Papers

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Physics Astrophysics High Energy Astrophysical Phenomena

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Wednesday 12 August

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

Large-Scale Dynamos Driven by Shear-Flow-Induced Jets

B. Tripathi, A. E. Fraser, P. W. Terry et al. (+3 more)

At every scale they occupy, magnetic fields affect various phenomena, including star formation, cosmic ray transport, charged particle acceleration, space weather, transport in planetary atmospheres, and laboratory plasmas. These fields are often generated and sustained by turbulent flows in a process called the dynamo. In 1955, E. N. Parker parameterized the effects of small-scale turbulence to propose a mean-field dynamo theory. The widely used theory reproduces observed large-scale fields but suffers from difficulty in tuning parameters as they are not justified from first principles: Studies of turbulent flows show tangled magnetic fields, which are folded and fragmented into small-scale structures due to shear-flow straining. Here, considering a shear flow that is unstable and driven, we develop analytic theory and perform three-dimensional (3D), advanced computer simulations of turbulence with up to 4096 x 4096 x 8192 grid points, showing ab initio generation of quasi-periodic, large-scale magnetic fields. The generation occurs via the mean-vorticity effect—an additional mean-field dynamo process postulated in 1990. Crucial to this dynamo is the prior generation of large-scale 3D jets, robustly produced as topologically protected and exact nonlinear solutions of the magnetohydrodynamic equations. The jet-driven dynamo applies to shear-driven laboratory and astrophysical systems. These include binary neutron star mergers, where the reported dynamo likely operates on microsecond timescales to produce in milliseconds some of the strongest magnetic fields in the Universe, providing signals for multimessenger astronomy.

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All authors B. Tripathi, A. E. Fraser, P. W. Terry, E. G. Zweibel, M. J. Pueschel, R. Fan

High Energy Astrophysical Phenomena

3D Radiative Transfer of Lyman-series Lines with SKIRT

N. Sameshima, A. Lauwers, B. Vander Meulen et al. (+4 more)

Context. High-resolution X-ray spectroscopy and polarimetry provided by XRISM and IXPE offer new diagnostics of the geometry and kinematics of photo-ionised plasmas around compact objects. Interpreting reprocessed X-ray emission in such systems requires full three-dimensional radiative transfer (3D RT) including photon-ion interactions. Aims. We extend the Monte Carlo (MC) RT code SKIRT by implementing the Lyman-series lines of H-like ions, enabling self-consistent modelling of resonance scattering, radiative recombination, and polarisation of these lines in X-ray photo-ionised plasmas. Methods. We implemented Lyman-series transitions (up to $n=10$) for ions with $Z=$1–30, including fine-structure splitting and linear polarisation in resonance scattering. Two channels for the production of the Lyman-series lines (resonance scattering and radiative recombination) are considered. Results. The implementation reproduces analytical expectations and shows good agreement with Cloudy. The SKIRT simulations naturally capture RT effects such as P Cygni profiles and line-profile distortion in optically thick media, which are inaccessible to the conventional 1D RT codes commonly used in X-rays. In 3D geometries, we find that anisotropic illumination and velocity fields significantly modify the Lyman series line ratios and profiles, all of which are observable with XRISM. Conclusions. The extended version of SKIRT provides a powerful framework for interpreting X-ray line spectra and polarisation from photo-ionised plasmas. It is particularly suited for constraining the geometry and velocity structure in the vicinity of compact objects in the XRISM and IXPE era.

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All authors N. Sameshima, A. Lauwers, B. Vander Meulen, M. Tsujimoto, L.-Y. Gu, M. Baes, P. Camps

High Energy Astrophysical Phenomena

Interacting Supernovae: a Radio and X-ray Strategy to Constrain the Structure of the Circumstellar Medium

Shunke Ai, Irene Tamborra and Leonardo Dinoi

The interaction of supernova (SN) ejecta with the dense circumstellar medium (CSM) converts shock kinetic energy into radiation across multiple wavebands. We investigate the dependence of the X-ray and radio emission on the CSM geometry, considering spherical, hourglass, and disk shapes for the CSM. We find that the spectral and light-curve properties, both in X-ray and radio, significantly differ for spherical and non-spherical CSM structures. For a non-spherical CSM, the radio light curve flattens out near the peak frequency, due to efficient free-free absorption by the unshocked CSM. Moreover, the early rise of the radio light curve is shallower when the CSM density along the observer line of sight is larger than that in other directions. If the CSM density is lower along the observer line of sight, the radio light curve flattens near its peak, and the reverse-shock component is negligible in X-rays. Building on these features, we provide a method to constrain the CSM structure based on the rising part the radio light curve in the proximity of its peak; we show that the decay part of the radio light curve, after its peak, carries insight on whether the CSM density profile is wind-like or not. We further adopt the X-ray signal to corroborate the information extracted from radio. We test our strategy on SN 1993j and SN 2023ixf. For both SNe, we find that an asymmetric CSM is in excellent agreement with radio and X-ray observations and provides a viable alternative to non-wind scenarios suggested in the literature. Our findings highlight the crucial insight provided by radio and X-ray signals into the mass-loss history of the SN progenitor.

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High Energy Astrophysical Phenomena

High-energy neutrino signatures of embedded GRB jets in AGN disks: a dynamic jet-propagation framework

Wei-Cheng Long and Yun-Wei Yu

Relativistic jets embedded in active galactic nucleus (AGN) accretion disks are promising high-energy neutrino sources, but their emission is often estimated from a single representative jet state. We develop a time-dependent framework that follows jet-head propagation, evolving reverse-shock conditions, and particle cooling until the jet chokes or breaks out, and apply it to the SG and TQM disk models. For the representative choked cases, neutrino emission is dominated by the high-dissipation phase near jet stalling, allowing a stalling-state approximation to reproduce the trajectory-integrated, detector-weighted event yield within approximately $14\%$. In breakout cases, however, rapid jet-head acceleration across steep disk-density gradients suppresses reverse-shock dissipation and can cause single-state estimates to overpredict the fluence, even after accounting for the available energy budget. Full trajectory integration also reshapes the high-energy spectral tail and produces distinct detectability patterns across SMBH mass and disk radius for the two disk models. Some lower-density outer-disk cases develop harder tails extending into the 10–100 PeV range, motivating future ultra-high-energy neutrino searches. Resolving jet propagation dynamics is therefore indispensable for evaluating embedded transients across AGN disk environments and avoiding systematic biases in multi-messenger modeling.

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High Energy Astrophysical Phenomena

Impact of Neutrino Flavour Conversion on the Diffuse Neutrino Background from Neutrino-dominated Accretion Flows

Yun-Feng Wei and Tong Liu

Neutrino-dominated accretion flows (NDAFs) are believed to form during the fallback accretion phase of some core-collapse supernovae (CCSNe). Such systems produce copious neutrino emission, whose cumulative contribution over cosmic history forms the diffuse NDAF neutrino background (DNNB). As neutrinos propagate from the source to Earth, flavour conversion can significantly modify the observed neutrino spectra and consequently the detectability of the DNNB. In this work, based on fallback CCSN simulations, we investigate the effects of progenitor mass, metallicity, and initial explosion energy on neutrino emission from NDAFs. We calculate the heavy-lepton neutrino ($\nu_x$) spectra from NDAFs and incorporate them into DNNB predictions. We find that the unoscillated $\nu_x$ spectra are more than an order of magnitude lower than those of electron antineutrinos $\bar{\nu}_e$. Using the latest neutrino oscillation parameters reported by the Jiangmen Underground Neutrino Observatory (JUNO), we evaluate the impact of flavour conversion on the DNNB and derive the corresponding spectra for both the normal and inverted mass orderings. We further estimate the expected event numbers in JUNO and Hyper-Kamiokande. We find that the predicted DNNB signal is strongly dependent on the neutrino mass ordering. While the DNNB may be detectable in the normal ordering with next-generation neutrino detectors, the signal is significantly suppressed in the inverted ordering, making detection considerably more challenging.

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

Transport properties in binary neutron star mergers: Effect of magnetic field

Pranjal Tambe and Debarati Chatterjee

In extreme environments such as binary neutron star mergers, temperatures as high as $50$ MeV and magnetic fields up to $10^{17}$ G, reach a regime where neutrino transport governs the macroscopic thermodynamic and chemical evolution. Existing merger simulations rely on zero magnetic field neutrino emissivity and opacity, potentially missing critical transport physics in highly magnetized neutron star cores. We present an exact framework for computing charged current Urca emissivity and neutrino opacity at finite temperature and magnetic field. We employ the Nucleon Width Approximation framework to account for the collisional broadening effects dominant in the high-density core. Our calculations demonstrate that extreme magnetic fields significantly enhance charged current neutrino opacity, effectively reducing the mean free path for thermal neutrinos.

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High Energy Astrophysical Phenomena

Constraining the gamma-ray efficiency of LINER outflows with Fermi-LAT and MEGARA

Alberto Domínguez, Alejandra León, Adithiya Dinesh et al. (+1 more)

Low-Ionization Nuclear Emission-line Regions (LINERs) commonly host ionized gas outflows, but their role as high-energy particle accelerators remains debated, particularly following the very-high-energy $\gamma$-ray detection of NGC 4278, which implied extreme radiative efficiencies. We empirically determine the $\gamma$-ray radiative efficiency of a local sample of LINERs to test whether their high-energy emission can be powered by extended ionized outflows or requires compact nuclear jets. We combine spatially resolved optical integral-field kinematics from the Multi-Espectrógrafo en GTC de Alta Resolución para Astronomía at the Gran Telescopio de Canarias, yielding ionized-outflow kinetic powers, with 17 years of Fermi-Large Area Telescope observations to derive 0.05–500 GeV luminosities or 95% confidence upper limits. We place the sample in an optical/$\gamma$-ray diagram alongside archetypal starbursts and radio galaxies. We present the first empirical upper limits on the $\gamma$-ray radiative efficiency of LINER outflows as a population. No LINER is formally detected ($TS \geq 16$). The strongest constraint is obtained for the radio-loud LINER NGC 1052, with $\eta < 41%$. For the remaining sources, the Fermi-LAT limits generally lie well above the outflow kinetic powers ($\eta \gg 100%$), while three sources show marginal hints of emission ($9 < TS < 16$). We conclude that extended ionized outflows in LINERs are highly inefficient high-energy particle accelerators, analogous to starburst superwinds. These constraints disfavor the outflows as the sole origin of extreme $\gamma$-ray efficiencies and favor compact nuclear jets for the most efficient $\gamma$-ray-emitting LINERs.

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All authors Alberto Domínguez, Alejandra León, Adithiya Dinesh, Armando Gil de Paz

High Energy Astrophysical Phenomena

Identification of a Large-Scale Diffuse Gamma-Ray Structure in the Southern Galactic Hemisphere

Zhen Xie, Xiaoyuan Huang, Bing Liu et al. (+1 more)

We identify and characterize a large-scale diffuse gamma-ray structure in the Southern Galactic Hemisphere using 17 yr of Fermi-LAT data. An energy-dependent likelihood analysis, including alternative Galactic diffuse-emission models, isotropic emission, the Fermi bubbles, and resolved 4FGL sources, reveals an extended excess that persists across the tested background models and spans tens of degrees. The excess broadly follows the X-ray-defined southern eROSITA Bubble (eB) region, while also overlapping the projected southern extension of Loop I. Template fits favor a filled eB-like morphology over the adopted Wolleben Loop I shell geometry, making the structure a plausible gamma-ray counterpart of the southern eB, although Loop-I-related or other localized foreground emission cannot be excluded. Under the eB template, the southern component is fainter and softer than the northern large-scale component, with an integrated luminosity lower by a factor of about seven, broadly consistent with the eROSITA-bubble asymmetry. If interpreted as Galactic-scale outflow emission, its faint, soft spectrum may indicate aged particles and/or distributed reacceleration in the outer bubble. A hadronic interpretation is energetically demanding, whereas a leptonic inverse-Compton scenario is more economical but requires rapid transport and/or local reacceleration of high-energy electrons.

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All authors Zhen Xie, Xiaoyuan Huang, Bing Liu, Ruizhi Yang

High Energy Astrophysical Phenomena

Spiral structure from the interference of gravitational eigenmodes in ultralight dark matter halos

Jacob Reinach and Hubert Bray

We use a variety of analytic and numerical techniques to approximate the geometry of individual dark matter halos when modeled as collections of ultralight scalar bosons (ULDM), followed by an analysis on the future directions and implications of this work. Ultimately, we aim to understand the morphology and creation of complex structures (like spirals) in galaxies from a geometric standpoint and to investigate the connection between dark matter and baryonic matter in galaxies. We find that superpositions of gravitational eigenmodes for ULDM in a fixed background potential can yield spiral density perturbations which rotate on the order of one hundred million years and appear within ten to twenty kpc of the halo center, both features comparable to realistic galaxies, and that this model provides a natural explanation for the density waves necessary to seed baryonic spirals.

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High Energy Astrophysical Phenomena

Discovery of 27 new Rotating Radio Transients by MeerTRAP

S. Singh, J. Tian, B. W. Stappers et al. (+15 more)

We present the discovery of 27 new Galactic transients made by the commensal MeerTRAP single pulse search programme at the MeerKAT telescope. We determine the location of 14 of these discoveries with arcsecond accuracy by imaging the data captured in the dedicated transient buffer. A preliminary estimate of the period was made for 8 sources using the arrival times of several pulses detected by MeerTRAP. The periods of these transients range between 0.78 s and 4 s. For the previously published MeerTRAP source MTP0040 (PSR J1357-6507), we are able to provide the position and period using new pulses detected since it was reported. We also estimate the radio fluences and discuss the burst rates derived from the commensal search detections. The accurate image-domain localizations were used to conduct follow-up observations and timing analysis. Furthermore, some follow-up observations revealed ordinary pulsar-like pulsed behavior for four of the new sources, illustrating the blurred separation between rotating radio transients and canonical pulsars. We also present coherent timing solutions for 4 sources, providing insight into their rotational properties and their place within the Galactic neutron star population.

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All authors S. Singh, J. Tian, B. W. Stappers, K. Shaji, K. M. Rajwade, L. Levin, J. D. Turner, M. C. Bezuidenhout, M. Caleb, I. Pastor-Marazuela, F. Jankowski, R. Karuppusamy, E. D. Barr, M. Kramer, R. Breton, C. J. Clark, T. Thongmeearkom, M. Burgay

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

Chemical fingerprints of binary mass transfer in massive stars

Harim Jin and Norbert Langer

The majority of massive stars are born in close binary systems. As stars expand when they age, mass transfer or even a merger with their companion is inevitable. However, most binary interaction products appear as single stars, such that the main evidence of their exciting past is lost. In a comprehensive grid of detailed massive binary evolution models we find systematic trends in chemical surface abundances that allow identifying the past mass gainers. We develop an analytic framework which is independent of specific evolutionary models, to constrain the amount and composition of the accreted material from their observed surface abundances. This yields tight constraints on the uncertain mass transfer physics in massive binary stars and allows us to reconstruct the past evolutionary history of the progenitor binary system. This method, which is shown to also constrain binary mergers (for example, SN 1987A), is applied to some of the best-studied OB stars so far. For {\gamma} Columbae, suggested to be an envelope-stripped star, we show that it is a mass gainer instead, whose companion star likely formed a stripped-envelope supernova. Our results highlight surface abundance measurements as a powerful tool to improve our understanding of massive binary systems evolving towards supernovae and compact object binaries.

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

SPORE: An Event-Level Sampling Pipeline for Multi-Telescope Neutrino Astronomy

Jeffrey Lazar, Perrine Wilmet and Gwenhaël de Wasseige

We present an open-source Python package for simulating neutrino events from astrophysical point and extended sources using tabulated instrument response functions (IRFs). The package encodes three detector response components - effective area, point spread function, and energy resolution - in a selection-agnostic HDF5 format, which can represent a neutrino telescope whose response is supplied in that form, whether from a public release or a private study. Sampling algorithms cover point sources (inverse-CDF with Poisson or fixed-count modes), extended sky distributions (hierarchical inverse-CDF sampling, including full RA- and declination-dependent flux maps), and multi-detector joint analyses. We validate the framework via a round-trip consistency test using the publicly available IceCube 10-year tracks data release: the released IRFs are ingested into the package and used to generate a synthetic event set, whose declination distribution reproduces the observed one to 10-15% across the northern sky. The reconstructed-energy distribution agrees to within about a third over the bulk of the sample but exceeds the data by up to a factor of three below 600 GeV, a discrepancy we trace to the coarse true-energy binning of the public smearing matrix rather than to the sampling: an independent forward fold of the same IRFs reproduces it. We further compare against the IceCube HESE 7.5-year public data release: the sampled deposited-energy spectrum tracks the published best-fit expectation, and the observed data fall within the goodness-of-fit distribution built from 1,000 sampled pseudo-experiments, though on its well-fitting side, as expected for an expectation that was itself fit to those data.

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High Energy Astrophysical Phenomena

Radio flares and X-ray hardening embedded in the long soft state of 4U 1543-475

Zuobin Zhang, Rob Fender, Jiachen Jiang et al. (+14 more)

We present a comprehensive multi-wavelength study of the black hole X-ray binary 4U 1543-475 during its 2021 outburst, focusing on radio flaring episodes that are commonly interpreted as signatures of episodic jet production and are embedded within states when the X-ray emission was dominated by an accretion disk component. The radio monitoring reveals at least two discrete flares that coincide with periods of enhanced Comptonized X-ray emission. Broadband spectral modelling shows a significant decrease in the reflection-to-disk flux ratio (by a factor of ~3-4) during these episodes, consistent with a temporary change in the geometry of the inner accretion flow, although the data do not allow the causal sequence to be firmly established. Optical photometry exhibits variability that broadly tracks the reflection fraction, consistent with changes in the illuminating component. The accompanying spectral hardening indicates that the radio flares were associated with short-lived excursions toward a "harder" state, departing from the soft state. X-ray timing analysis suggests that the radio flares may be associated with changes in the fractional rms variability; however, no consistent or unified pattern can be firmly established across different events. These results provide a multi-wavelength observational example of radio flaring activity in a black hole binary and highlight the complex interplay between accretion flow geometry, coronal emission, and jet-related phenomena.

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All authors Zuobin Zhang, Rob Fender, Jiachen Jiang, Payaswini Saikia, David M. Russell, Andrew Hughes, Honghui Liu, Francesco Carotenuto, James F. Steiner, Fraser J. Cowie, John A. Tomsick, Cosimo Bambi, Yimin Huang, Xian Zhang, Wenfei Yu, Yuexin Zhang, Rittick Roy

High Energy Astrophysical Phenomena

Cherenkov light as a mechanism for light flashes seen by astronauts in space

Dominika Švecová, Pavol Bobík and Blahoslav Pastirčák

Astronauts first reported light flashes during the Apollo 11 mission. These events have since been associated with cosmic rays, although their underlying mechanism remains uncertain. This study investigates possible formation processes using Geant4 simulations of cosmic ray interactions in a simplified model of the human eye. We apply published models of human visual perception to the simulated particle induced photons and compare the resulting light flash rates with experimental observations. Our results indicate that, in interplanetary space and in low Earth orbit outside the South Atlantic Anomaly, Cherenkov radiation generated in the eye produces retinal responses consistent with the observed frequency of astronaut light flashes. The dominant contributing primaries are found to be high Z nuclei, primarily iron, with additional contributions from oxygen and carbon nuclei. In contrast, conditions in the South Atlantic Anomaly suggest that additional mechanisms may be required to explain observed light flashes. We also find that the absence of light flashes at Earth's surface is consistent with insufficient retinal stimulation from muon induced Cherenkov radiation under typical geometrical and flux conditions.

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

LIGO A$^\sharp$: Detector Design and Science Prospects Beyond A+

L. Sun, K. Kuns, B. J. J. Slagmolen et al. (+1153 more)

We present the LIGO A$^\sharp$ detector concept, an upgrade for the LIGO observatories based on room-temperature interferometers beyond the fifth observing run (O5). Building on the A+ sensitivity, A$^\sharp$ targets broadband sensitivity improvements through heavier test masses, improved suspensions and seismic isolation, increased arm-cavity power, enhanced frequency-dependent squeezing, reduced coating thermal noise considering two scenarios, and improved control of mechanical motion and optical modes. We describe the principal design choices, projected noise performance, and corresponding astrophysical prospects. LIGO A$^\sharp$ substantially increases compact-binary detection rates, strengthens population inference, and improves both early-warning times and localization for binary neutron star mergers. The improved sensitivity enables more detailed studies of compact-binary coalescences, including higher-order multipoles, intermediate-mass black holes, remnant black hole ringdown, and the neutron star equation of state. It also broadens the discovery potential for new gravitational-wave sources such as continuous waves and bursts, should enable detection of the stochastic background from compact binary mergers if it remains undetected after O5, and strengthens the role of gravitational-wave detectors as probes of fundamental physics. We discuss key technical challenges and the role of A$^\sharp$ as both a major scientific upgrade for the 2030s and a technology pathfinder for next-generation gravitational-wave observatories, such as Cosmic Explorer.

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All authors L. Sun, K. Kuns, B. J. J. Slagmolen, P. Fritschel, P. Schmidt, B. T. Lantz, S. S. Y. Chua, Divyajyoti, S. W. Ballmer, M. A. Barton, A. V. Cumming, K. L. Dooley, J. C. Driggers, A. Effler, M. Evans, B. Farr, G. González, N. Lu, D. J. Ottaway, C. Palomba, O. J. Piccinni, G. Pratten, S. Raja, A. P. Subhash, P. J. Sutton, K. Toland, R. L. Ward, A. G. Abac, I. Abouelfettouh, K. Ackley, A. Adam, S. Adhicary, D. Adhikari, R. X. Adhikari, V. K. Adkins, S. Afroz, M. Agathos, N. Aggarwal, S. Aggarwal, O. D. Aguiar, P. Ajith, L. Albers, S. Al-Kershi, S. Al-Shammari, J. A. Alvarez, S. Alvarez-Lopez, O. Amarasinghe, A. Amato, S. An, A. B. Anand, C. Anand, A. Ananyeva, S. B. Anderson, W. G. Anderson, F. Andrade-Oliveira, M. Andrés-Carcasona, J. L. Andrey, T. Andric, J. Anglin, J. Anna, J. M. Antelis, L. V. da Conceição, T. Aoki, E. Z. Appavuravther, E. A. Appelt, S. Appert, S. K. Apple, K. Arai, M. C. Araya, J. S. Areeda, M. Ramos Arevalo, S. Armstrong, M. Arogeti, S. M. Aronson, K. G. Arun, G. Ashton, S. M. Aston, K. AultONeal, G. Avallone, E. A. Avila, C. Badger, S. Bae, K. A. Baker, T. Baker, M. Ball, S. Banagiri, D. Bankar, T. M. Baptiste, P. Baral, J. C. Barayoga, K. Baric, B. C. Barish, D. Barker, N. Barman, B. Barr, M. Barrios, L. Barsotti, I. Bartos, A. Basalaev, R. Bassiri, J. C. Bayley, A. C. Baylor, P. A. Baynard II, B. Becher, V. M. Bedakihale, A. S. Bell, D. S. Bellie, W. Benoit, F. Bergamin, B. K. Berger, M. Beroiz, C. P. L. Berry, I. Berry, J. Betzwieser, D. Beveridge, N. Bevins, R. Bhandare, R. Bhatt, A. Bhattacharjee, D. Bhattacharjee, S. Bhattacharyya, S. Bhaumik, I. A. Bilenko, G. Billingsley, S. Bini, O. Birnholtz, S. Biscoveanu, A. Bisht, S. Blaber, J. K. Blackburn, L. A. Blagg, C. D. Blair, D. G. Blair, N. Bode, N. Boettner, P. Bogdan, G. N. Bolingbroke, L. D. Bonavena, V. A. Bonhomme, E. Bonilla, M. S. Bonilla, A. Bonino, A. Borchers, S. Bose, V. Bossilkov, T. D. Boybeyi, M. Boyle, M. J. Brady, P. R. Brady, A. Branch, M. Brinkmann, P. Brockill, E. Brockmueller, A. F. Brooks, D. D. Brown, S. Brunett, R. Bruntz, J. Bryant, Y. Bu, A. Buonanno, K. Burtnyk, J. Calderón Bustillo, R. L. Byer, V. A. Cáceres-Barbosa, L. Cadonati, C. Cahillane, A. Calafat, J. D. Callaghan, T. A. Callister, S. R. Callos, V. Cantory, H. Cao, L. A. Capistran, E. Capote, C. Capuano, K. J. Cardona-Martínez, M. Carlassara, J. Yébana Carrilero, G. Carrillo, G. Carullo, S. Caudill, M. Cavaglià, A. Ceja, N. Chabbra, A. Chakraborty, P. Chakraborty, S. Chakraborty, C. Chan, J. C. L. Chan, M. Chan, K. Chang, S. Chao, P. Charlton, C. Chatterjee, Debarati Chatterjee, Deep Chatterjee, M. Chaturvedi, A. Chen, H. Y. Chen, S. Chen, Yanbei Chen, Yiwen Chen, G. Cheng, H. P. Cheng, T. Cheunchitra, H. T. Cheung, S. Y. Cheung, G. Chiarini, M. Chicoine, D. Chintala, S. Choudhary, N. Christensen, Y. K. Chu, B. Cirok, F. Clara, J. A. Clark, T. A. Clarke, A. Claveus, M. R. Claypool, S. M. Clyne, D. E. Cohen, E. Colangeli, O. Cole, G. D. Cole, M. Colleoni, C. G. Collette, J. Collins, S. Colloms, C. M. Compton, G. Connolly, T. R. Corbitt, N. J. Cornish, A. Corsi, L. Cotnoir, R. Cottingham, J. A. Cotturone, M. W. Coughlin, P. Couvares, R. Coyne, J. D. E. Creighton, T. D. Creighton, S. Crook, R. Crouch, J. Csizmazia, T. J. Cullen, Y. Dang, O. Danner, K. Danzmann, K. E. Darroch, C. Darsow-Fromm, L. P. Dartez, R. Das, S. Das, A. Dasgupta, I. Dave, A. Davenport, T. F. Davies, D. Davis, M. C. Davis, E. J. Daw, M. Dax, E. deBruin, M. Deenadayalan, O. M. del Rio, N. Demos, T. Dent, N. DePergola, E. K. Derrick, M. Desai, D. DeSantis, S. Deshmukh, V. Deshmukh, S. Determan, A. Dhani, R. Dhatri, R. Dhurkunde, R. Diab, M. C. Díaz, T. Dietrich, C. Di Fronzo, A. Dmitriev, J. P. Docherty, Z. Doctor, N. Doerksen, E. Dohmen, A. Doke, F. Donovan, S. Doravari, F. Dosopoulou, R. S. Dumbreck, S. Dwivedi, S. E. Dwyer, C. Eassa, M. Eberhardt, M. Ebersold, M. Ebiri, T. Eckhardt, G. Eddolls, J. Eichholz, M. Emma, R. Enficiaud, R. Espinosa, R. C. Essick, H. Estellés, T. Etzel, T. Evstafyeva, J. M. Ezquiaga, S. Fairhurst, X. Fan, A. M. Farah, W. M. Farr, M. Favata, M. Fazio, J. Feicht, M. M. Fejer, J.-N. Feldhusen, J. Fernandes, D. Fernando, T. A. Ferreira, M. Ferrer-Martinez, M. Fishbach, R. P. Fisher, S. K. Fitzgerald, B. Flanagan, S. M. Fleischer, L. S. Fleming, E. Floden, H. Fong, F. Fontinele-Nunes, C. Foo, B. Fornal, P. W. F. Forsyth, A. Franco-Ordovas, J. P. Freed, Z. Frei, R. Frey, W. Frischhertz, V. V. Frolov, M. Fuentes-Garcia, P. Fulda, M. Fyffe, J. R. Gair, V. Galdi, A. Gamboa, S. Gamoji, A. Ganguly, C. García-Quirós, J. W. Gardner, A. Garron, P. A. Garver, V. Gayathri, T. Gayer, J. George, R. George, D. George, O. Gerberding, L. Gergely, Sayantan Ghosh, Shaon Ghosh, Shrobana Ghosh, Suprovo Ghosh, Tathagata Ghosh, J. A. Giaime, K. D. Giardina, D. R. Gibson, C. Gier, J. Glanzer, J. Godfrey, R. V. Godley, O. Godwin, A. S. Goettel, E. Goetz, J. Golomb, P. Goodarzi, S. R. Goode, S. M. Goss-Grubbs, D. W. Gould, K. Govorkova, V. Graham, A. E. 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Kokeyama, P. Kolitsidou, K. Kompanets, A. K. H. Kong, A. Kontos, K. Kopczuk, L. M. Koponen, M. Korobko, X. Kou, N. Kouvatsos, D. B. Kozak, V. Kringel, N. V. Krishnendu, S. Kroker, K. Kruska, G. Kuehn, D. Kukla, Achal Kumar, Anil Kumar, Dhruv Kumar, Praveen Kumar, Prayush Kumar, Rahul Kumar, Rakesh Kumar, Ravi Kumar, V. Kumar, N. Kuntimaddi, K. Kwan, G. Lacaille, D. Laghi, A. H. Laity, E. Lalande, S. Lalvani, M. Landry, R. N. Lang, A. Lange, R. Langgin, I. La Rosa, O. Laske, P. D. Lasky, J. Lawrence, M. Laxen, A. Lazzarini, L. Leali, Y. K. Lecoeuche, J. Lee, K. Lee, R. Lee, S. Lee, Y. Lee, I. N. Legred, J. Lehmann, L. Lehner, M. Lesovsky, Y. Levin, K. Leyde, X. Li, Y. Li, Z. Li, Q. Liang, F. Lin, C. Lindsay, S. D. Linker, A. Liu, Jian Liu, S. Liu, J. Llobera-Querol, R. K. L. Lo, S. C. G. Loggins, L. T. London, R. Rodriguez Lopez, A. Lorenzo-Medina, M. Lormand, T. P. Lott IV, J. D. Lough, H. A. Loughlin, C. O. Lousto, N. K. Y. Low, H. Lück, O. Lukina, A. P. Lundgren, A. W. Lussier, X. 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Miller, M. Millhouse, A. Mishra, C. Mishra, T. Mishra, A. Mitchell, J. G. Mitchell, O. Mitchem, S. Mitra, V. P. Mitrofanov, R. Mittleman, G. Mo, S. R. P. Mohapatra, M. Molina-Ruiz, M. Mondin, C. J. Moore, D. Moraru, A. More, S. More, C. Moreno, E. A. Moreno, G. Moreno, C. Morgan, M. Mould, C. M. Mow-Lowry, Arunava Mukherjee, D. Mukherjee, Samanwaya Mukherjee, Soma Mukherjee, Subroto Mukherjee, Suvodip Mukherjee, N. Mukund, A. Mullavey, C. L. Mungioli, P. G. Murray, S. Muusse, S. A. Vallejo-Peña, N. Nagarajan, A. Nakamura, M. Nakano, D. Nandi, S. U. Naqvi, P. Narayan, R. K. Nayak, J. Neeson, A. Nela, C. Nelle, A. Nelson, T. J. N. Nelson, A. Neunzert, M. Newell, S. Ng, A. B. Nielsen, W. Niu, J. Noller, M. Norman, C. North, A. Numic, G. Nurbek, L. K. Nuttall, J. Oberling, C. E. Ochoa, C. O'Connor, J. O'Dell, E. Oelker, J. J. Oh, T. O'Hanlon, F. Ohme, I. Oke, R. Omer, N. O'Neill, P. Ophardt, R. J. Oram, B. O'Reilly, R. O'Shaughnessy, J. Ostrovska, A. Osumi, I. Ota, G. Othman, H. 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Wang, Z. Wang, P. Wang, J. Warner, N. Y. Washington, B. Weaver, S. A. Webster, N. L. Weickhardt, M. Weinert, A. J. Weinstein, O. Weisenberger, R. Weiss, L. Wen, K. Wette, C. Wheeler, J. T. Whelan, B. F. Whiting, E. G. Wickens, D. Wilken, B. M. Williams, D. Williams, M. J. Williams, N. S. Williams, J. L. Willis, B. Willke, C. W. Winborn, A. Wingfield, J. Winterflood, C. C. Wipf, G. Woan, N. E. Wolfe, H. T. Wong, J. L. Wright, B. Wu, D. S. Wu, K. Wu, E. Wuchner, D. M. Wysocki, Y. Xia, V. A. Xu, Y. Xu, M. Ben Yaala, H. Yamamoto, T. Yan, H. Yang, K. Z. Yang, Z. Yarbrough, A. B. Yelikar, X. Yin, M. Yoshihara, S. Yuan, M. Zanolin, M. Zeeshan, M. Zevin, H. Zhang, L. Zhang, N. Zhang, R. Zhang, T. Zhang, C. Zhao, Y. Zhao, L.-M. Zheng, Y. Zheng, H. Zhong, H. Zhou, H. O. Zhu, Z. Zhu, D. Z. Zieba, A. B. Zimmerman, M. E. Zucker, R. Arès, J. J. Carter, S. J. Madden, K. McKenzie, E. R. Rees, B. Shapiro

High Energy Astrophysical Phenomena

A Radiation-Hydrodynamic Light Curve Grid and Interpolation Framework for Stripped-Envelope Supernovae

Qiliang Fang and Takashi J. Moriya

We present a grid of 8,148 stripped-envelope supernovae (SESNe) light curves based on radiation hydrodynamic simulations of exploding helium-star progenitors. The grid spans an ejecta-mass range representative of typical SESNe, together with broad ranges of explosion energies, radioactive nickel masses, and degrees of material mixing. We systematically investigate how these physical parameters shape the light curves and develop an interpolation-based parameter inference framework that enables the application of the model grid to observational data. Using the simulated light curves as mock observations, we assess the reliability of the widely used Arnett model. Although it reproduces the overall light-curve morphology, the inferred ejecta masses show no significant correlation with the true values. Moreover, the analytical model produces a spurious correlation between explosion energy and nickel mass, despite these parameters being independent in the underlying model grid. These results demonstrate that good light-curve fits do not necessarily imply reliable physical parameter estimates and highlight the need for physically motivated radiation hydrodynamic models in population studies of SESNe.

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

Constraints on ultralight bosons from merging binary and remnant black holes observed during the second and third parts of the fourth LIGO-Virgo-KAGRA observing run

The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration: A. G. Abac et al. (+1807 more)

We present constraints on ultralight bosons using binary black hole mergers observed in the second and third parts of the fourth LIGO-Virgo-KAGRA observing run. Directed searches are conducted for long-transient gravitational waves from ultralight vector boson clouds around merger remnants, using a hidden-Markov-model (HMM) tracking scheme. We target the remnant black holes formed in the binary coalescences that produced GW250114 and GW250207. We find no evidence for such signals from either target. Estimating our search sensitivity at a threshold corresponding to a 1% false alarm probability, we thus disfavor vector boson masses in the range of $[2.80, 3.95]\times 10^{-13}$ eV with greater than 90% confidence. In addition, we derive constraints on ultralight scalar and vector bosons from the inferred high spins of the constituent black holes in three binaries, using events GW240515, GW241113, and GW241225_08. The excluded mass ranges in this approach depend on the assumed black-hole ages. At $10^5$ years, corresponding to typical dynamically formed binaries, we exclude scalar and vector bosons in the ranges $[1.39, 6.94]\times 10^{-13}$ eV and $[0.32, 14.4]\times 10^{-13}$ eV at 90% confidence, respectively.

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All authors The LIGO Scientific Collaboration, the Virgo Collaboration, the KAGRA Collaboration: A. G. Abac, A. Abe, I. Abouelfettouh, F. Acernese, K. Ackley, A. Adam, S. Adhicary, D. Adhikari, R. X. Adhikari, V. K. Adkins, S. Afroz, A. Agapito, D. Agarwal, M. Agathos, N. Aggarwal, S. Aggarwal, O. D. Aguiar, I.-L. Ahrend, L. Aiello, A. Ain, P. Ajith, T. Akutsu, L. Albers, W. Ali, S. Al-Kershi, C. Allene, A. Allocca, S. Al-Shammari, J. A. Alvarez, S. Alvarez-Lopez, W. Amar, O. Amarasinghe, A. Amato, F. Amicucci, C. Amra, A. B. Anand, C. Anand, A. Ananyeva, S. B. Anderson, W. G. Anderson, M. Andia, M. Ando, F. Andrade-Oliveira, M. Andrés-Carcasona, J. L. Andrey, T. Andrić, J. Anglin, J. Anna, J. M. Antelis, S. Antier, T. Aoki, M. Aoumi, E. Z. Appavuravther, E. A. Appelt, S. Appert, S. K. Apple, K. Arai, A. Araya, M. C. Araya, F. Arciprete, J. S. Areeda, N. Aritomi, F. Armato, S. Armstrong, N. Arnaud, M. Arogeti, S. M. Aronson, K. G. Arun, G. Ashton, Y. Aso, L. Asprea, M. Assiduo, S. Assis de Souza Melo, S. M. Aston, P. Astone, P. S. Aswathi, F. Attadio, F. Aubin, K. AultONeal, G. Avallone, N. Avdeev, E. A. Avila, S. Babak, C. Badger, S. Bae, S. Bagnasco, S. Baimukhametova, L. Baiotti, T. Baka, K. A. Baker, T. Baker, G. Balbi, G. Baldi, N. Baldicchi, M. Ball, G. Ballardin, M. Ballelli, S. W. Ballmer, S. Banagiri, B. Banerjee, D. Bankar, T. M. Baptiste, P. Baral, M. Baratti, J. C. Barayoga, K. Baric, B. C. Barish, D. Barker, N. Barman, F. Barone, B. Barr, M. Barrios, L. Barsotti, M. Barsuglia, D. Barta, M. A. Barton, I. Bartos, A. Basalaev, R. Bassiri, A. Basti, M. Bawaj, J. C. Bayley, A. C. Baylor, P. A. Baynard II, M. Bazzan, V. M. Bedakihale, F. Beirnaert, M. Bejger, A. S. Bell, C. Bellani, D. S. Bellie, D. Beltran-Martinez, E. Benedetti, W. Benoit, I. Bentara, M. Ben Yaala, S. Bera, F. Bergamin, B. K. Berger, M. Beroiz, I. Berry, D. Bersanetti, T. Bertheas, A. Bertolini, J. Betzwieser, D. Beveridge, N. Bevins, J. Bezerra-Sobrinho, R. Bhandare, R. Bhatt, A. 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Rajbhandari, M. R. Raj Sah, K. E. Ramirez, F. A. Ramis Vidal, M. Ramos Arevalo, A. Ramos-Buades, S. Ranjan, M. Ranjbar, K. Ransom, P. Rapagnani, B. Ratto, A. Ravichandran, A. Ray, V. Raymond, M. Razzano, J. Read, J. Redepenning, J. Regan, T. Regimbau, T. Reichardt, S. Reid, C. Reissel, D. H. Reitze, A. I. Renzini, B. Revenu, A. Revilla-Peña, F. Ricci, M. Ricci, A. Ricciardone, J. Rice, J. W. Richardson, M. L. Richardson, K. Riles, H. K. Riley, A. Riminucci, F. Robinet, M. Robinson, A. Rocchi, J. Rodriguez, R. Rodriguez Lopez, L. Rolland, J. G. Rollins, A. E. Romano, R. Romano, A. Romero-Rodríguez, I. M. Romero-Shaw, J. H. Romie, S. Ronchini, T. J. Roocke, T. J. Rosauer, C. A. Rose, D. Rosińska, M. P. Ross, M. Rossello-Sastre, S. Rowan, K. Rowlands, S. K. Roy, S. Roy, T. RoyChowdhury, D. Rozza, P. Ruggi, G. H. Ruiz, E. Ruiz Morales, K. Ruiz-Rocha, V. Russ, S. M. S, S. Sachdev, T. Sadecki, F. Safai Tehrani, P. Saffarieh, S. Safi-Harb, S. Saha, T. Sainrat, S. Sajith Menon, K. Sakai, Y. Sakai, M. Sakellariadou, S. Sakon, F. Salces-Carcoba, L. Salconi, M. Saleem, F. Salemi, M. Sallé, M. Salomé, S. U. Salunkhe, S. Salvador, A. Salvarese, A. Samajdar, P. M. Samir, A. Sanchez, E. J. Sanchez, J. Sanchez, D. Sanchez-Cid, N. Sanchis-Gual, J. R. Sanders, E. M. Sänger, F. Santoliquido, E. Sapkin, F. Sarandrea, T. R. Saravanan, P. Sarkar, A. Sasli, P. Sassi, B. Sassolas, B. S. Sathyaprakash, O. Sauter, R. L. Savage, T. Savicheva, T. Sawada, H. L. Sawant, D. Schaetzl, M. Scheel, A. Schiebelbein, M. G. Schiworski, K. Schluterman, P. Schmidt, R. Schnabel, M. Schneewind, R. M. S. Schofield, M. Schoor, K. Schouteden, B. W. Schulte, M. Schulz, B. F. Schutz, E. Schwartz, M. Scialpi, J. Scott, S. M. Scott, R. M. Sedas, T. C. Seetharamu, M. Seglar-Arroyo, Y. Sekiguchi, D. Sellers, N. Sembo, E. G. Seo, J. W. Seo, G. Seong, V. Sequino, M. Serra, C. K. Sethi, A. Sevrin, T. Shaffer, U. S. Shah, M. A. Shaikh, L. Shao, J. Sharkey, A. K. Sharma, Preeti Sharma, Priyanka Sharma, Sushant Sharma-Chaudhary, P. Shawhan, T. Shen, Z.-H. Shi, K. Shimode, H. Shinkai, S. Shirke, D. H. Shoemaker, D. M. Shoemaker, R. W. Short, S. ShyamSundar, H. Siegel, N. Siemonsen, V. Sierra, D. Sigg, L. Silenzi, P. J. S. Silva, L. Silvestri, M. Simmonds, L. P. Singer, A. Singh, D. Singh, M. K. Singh, N. Singh, S. Singh, M. R. Sinha, A. M. Sintes, V. Skliris, B. J. J. Slagmolen, T. J. Slaven-Blair, J. Smetana, D. A. Smith, J. R. Smith, J. Smith, L. Smith, W. J. Smith, S. Soares de Albuquerque Filho, M. Soares-Santos, K. Somiya, I. Song, S. Soni, V. Sordini, F. Sorrentino, H. Sotani, N. E. Sovitzky, F. Spada, V. Spagnuolo, A. P. Spencer, M. Spera, P. Spinicelli, A. K. Srivastava, F. Stachurski, V. V. Stanford, A. Stanton, D. A. Steer, N. Steinle, J. Steinlechner, S. Steinlechner, C. Stephens, N. Stergioulas, M. StPierre, J. Stremiz, M. D. Strong, A. Strunk, M. Suchenek, S. Sudhagar, R. Sugimoto, L. Suleiman, K. D. Sullivan, J. Sun, L. Sun, S. Sunil, J. Suresh, P. J. Sutton, K. Suzuki, M. Suzuki, A. Svizzeretto, B. L. Swinkels, A. Syx, M. J. Szczepańczyk, M. Tacca, M. Tagliazucchi, H. Tagoshi, S. C. Tait, H. Takaba, K. Takada, H. Takahashi, R. Takahashi, A. Takamori, S. Takano, H. Takeda, I. Takimoto Schmiegelow, C. Talbot, M. Tamaki, N. Tamanini, D. Tanabe, K. Tanaka, S. J. Tanaka, S. Tanioka, D. B. Tanner, W. Tanner, L. Tao, R. D. Tapia, E. N. Tapia San Martín, A. Taruya, J. D. Tasson, J. G. Tau, A. Tejera, J. G. Temple, Y. Teng, H. Themann, A. Theodoropoulos, M. P. Thirugnanasambandam, L. M. Thomas, M. Thomas, P. Thomas, J. E. Thompson, S. R. Thondapu, E. Thrane, J. Tissino, A. Tiwari, Pawan Tiwari, Praveer Tiwari, S. Tiwari, V. Tiwari, M. R. Todd, E. Tofani, M. Toffano, A. M. Toivonen, K. Toland, T. Tomaru, V. Tommasini, H. Tong, C. I. Torrie, I. Tosta e Melo, E. Tournefier, A. Trapananti, R. Travaglini, F. Travasso, G. Traylor, L. Traylor, M. Trevor, M. C. Tringali, A. Tripathee, G. Troian, A. Trovato, L. Trozzo, R. J. Trudeau, T. Tsang, S. Tsuchida, K. Tsuji, L. Tsukada, A. Tuci, M. Turconi, C. Turski, H. Ubach, A. S. Ubhi, N. Uchikata, T. Uchiyama, R. P. Udall, T. Uehara, V. Undheim, V. Upadhyaya, L. E. Uronen, T. Ushiba, M. Vacatello, H. Vahlbruch, G. Vajente, J. Valencia, M. Valentini, E. Vallejo-Pagès, S. A. Vallejo-Peña, S. Vallero, M. van Dael, E. Van den Bossche, J. F. J. van den Brand, C. Van Den Broeck, M. van der Kolk, M. van der Sluys, A. Van de Walle, J. van Dongen, K. Vandra, M. VanDyke, H. van Haevermaet, J. V. van Heijningen, P. Van Hove, J. Vanier, J. Vanosky, N. van Remortel, M. Vardaro, A. F. Vargas, V. Varma, A. Vecchio, G. Vedovato, J. Veitch, P. J. Veitch, S. Venikoudis, P. Verdier, M. Vereecken, D. Verkindt, B. Verma, S. Verma, Y. Verma, S. M. Vermeulen, F. Vetrano, A. Veutro, A. Viceré, S. Vidyant, A. D. Viets, A. Vijaykumar, A. Vilkha, N. Villanueva Espinosa, E. T. Vincent, J.-Y. Vinet, S. Viret, S. Vitale, A. Vives, L. Vizmeg, B. Vizzone, H. Vocca, D. Voigt, E. R. G. von Reis, J. S. A. von Wrangel, W. E. Vossius, L. Vujeva, S. P. Vyatchanin, J. Wack, L. E. Wade, M. Wade, K. J. Wagner, L. Wallace, R.-Z. Wan, H. Wang, P. Wang, W. H. Wang, Y. F. Wang, Z. Wang, R. L. Ward, J. Warner, M. Was, T. Washimi, N. Y. Washington, D. Watarai, B. Weaver, S. A. Webster, N. L. Weickhardt, M. Weinert, A. J. Weinstein, R. Weiss, L. Wen, K. Wette, C. Wheeler, J. T. Whelan, B. F. Whiting, E. G. Wickens, D. Wilken, B. M. Williams, D. Williams, M. J. Williams, N. S. Williams, J. L. Willis, B. Willke, M. Wils, L. Wimmer, C. W. Winborn, A. Wingfield, J. Winterflood, C. C. Wipf, G. Woan, N. E. Wolfe, H. T. Wong, I. C. F. Wong, T. Wouters, J. L. Wright, M. Wright, B. Wu, C. Wu, D. S. Wu, H. Wu, K. Wu, Z. Wu, E. Wuchner, D. M. Wysocki, V. A. Xu, Y. Xu, N. Yadav, H. Yamamoto, K. Yamamoto, T. S. Yamamoto, T. Yamamoto, R. Yamazaki, T. Yan, H. Yang, K. Z. Yang, Y. Yang, Z. Yarbrough, J. Yébana Carrilero, A. B. Yelikar, X. Yin, J. Yokoyama, T. Yokozawa, M. Yoshihara, S. Yuan, H. Yuzurihara, M. Zanatta, M. Zanolin, M. Zeeshan, T. Zelenova, J.-P. Zendri, M. Zeoli, M. Zerrad, M. Zevin, H. Zhang, J. Zhang, L. Zhang, N. Zhang, R. Zhang, T. Zhang, C. Zhao, J. Zhao, Yue Zhao, Yuhang Zhao, L.-M. Zheng, Y. Zheng, L. Zhizhong, H. Zhong, H. Zhou, H. O. Zhu, X.-J. Zhu, Z.-H. Zhu, Z. Zhu, D. Z. Zieba, A. B. Zimmerman, L. Zimmermann, M. E. Zucker

Tuesday 11 August

High Energy Astrophysical Phenomena

Long-duration GW Searches for Sub-solar NSs and Superkilonovae using CoCoA

Abby Tejera, Divyajyoti, Alessandra Corsi et al. (+3 more)

On 2025 August 18, the LIGO-Virgo-KAGRA collaboration reported a sub-threshold gravitational-wave (GW) candidate, S250818k, consistent with a binary neutron star (NS) merger potentially involving a sub-solar-mass compact object. Follow-up electromagnetic (EM) observations identified a Type IIb supernova, SN 2025ulz within the broad localization area of the GW signal. This potential link between a sub-solar GW event candidate and a Type IIb SN, while not confirmed given the low statistical significance of S250818k, has nonetheless sparked renewed interest in the "superkilonova" scenario, where sub-solar-mass NSs form through processes like the fragmentation of an accretion disk or core fission in a collapsing star. In this picture, the in-spiral and merger of a sub-solar NS-NS binary is followed by the merger of the NS-NS remnant with the central black hole (BH), producing chirp-like GW signals. For sub-solar NSs with masses in the (0.1-1)M_sun range and BH masses in the so-called lower mass gap range of ~(3-5) M_sun, these signals can persist in the 20 - 1024 Hz frequency band of ground-based GW detectors for (10^2-10^3)s, potentially offering an opportunity to probe the superkilonova scenario, as well as the lower mass gap between NSs and stellar-mass BHs. However, the complexity of the underlying astrophysics may yield waveforms that deviate from standard templates, limiting the use of matched filtering in real GW searches. We therefore explore the detectability of such signals using the Cross-Correlation Algorithm (CoCoA), a more robust though less sensitive cross-correlation method. We discuss general strategies for implementing CoCoA superkilonova searches via either targeted follow-up of candidate chirps identified in matched-filter searches, or EM-triggered searches of stripped-envelope core-collapse SNe.

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All authors Abby Tejera, Divyajyoti, Alessandra Corsi, Yossef Zenati, Robert Coyne, Logan Cote

High Energy Astrophysical Phenomena

XRISM Spectroscopy of Variable Accretion-driven Disk Winds in NGC 4151: When, Where, and How Fast Outflows are Launched

Xin Xiang, Jon Miller, Missagh Mehdipour et al. (+12 more)

X-ray observations probe the inner accretion flow within active galactic nuclei, revealing the highest gas column densities and fastest winds. The most diverse winds yet revealed with the Resolve calorimeter spectrometer aboard XRISM are found in NGC~4151, a nearby Seyfert-1 AGN that may qualify as a “changing-look” source (CLAGN). Herein, we report on wind variability in 14 XRISM observations of NGC~4151, summing to 0.9~Ms of exposure over a period of 395 days. We examined the dependence of key wind parameters on hardness and intensity selections, and as a function of time relative to flaring and dip events. The results suggest a globally organized but locally complex wind structure. Slow “warm absorber” components (WAs; $v_{\rm{out}} \sim 100-1000~\rm{km~s^{-1}}$) are always observed and likely represent failed winds at radius of $10^4 - 10^5 GM/c^2$, within the inner wall of the torus. In contrast, “very fast” and “ultra-fast” outflows (VFOs and UFOs; $v_{\rm{out}} \sim 10^3-10^4~\rm{km~s^{-1}}$, $v_{\rm{out}} \sim 0.033-0.33~c$) are strongest 10~ks after the peak of flares, and during periods with low flux. Ten kiloseconds is among the shortest flare–wind response timescales reported in an AGN, suggesting that the winds are observed close to the launching site. The absorption measure distribution (AMD) and the large outflow momentum rates suggest that the high-velocity flows visible in the Fe~K band are magnetically driven, while locally clumpy, likely owing to radiation pressure; one or both of these mechanisms may be enhanced following a flare and most visible during low-flux windows.

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All authors Xin Xiang, Jon Miller, Missagh Mehdipour, Ehud Behar, W. Niel Brandt, Laura Brenneman, Luigi Gallo, Elias Kammoun, Peter Kosec, Liyi Gu, Doyee Byun, Richard Mushotzky, Stephane Paltani, Elisa Costantini, Abderahmen Zoghbi

High Energy Astrophysical Phenomena

A Diverse Distribution of Black Hole Spins from Stable Mass Transfer

Linhao Ma, Jakub Klencki, Eliot Quataert et al. (+1 more)

Gravitational wave observations have found over 300 merging binary black holes, yet their origins remain uncertain. Recent work showed that many may come from isolated stellar binaries whose orbits shrink through stable mass transfer. If true, their spins may help to distinguish this channel from other formation pathways. We investigate the tidal spin up of black hole progenitor stars with detailed modeling of binaries undergoing stable mass transfer. We calculate the tidal torques by solving tidally excited oscillation modes and predict the resulting black hole spins. We find a diverse spin distribution strongly affected by the mass transfer histories of the progenitors. Binaries can form black holes with moderate spins ($0.1\lesssim\chi_\mathrm{eff}\lesssim0.3$) if they only go through case A or case B mass transfer. In the former case, they can become super-synchronized upon detachment, while in the latter case, the donor is usually only partially stripped, leaving a puffy envelope where strong tides are excited. If both case A and case AB mass transfer occur, the resulting black hole spins are almost always negligible. As the mass transfer history is jointly determined by mass ratio and initial binary period, our results predict an anti-correlation between black hole spins and mass ratio, consistent with limited evidence from data. Our results can also potentially explain the case of GW190412, a moderately-spinning binary with a high mass ratio. We discuss the limitations of our methods and additional physics (e.g., nonlinear tides, case C, and L2 mass transfer) that need to be incorporated in future work.

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All authors Linhao Ma, Jakub Klencki, Eliot Quataert, Lieke van Son

High Energy Astrophysical Phenomena

ATLAS22kjn (AT 2022fpx): A Coronal Line Emitter with an Early Light Curve Bump and Mid-Infrared Dust Echo

Athena C. Engholm, Jason T. Hinkle, Benjamin J. Shappee et al. (+14 more)

We present an analysis of ATLAS22kjn (AT 2022fpx), whose high-ionisation coronal lines (CLs) and pre-peak light curve bump provide distinctive opportunities to investigate the physical mechanisms powering tidal disruption events (TDEs). In addition to CLs, the optical spectra show common TDE features, including a strong, blue continuum and broad Balmer and He II lines. The CLs appear before UV/optical light curve peak, preceding the detection of X-rays by $\sim 300$ days and persisting after X-rays are no longer detected, suggesting the X-ray emission is obscured at both early and late times. Using the CL luminosities, we constrain the temperature evolution of the ionising source, finding a decrease of $\lesssim 10 \%$ over 500 days. In the UV/optical light curve, we observe a $9 \substack{+4 \\ -2}$ day bump that peaks $125 \substack{+5 \\ -3}$ rest-frame days before the peak of the main flare. Although we cannot definitively determine the origins of the bump, we find that its timescale and luminosity are most consistent with theoretical predictions for a precursor feature produced by a stream-stream collision or a wind-stream collision. ATLAS22kjn also shows a prominent dust echo in its mid-infrared (MIR) light curves, indicating a high dust covering fraction $f_c \simeq 0.40 \pm 0.03$, similar to the covering fractions of other CL-emitting TDEs. From the multi-wavelength observations of ATLAS22kjn, we estimate the size and relative radii of the emission regions in its nuclear environment and determine that the CL region lies between the broad line region and the MIR-emitting dust. ATLAS22kjn demonstrates the importance of multi-wavelength and early-time observations, and the utility of CLEs in characterising the otherwise unobservable EUV/ultrasoft X-ray emission of TDEs.

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All authors Athena C. Engholm, Jason T. Hinkle, Benjamin J. Shappee, Katie Auchettl, Dhvanil D. Desai, Willem B. Hoogendam, Christopher S. Kochanek, Nicholas Earl, K. Decker French, Michael A. Tucker, Chris Ashall, Aaron Do, Allison Blum, Thomas de Jaeger, Mark E. Huber, Anna Payne, Jose L. Prieto

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

All You Need is not $\Omega_\mathrm{gw}$: Beyond the Mean of the Cross-Correlation Estimator when Searching for an Astrophysical Gravitational-Wave Background

Haowen Zhong, Francesco Iacovelli, Vuk Mandic et al. (+1 more)

Searches for the stochastic gravitational-wave background (SGWB) using ground-based detectors rely heavily on the cross-correlation estimator $\bar C_f$, whose statistical properties determine the theoretical foundation for inference frameworks built on it. Past analyses usually assume Gaussianity of $\bar C_f$, but this assumption has not been systematically tested for a background of astrophysical origin like the one produced by compact binary coalescences. In this work, we decompose $\bar C_f$ into three physically motivated components: (1) the mean intensity, (2) the geometrical shot noise, and (3) the polarization leakage, and we compute 90% credible intervals for its cumulants up to fourth order for the binary black hole, binary neutron star, and neutron star-black hole populations by propagating local merger rate uncertainties. We find that for the upcoming LIGO O5 sensitivity, $\bar C_f$ remains effectively Gaussian for all three populations, validating current Gaussian likelihood frameworks. For Cosmic Explorer (CE), however, the $\bar C_f$ produced by binary black holes becomes non-Gaussian, with skewness and excess kurtosis of $0.31^{+0.04}_{-0.03}$ and $1.3^{+0.4}_{-0.3}$, respectively, in the most sensitive band over a one-year observation period. For binary neutron star and neutron star - black hole mergers, $\bar C_f$ remains largely Gaussian even at CE. These results indicate that the Edgeworth expansion provides an adequate leading-order description of the non-Gaussianity expected in the next-generation era, while also motivating the development of more sophisticated statistical methods for a more accurate treatment.

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All authors Haowen Zhong, Francesco Iacovelli, Vuk Mandic, Emanuele Berti

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

Fitting trends in quasar emission and absorption line redshifts

Netra K Subramanian, Prasad Subramanian and Nimisha G Kantharia

The spectrum of a quasar consists of a few emission lines whose wavelengths are shifted by similar redshifts and numerous absorption lines whose wavelengths are shifted by different redshifts. Hence each quasar is characterised by an emission line redshift and the absorption lines redshifts are all less than the emission line redshift. The distribution of observed absorption line redshifts ($z_{abs}$) with respect to emission line redshift ($z_{em}$) for a large sample of quasars shows a systematic trend as pointed out by \citet{2016arXiv160901593K}. They noticed that increase in $z_{em}$ is accompanied by a monotonic increase in the lowest detected value of $z_{abs}$ and inferred that the emission and absorption lines were all formed in the quasar. This study focuses on modeling the systematic trend in the observed $z_{em} \rightarrow z_{abs}$ distribution. We considered the redshift data of absorption lines of singly ionized magnesium (denoted by MgII) and triply ionized carbon (denoted by CIV) for a large sample of quasars. We find that the envelope of data points defining the lowest value of the MgII absorption line redshift (which we denote by $z_{MgIImodel}$) for a given $z_{em}$ satisfies $z_{MgIImodel} = (0.418 \pm 0.008) z_{em} - (0.482 \pm 0.02)$ with an $R^2$ value of 0.99. The model can be used to predict the lowest expected MgII absorption line redshift for any $z_{em}$. We find a similar model for the lowest expected redshift of triply ionized carbon lines for any $z_{em}$ which is $z_{CIVmodel} = 0.845 (\pm 0.0002) z_{em} - 0.153 (\pm 0.0006)$.

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High Energy Astrophysical Phenomena

Wind-confined jet collimation revealed by the acceleration-phase photosphere of GRB 220426A

Felix Ryde and Asaf Pe'er

We analyze the prompt emission of the exceptionally bright GRB 220426A observed by Fermi/GBM, whose time-resolved spectra are among the narrowest measured in any GRB. Here we show that observations during the first $\sim 5$~s are consistent with the signal being emitted while the jet was still in the initial radiation-dominated acceleration phase. The time-resolved spectra allow the effective launch radius, $r_0$, to be inferred with unusual precision. We find $r_0 \sim \mathrm{few} \times 10^{10}\,\mathrm{cm}$, increasing linearly with time. These findings match the theoretical expectation for the recollimation shock, implying that this GRB shows the first clear evidence for the existence and evolution of a recollimation shock. Using this interpretation, the linear increase observed is sustained over a period longer than expected from a pure jet breakout. Therefore, the jet collimation must have persisted even after breakout. We suggest that the collimation was maintained by a finite, dense, wind-like circumburst medium, which would reproduce the observed behavior of the prompt emission. We conclude that late-stage progenitor mass-loss can shape the earliest prompt emission and that the photospheric emission provides a way to probe both the jet collimation and the innermost region of the circumburst medium (CBM) surrounding the progenitor, independently of the constraints from interacting supernovae.

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

Radiative Signatures from Warp Drives Traveling Through the Earth's Atmosphere

Shaun David Brocus Fell and Abraham Loeb

We investigate the observable signatures of zero ADM mass warp drive spacetimes traversing Earth's atmosphere. Numerical simulations indicate that an aircraft-scale spacetime bubble moving at relativistic velocities would have a pronounced observational signature, where interaction with the atmosphere can produce luminosities exceeding one terawatt. The signature of a spacetime bubble at rest or moving at low velocity relative to the Earth would not generate such extreme luminosities. These results establish observational constraints on spacetime-based propulsion operating within the terrestrial environment and provide a framework for identifying potential high-velocity signatures. In particular, a warp drive traveling through the atmosphere at speeds exceeding approximately 10% of the speed of light would produce a unique brilliant glow.

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High Energy Astrophysical Phenomena

Synchrotron-Regulated Relativistic Magnetohydrodynamic Turbulence: Emission, Polarization, and Faraday Rotation

Xiaochen Sun, Luca Comisso, Lorenzo Sironi et al. (+2 more)

Relativistic magnetized plasmas in many high-energy astrophysical systems are both turbulent and strongly radiative, yet their nonlinear dynamics and radiative outcomes remain poorly understood. Here we present results from three-dimensional driven turbulence simulations in relativistic magnetohydrodynamics with synchrotron cooling. We compute Faraday rotation measures, synthetic synchrotron spectra and linear polarization maps from the simulated turbulence. The balance between energy injection from turbulent driving and synchrotron cooling keeps the plasma, on average, relativistically hot, thereby influencing the rotation measure. Synchrotron cooling triggers the thermal instability and drives the plasma into hot dilute and cold dense phases, which enhances the spatial and temporal variability of synchrotron emission, especially at high frequencies. These diagnostics show qualitative similarities to observations of fast radio bursts, pulsar wind nebulae, and blazars, suggesting that turbulence may play an important role in shaping emission and propagation effects around high-energy sources.

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All authors Xiaochen Sun, Luca Comisso, Lorenzo Sironi, Anatoly Spitkovsky, Alexander Philippov

High Energy Astrophysical Phenomena

Real-time observations of the transition to the quiescent state in an accreting magnetised neutron star: No propeller required?

Sergey S. Tsygankov, Galina Lipunova, Valery F. Suleimanov et al. (+6 more)

The final stages of outbursts in transient X-ray pulsars (XRPs), which are characterised by a significant decline in the mass accretion rate, provide valuable insight into the physics of the accretion disc and its interaction with the strong magnetic field of the neutron star (NS). In particular, the `propeller effect', or centrifugal inhibition of accretion, has been proposed as a key mechanism governing both the onset luminosity and the timescale of the rapid transition to the quiescent state. In addition, it offers an independent method for estimating the magnetic field strength of the NS. On the other hand, the decrease in the mass accretion rate itself is driven by processes occurring in the accretion flow at larger distances from the NS. Recovering the information encoded in the light curve therefore requires sensitive high-cadence X-ray monitoring capable of capturing the rapid and often unpredictable transition from the accreting regime to the quiescent regime. In this study, we present the results of the first comprehensive monitoring campaign that tracks the entire transition to quiescence in the transient XRP 4U 0115+63 utilising observations by the NICER X-ray telescope. We show that the observed behaviour can be explained by the thermal-viscous disc instability model (DIM), with the emission observed immediately after an outburst possibly arising from the ongoing accretion from the recombined (`cold') disc and the subsequent quiescent emission being produced by the cooling NS. We further applied this model to a larger sample of XRPs encompassing a broad range of physical parameters. Ultimately, our findings indicate that the temporal behaviour of XRPs, including the quiescent state, can be consistently explained within the DIM framework without requiring the propeller effect as the primary mechanism governing the observed transition.

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All authors Sergey S. Tsygankov, Galina Lipunova, Valery F. Suleimanov, Alexander Salganik, Alexander A. Mushtukov, Sofia V. Forsblom, Andrey S. Tavleev, Aleksei V. Kuzin, Juri Poutanen

High Energy Astrophysical Phenomena

Transmutation Timescales for Dark Matter Induced Collapse of Compact Stars into Black Holes

H. A. Adarsha, Chandrachur Chakraborty and Sudip Bhattacharyya

Ultra-heavy asymmetric dark matter (DM) particles captured by compact stars can thermalize, self-gravitate, and collapse to form an endoparasitic black hole (EBH), whose subsequent growth may transmute the host star into a black hole. The continued existence of old millisecond pulsars (MSPs) and white dwarfs (WDs) thus places powerful constraints on the DM particle mass $m_\chi$ and the DM-nucleon scattering cross-section $\sigma_{\rm n\chi}$. We derive an analytical expression for the transmutation timescale by solving the EBH growth equation, consistently accounting for Bondi accretion of stellar matter, Hawking evaporation, and sustained DM feeding of the EBH in a steady-state capture regime. We also incorporate quantum effects in baryonic accretion when the hydrodynamic description breaks down, providing a unified treatment of EBH growth across both particle and fluid regimes. Adopting a physically transparent collapse criterion for fermionic and bosonic asymmetric DM, we compute EBH transmutation timescales for representative MSPs and WDs in environments with different DM densities. Although the physical ingredients are broadly similar to previous studies, this work derives updated constraints through a closed-form analytical treatment of EBH growth and an adopted prescription for the EBH formation timescale, yielding a lower critical EBH mass for sustained growth and revised transmutation timescales. Requiring the transmutation time to exceed $\sim 1$ Gyr for MSPs and $\sim 10$ Gyr for WDs, we derive revised constraints on $\sigma_{\rm n\chi}$ over $m_\chi \sim 10^{6}$–$10^{14}$ GeV, and show that EBHs with initial masses as small as $\sim 4\times10^{4}$ kg can undergo sustained growth, extending the region of DM parameter space probed by compact stars.

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

Two-Fluid Schwarzschild Solution

Rico Zöllner and Burkhard Kämpfer

We consider the interior two-fluid Schwarzschild solution. That is a model of compact (neutron) stars with admixed dark matter. The two constant energy densities generalize the interior Schwarschild solution to the case of two fluids (representing standard model matter and dark matter, for instance), interacting mutually solely by the common gravitational field. In general, the two-fluid core is surrounded by a one-fluid corona (envelope). Only for special parameters (the model depends on energy densities $e_1,e_2$ and central pressures $p_{\mathrm{c}1},p_{\mathrm{c}2}$ of the fluids), both fluids occupy the same region. Despite the sum of two energy densities in that region, the compactness bound of 8/9 is not exceeded. A conceivable object is one with a stark leakage of one fluid (e.g. dark matter) beyond the two-fluid core.

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High Energy Astrophysical Phenomena

Electromagnetic responses driven by gravitational-wave memory in magnetar-flare outflows

Wen-Biao Han

An asymmetric relativistic outflow from a magnetar giant flare produces a step-like gravitational-wave (GW) memory. In the magnetized pair plasma surrounding the star, such GW memory drives transverse electromagnetic (EM) X-mode/fast-magnetosonic responses at the corresponding frequencies. We use this GW-memory spectrum to drive a global wave equation for a cold electron–positron pair plasma. With radiative boundary conditions excluding incoming waves, the driven response forms an outgoing EM mode that reaches the outer boundary of the source region. For central-engine energy-release timescales of $10$, $1$, and $0.15\,\mu\mathrm{s}$, 90% of the integrated response energy lies below 23.3 kHz, 233 kHz, and 1.51 MHz, respectively. The principal response occupies the 10 kHz–1 MHz frequency band; a substantial extension into the 1–3 MHz frequency band also appears when a submicrosecond asymmetric-energy component is present. The electromagnetic response can escape from the source region and potentially propagate in the interstellar medium.

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Physics › Astrophysics › High Energy Astrophysical Phenomena

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Physics Astrophysics High Energy Astrophysical Phenomena