teleparallel torsion and white dwarf structure in \(f(T)=T+\Xi T^2\) gravity

Edson Otoniel, Jonathan A. Reboucas and Iarley P. Lobo

We investigate how quadratic torsion modifies the equilibrium structure of white dwarfs in covariant $f(T)=T+\Xi T^2$ gravity. Static spherical configurations are calculated with a fixed equation of state for cold carbon matter, including relativistic electron degeneracy and Coulomb lattice corrections. The stellar interior is matched to a vacuum exterior, and the mass is determined from the asymptotic geometry. At fixed central density, negative couplings produce more massive and more compact configurations than general relativity, whereas positive couplings give smaller masses and larger radii. The deviations increase with central density and are more pronounced in mass than in radius. The first limiting feature of each sequence depends on the coupling. For $\Xi=-10^{18}\,\mathrm{cm}^{2}$, the sequence remains monotonic up to the electron capture density and reaches $1.508\,M_\odot$. General relativity and $\Xi=+10^{18}\,\mathrm{cm}^{2}$ instead reach mass turning points at $1.385\,M_\odot$ and $1.366\,M_\odot$, respectively. The positive extreme can be continued as an equilibrium solution to the capture density, where its mass decreases to $1.24\,M_\odot$, but this configuration lies beyond the turning point and is not the maximum mass along that sequence. These results identify a density dependent structural response to torsion that changes the stellar mass scale without modifying the matter equation of state.
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High Energy Astrophysical Phenomena

Hierarchical Population Inference with Normalizing Flows for Binary Black Holes

Leonardo Iampieri and Simone Mastrogiovanni

Low-dimensional parametric mass models are standard in gravitational-wave population inference, but their rigidity can bias the recovered distribution and the conclusions drawn from it. We present a pipeline in which the source-frame binary-black-hole population in $(z,m_1,m_2)$ is represented by a normalizing flow trained directly through the hierarchical likelihood, with event posterior samples propagating measurement uncertainty and detected injections accounting for selection effects. We restrict population statements to the region supported by the injection campaign; conditioning on this region can itself induce an apparent association between mass and redshift. We therefore introduce a mutual-information diagnostic that compares the reconstruction with a redshift-independent reference under the same support restriction, testing for dependence beyond that induced by the support geometry. We validate the method on two simulated catalogues differing only in whether the characteristic primary-mass scale evolves with redshift. The reconstruction recovers the injected mass structure in both, and the benchmarks establish how the diagnostic behaves in the presence and absence of intrinsic evolution. Applied to the GWTC-5.0 catalogue, the method recovers features near $10\,M_\odot$ and $35\,M_\odot$, consistent with the LVK population analysis of the same catalogue, and finds no evidence for intrinsic evolution of the primary-mass spectrum with redshift. More broadly, the pipeline addresses a problem common to many observational sciences: recovering a population distribution from noisy, indirect, and selection-biased measurements of its members.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph

Solar Neutrino Constraints on Inelastic Dark Matter Scattering in Light of Recent LUX-ZEPLIN Observations

Thong T.Q. Nguyen, Tim Linden and Dan Hooper

The LUX-ZEPLIN (LZ) Collaboration recently reported the detection of a single nuclear recoil candidate event with a very high recoil energy. The lack of any corresponding low-energy events motivates models in which dark matter scattering with nuclei has a nontrivial momentum dependence or proceeds inelastically, suppressing the rate of low-energy recoils. In this study, we consider the constraints on inelastic dark matter, including scenarios favored by the LZ event, from the absence of an excess of high-energy neutrinos from the Sun in IceCube observations. We confirm the results of Pospelov & Ramani and show, more generally, that the lack of an excess of high-energy neutrinos from the Sun strongly constrains the parameter space in this class of models.
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High Energy Astrophysical Phenomena

Spectral evolution of NS binary system GX 349+2 using AstroSat observations

Garima Tyagi, Suchismito Chattopadhyay, Sree Bhattacherjee et al. (+3 more)

We present a broadband spectral study of the Sco-like Z source GX 349+2 using AstroSat LAXPC and SXT observations obtained during 2019 and 2024. The X-ray light curves exhibit large variability, and the hardness-intensity diagram traces the characteristic Z-shaped track. Using hardness ratio and intensity, the Z-track is segmented into six regions comprising normal branch, soft apex, and an extended flaring branch. We perform simultaneous broadband spectral fitting in the energy range 0.7-25.0 keV using two model configurations, tbabs*(thcomp*bbodyrad+diskbb) and tbabs*(bbodyrad+thcomp*diskbb), to study the evolution of emission from the neutron-star boundary layer, accretion disk, and Comptonizing corona along the Z-track. The comparative analysis reveals that, irrespective of the adopted Comptonization geometry, the inferred inner disk radius remains large (~100 km) and exhibits no systematic inward motion as the source luminosity increases. This suggests that the accretion disk remains truncated and the disk luminosity tends to saturate, consistent with a radiation pressure influenced inner disk. The relatively small variation in the inferred mass accretion rate across the branches indicates that changes in $\dot{M}$ alone cannot account for the observed Z-track evolution. Instead, the boundary-layer component becomes progressively dominant toward the flaring branch, with both its temperature and flux increasing with total luminosity, while the relative contribution from the disk decreases. These results indicate a redistribution of accretion power toward the boundary layer and the associated Comptonizing region, suggesting that the primary energy dissipation in GX 349+2 occurs within the boundary layer region of the neutron star.
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All authors Garima Tyagi, Suchismito Chattopadhyay, Sree Bhattacherjee, Akash Garg, Ranjeev Misra, Somasri Sen

High Energy Astrophysical Phenomena

Relativistic Magnetohydrodynamics from Myers-Pospelov Lorentz-Violating Electrodynamics

Matheus Duarte and Vitor de Souza

We derive the equations of relativistic magnetohydrodynamics from Lorentz-violating Myers-Pospelov electrodynamics. Starting from the modified fermionic and electromagnetic equations of motion, we employ the covariant Wigner formalism to establish the semiclassical spectral constraints and distribution function, which, combined with Noether's theorem, yield the energy-momentum tensor, particle current, and corresponding conservation laws in the presence of Lorentz violation. The resulting hydrodynamic description contains Lorentz-violating corrections to the thermodynamic quantities and to the fluid currents. In the purely timelike sector, these corrections can be absorbed into effective thermodynamic quantities, preserving the isotropic structure of the fluid equations. In contrast, spacelike backgrounds introduce explicit contributions along the preferred direction, which cannot be absorbed into the standard hydrodynamic variables and give rise to anisotropic forces and torques. These effects lead to departures from standard relativistic magnetohydrodynamics and provide a direct macroscopic manifestation of the Lorentz-violating background. Our results provide a first-principles derivation of Lorentz-violating relativistic magnetohydrodynamics and establish a framework for investigating the macroscopic consequences of Lorentz violation in magnetized relativistic fluids.
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High Energy Astrophysical Phenomena · Cross-listed from nucl-th

Nuclear-physics-guided Gaussian Processes

Javier Rozalén Sarmiento, Hristijan Kochankovski, Arnau Rios et al. (+1 more)

Gaussian Process Regression is a powerful nonparametric Bayesian method that provides both predictions and principled uncertainty estimates in closed form. The majority of past applications have relied on agnostic priors, but physics knowledge can be systematically encoded into Gaussian Processes through physically-motivated mean functions and kernels. We exploit this capability in the context of nuclear physics, applying physics-guided Gaussian Process Regression to three problems: nucleon-nucleon scattering phase shifts, mass excesses, and the finite-temperature equation of state of dense matter. In each case, we demonstrate that encoding known theoretical structures yields substantial and systematic improvements in interpolation accuracy, uncertainty calibration, and extrapolation reliability over agnostic baselines. Our results highlight that the design of the prior, and in particular the mean function, is key for obtaining a reliable and well-calibrated Gaussian Process Regression.
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All authors Javier Rozalén Sarmiento, Hristijan Kochankovski, Arnau Rios, Àngels Ramos

High Energy Astrophysical Phenomena

One Precessing Jet Pair, Diverse Core-Collapse Supernova Remnant Morphologies

Jessica Braudo and Noam Soker

We produce a diverse set of observed core-collapse supernova (CCSN)-type morphologies using a precessing pair of opposite jets within the jittering-jets explosion mechanism (JJEM) framework. We conduct a three-dimensional hydrodynamical simulation of a precessing pair of jets that explode a massive star, and find that a single precessing pair of opposite jets can generate S-shaped structures, pipe-spout-blowout features as observed in the Cygnus Loop, multiple apparent pairs of opposite protrusions similar to some morphological features in S147, and H-shaped structures with a prominent bar, similar to the one observed in the 3C 397 remnant. At small scales, the jets form clumps and filaments, resulting from instabilities and vortices that the jets induce in the ejecta as they interact with the stellar material. We did not aim the simulation to reproduce any particular CCSN remnant, but rather to explore the resulting morphological features. Our finding of simulated features similar to observed ones supports the role of jets in exploding CCSNe and, in turn, supports the claim that the JJEM is the primary explosion mechanism of CCSNe.
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High Energy Astrophysical Phenomena

Probing the details of relativistic electrons with multifrequency observations of M87 black hole

J.G.J. Keuper and M. Moscibrodzka

Beginning in March 2026, the Event Horizon Telescope (EHT) conducted a two-month observing campaign aimed at obtaining the first time-resolved sequence of images of the black hole M87* at the center of the Virgo A galaxy. The primary scientific objectives of this campaign are to constrain the black hole spin and to investigate the temporal variability of the magnetic field and plasma properties within the horizon-scale jet-launching region. In this work, we present theoretical predictions for the spectral index maps expected from these observations. Our predictions are based on Magnetically Arrested Disk simulations performed with the EBHLIGHT code and post-processed using the IPOLE general relativistic ray-tracing code. We investigate the temporal evolution of the spectral index for a range of electron distribution models and five different black hole spin values. The analysis includes both frequency bands currently present within the EHT and neighboring frequencies proposed for future extensions of the EHT array. In addition to extending previous studies to a broader range of observing frequencies, our work systematically investigates the time variability of the predicted spectral index maps. In purely thermal electron models, the temporal variability of the spectral index maps closely traces variations in the magnetic field strength and electron temperature in the immediate vicinity of the event horizon. By contrast, models incorporating a non-thermal electron population exhibit substantially weaker spectral index variability, owing to the contribution of a power-law component with a fixed spectral slope. Our numerical results are consistent with theoretical expectations. Finally, a comparison with the recently measured integrated spectral index of the M87* enables us to place preliminary constraints on the model parameters.
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High Energy Astrophysical Phenomena

Cosmological Evolution of Primordial Black Holes: UV/IR Decoupling and the KM3NeT 220 PeV Neutrino Anomaly

Debdatta Dey, Tausif Parvez and S. Shankaranarayanan

The recent observation of a 220 PeV neutrino event (KM3-230213A) by the KM3NeT observatory presents a formidable challenge to standard astrophysical source models. We investigate the hypothesis that this ultra-high-energy signature originates from the terminal evaporation burst of a Primordial Black Hole (PBH). Since PBH evolution spans cosmic history, static vacuum approximations fail to capture early-universe dynamics. Embedding the PBH in a cosmological background via the McVittie spacetime, we demonstrate that early-universe cosmological accretion and expansion-suppressed Hawking emission shift the required initial mass window for a terminal burst occurring today. We show that although the early universe environment dictates the black hole's overall lifespan, its final explosion today ($z \approx 0$) is governed by standard Schwarzschild thermodynamics. This mechanism naturally produces the intense 220 PeV local flux while suppressing early emissions, thereby satisfying diffuse isotropic background limits. Consequently, this dynamical framework alters the mapping between current ultra-high-energy neutrino observables and the primordial curvature perturbations that seeded them.
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High Energy Astrophysical Phenomena

Spin-down of the accreting magnetar candidate 4U 0114+65: possible first evidence for a strong coupling regime

Graciela Sanjurjo-Ferrín, Jose Miguel Torrejón, Konstantin Postnov et al. (+3 more)

4U~0114+65 is a high-mass X-ray binary composed of the B1\,Ia supergiant V*~V662~Cas and one of the slowest known accreting neutron stars, with a spin period of $\sim$9.4 ks. In 2025, its long X-ray pulsations became undetectable in Swift/BAT monitoring, motivating a Director's Discretionary Time observation with XMM-Newton. We compare this observation with a 2015 XMM-Newton observation, when the source was brighter and clearly pulsed, and analyze the long-term spin evolution using Swift/BAT data. We performed average and pulse-phase-resolved spectroscopy using the same model as in previous work. The 2025 observation still reveals weak pulsations, with a period of about 9.3 ks, despite their non-detection in Swift/BAT. The overall spectral shape remains similar in both epochs, but the luminosity decreased by about one order of magnitude, mainly due to strong suppression of the bulk-motion Comptonization component. Although the absorbing column is higher in 2025, the inferred wind properties remain broadly compatible with those from 2015, suggesting that no major global change in the donor wind is required. Instead, the results point to a substantial reduction in accretion efficiency close to the neutron-star magnetosphere. We propose that 4U~0114+65 may be evolving toward partial centrifugal inhibition in the strong-coupling regime, where the toroidal magnetic-field component is comparable to the poloidal one. If confirmed, this would represent the first observational evidence of this state. Accretion would become progressively less efficient and more intermittent without reaching a fully developed propeller regime. The apparent disappearance of the pulse in long-term hard X-ray monitoring would then result from the lower luminosity and reduced absolute pulsed flux, rather than from the loss of the underlying spin modulation.
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All authors Graciela Sanjurjo-Ferrín, Jose Miguel Torrejón, Konstantin Postnov, Jose Joaquín Rodes-Roca, Lida Oskinova, Jessica Planelles-Villalva

High Energy Astrophysical Phenomena

Nonbirefringent model of orthogonal polarization modes in radio pulsars - New view on S swing and mode structure in pulsar beam

J. Dyks and A. Frankowski

Two orthogonal polarization modes observed in radio pulsar signals have long been attributed to proper modes of wave oscillation in strongly magnetized plasma. Yet it has been shown recently that they show up readily for extended emission regions that produce incoherently-superposed polarization signal. In this paper we present a two-dimensional polarization model based on incoherent superposition of radio signals. The model involves a single proper mode, say the O mode, but leads to the appearance of two orthogonal polarization tracks and naturally produces the triple form of polarization mode segregation in averaged profiles (central mode flanked on boths sides by another mode), as well as the displacement of modes in latitude, previously inferred from beam mapping. In the case of conal emission regions, the modelled polarization tends to mimic general polarization properties of the rotating vector model (RVM). However, the reason for this is the symmetry of the emission region - not the usual projection of dipolar magnetic azimuths. Thus the emerging RVM parameters reveal geometry of the emission region, not of the dipolar magnetic field. The results strongly support the vital role of nonbirefringent modal effects in radio pulsar profiles. Two proper modes may not be needed to explain observations of two orthogonal polarization tracks.
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High Energy Astrophysical Phenomena

Evidence for the binary nature of the long-period radio transient ASKAP/DART J1832-0911

Csanád Horváth, Natasha Hurley-Walker, Ziteng Wang et al. (+2 more)

Long-period transients are a class of periodic pulsed radio source repeating on the minute to hour timescale. Recently, an increasing number of them are being identified as binary systems, specifically white dwarfs with low-mass main-sequence companions. In this work we analyse the most luminous long-period transient discovered to date, ASKAP/DART J1832-0911, with two years of radio data, and propose that it, too, may be a white dwarf system, although in a far more compact orbit than the aforementioned. The pulses are composed of quasi-periodic components which evolve in a systematic way over days and months. The source is highly linearly or elliptically polarised and its brightness enabled very high signal-to-noise measurement of the time-resolved Faraday rotation measure, which was found to vary across pulse phase. The linear polarisation position angle, circular polarised fraction, and spectral index also varied systematically in ways not typical of pulsars and magnetars. We show that an ultra-compact asynchronous polar explains much of the phenomenology of ASKAP/DART J1832-0911, in particular the evolution of the pulse morphology, rotation measure variation, and periodic X-ray emission, although we cannot conclusively prove a binary nature. However, our model makes testable predictions.
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All authors Csanád Horváth, Natasha Hurley-Walker, Ziteng Wang, Andrew Zic, Emil Lenc

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

A prolonged plateau-to-tail transition in the Type II supernova SN2025abyc

Luhan Li, Bo Wang, Jujia Zhang et al. (+6 more)

We present optical photometric and spectroscopic observations of the Type II supernova SN2025abyc. During the optically thick phase between approximately 10 and 70 d after explosion, its light curves show strongly wavelength-dependent decline rates of approximately 2.7, 2.1, 0.9, and 0.8 mag/100d in the g, c, r, and o bands, respectively. At approximately 70 d, the light curves begin to depart from their nearly linear plateau evolution and gradually transition toward the radioactive tail. A Fermi-Dirac fit to the well-sampled ATLAS o-band light curve yields a transition midpoint of t_PT ~ 100.5d. The interval between the end of the linear plateau and this transition midpoint is approximately 30 d, indicating a prolonged plateau-to-tail transition. This timescale is comparable to those measured for SN2013by, SN2013ej, and SN2014G. Spectroscopically, at +13 d post-explosion, the Halpha profile appears weak and broad, whereas Hbeta and Hgamma display clear P-Cygni profiles. This morphology can be explained by the normal early spectroscopic evolution of SNe II, although partial filling of the Halpha absorption trough by emission associated with circumstellar interaction cannot be excluded. SN2025abyc otherwise follows the general photospheric velocity evolution of SNe II, while remaining toward the high-velocity side of the comparison distribution in Halpha, Hbeta, and FeII. Exploratory light-curve modelling suggests a synthesized Ni mass of approximately 0.03-0.04 solar mass. We suggest that the extended circumstellar environment, Ni distribution, and hydrogen-envelope structure could all play a role in shaping the observed light-curve evolution, particularly the prolonged plateau-to-tail transition.
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All authors Luhan Li, Bo Wang, Jujia Zhang, Zhengyang Zhang, Xinjie Luo, Shiyang Dong, Saien Xu, Zhengwei Liu, Zhanwen Han

High Energy Astrophysical Phenomena

IceCube neutrino point-source searches in the direction of the KM3NeT ultra-high-energy event

R. Abbasi, M. Ackermann, J. Adams et al. (+416 more)

While still under construction, the KM3NeT Astroparticle Research with Cosmics in the Abyss (ARCA) detector recorded a $\sim$200 PeV neutrino on February 13th, 2023. This event is the highest-energy neutrino reported. IceCube, a cubic kilometer neutrino detector located at the geographic South Pole, has previously detected neutrinos up to approximately 10 PeV. We search for high-energy neutrinos from the location of the KM3NeT event using 15 years of IceCube data and considering three temporal hypotheses: steady or flaring in time coincidence, or at an arbitrary time. We find no evidence for neutrino emission for any of the studies performed. Correspondingly, we set upper limits on the neutrino flux from a point source in the direction of KM3-230213A. We compare these limits to KM3NeT's estimated flux and show that an astrophysical explanation of this event is strongly constrained for a variety of spectral assumptions for a steady or transient point source with the flux inferred from the single KM3NeT ultra-high-energy event assuming a spectral index of 2.0.
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All authors R. Abbasi, M. Ackermann, J. Adams, J. A. Aguilar, M. Ahlers, J.M. Alameddine, S. Ali, N. M. Amin, K. Andeen, C. Argüelles, S. Athanasiadou, S. N. Axani, R. Babu, X. Bai, A. Balagopal V., S. W. Barwick, V. Basu, R. Bay, J. J. Beatty, J. Becker Tjus, J. Beise, C. Bellenghi, S. Benkel, S. BenZvi, D. Berley, E. Bernardini, D. Z. Besson, E. Blaufuss, L. Bloom, S. Blot, F. Bontempo, J. Y. Book Motzkin, C. Boscolo Meneguolo, S. Böser, O. Botner, J. Braun, B. Brinson, Z. Brisson-Tsavoussis, L. Brusa, R. T. Burley, D. Butterfield, K. Carloni, J. Carpio, N. Chau, Y. C. Chen, Z. Chen, D. Chirkin, S. Choi, A. Chubarov, B. A. Clark, D. A. Coloma Borja, A. Connolly, J. M. Conrad, D. F. Cowen, C. De Clercq, J. J. DeLaunay, D. Delgado, T. Delmeulle, S. Deng, P. Desiati, K. D. de Vries, G. de Wasseige, T. DeYoung, J. C. Díaz-Vélez, S. DiKerby, T. Ding, M. Dittmer, A. Domi, L. Draper, L. Dueser, D. Durnford, K. Dutta, M. A. DuVernois, T. Ehrhardt, L. Eidenschink, A. Eimer, C. Eldridge, P. Eller, E. Ellinger, D. Elsässer, R. Engel, H. Erpenbeck, W. Esmail, S. Eulig, J. Evans, P. A. Evenson, K. L. Fan, K. Fang, K. Farrag, A. Fattorini, A. R. Fazely, A. Fedynitch, N. Feigl, C. Finley, D. Fox, A. Franckowiak, S. Fukami, P. Fürst, J. Gallagher, A. Garcia, M. Garcia, E. Genton, L. Gerhardt, A. Ghadimi, C. Glaser, T. Glüsenkamp, J. G. Gonzalez, S. Goswami, A. Granados, D. Grant, S. J. Gray, S. Griffin, S. Griswold, K. M. Groth, D. Guevel, C. Günther, P. Gutjahr, C. Ha, A. Hallgren, F. Halzen, M. Handt, K. Hanson, J. Hardin, A. A. Harnisch, P. Hatch, A. Haungs, J. Häu\ssler, K. Helbing, J. Hellrung, B. Henke, L. Hennig, F. Henningsen, L. Heuermann, R. Hewett, N. Heyer, S. Hickford, A. Hidvegi, C. Hill, G. C. Hill, R. Hmaid, K. D. Hoffman, A. Hollnagel, D. Hooper, S. Hori, K. Hoshina, M. Hostert, W. Hou, M. Hrywniak, T. Huber, K. Hultqvist, K. Hymon, A. Ishihara, W. Iwakiri, M. Jacquart, S. Jain, O. Janik, M. Jansson, M. Jin, N. Kamp, D. Kang, W. Kang, A. Kappes, L. Kardum, T. Karg, A. Karle, A. Katil, M. Kauer, J. L. Kelley, B. Kern, M. Khanal, A. Khatee Zathul, A. Kheirandish, T. Kim, H. Kimku, F. Kirchner, J. Kiryluk, C. Klein, S. R. Klein, Y. Kobayashi, S. Koch, A. Kochocki, R. Koirala, H. Kolanoski, T. Kontrimas, L. Köpke, C. Kopper, D. J. Koskinen, P. Koundal, M. Kowalski, T. Kozynets, A. Kravka, N. Krieger, T. Krishnan, K. Kruiswijk, E. Krupczak, E. Kun, N. Kurahashi, C. Lagunas Gualda, L. Lallement Arnaud, M. J. Larson, F. Lauber, J. P. Lazar, K. Leonard DeHolton, A. Leszczyńska, C. Li, J. Liao, C. Lin, Q. R. Liu, Y. T. Liu, M. Liubarska, C. Love, L. Lu, F. Lucarelli, W. Luszczak, Y. Lyu, M. Macdonald, E. Magnus, Y. Makino, E. Manao, S. Mancina, A. Mand, I. C. Mariş, S. Marka, Z. Marka, I. Martinez-Soler, R. Maruyama, J. Mauro, F. Mayhew, F. McNally, K. Meagher, A. Medina, M. Meier, Y. Merckx, L. Merten, J. M. Mitchell, L. Molchany, S. Mondal, T. Montaruli, R. W. Moore, Y. Morii, A. Mosbrugger, D. Mousadi, E. Moyaux, T. Mukherjee, M. Nakos, U. Naumann, R. Neshat, L. Neste, M. Neumann, M. U. Nisa, K. Noda, A. Noell, A. Novikov, A. Obertacke, V. O'Dell, A. Olivas, R. Orsoe, J. Osborn, E. O'Sullivan, B. Owens, V. Palusova, H. Pandya, A. Parenti, C. Parisel, N. Park, V. Parrish, E. N. Paudel, L. Paul, C. Pérez de los Heros, T. Pernice, T. C. Petersen, J. Peterson, S. Pick, M. Plum, A. Pontén, V. Poojyam, B. Pries, R. Procter-Murphy, G. T. Przybylski, L. Pyras, C. Raab, J. Rack-Helleis, N. Rad, M. Ravn, K. Rawlins, Z. Rechav, A. Rehman, R. Reimann, I. Reistroffer, E. Resconi, C. D. Rho, W. Rhode, L. Ricca, B. Riedel, A. Rifaie, E. J. Roberts, S. Rodan, M. Rongen, A. Rosted, C. Rott, T. Ruhe, L. Ruohan, D. Ryckbosch, J. Saffer, D. Salazar-Gallegos, P. Sampathkumar, A. Sandrock, G. Sanger-Johnson, M. Santander, S. Sarkar, M. Scarnera, M. Schaufel, H. Schieler, S. Schindler, L. Schlickmann, B. Schlüter, F. Schlüter, N. Schmeisser, T. Schmidt, F. Schmitt, A. Scholz, F. G. Schröder, S. Schwirn, S. Sclafani, D. Seckel, L. Seen, M. Seikh, S. Seunarine, P. A. Sevle Myhr, R. Shah, S. Shah, A. Sharma, S. Shefali, N. Shimizu, M. Shin, R. Singh, B. Skrzypek, R. Snihur, J. Soedingrekso, D. Soldin, P. Soldin, G. Sommani, D. Song, C. Spannfellner, G. M. Spiczak, C. Spiering, J. Stachurska, M. Stamatikos, T. Stanev, T. Stezelberger, T. Stürwald, T. Stuttard, G. W. Sullivan, I. Taboada, S. Ter-Antonyan, A. Terliuk, A. Thakuri, P. Thelen, M. Thiesmeyer, W. G. Thompson, J. Thwaites, W. Tian, S. Tilav, K. Tollefson, J. A. Torres, S. Toscano, D. Tosi, K. Upshaw, A. Vaidyanathan, N. Valtonen-Mattila, J. Valverde, J. Vandenbroucke, T. Van Eeden, N. van Eijndhoven, L. Van Rootselaar, J. van Santen, J. Vara, F. Varsi, M. Velazquez, M. Venugopal, M. Vereecken, S. Vergara Carrasco, S. Verpoest, A. Vijai, J. Villarreal, C. Walck, A. Wang, E. H. S. Warrick, C. Weaver, P. Weigel, A. Weindl, J. Weldert, A. Y. Wen, C. Wendt, J. Werthebach, M. Weyrauch, N. Whitehorn, C. H. Wiebusch, D. R. Williams, L. Witthaus, J. Woodward, G. Wrede, X. W. Xu, J. P. Yanez, Y. Yao, E. Yildizci, S. Yoshida, F. Yu, S. Yu, T. Yuan, S. Yun-Cárcamo, A. Zander Jurowitzki, A. Zegarelli, S. Zhang, Z. Zhang, P. Zhelnin, P. Zilberman, C. Zilleruelo Cañas, M. Zimmermann

Wednesday 9 September

High Energy Astrophysical Phenomena

XRISM observations of the Perseus cluster along two arms: Chaotic ICM motions probed by resonant scattering

Annie Heinrich, Irina Zhuravleva, Congyao Zhang et al. (+13 more)

XRISM has mapped gas velocities across the core of the Perseus cluster, separating the kinematic effects of mergers and AGN feedback. The physical properties of these motions remain unclear: are they a superposition of bulk flows, predominantly random/turbulent motions, or a mixture of both? Without resolving this question, constraints on the nonthermal pressure fraction and heating rate remain uncertain, as both assume predominantly random motions. Unlike emission line broadening, resonant scattering is most sensitive to small-scale, random motions rather than coherent bulk flows. Taking advantage of the extensive XRISM coverage of the Perseus cluster, we detect the full effects of resonant scattering on the He{\alpha} w line for the first time. This includes flux suppression in the cluster center, enhancement in the outer regions, and non-Gaussianity in the emission line. We employ radiative transfer simulations to constrain the amplitude of small-scale ICM velocities in the inner 60 kpc of Perseus, finding them to be consistent with the line broadening measurements within the uncertainties. This indicates the observed velocity dispersion is primarily due to small-scale random motions in the central Perseus regions rather than coherent bulk flows. We further explore potential anisotropy of these motions, showing that they are consistent with isotropic or radial motions rather than tangential ones. Longer XRISM observations are required to improve these anisotropy constraints. Finally, we explore azimuthal variations between the two complete radial arms observed by XRISM.
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All authors Annie Heinrich, Irina Zhuravleva, Congyao Zhang, Anna Ogorzalek, Ayşegül Tümer, François Mernier, Phillip C. Stancil, Elena Bellomi, Lior Shefler, John ZuHone, Yutaka Fujita, Julie Hlavacek-Larrondo, Yuto Ichinohe, Kyoko Matsushita, Nhut Truong, Shutaro Ueda

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

Frozen-composition effects on rotational failure of neutron-star crusts

Elia Giliberti

The elastic response of a neutron-star crust to rotational loading depends on whether weak interactions can restore chemical equilibrium during the deformation. We quantify this effect using unified equations of state and compare chemically equilibrated and frozen-composition responses within the same Newtonian hydro-elastic framework. Frozen composition increases the effective bulk modulus and redistributes the strain throughout the inner crust rather than producing a simple global rescaling. For BSk24, the breaking frequency decreases from $0.4997\Omega_K$ to $0.3912\Omega_K$, a reduction of 21.7 per cent, while the location of first failure moves to higher density. Comparable reductions are obtained for BSk21, whereas SLy4 gives a smaller effect of 16.7 per cent. For BSk24 the relative reduction remains close to 21–22 per cent over the mass range $1.2$–$2.0,M_\odot$. A density-resolved perturbation analysis shows that the result is controlled by the radial overlap between the microphysical frozen-composition stiffening and the mechanical susceptibility of the crust, with most of the linear sensitivity in the BSk models arising from $0.01<n_B<0.03,{\rm fm}^{-3}$. These results show that chemical non-equilibrium can substantially modify both the rotational failure threshold and the layer in which crustal failure begins.
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High Energy Astrophysical Phenomena

Low-Mass Magnetic Monopoles in the Galaxy: Simulations and Comparison with Ultra-High-Energy Cosmic-Ray Data

Ala'a AL-Zetoun, Igor Ostrovskiy, Peiwen Mi et al. (+1 more)

Origin and composition of ultra-high energy cosmic rays are still uncertain, particularly the rare events exceeding the Greisen-Zatsepin-Kuzmin cutoff and whose apparent arrival directions point to the Local Void. This work is an in-depth investigation of the possibility that such cosmic rays contain low-mass magnetic monopoles predicted in several recent theoretical models. Using a custom extension to CRPropa, a state-of-the-art code for modeling cosmic ray propagation, monopoles are tracked in the galactic environment under realistic assumptions on mass, magnetic charge, and initial phase-space distributions. Our simulations demonstrate that relic MMs follow filamentary “Galactic magnetic funnels”, producing anisotropic arrival directions at Earth. The expected arrival directions are concentrated in a small region of the sky, which has significant implications for the design and interpretation of future searches. A comparison of the simulated arrival directions with the Pierre Auger Observatory dataset shows that the null hypothesis - no monopole contribution - is statistically preferred for the majority of cases. Using a profile-likelihood analysis that incorporates both directional and energy information, we set 90% C.L. upper limits on the integral MM flux of $< 2.1\times10^{-23}$ $\mathrm{cm^{-2}s^{-1}sr^{-1}}$.
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All authors Ala'a AL-Zetoun, Igor Ostrovskiy, Peiwen Mi, Daniele Perri

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

Binary-black hole spin population results may be driven by prior degeneracies

Noah E. Wolfe, Asad Hussain, Jack Heinzel et al. (+1 more)

Gravitational waves carry information on the spins of merging binary-black holes. The orientations of their spins relative to their orbits ("tilts")—while challenging to measure—differentiate the astrophysical formation mechanisms by which merging black hole binaries may form. Multiple analyses have reported tentative evidence that black hole spins are preferentially oriented in the plane of the binary orbit. We show that these results are likely extrapolated from more easily measurable "effective spin" parameters which characterize the gravitational-wave inspiral of black hole binaries but may not uniquely constrain their astrophysical formation. In particular, we reproduce a peak in the spin tilt distribution with information about the marginal effective spin distributions alone. We propose a geometric picture to compare constraints on effective spins to standard population modeling assumptions, suggesting that current inferences of a preferred spin orientation are spurious.
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All authors Noah E. Wolfe, Asad Hussain, Jack Heinzel, Salvatore Vitale

High Energy Astrophysical Phenomena

Teglon: A Pixel-Level Pipeline for Galaxy-Informed Gravitational-Wave Follow-up Planning and Efficiency Analysis

D. A. Coulter, P. Darc, C. D. Kilpatrick et al. (+4 more)

We describe Teglon, an open-source database and analysis pipeline engineered to optimize the search for electromagnetic (EM) counterparts to gravitational wave (GW) sources. Teglon constructs a 3D galaxy completeness metric from an input galaxy catalog and convolves it with the 3D localization volume of a GW event, producing an updated posterior map informed by known galaxy distributions. Using Teglon, users can ingest arbitrary instrument footprints — or download them directly from the Treasure Map — to generate dynamic observation plans that seamlessly interpolate between targeted galaxy pointing and region tiling. By focusing efforts on high-probability volumes, Teglon significantly reduces the predicted search area to find EM counterparts and increases observational efficiency, especially for small field-of-view (<= 1 deg^2) instruments like the Nancy Grace Roman Space Telescope. Furthermore, Teglon integrates with Redback to calculate pixel-level model detection efficiencies, enabling custom, event-specific observing strategies or retrospective detection efficiencies on an arbitrary grid of EM transient models. Teglon also supports custom science cases, such as prioritizing Active Galactic Nuclei searches for EM counterparts to binary black hole mergers. Having supported Gravity Collective and related programs from the LIGO-Virgo-KAGRA third observing run (O3) through O4, Teglon is being continuously developed to support O5 and beyond. We document the public repository lineage and packaging, and provide Version 2.0 as an open-source tool for the community.
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All authors D. A. Coulter, P. Darc, C. D. Kilpatrick, R. J. Foley, P. McGill, S. D. Wyatt, R. Hausen

High Energy Astrophysical Phenomena

Detection of hard X-ray pulsations in non-ULX X-ray pulsar 3X J0042 in M31

Ketan Rikame and Biswajit Paul

We report the detection of hard X-ray pulsations from the M31 accreting non-ULX X-ray pulsar 3X J0042 (3XMM J004232.1+411314) using archival NuSTAR observations. The source has a spin period of ~3 s and an orbital period of ~4.15 hr, with coherent pulsations previously detected only in XMM-Newton observations. We reanalyse all five publicly available NuSTAR observations by correcting the photon arrival times for binary motion and optimizing the orbital epoch and projected semi-major axis. Coherent pulsations are detected in all five observations. The broad-band pulse profiles show similar morphology across the five observations spanning ~2.3 yr, with no significant long-term evolution. The pulse profile also shows energy dependence, with structured, non-sinusoidal profiles below ~20 keV and a less structured profile at higher energies. The pulse periods show an overall decrease over the ~2.3 yr NuSTAR baseline, continuing the long-term spin-up trend observed in the ~16 yr of XMM-Newton observations, but with a faster average spin-up rate of ~-1.1e-10 s/s compared to the earlier reported ~-6e-11 s/s. The short orbital period and inferred low-mass companion star shows it to be a low-mass X-ray binary containing a magnetized neutron star, with systems such as Her X-1, 3A 1822-371, and XMM J174457-2850.3 providing closer Galactic comparisons. This work represents the first detection of hard X-ray pulsations from a non-ULX extragalactic accreting pulsar.
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High Energy Astrophysical Phenomena

Strong Black Hole Natal Kicks in Magnetized Accretion-Powered Explosions

Sean E. Li, Ore Gottlieb and Brian D. Metzger

Asymmetric stellar explosions impart an impulse, or natal kick, to their compact remnants by linear momentum conservation. Black hole (BH) natal kicks are often assumed to be weaker than neutron star kicks because of greater mass accretion, and they are harder to constrain observationally because isolated BHs are electromagnetically faint. Using 3D general-relativistic magnetohydrodynamic simulations lasting up to ~30 s, we show that BHs formed from the collapse of rapidly rotating massive stars (collapsars) threaded by strong large-scale magnetic fields can acquire large natal kicks 10^2–10^3 km/s. Asymmetric electromagnetic outflows, magnetic-flux eruptions, and the gravitational pull of aspherical ejecta shape the kick magnitude, and their relative contributions depend on the progenitor structure, magnetic-flux history, and BH spin. More rapidly spinning BHs receive stronger, more nearly spin-aligned kicks, primarily through the gravitational pull of asymmetric jet-driven ejecta. Delayed transitions to the magnetically arrested state produce more asymmetric outflows and can generate even stronger recoils. Because the large-scale magnetic flux required in our models is also a key ingredient of relativistic gamma-ray burst jets and their associated energetic, jet-driven supernovae, natal kicks may be a natural consequence of magnetized collapsars. Such kicks could substantially alter BH retention in dense stellar environments, binary survival, spin-orbit misalignment, and the viability of magnetized collapsars in producing highly spinning BHs within the pair-instability mass gap.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Wave optical imaging of an oscillating electric dipole orbiting a black hole

Filipe Nazaré, João S. Santos, Vitor Cardoso et al. (+1 more)

We study the electromagnetic radiation and wave-optical imaging of an oscillating electric dipole orbiting a Kerr black hole. We derive the effective 4-current associated with a pointlike oscillating electric dipole in curved spacetime, and use black hole perturbation theory to compute the resulting radiation field at future null infinity, from first principles. We then develop a wave-optical imaging framework for a moving electromagnetic source in curved spacetime. We obtain images of an orbiting electric dipole, displaying relativistic beaming, gravitational lensing, and Einstein rings. We study polarization-dependent scattering by comparing the images produced by spinning dipoles with opposite helicities, finding a displacement that roughly decreases with the inverse of the radiation frequency, as expected for a beyond-geometric-optics effect. Our results provide a first-principles benchmark for beyond-geometric-optics descriptions of electromagnetic radiation in Kerr spacetime.
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All authors Filipe Nazaré, João S. Santos, Vitor Cardoso, José Natário