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Physics Astrophysics High Energy Astrophysical Phenomena

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High Energy Astrophysical Phenomena

Seeing Double: The Theory Defying Twin Flares of TDE 2022dbl

Xinze Guo, Ryan Chornock, Raffaella Margutti et al. (+13 more)

Partial tidal disruption events, in which a star survives a close passage by a supermassive black hole and may be disrupted again on a subsequent encounter, provide a unique probe of supermassive black hole properties and accretion physics. We examine TDE 2022dbl, a partial tidal disruption event candidate that exhibits two separate UV/optical flares, using 11 new optical spectra, updated UV/optical photometry, and a Keck-II/ESI host-galaxy spectrum. We trace the evolution of the prominent blended N III + He II feature across both flares and find that the blend evolves from N III-dominated to He II-dominated emission, which may reflect changing ionization conditions and a declining efficiency of Bowen fluorescence. The two flares show similar thermal evolution and spectral features, supporting a partial-disruption scenario. The second flare exhibits a broader, plateau-like peak, a longer decline timescale, and less extreme line velocities than the first flare. We suggest that these differences arise from the interaction between debris from the second disruption and an accretion disk formed during the first flare. From the host-galaxy velocity dispersion, we infer a black hole mass of $\log_{10}(M_{\rm BH}/M_\odot)=6.01\pm0.45$. No third flare has been detected at the expected recurrence epoch, leading us to propose a new interpretation in which a positive-energy kick during ballistic core reformation delays the return of the surviving remnant.
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All authors Xinze Guo, Ryan Chornock, Raffaella Margutti, Yuhan Yao, Erica Hammerstein, Natalie LeBaron, S. Bradley Cenko, Matthew J. Graham, Dina Ibrahimzade, Itai Sfaradi, Jean Somalwar, Robert Stein, Eli Wiston, Joahan Castaneda Jaimes, Mansi M. Kasliwal, Russ R. Laher

High Energy Astrophysical Phenomena

Evidence for Distinct One-Off and Repeating Subpopulations in CHIME/FRB Catalog 2

Sloane Sirota and Duncan R. Lorimer

The Canadian Hydrogen Intensity Mapping Experiment (CHIME) has published its second catalog of 3,641 fast radio bursts (FRBs). While this sample includes 981 bursts from 83 repeating sources, only 2.3% of CHIME FRBs are observed to repeat. This raises the question of whether the FRB population truly consists of a single repeating population or includes a distinct subpopulation of one-off sources. We apply Simulation Based Inference (SBI), a likelihood-free machine learning framework, to model the CHIME/FRB Catalog 2 dataset, testing eight FRB population models, half of which include a subpopulation of truly one-off sources. The current catalog strongly and decisively favors models including such a subpopulation, with the best-fitting model combining a log-normal burst rate distribution, a Poissonian wait-time distribution, and a one-off subpopulation. This preference is corroborated by an independent random forest classifier and by the ability of one-off models to naturally reproduce the hyperactive repeating sources present in the catalog without having been trained on them. We place upper limits on the potentially observable CHIME/FRB population of 36,000 repeating sources and 19 one-off sources per day in the CHIME sky. Models with a one-off subpopulation naturally account for the hyperactive repeating sources present in the catalog without having been trained on them, providing an independent consistency check on our results. We predict the repeater percentage will fall below 2% in the next five years, eventually declining to ~0.5% as the sample saturates with one-off detections.
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High Energy Astrophysical Phenomena

The compact jets of the black hole X-ray binary Swift J1753.5-0127 during its 2023-2024 outburst

Noa Grollimund, Stéphane Corbel, Lauren Rhodes et al. (+14 more)

X-ray binaries are excellent laboratories to study the coupling between accretion and ejection phenomena around compact objects through multiwavelength observations. Swift J1753.5-0127 is a black hole low-mass X-ray binary discovered in outburst in 2005 that remained active for 11 years, followed by two mini-outbursts. We investigate the behavior of the compact jets of Swift J1753.5-0127 during its 2023-2024 outburst. We report a dense multiwavelength monitoring in the radio, NIR/optical/UV and X-ray bands. Using new and archival luminosity measurements, we construct a refined, smoother radio/X-ray plane that covers the steep/outlier and shallow/transition branches of the radio/X-ray correlation. We also present spectral energy distributions (SEDs) constructed using quasi-simultaneous observations from four epochs. Swift J1753.5-0127 underwent a faint, hard-only, double-peaked outburst, followed by a re-brightening in the optical. The updated radio/X-ray plane offers a clear view on the region occupied by this source, similar to MAXI J1348-630, but at lower radio luminosities than H 1743-322, and we confirm its hybrid behavior. The broad-band SED fitting reveals that a cool, truncated accretion disk dominates the NIR/optical/UV band. We find that the compact jets have a variable but weak contribution in the NIR, with a break frequency $\nu_\mathrm{break} \lesssim 5 \times 10^{12}~\mathrm{Hz}$, providing additional evidence that radio-quiet sources are also infrared-quiet. We also find evidence that the radio spectral index evolves with X-ray luminosity, transitioning from inverted values near quiescence to flatter or negative values at higher luminosities. In the context of adiabatic jet models, this trend may indicate that the jet geometry becomes increasingly confined as the accretion rate rises.
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All authors Noa Grollimund, Stéphane Corbel, Lauren Rhodes, David M. Russell, M. Cristina Baglio, Francesco Carotenuto, Tristan Bouchet, Payaswini Saikia, Rob P. Fender, Sara E. Motta, Piergiorgio Casella, Kevin Alabarta, Fraser Lewis, Andrew K. Hughes, Fraser J. Cowie, Justine Crook-Mansour, Xian Zhang

High Energy Astrophysical Phenomena

Multimessenger Constraints on Nuclear Acceleration in Neutrino-Emitting Seyfert Coronae

Chengchao Yuan

High-energy neutrinos from Seyfert galaxies probe particle acceleration near supermassive black holes, but the accelerated nuclear composition remains uncertain. We connect stochastic acceleration to nuclear and radiative cascades to assess nuclear contributions. Acceleration and losses limit the energy per nucleon available to nuclear cascades; without secondary reacceleration, fragmentation cannot raise this scale. For NGC~1068, joint neutrino and gamma-ray constraints depend on the nuclear mixture: helium-dominated injection permits larger nuclear power fractions than the heavier mixtures considered. For the harder candidate {neutrino} spectrum of NGC~7469, the adopted model yields more energetic nuclear cascades, while the source-specific flux selections allow larger nuclear fractions for the heavier mixtures than in NGC~1068. These results show that composition constraints depend on nuclear yields as well as acceleration conditions and available power.
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High Energy Astrophysical Phenomena

The ePESSTO+ census of ZTF nuclear transients. I. What flares in galactic nuclei?

E. Concepción, T. Petrushevska, G. Leloudas et al. (+21 more)

Transients in galactic nuclei arise from distinct processes, only some of which trace the supermassive black hole (SMBH). These include tidal disruption events (TDEs), changing-look active galactic nuclei, Bowen fluorescence flares (BFFs) and ambiguous nuclear transients, alongside supernovae that appear nuclear but are unrelated to the SMBH. Reliable classification requires spectroscopy, which will not scale to the alert volumes of the Legacy Survey of Space and Time (LSST). We aim to characterise the population of nuclear transients, to identify early observables capable of distinguishing SMBH-related flares, and TDEs in particular, from the dominant supernova background, and to assess the biases this selection introduces. We implemented a real-time filter on the Lasair broker, selecting transients from the Zwicky Transient Facility (ZTF) alert stream by nuclear coincidence with the host galaxy, with no photometric cuts, to retain SMBH-related flares in both quiescent and active hosts. The filter ran over 16 months, with candidates reported for classification through ePESSTO+ and other facilities. The filter returned 476 candidates, of which 202 were spectroscopically classified, yielding predominantly supernovae, 10 confirmed TDEs (5%) and one BFF. The mean g-r colour and the rise time separate TDEs from the supernova background. Our filter recovers 10 of the 25 TDEs classified in the same period and declination range; most misses are technical or observational rather than physical. Simple real-time filtering combined with basic photometric criteria can already isolate TDEs efficiently from nuclear transient alert streams, and high completeness is achievable. In the LSST era, where samples will be predominantly photometric, selection bias will become as important as contamination, and retaining flares in active hosts is necessary if unusual events are not to be excluded.
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All authors E. Concepción, T. Petrushevska, G. Leloudas, D. Ilić, M. Gromadzki, S. Bhattacharyya, P. Charalampopoulos, A. Gomboc, N. Ihanec, M. Nicholl, P. J. Pessi, D. R. Young, P. Wiseman, T.-W. Chen, M. Dennefeld, Y. Dgany, C. P. Gutiérrez, C. Inserra, L. Makrygianni, T. E. Müller-Bravo, S. Nissen, F. Onori, R. Roy, M. Quilt

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

Black hole spin-mass correlation and accretion disks at birth stage of dense star clusters

Zacharias Roupas

We review the accretion-driven channel of stellar black-hole growth and spin-up in gaseous star clusters, developed within the framework of our MSCA project "protoBH". Our detailed calculations involving semi-analytic modelling, dynamical and hydrodynamic simulations suggest that the growth and spin-up of initially low-mass stellar black holes is an integral element of the formation process of dense massive star clusters, such as the proto-globular clusters observed at high redshift. The black holes accrete residual gas, remaining from the first star formation event, and form accretion disks generated by gas angular momentum induced by the black-holes' own curved orbits. Assuming initial black hole masses below the pair-instability mass gap $\leq 55\,{\rm M}_{\odot}$, the gap gets populated with black-hole masses growing to $\sim 10^2\,{\rm M}_{\odot}$, and even reaching several hundred solar masses for sufficiently dense and massive proto-clusters. We predict a consistent spin-mass relation with low black hole spins $\lesssim 0.2$ for low black hole masses $\lesssim 20\,{\rm M}_{\odot}$, spanning all intermediate spins for higher masses and saturating to high spins $\gtrsim 0.8$ for high masses $\gtrsim 70\,{\rm M}_{\odot}$. We find evidence in favour of such an accretion-driven subpopulation of black holes in the GWTC-5.0 released by the LIGO-Virgo-KAGRA collaboration.
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High Energy Astrophysical Phenomena

Broadband non-thermal emission predictions based on 3D simulations of supernova explosions within active galactic nuclei jets

B. Longo, V. Bosch-Ramon, M. Perucho et al. (+1 more)

Thermonuclear and core-collapse supernovae are statistically expected to happen within extragalactic jets, as these jets cross the inner regions of their host galaxies, and supernova ejecta-jet interactions can potentially lead to strong non-thermal activity. We model the non-thermal emission from a supernova interacting with a jet on kiloparsec scales, using detailed numerical simulations of the interaction. Using a post-processing method, we applied a non-thermal model of the acceleration and transport of electron and their synchrotron and inverse Compton emissions, simplified and tuned for flexibility and computational speed, to the results of a three-dimensional relativistic hydrodynamics simulation of the ejecta of a supernova interacting with an extragalactic jet. For intermediate jet powers, radio, optical and X-ray fluxes from supernova ejecta-jet interactions may be detectable for distances < 100Mpc. The non-thermal luminosity budget and local conditions associated with these interactions could be enough to explain knots seen in kiloparsec scale jets at different energies. These conditions might also be suitable for the production of heavy ultra high-energy cosmic rays, but photon and neutrino generation from hadronic processes would be minor on kiloparsec scales. The leptonic gamma-ray fluxes are modest but might non-negligibly contribute in TeV for the nearest or more powerful jet sources.
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All authors B. Longo, V. Bosch-Ramon, M. Perucho, J.M. Martí

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

Tidal Excitation of Relativistic Stars

Zhiqiang Miao, Junquan Su, Neev Khera et al. (+1 more)

How a relativistic star responds to a time-dependent tide has lacked a first-principles counterpart of the Newtonian normal-mode expansion. In general relativity, the tidal field is gauge sensitive, radiative modes are non-Hermitian and incomplete, and the direct and late-time responses are intrinsically nonmodal. In this work we present, to our knowledge, the first causal relativistic theory that treats all of these components on equal footing. We first develop the spectral decomposition of the retarded Green function of the matched stellar interior–Schwarzschild exterior, which classifies four separate regimes in time domain: acausal region, prompt wave, surface-reflected wave, and mode+tail. The prompt signal is identical to that of a Schwarzschild black hole with the same mass, which is combined with the surface-reflected wave to be referred as the "direct part". With the Green function and a complex bilinear form on the full metric–fluid phase space, we decompose the linear response of a nonrotating perfect-fluid star into direct, quasinormal-mode, and late-time-tail sectors. Crucially, every sector admits an explicit first-order driven evolution equation: discrete bilinear projections determine the dynamically evolving quasinormal-mode amplitudes, while continuum projections of the same tidal source onto branch-cut states determine the direct and tail amplitudes. The result is a complete modal–nonmodal decomposition of the spacetime and fluid perturbations, which is physically described by the dynamics of a discrete and a continuous-frequency set of oscillators. We verify the decomposition numerically under generic time-dependent tidal driving and discuss applications to black hole perturbations.
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All authors Zhiqiang Miao, Junquan Su, Neev Khera, Huan Yang

High Energy Astrophysical Phenomena

Delving into the depths of NGC 3783 with XRISM VI. Evidence for a failed wind based on Fe xxv absorption line variability

Chen Li, Jelle S. Kaastra, Liyi Gu et al. (+7 more)

NGC 3783 exhibits a prominent Fe XXV absorption trough in the time-averaged XRISM/Resolve spectrum. To investigate its short-term variability, we present a time-resolved analysis of the Fe XXV absorption line during the continuous 10-day observation. We divided the resolved absorption profile into five fixed velocity intervals and measured their normalized equivalent widths in 19 time-resolved spectra. Three velocity intervals exhibit significant equivalent-width (EW) variability. Two velocity intervals respond differently to low- and high-flux states with less emission line contamination. The time-dependent photoionisation modelling is unable to reproduce the most significant observed EW variation ($3.5 \, \sigma$), possibly owing to uncertainties in the assumed initial equilibrium state, which prevent a precise density measurement. Instead, using photoionisation calculations and assuming the high-density limit, we derive approximate constraints on the ionisation parameters of the two relevant components. The low-velocity component (-320 to -680 km/s) shows a delayed inverse response, indicating a high ionisation parameter, while its relatively short lag timescale indicates a relatively high density and a distance upper limit of 0.05 pc. In contrast, the high-velocity component (-680 to -1040 km/s) manifests a positive response with a longer lag to the ionising continuum, implying a relatively low ionisation parameter. This component appears to be less dense, with an inferred distance upper limit of 0.25 pc. The low-velocity component is consistent with a failed wind, as its outflow velocity is below the local escape velocity, whereas the high-velocity component lies near the escape threshold. Together with the lower-ionisation failed wind detected in 2001, this supports a multiphase failed-wind scenario in the unobscured state of NGC~3783 over more than two decades.
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All authors Chen Li, Jelle S. Kaastra, Liyi Gu, Missagh Mehdipour, Keigo Fukumura, Matteo Guainazzi, Misaki Mizumoto, Ehud Behar, Shoji Ogawa, Keqin Zhao

High Energy Astrophysical Phenomena

Reconstruction of Interstellar Cosmic Ray Anisotropy via Heliospheric Propagation Modeling and SVD Inversion

Reilly Tom, Paolo Desiati, Juan Carlos Díaz-Vélez et al. (+1 more)

Ground-based experiments such as the IceCube Neutrino Observatory and the High-Altitude Water Cherenkov Gamma-Ray Observatory detect cosmic-ray anisotropy on Earth, but magnetic deflections within the heliosphere complicate interpretation. Understanding the original spatial distribution of cosmic rays in the interstellar medium requires modeling particle propagation across the heliospheric boundary. We constructed a simulated transport model that backtracks antiprotons from Earth to the interstellar medium and maps spatial transfer probabilities across energies using HEALPix representations. Because our transfer matrices are singular, inversion relies on singular value decom- position regularization. Ground-based observations lose the equatorial North-South anisotropy component, severely degrading interstellar map recovery. We developed a geometric circle-fitting algorithm to estimate and reintroduce the missing component into the observed signals. Our results show that restoring the North-South anisotropy en- ables more accurate recovery of the interstellar dipole structure. Furthermore, Poisson statistical fluctuations on the detected event counts dominate matrix-transformation errors when spread over multiple energies.
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All authors Reilly Tom, Paolo Desiati, Juan Carlos Díaz-Vélez, Perri Zilberman

High Energy Astrophysical Phenomena

Two sides of the same spin: tracking optical and radio pulsations of SAX J1808.4-3658 from outburst to quiescence

C. Ballocco, A. Miraval Zanon, A. Papitto et al. (+25 more)

High-time-resolution optical and UV observations have revealed bright coherent pulsations from accreting millisecond pulsars, exceeding the luminosity expected from thermal emission from NS hotspots or X-ray reflection by the accretion disk. Characterizing optical pulsations over a wide range of accretion rates through coordinated multi-wavelength observations can shed light on their origin. We present a timing study of the AMSP SAX J1808.4-3658 during its 2022 outburst and quiescence, using optical TNG/SiFAP2 observations, simultaneous NICER X-ray data, LCO optical monitoring, and MeerKAT radio observations in quiescence. During the outburst, we detect coherent optical pulsations with pulsed luminosities of 1.3x10^(30)erg/s. Combined with previous detections, our results suggest that the optical pulsed amplitude increases as the X-ray flux decreases. The X-ray and optical pulsed luminosities show opposite trends with X-ray luminosity, suggesting different responses to changes in the accretion rate. We measure X-ray-to-optical delays of 0.88+-0.04ms and 0.51+-0.03 ms in two outburst observations, indicating that the relative timing between the signals is not constant. Together with the spectral energy distribution, these results support different emission mechanisms: non-thermal emission from relativistic particles for optical pulsations and channeled accretion onto the NS surface for X-ray pulsations. During quiescence, we detect no coherent optical pulsations, obtaining a 95% confidence upper limit of <2.2x10^(29)erg/s on the optical pulsed luminosity, corresponding to an optical efficiency comparable to those of spider radio millisecond pulsars. Simultaneous MeerKAT observations reveal no radio pulsations down to ~10{\mu}Jy, significantly improving previous constraints but not excluding an active rotation-powered pulsar whose radio emission may be absorbed by intra-binary material.
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All authors C. Ballocco, A. Miraval Zanon, A. Papitto, M. Burgay, M. C. Baglio, C. Malacaria, F. Ambrosino, A. Possenti, G. Illiano, E. D. Barr, R. P. Breton, L. Burderi, S. Campana, C. J. Clark, F. Coti Zelati, D. de Martino, T. Di Salvo, M. Kramer, R. La Placa, F. Lewis, A. Marino, D. M. Russell, A. Sanna, L. Stella, B. Stappers, J. D. Turner, M. Cecconi, A. Ghedina

High Energy Astrophysical Phenomena

Cell-based theoretical criteria on the onset and stability limit of thermonuclear detonation

Kazuya Iwata, Keiichi Maeda and Ken J. Shen

One of the key unresolved problems in thermonuclear explosions of white dwarfs (WDs), including type Ia supernovae, is the condition for ignition and propagation of thermonuclear flame. Given the limitation of hydrodynamic simulations in resolving the flame front involved in the explosion process, theoretical considerations for these criteria merit accurate prediction of the onset of deflagration and detonation (deflagration-to-detonation transition or direct initiation) and subsequent stable propagation. Application of cell-based theories, which are originally designed for terrestrial detonation incorporating the size of the cellular structure, to pure-helium detonation in a WD envelope was proven to be powerful. In the present work, we extend this for detonation in helium-carbon and carbon-oxygen mixtures, both of which are associated with the double-detonation model for type Ia supernovae. Comparing with previous hydrodynamic studies in terms of the minimum initiation energy and critical stellar mass for stable propagation, the agreement is satisfactory. For the helium-carbon detonation, it is theoretically substantiated that even an extremely low-mass WD envelope $\sim 10^{-3}$ M$_{\odot}$ can accommodate stable detonation. For the carbon-oxygen detonation, the oxygen-scale cell width is shown to be a good diagnosing indicator. In addition, it is indicated that direct initiation of the carbon-oxygen detonation is only available for a WD heavier than 0.6 M$_\odot$. The findings of this study enable first-order calibration of the explosion model by a simple calculation through the analogy between astrophysical and terrestrial burning, the latter of which can be tested and observed in a laboratory-scale experiment.
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High Energy Astrophysical Phenomena

Fast Radio Bursts from Monster Shocks and Flares of Inspiraling Binary Neutron Stars: A Kinetic Model for Double Pulsar

Jan Benáček, Benoît Cerutti, Martin Pohl et al. (+2 more)

The coalescence of binary neutron star systems offers unprecedented possibilities for multimessenger observations, including the detection of gravitational waves, gamma-ray bursts, kilonovae, and potentially fast radio bursts. For a detailed investigation of the latter, one requires a kinetic plasma model to describe the interacting magnetospheres of the stars. We present a three-dimensional particle-in-cell kinetic simulation of the combined magnetosphere of a binary neutron star in which the two stars physically orbit one another so that the orbital motion itself twists the magnetic loops. We find that the stellar magnetic-field intensity ratio controls the emergence of flares, while the stellar spins set the direction and modulation of the flare. We identify four spatially and dynamically distinct regions of strong electromagnetic energy release: (i) an expanding fast magnetosonic wave that steepens into a monster shock, (ii) a plasma flare being pushed by (iii) an expanding fireball and containing (iv) a reconnecting current sheet. The fast magnetosonic wave is a promising source of coherent radio emission. It is released when orbital motion cuts a closed plasma loop. The electric and magnetic wave amplitudes are similar and reach that of the background magnetic field. Our kinetic treatment yields particle spectra and plasma structures that can be used to assess coherent emission in kinetic-scale simulations. In conclusion, the stellar orbital motion constitutes a driving channel distinct from models with spin-driven magnetospheric twisting.
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All authors Jan Benáček, Benoît Cerutti, Martin Pohl, Tim Dietrich, Anna Neuweiler

High Energy Astrophysical Phenomena

Low-frequency spectra and scattering of pulsars towards the Gum Nebula with the MWA

Ting Yu, Zhifu Gao, Zhongli Zhang et al. (+1 more)

Context. The Gum Nebula is a nearby ionised complex with sight-line-dependent pulsar propagation. Aims. We test whether a smooth ionised structure can explain low-frequency spectral turnovers and pulse broadening, or whether smaller-scale material is required. Methods. We analysed Murchison Widefield Array observations of six pulsars at 80–240 MHz, combining sub-band flux densities with literature data. We compared power-law, free–free absorption (FFA), and turnover-constrained broken-power-law (BPL) spectra, and modelled scattering through pulse-profile convolution. PSR J0820-4114 and the Vela pulsar were fitted jointly across frequency. Results. All six spectra depart from a single power law. FFA is favoured for PSRs J0737-3039A and J0820-4114, and BPL for J0742-2822 and J0835-4510; the other two classifications depend on assumed error floors. Conditional FFA solutions imply emission measures of $10^4$–$10^5$ pc cm$^{-6}$ for electron temperatures of $3\times10^3$–$10^4$ K, far exceeding smooth-shell expectations. PSRs J0737-3039A and J0837-4135 have scattering laws consistent with $\tau_{\rm sc}\propto\nu^{-4}$. We obtain $\alpha_{\rm sc}=-3.07\pm0.11$ for J0742-2822 and $-1.59\pm0.44$ for J0820-4114 using a joint two-component model. The Vela pulsar is best described by an effective thick-screen model with $\alpha_{\rm sc}\simeq-2.74$. Neither tested Galactic electron-density model reproduces both independent distances and low-frequency scattering uniformly. Conclusions. The results favour a structured Gum–Vela magneto-ionic environment in which neighbouring sight lines probe different absorbing and scattering material; these effects need not arise in the same plasma component.
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All authors Ting Yu, Zhifu Gao, Zhongli Zhang, Weicong Jing

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

Finite-Temperature Equations of State for Neutron-Star Mergers within the Quark Mean-Field Model

Shuochong Han, Xiangdong Sun, Zhenyu Zhu et al. (+1 more)

We extend the quark mean-field (QMF) model to finite temperature and systematically investigate the thermodynamic properties of uniform nuclear matter, using the relativistic mean-field (RMF) model as a reference. For each model, we consider two parameter sets calibrated to the same selected nuclear-matter saturation properties but with different nucleon Dirac effective-mass ratios at saturation. We examine the effective nucleon mass and the composition of $\beta$-equilibrium matter, together with the free energy, energy density, pressure, entropy, and heat capacities of symmetric nuclear matter, pure neutron matter, and $\beta$-equilibrium matter. The QMF and RMF models exhibit similar qualitative trends, but their predictions increasingly differ at high density, where the effective masses have distinct density dependences. These differences are particularly evident in the thermal pressure and thermal index. For the two parameter sets considered in this work, we further provide compact analytical representations of the thermal index, $\Gamma_{\rm th}(\rho_{\rm b},T,\beta)$ over baryon densities of 0.08-1.0 $\rm fm^{-3}$, temperatures of 5-100 MeV, and isospin asymmetries of 0-1. The fits reproduce the numerical results with an accuracy better than $2\%$ and can be directly implemented in binary neutron-star merger simulations. This study establishes a finite-temperature extension of the QMF framework and provides a basis for future assessments of how a quark-structure-based description of nuclear matter affects thermal support and post-merger dynamics in binary neutron-star mergers.
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All authors Shuochong Han, Xiangdong Sun, Zhenyu Zhu, Ang Li

High Energy Astrophysical Phenomena

A0538-66: A transient ultraluminous X-ray source with a relativistic outflow, 69ms pulsations, and anomalous optical activity

Lorenzo Ducci, Sandro Mereghetti, Ciro Pinto et al. (+8 more)

A0538-66 is a peculiar Be/X-ray binary in the Large Magellanic Cloud, hosting the fastest spinning neutron star of its class (~69ms) and showing the brightest optical bursts of any system of this type. We report four XMM-Newton observations obtained near periastron in 2025, together with MAXI and REM monitoring, and a reanalysis of archival RXTE data. On 30 September 2025 the source reached L_X~1.5E39 erg/s (0.2-10 keV), the highest level since 1980, and in February, May, and August 2026, MAXI detected similarly bright outbursts. During the XMM-Newton observation taken on 30 September 2025, we detected the pulsations, measuring P_spin=69.25878(2) ms and dP_spin/dt=6.58(9)E-10 s/s; the pulsed fraction was low (~3% in 1-10 keV), increased with energy, and the soft and hard pulse profiles were shifted by half a cycle. A new detection in RXTE data of 3 December 1998 gives a faster spin period of P_spin=68.88813(28) ms. The XMM-Newton/RGS spectra show emission lines from photoionised plasma at rest and blueshifted absorption lines that imply an outflow at ~0.12c. This indicates a highly super-Eddington accretion rate and an intrinsic L_X~1.5E39 erg/s, and it makes A0538-66 a transient ultra-luminous X-ray pulsar, a class of which only a few objects are known so far. Since 2023 the optical bursts observed by REM have become longer and brighter, resembling those of the 1980s, but most of them lack a luminous X-ray counterpart (L_X>1E37 erg/s). We interpret these results in terms of a radiation pressure dominated accretion disc whose geometrically thick inner regions intermittently screen the innermost emitting regions.
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All authors Lorenzo Ducci, Sandro Mereghetti, Ciro Pinto, Matteo Bachetti, Motoki Nakajima, Rahul Sharma, Stefano Covino, Michela Rigoselli, Caterina Tresoldi, Tatehiro Mihara, Mutsumi Sugizaki

High Energy Astrophysical Phenomena

IC 1297: The Most Distant Known X-ray Planetary Nebula and One of the Most Luminous

H. Yuan, Q. A. Parker and M. A. Guerrero

We present the first targeted Einstein Probe (EP) X-ray observations of any planetary nebula (PN). Using the onboard Follow-up X-ray Telescope (FXT), we detect X-ray emission within the central region of IC 1297. The spectral analysis yields a plasma temperature of $kT = 0.086^{+0.054}_{-0.058}$ keV ($T\sim1.0 \times 10^{6}$ K), characteristic of shocked wind bubbles in PNe, whereas there is no evidence that its Wolf-Rayet central star emits X-rays. The absorption-corrected X-ray luminosity in the 0.3–2.0 keV energy band is $L_{\mathrm{X}} = 2.8 \times 10^{32}$ erg s$^{-1}$, also consistent with a hot bubble. At an adopted distance of $\sim3.8$ kpc, IC 1297 is the most distant X-ray emitting PN found to date, opening up a new observational window on hot-bubble formation and evolution. It is also among the most luminous known X-ray-emitting PNe. Our results demonstrate the capability of the EP FXT for detecting and characterizing faint, extended X-ray sources in the soft X-ray band for distant PNe, extending the known spectral properties of detectable X-ray emitting PNe. We also compiled the X-ray properties of all 41 known Galactic XPNe, finding a clear correlation between distance and X-ray luminosity that reflects an observational bias toward detecting the brightest sources at large distances. The compilation also shows a separation in X-ray luminosity between hot bubbles powered by H-rich and [WR]-type central stars, with the latter reaching luminosities up to an order of magnitude higher. The ten most luminous XPNe all host [WR]/PG 1159 central stars.
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High Energy Astrophysical Phenomena

The Promise of Gravitational-Wave Astronomy

Parameswaran Ajith

We review the promise of upcoming gravitational-wave (GW) observations in addressing some of the important open questions in astrophysics and cosmology. A decade after the first direct detection of GWs, the field is entering a transformative phase driven by progressive detector upgrades and the anticipated advent of space-based and next-generation ground-based observatories. These instruments will not only push the distance horizon of GW observations to cosmological redshifts, but will dramatically extend the accessible frequency band, opening entirely new source classes that lie beyond the reach of current detectors. The source landscape is rich enough that surprises are likely. This review surveys our current understanding across this landscape and offers some perspective on the discoveries that upcoming GW observations are poised to deliver.
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High Energy Astrophysical Phenomena

Observational evidence of black hole event horizon from ultra-compact X-ray binaries

Qian-Qi Ma, Wei-Min Gu, Shan-Shan Weng et al. (+1 more)

The event horizon is the most crucial feature that distinguishes black hole (BH) from all other objects in the universe. However, since no radiation can escape from the event horizon, its direct observational evidence remains lacking. Although both are compact objects, the event horizon leads to differences in the radiative behavior between black hole and neutron star (NS) X-ray binaries. Historically efforts to probe the existence of event horizons revealed that the BH X-ray binaries are fainter than NSs with similar orbital periods in their quiescent states. Here, we use a special class of X-ray binaries namely the ultra-compact X-ray binaries (UCXBs), to reveal the existence of the event horizon near stellar-mass black holes. In short-period UCXBs, gravitational radiation dominates the orbital angular momentum loss, allowing us to accurately determine their accretion rates. Based on five UCXBs with orbital periods shorter than 40 min, located in globular clusters, and identified accretors (NS or BH), we obtained their accretion rates. Combining their accretion rates and X-ray luminosities, we calculated the X-ray radiative efficiencies of NS and BH. The radiative efficiency of BH is about two to three orders of magnitude lower than that of NS systems, indicating the accretion energy is swallowed by the BH, thereby indirectly probe the presence of the event horizon.
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All authors Qian-Qi Ma, Wei-Min Gu, Shan-Shan Weng, Mouyuan Sun

Monday 12 October

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

Unveiling photometric transients with the ILMT and their follow-up using DOT

Priyanshi Kumari, Bhavya Ailawadhi, Talat Akhunov et al. (+10 more)

The two 4-m class telescopes at the Devasthal site in India are complementary: the 4-m International Liquid Mirror Telescope (ILMT) is dedicated to the discovery of new transient phenomena, which can be followed up using the 3.6-m Devasthal Optical Telescope (DOT) for their optical characterisation. The ILMT continuously surveys a $22.3^\prime \times 22.3^\prime$ wide strip of the zenith sky. A dedicated transient detection and classification pipeline, PyLMT, based on optimised image subtraction and convolutional neural network (CNN) techniques, enables the discovery of numerous photometric transients with the ILMT. However, these transient discoveries still require spectroscopic confirmation to determine their types, for which spectra obtained with the DOT are essential. Here, we present a selection of photometric transients, specifically supernova candidates. We investigate their photometric and spectroscopic properties using ILMT light curves, supplemented with ZTF data and DOT spectroscopic observations.
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All authors Priyanshi Kumari, Bhavya Ailawadhi, Talat Akhunov, Monalisa Dubey, Naveen Dukiya, Sara Filali, Paul Hickson, Gokul Singh Mehra, Kuntal Misra, Vibhore Negi, Kumar Pranshu, Jean Surdej, Sarvesh Kumar Yadav

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

Internal Nucleon Properties and the Equation of State of Ultra-Dense Matter

Bikram Keshari Pradhan, Jérôme Margueron, Guy Chanfray et al. (+1 more)

The question of the link between the nucleon properties and the equation of state of ultra-dense matter, both being composed of quarks and gluons, is investigated by adopting a soliton model to describe internal nucleon properties and a direct mapping between nucleon and quark matter to obtain the equation of state of ultra-dense matter. We compare $\pi+\omega$ and $\pi+\omega+\rho$ soliton models and analyze the presence of a pressure singularity at the nucleon center due to the $\rho$ field. This singularity impacts the equation of state in ultra-dense matter. Only the pressure derived from the canonical energy-momentum tensor has a singularity, while the Belinfante pseudo-gauge transformation of the energy-momentum tensor generates an internal pressure without a singularity. We then investigate predictions for the equation of state of ultra-dense matter based on different prescriptions for the nucleon pressure. It is shown that none of the prescriptions agree with the thermodynamical pressure defined in uniform matter. The mismatch between any equation of state and the thermodynamical one questions the simplicity of the direct mapping between finite-size nucleon properties and uniform matter as well as the role of the nucleon surface in the internal energy density and the pressure.
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All authors Bikram Keshari Pradhan, Jérôme Margueron, Guy Chanfray, Hubert Hansen

High Energy Astrophysical Phenomena

Discovery of 51 pulsars in a reanalysis of the Green Bank North Celestial Cap Survey and a revised pulsar census

R. Sengar, L. Vleeschower, D. L. Kaplan et al. (+13 more)

We present results from a reanalysis of the Green Bank North Celestial Cap (GBNCC) survey, conducted at 350 MHz with the Green Bank Telescope between 2009 and 2020, covering the sky with declinations $\delta>-40^\circ$. We searched the survey data using an FFT-based periodicity search, with candidate selection extending to very low spectral signal-to-noise ratios and summing up to 32 harmonics. From the 60 promising candidates identified in this search, we confirmed 51 new pulsars using the Green bank and CHIME. We also used a direct folding search method (DFSM) to search for slow pulsars between 500 ms and 10 s. Of the 51 pulsars identified in the FFT search, 43 fall within this period range, all of which were found by the DFSM. The DFSM also found an additional pulsar that had been missed during the inspection of the FFT candidates. Most of the new discoveries are canonical pulsars, with spin periods ranging from 299 ms to 4.4 s and dispersion measures from 10 to 192 $\rm pc \, cm^{-3}$. We also found a binary millisecond pulsar with a spin period of 3.2 ms in a 4.5-d orbit. We redetected 855 pulsars in the data, 825 of which were found in the FFT search. Within the effective parameter space of our periodicity search, the FFT search recovered $\sim$98 % of the known pulsars within the survey sensitivity limits. After accounting for previously reported pulsars whose observations were not processed or whose parameters lay outside our search range, the updated GBNCC census now includes 964 pulsars.
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All authors R. Sengar, L. Vleeschower, D. L. Kaplan, G. Y. Agazie, M. Bailes, A. Cassity, H. T. Cromartie, M. E. Decesar, T. Dolch, W. Fiore, E. Fonseca, R. S. Lynch, E. Parent, S. M. Ransom, I. H. Stairs, J. van Leeuwen

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

An upper limit on Galactic OB+black hole binaries from SDSS-V

J. Müller-Horn, H.-W. Rix, S. Shahaf et al. (+14 more)

Binaries composed of a luminous OB star and a black hole (BH) are a key evolutionary link between massive stellar binaries and merging compact-object binaries, but only a handful are known and their occurrence fraction remains poorly constrained. We use multi-epoch spectroscopy from the SDSS-V Milky Way Mapper to place a first rigorous empirical upper limit on the fraction of Galactic massive ($\geq 10\,\mathrm{M}_\odot$) OB stars with a close BH companion, $f_\mathrm{BH}$. Radial-velocity (RV) variability alone cannot distinguish BH companions from the far more numerous luminous binaries. We therefore combine the SDSS-V RV variability measurements of 3130 massive OB stars with high-resolution follow-up and literature information to identify luminous companions among the RV-variable subset. Forward-modelling the detectability of OB+BH systems using BH masses and orbital parameters from binary-evolution models, we find $f_\mathrm{BH} \lesssim 3\%$ at 95% credibility. This empirical upper limit approaches, but does not exclude, theoretical predictions for the OB+BH fraction. The constraint is primarily limited by the number of RV-variable systems that can be decisively classified, highlighting the importance of complete, high-quality follow-up for future searches.
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All authors J. Müller-Horn, H.-W. Rix, S. Shahaf, B. Pennell, E. Zari, M.C. Ramírez-Tannus, A. Farah, R. Essick, J.I. Villaseñor, M.R. Blanton, J.G. Fernández-Trincado, J.A. Kollmeier, C. Lam, K. Maltsev, A. Roman-Lopes, D.P. Schneider, A. Tkachenko

High Energy Astrophysical Phenomena

Scaling Up: A Global Optical/X-ray Correlation For Reprocessing Across Black Hole Masses

Changhyun Cho, David M. Russell, Aaryan Sharma et al. (+9 more)

This study extends the optical/X-ray correlation from black hole low-mass X-ray binaries (XRBs) to active galactic nuclei (AGN), bridging scales from stellar-mass to supermassive black holes (SMBHs). In XRBs, optical emission predominantly originates from the thermal reprocessing of high-energy photons on the surface of the geometrically thin, optically thick accretion disk. The reprocessed optical luminosity follows a power-law relation of the form $L_{V} \propto L_{X}^{\beta} a$, with $\beta \sim 0.5$, where $L_X$ is the X-ray luminosity and the orbital separation $a$ serves as a proxy for the disk size. To test the universality of this relationship across all mass scales, we analyzed quasi-simultaneous X-ray and optical flux data from a sample of XRBs and AGN that have estimates of the radius of the optically emitting disk. To bridge the structural differences between these populations, we utilized the characteristic optical/X-ray time lag derived from reverberation mapping as a physical proxy for the reprocessing radius. Our analysis reveals a tight, global correlation across all black hole masses, described by $\log L_V = 0.48\log L_X + 0.96\log a_R + 6.5$ with a scatter of $\sim 0.20$ dex, where $a_R$ is the reprocessing radius derived from the lag. Incorporating a geometric correction for the disk inclination angle ($\cos i$) slightly reduces this scatter to $0.18$ dex. These results suggest that X-ray reprocessing is scale-invariant across accretion disks, from stellar-mass black holes to SMBHs. This scaling relation provides new constraints for models of X-ray emission regions in accreting black holes.
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All authors Changhyun Cho, David M. Russell, Aaryan Sharma, Payaswini Saikia, Maria Cristina Baglio, Kevin Alabarta, Sandeep K. Rout, Yi-Jung Yang, Eleonora Caruso, Mokhine Motsoaledi, Meriana Allah, Ian M. McHardy

High Energy Astrophysical Phenomena

Radio and Gamma-Ray Timing of a Newly Discovered Millisecond Pulsar

L. Vleeschower, R. Sengar, L. Nieder et al. (+17 more)

We report the discovery and timing of PSR J2147-3604, a fully recycled millisecond pulsar with a spin period of 3.2 ms, discovered in a reprocessing of the 350-MHz Green Bank North Celestial Cap (GBNCC) survey and later serendipitously confirmed by the MeerKAT TRAPUM UHF survey of Fermi-LAT unidentified sources. We followed up this pulsar with Murriyang/Parkes radio telescope and obtained a phase-connected timing solution spanning one year, revealing a 4.5-day binary orbit with very low eccentricity (e ~ 1.9 x $10^{-5}$). A follow-up search in LAT data revealed gamma-ray pulsations, allowing for a joint radio and gamma-ray timing analysis. Assuming a neutron-star mass of 1.5 Msun, the inferred median companion mass (~0.2 Msun) is consistent with a helium white dwarf. The pulsar has a low dispersion measure of 17.0 pc cm$^{-3}$ and shows strong scintillation, leading to it being detected in ~72% of the observations covering the 704-1174 MHz band with Murriyang. The pulsar has a narrow duty cycle of ~6.5%, which leads to individual time of arrival (ToA) uncertainties of ~4.5 us for a 10 min integration with MeerKAT, suggesting this pulsar is well suited for inclusion in PTA experiments.
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All authors L. Vleeschower, R. Sengar, L. Nieder, C. J. Clark, D. L. Kaplan, A. Anumarlapudi, R. Girgaonkar, T. Thongmeearkom, G. Y. Agazie, M. Bailes, E. D. Barr, R. P. Breton, M. E. Decesar, T. Dolch, M. Kramer, R. S. Lynch, E. Parent, S. M. Ransom, B. W. Stappers, J. van Leeuwen

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

Universal relations for hybrid stars and their quark cores: a systematic scan of the quark-matter parameter space

J. P. Carlomagno, G. A. Contrera, A. G. Grunfeld et al. (+1 more)

Universal, equation-of-state (EOS) insensitive relations among the global properties of compact stars are well established for hadronic neutron stars and for self-bound strange stars. We ask whether analogous relations hold for the quark core of a hybrid star, and whether the core can be constrained from the surface. Describing quark matter with the three-flavor MIT bag model with repulsive vector interactions, matched to the hadronic DD2 EOS through a Maxwell construction, we scan the full $(B^{1/4},G_V)$ plane and obtain 1112 hybrid EOSs with maximum masses above $2\,M_\odot$, broadly compatible with current multimessenger constraints. For every stable configuration we evaluate the mass, radius, moment of inertia, and tidal deformability both at the stellar surface and at the boundary of the quark core. Global quantities follow the relations of hadronic stars—the $I$–Love relation to within $0.5\%$—while core quantities follow those of self-bound strange stars with median deviations of $6$–$9\%$. We explain the latter by expanding the structure of the core in powers of its compactness: to first order, the core mass, baryon mass, moment of inertia, and tidal deformability depend only on the compactness and on the properties of the hadron–quark interface, chiefly the ratio $\xi=p_{\rm tr}/\varepsilon_+$ of transition pressure to quark energy density. The strange-star relations are the $\xi\to0$ member of this family, and the deviations from them measure $\xi$. The fractional core mass and radius of all configurations follow the normalized mass profile of the star, and no global observable allows the core size to be inferred. Evanescent cores dominate the viable parameter space, while sizable cores require low bag constants and strong vector couplings.
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All authors J. P. Carlomagno, G. A. Contrera, A. G. Grunfeld, G. Lugones

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

MeV dark matter decay forecasts for the COSI mission

Robin Anthony-Petersen, Orion Ning, Yu Watanabe et al. (+21 more)

The decay of dark matter (DM) is a generic prediction of many particle physics models, producing distinctive monochromatic signatures in environments such as the Galactic halo. Searches for decaying DM in the elusive 'MeV gap' have remained conspicuously under-explored, despite well-motivated models including axion-like particles, sterile neutrinos, and hidden-sector scenarios predicting signatures in this energy range. The upcoming Compton Spectrometer and Imager (COSI) telescope will help bridge this gap. Designed to probe this energy band with high spectral resolution, low background, and wide field of view, COSI is well-suited for DM line searches at the MeV scale. In this work, we make projections for COSI's 2-year sensitivity for DM decay in the Milky Way halo using dedicated all-sky simulations incorporating COSI's predicted instrument response. We conclude that COSI will improve the sensitivity to the DM lifetime by more than an order of magnitude over the DM mass range 0.4 to 10 MeV.
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All authors Robin Anthony-Petersen, Orion Ning, Yu Watanabe, Benjamin R. Safdi, Maíra Dutra, Francesca Calore, Savitri Gallego, William Guan, Christopher M. Karwin, Alexander Kusenko, Israel Martinez-Castellanos, Shigeki Matsumoto, Michela Negro, Uwe Oberlack, Field R. Rogers, Thomas Siegert, Tadayuki Takahashi, Haoyu Xie, Hiroki Yoneda, Andreas Zoglauer, Steven E. Boggs, Dieter H. Hartmann, Carolyn A. Kierans, John A. Tomsick

High Energy Astrophysical Phenomena

MRI Turbulence versus $\alpha$-Viscosity in Circumbinary Disks: Implications for Gravitational-Wave Dephasing and Accretion Variability

Mudit Garg and Yan-Fei Jiang

Our understanding of gas torques on massive black hole binaries (MBHBs) relies on hydrodynamical (HD) simulations of circumbinary disks (CBDs) in which an $\alpha$-viscosity models angular momentum transport. However, CBDs around MBHBs near merger are hot, magnetized plasmas where transport is driven by magnetohydrodynamical (MHD) turbulence sustained by the magnetorotational instability (MRI). We test how well an $\alpha$-viscosity captures MRI turbulence with 3D global Athena++ simulations of a locally isothermal CBD around an equal-mass, circular MBHB, run in HD and MHD from the same initial torus on identical grids, so that only the transport mechanism differs. Excising the region within twice the binary separation, $r<2~a_{\rm bin}$, allows $1000$ orbits of evolution, several times longer than previous MHD simulations. Both disks deliver the same accretion rate, and the gas beyond $2~a_{\rm bin}$ exerts a positive torque in both, yet the MHD torque is $3.5$ times larger and $3$ times more variable. Near the midplane, transport is similar in the disk body but three times weaker in MHD at the cavity edge, where $2$-$3$ times more mass piles up in a more eccentric cavity, raising the torque. The accretion rate is modulated mainly at twice the binary frequency in HD, but by a persistent lump at the cavity edge and its beat with the binary in MHD. The outer-disk torque therefore implies a contribution to the gas-induced phase shift in the gravitational-wave signal of LISA binaries $3.5$ times larger than in $\alpha$-disk models, and a different variability signature for LSST and Roman.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

Vanishing Love Numbers of Kerr-Newman Black Holes

Sumanta Chakraborty, Takuya Katagiri, Paolo Pani et al. (+1 more)

Tidal Love numbers characterize the conservative response of compact objects to external perturbations and provide a powerful probe of their nature. While the static Love numbers of Schwarzschild, Kerr, and Reissner–Nordström black holes remarkably vanish, the tidal response of a generic Kerr–Newman black hole has remained unexplored due to the intrinsic coupling between gravitational and electromagnetic perturbations. Exploiting a recent breakthrough in the separability of these perturbations, we analytically determine the static tidal response of the most general stationary black hole in four-dimensional Einstein–Maxwell theory. For arbitrary multipole order, charge, and spin, we show that the entire matrix of conservative Love numbers vanishes, including the mixed gravito-electromagnetic couplings. We also compute the nonvanishing static dissipative response induced by frame dragging.
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All authors Sumanta Chakraborty, Takuya Katagiri, Paolo Pani, Jun-Xi Shi

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

Cosmic Colliders in Binary Blazars Probing Ultra-High-Energy Particle Physics

Giorgio Galanti

While terrestrial colliders and fixed-target cosmic-ray interactions are bounded at center-of-mass (CM) energies $\sqrt{s} \lesssim \mathcal{O}(10^5)\,\text{GeV}$, we demonstrate that bound sub-parsec binary blazars form broad-band, beam-beam hadronic “Cosmic Colliders”, overcoming such limitation. Driven by modest jet misalignments ($\theta_{\rm mis} \sim 1^\circ - 6^\circ$), co-streaming proton beams collide at CM energies reaching $\sqrt{s} \sim 10^{10}\,\text{GeV}$ - six orders of magnitude above the Large Hadron Collider. Operating in a strictly optically thin regime ($\tau_{pp} \ll 1$), the system performs a continuous CM energy scan, probing asymptotic QCD scaling, gluon saturation, and Froissart unitarity, while opening a possible high-sensitivity window into physics beyond the Standard Model. Secondary PeV-EeV neutrinos and sub-TeV $\gamma$-rays fall directly within reach of current and planned observatories such as LHAASO, CTAO, IceCube, and GRAND, establishing binary blazars as laboratories for physics at the ultimate energy limit.
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