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Physics Astrophysics

astro-ph Watch Astrophysics

Saturday 14 February

High Energy Astrophysical Phenomena

Dynamical Preconditions for Ice Formation in Supernova Remnant and Cloud Interactions: A 2D MHD Study

A. Yeghikyan, M. Rah, S. Shamyar et al. (+1 more)

Water ice has been detected in several supernova remnants despite the strong heating and radiation in these environments. This challenges standard expectations for dust survival. Using two dimensional magnetohydrodynamic simulations, we study how a supernova shock interacts with a dense interstellar cloud. The simulations show that the shock naturally compresses the cloud into dense structures similar to those inferred in well known remnants. Although temperatures remain high in the adiabatic phase, simple considerations indicate that cooling would act quickly once included. These results suggest that shock cloud interactions create the physical conditions needed for water ice to form. Future work including radiative cooling and grain surface chemistry will allow direct modelling of ice growth in these compressed regions.
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All authors A. Yeghikyan, M. Rah, S. Shamyar, S. Khachatryan

High Energy Astrophysical Phenomena

Dust and Ices in the SNR

A. Yeghikyan, M. Rah and S. Shamyar

The presence of dust in supernova remnants (SNRs) is confirmed by extensive infrared data from observatories such as Spitzer, Herschel, and JWST, alongside theoretical models of dust formation. This study explores the existence of dust and ices, particularly water ice via 62 {\mu}m in SNRs such as the Crab Nebula and N49, using observational data and preliminary modeling with Cloudy. Observations suggest that water ice may be present in IC 443 and possibly other remnants, though the 63 {\mu}m band could also indicate [OI] emission. Theoretical models indicate that water ice could survive under certain conditions in SNRs, with densities and temperatures analyzed. Further observations and refined simulations are needed to confirm these findings.
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High Energy Astrophysical Phenomena

Detection of Cyclotron Absorption in the Radio Emission of GPM 1839-10

Yunpeng Men, Ewan Barr, Yuanhong Qu et al. (+8 more)

GPM 1839-10 is an intriguing long-period radio transient (LPT), distinguished by its activity spanning at least three decades and its highly unusual emission characteristics. These features include orthogonal polarization mode (OPM) switches, down-drifting sub-structures, and distinct linear-to-circular polarization conversion behaviors. In this work, we present follow-up observations utilizing the FAST telescope at L-band, yielding a total of seven detected radio pulses. We find a consistent association between OPM switches and a decrease in polarized intensity. This feature strongly supports the hypothesis that the OPM switches are generated by the incoherent summation of OPMs. Our measured Rotation Measures (RMs) are consistent with previous observations, indicating that the magneto-ionic environment is stable. If the source is in a binary system, such stability suggests it may host a weakly magnetized companion. Crucially, we firstly observe clear evidence of a cyclotron absorption feature in one radio pulse, a signature rarely observed in radio sources. This feature allows us to infer that the magnetic field strength at the absorption site has a lower limit of tens of Gauss, which is necessary for the phenomenon to occur. This characteristic can be explained in a scenario where GPM 1839-10 possesses a weakly magnetized companion star.
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All authors Yunpeng Men, Ewan Barr, Yuanhong Qu, Csanad Horvath, Jinchen Jiang, Gregory Desvignes, Natasha Hurley-Walker, Michael Kramer, Rui Luo, Samuel J. McSweeney, Jason Wu

High Energy Astrophysical Phenomena

Pulsars and Millisecond Pulsars III: Tracing Compact Object Dynamics in Globular Clusters with NBODY6++GPU

M. Rah, R. Spurzem, F. Flammini Dotti et al. (+1 more)

Neutron stars in globular clusters follow complex evolutionary pathways shaped by binary interactions, mass transfer, and dynamical exchanges. Direct N-body simulations such as NBODY6++GPU successfully model stellar dynamics and compact object formation, but they usually do not track pulsar spin evolution or magnetic field decay explicitly. Building on Papers I and II of this series, we identify this gap and present a case study from an existing simulation with N = 105000 particles, showing how a neutron star forms and evolves for 200 Myr without any pulsar-physics tracking. We compare this situation with recent implementations and outline a seven-scenario framework that includes magnetic dipole spin-down, exponential magnetic field decay, environmental torques, accretion-driven spin-up, gravitational-wave emission, and merger-driven evolution. As an example, the neutron star we label Pulsar973 forms at t = 800 Myr with a post-supernova mass of 5.35 solar masses and evolves to 2.52 solar masses by t = 1000 Myr, but still lacks period P, period derivative Pdot, magnetic field B, and scenario classification. We provide mathematical formulations and specific integration points within NBODY6++GPU (Hermite scheme, Ahmad-Cohen neighbors, KS regularization, and BSE stellar evolution) to enable scenario-based pulsar evolution within direct N-body simulations.
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All authors M. Rah, R. Spurzem, F. Flammini Dotti, A. Mickaelian

Solar and Stellar Astrophysics

Modelling the Break in the Specific Angular Momentum within the Envelope-Disk Transition Zone

Indrani Das, Shantanu Basu, Nagayoshi Ohashi et al. (+2 more)

The observations of protostellar systems show a transition in the radial profile of specific angular momentum (and rotational velocity), evolving from $j\sim{\rm constant}$ ($v_{\phi}\sim r^{-1}$) in the infalling-rotating envelope to $j\propto r^{1/2}$ ($v_{\phi}\sim r^{-1/2}$) in the Keplerian disk. We employ global MHD disk simulations of gravitational collapse starting from a supercritical prestellar core, that forms a disk and envelope structure in a self-consistent manner, in order to determine the physics of the Envelope-Disk Transition Zone (ENDTRANZ). Our numerical results show the transition from the infalling-rotating envelope to Keplerian disk happens through a jump in the $j-r$ profile over a finite radial range, which is characterized by the positive local gravitational torques. The outer edge of the ENDTRANZ is identified where the radial infall speed ($v_r$) begins a sharp decline in magnitude and $j$ begins a transition from $j\sim{\rm constant}$ toward $j\sim r^{1/2}$. Moving radially inward, the centrifugal radius ($r_{\rm CR}$) is defined where $v_{\phi}$ first transitions to Keplerian velocity at the disk's edge. Farther inward of $r_{\rm CR}$, model disk develops a super-Keplerian rotation due to self-gravity. The inner edge of the ENDTRANZ is defined at the centrifugal barrier ($r_{\rm CB}$) where $v_r$ drops to negligible values. Inside $r_{\rm CB}$, a net negative gravitational torque drives mass accretion onto the protostar. On observational grounds, we identify a jump in the observed $j-r$ profile in L1527 IRS for the first time using the ALMA eDisk data. Comparison with the numerical radial behavior from our MHD disk simulations suggests the observed $j-r$ jump can be used as a kinematical tracer for the existence of ENDTRANZ. Our results offer insights into the observable imprint of angular momentum redistribution mechanisms during star-disk formation.
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All authors Indrani Das, Shantanu Basu, Nagayoshi Ohashi, Eduard Vorobyov, Yusuke Aso

Solar and Stellar Astrophysics

AT 2025abao: The fourth luminous red nova in M 31

A. Reguitti, A. Pastorello, G. Valerin et al. (+15 more)

We present photometric and spectroscopic observations of the luminous red nova (LRN) AT 2025abao, the fourth discovered in M 31. The LRN, associated to the asymptotic giant branch (AGB) star WNTR23bzdiq, was discovered during the fast rise following the minimum phase. It reached its peak at $g=15.1$ mag ($M_g=-9.5\pm0.1$ mag), and then it settled onto a long-duration plateau in the red bands, lasting 70 days, while it was slowly linearly declining in the blue bands. At the peak the object showed similarities with the canonical LRNe V838 Monocerotis, V1309 Scorpii, and the faint and fast-evolving AT 2019zhd, which is the third LRN in M31, though the later evolution is different. Spectroscopically, AT 2025abao evolved as a canonical LRN: the early spectra present a blue continuum with narrow Balmer lines in emission; at the peak, the spectral continuum has cooled to a yellow colour, with a photospheric temperature of 6000 K. Balmer lines had weakened, while absorption lines from metals (Fe I, Fe II, Sc II, Ba II, Ti II) had developed, and they were particularly broad from the UV Ca II H&K lines. Medium- and high-resolution spectra reveal narrow ($\sim$50 km/s) absorption and broad ($\sim$450 km/s) emission profiles in the Balmer lines, from a slower wind and a faster outflow, respectively. Finally, late-time spectra show an orange continuum ($T\sim4000-5000$ K), a return in strength of the Balmer lines and the formation of molecular absorption bands. AT 2025abao is the rare case of an LRN with detailed archival information regarding the progenitor system. For the first time, we obtained the spectral energy distribution in the infrared of the precursor of an LRN, which is consistent with that of an M~giant/AGB. We propose that the dichotomy of light-curve behaviour in LRNe (two peaks vs. plateau) can be explained by the extent and H-richness of the common envelope.
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All authors A. Reguitti, A. Pastorello, G. Valerin, F. D. Romanov, A. Siviero, Y.-Z. Cai, S. Ciroi, N. Elias-Rosa, T. Iijima, E. Kankare, N. Koivisto, T. Kravtsov, E. Mason, K. Matilainen, A. C. Mura, P. Ochner, T. M. Reynolds, M. D. Stritzinger

Solar and Stellar Astrophysics

Solar active region scaling laws revisited

Guilherme A. L. Nogueira, Robertus Erdelyi, Ruihui Wang et al. (+1 more)

The systematic variation of solar active region (AR) properties with their magnetic flux has been the subject of numerous studies but the proposed scaling laws still vary rather widely. A correct representation of these laws and the deviations from them is important for modelling the source term in surface flux transport and dynamo models of space climate variation, and it may also help constrain the subsurface origin of active regions. Here we determine active region scaling laws based on the recently constructed ARISE active region data base listing bipolar ARs for cycle 23, 24 and 25. For the area $A$, pole separation $d$ and tilt angle $\gamma$ we find scalings against magnetic flux $\Phi$ and heliographic latitude $\lambda$. Residuals from these relations are also modelled. These scaling relations are recommended for use in space climate research for the modelling of future data or missing past data, as well as for the identification of candidate rogue ARs.
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All authors Guilherme A. L. Nogueira, Robertus Erdelyi, Ruihui Wang, Kristof Petrovay

Solar and Stellar Astrophysics

Unprecedented Multipoint Observation of Spatially Varying ICME Turbulence of Different Ages during October 2024 Extreme Solar Storm at 1 AU

Shibotosh Biswas, Ankush Bhaskar, SG Abitha et al. (+4 more)

Understanding turbulence in interplanetary coronal mass ejections (ICMEs) is fundamental to space plasma research and critical for assessing the impact of space weather on geospace. Turbulence governs energy cascade, plasma heating, magnetic reconnection, and solar wind magnetosphere coupling, thereby influencing both ICME evolution and geoeffectiveness. While previous event based and statistical studies have examined ICME turbulence and its radial evolution in great detail, no significant measurements of ICME magnetic turbulence at a single vantage point have been obtained from multiple observatories separated azimuthally. Here, we present the first multipoint analysis of magnetohydrodynamic (MHD) turbulence across ICME plasma regions, using four spacecraft at the Sun-Earth L1 point, separated by 80 RE (mesoscale) along the dawn-dusk direction. Using high-resolution magnetic field observations from ISRO's Aditya L1, NASA's Wind and ACE, and NOAA's DSCOVR, we analyze turbulence associated with the October 10, 2024, solar storm, which triggered the second strongest geomagnetic storm of solar cycle 25. Our results reveal significant variability and differing turbulence maturity across small separations, supported by analysis of field-aligned and perpendicular magnetic-field cascades, indicating strong anisotropies. Sheath turbulence is substantially modified by shock induced energy injection. Evidence of compressible turbulence and plasma energization at the flux rope interaction region indicates that internal processes, such as magnetic reconnection, strongly influence ICME plasma evolution, highlighting pronounced spatial variability in turbulence and plasma states observed by multiple L1 monitors near Earth and underscoring their potential role in space weather impacts.
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All authors Shibotosh Biswas, Ankush Bhaskar, SG Abitha, Omkar Dhamane, Sanchita Pal, Dibyendu Chakrabarty, Vipin K Yadav

Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Harmonic Analysis on Correlation for Gravitational-Wave Backgrounds of Arbitrary Polarization from Interfering Sources in Generic Dispersion Relation

Yan-Chen Bi, Yu-Mei Wu and Qing-Guo Huang

The Hellings-Downs (HD) correlation serves as the fundamental benchmark for detecting the gravitational-wave background (GWB) in pulsar timing arrays (PTAs) within General Relativity (GR). However, this canonical signature relies on the idealization of a continuum of sources without interference. In realistic astrophysical scenarios dominated by supermassive black hole binaries (SMBHBs), interference between discrete sources induces intrinsic deviations in the spatial correlation, which may mimic or obscure signatures of modified gravity. In this work, we derive the closed-form spatial correlation functions for a GWB with arbitrary polarization and generic GW dispersion relations, in the presence of source interference. Through a rigorous harmonic analysis, we demonstrate that source interference modifies the correlation shape but strictly preserves the lowest non-vanishing multipole moment characteristic of each polarization, specifically the quadrupole for tensor, dipole for vector, and monopole for scalar modes. The truncation at higher-order multipoles is governed by the interplay between pulsar distances and dispersion effects. Furthermore, we quantify the statistical degeneracy between interference-induced variation and modified gravity signatures. We conclude that access to only a single realization of the Universe imposes a fundamental theoretical limit on distinguishing modified gravity from GR using spatial correlations alone.
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Earth and Planetary Astrophysics · Cross-listed from physics.class-ph

Description of 4 Spacecraft, Moving on Elliptic Kepler Orbits

Vladimir P. Zhukov, Nikolai K. Iakovlev, Alexander A. Bochkarev et al. (+4 more)

The four-spacecraft formation is essential for measurements of various physical fields. The use of this formation on substantially elliptical heliocentric Kepler orbits allows measuring gradients of gravitation field in Solar system. The accuracy of the measurements will be sufficient to confirm or to refute modified theories of gravity. In this paper a new approach for the description of this formation is presented. The analytical solutions of the linearized motion equations are obtained. The distinctive feature of the solutions is that they use Cartesian coordinates of one of the spacecraft, termed the chief. These solutions have a clear physical meaning. It is shown, that the volume of a tetrahedron formed by spacecraft is a polynomial of 3-rd degree of Cartesian coordinates of the chief. The polynomial's coefficients are functions of initial spacecraft coordinates and velocities and linearly depend on time. If all spacecraft have the same periods of rotation around the Sun, the volume is a polynomial of 2-nd degree of the chief coordinates with time-independent coefficients. In this case the volume can be zeroed from 0 to 4 times per the period. Suggested approach can significantly simplify planning missions for measurements of various interplanetary fields.
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All authors Vladimir P. Zhukov, Nikolai K. Iakovlev, Alexander A. Bochkarev, Nikita E. Logvinenko, Sergei M. Kurchev, Vlas A. Karavaikin, Ivan A. Radko

Astrophysics of Galaxies

Modelling the non-equilibrium chemistry of the Milky Way's cold nuclear wind

Karlie A. Noon, Mark R. Krumholz, Naomi M. McClure-Griffiths et al. (+2 more)

Cold atomic and molecular gas are commonly observed in the winds of both external galaxies and the Milky Way, yet the survival and origin of these cool phases within hot galactic winds is poorly understood. To help gain insight into these problems, we carry out time-dependent chemical modelling of cool clouds in the Milky Way's nuclear wind, which possess unusual molecularto-atomic hydrogen ratios that are inconsistent with both disc values and predictions from chemical equilibrium models. We confirm that CO and Hi emission comparable to that in the observed nuclear wind clouds cannot be produced by gas in chemical equilibrium, but that such conditions can be produced in a molecule-dominated cloud that has had its atomic envelope rapidly removed and has not yet reached a new chemical equilibrium. Clouds in this state harbour large reservoirs of molecular gas and consequently have anomalously large CO-to-H2 conversion factors, suggesting that the masses of the observed clouds may be significantly larger than suggested by earlier analyses assuming disc-like conversions. These findings provide a new framework for interpreting cold gas in galactic winds, providing strong evidence that cold outflows can originate from the galactic disc molecular clouds that survive acceleration into the wind but lose their diffuse atomic envelopes in the process, and suggesting that the Milky Way's nuclear outflow may be more heavily mass-loaded than previously thought.
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All authors Karlie A. Noon, Mark R. Krumholz, Naomi M. McClure-Griffiths, Enrico M. Di Teodoro, Lucia Armillotta

Astrophysics of Galaxies

New Dynamical Measurements from a Lensed Quasar Sample: Joint Analysis Constrains the Mass Profile Evolution of Lens Galaxies

Ziyu Guo, Yun Chen, Yiping Shu et al. (+4 more)

We present a systematic study of the internal mass structure of early-type galaxies (ETGs) based on 106 galaxy-scale strong gravitational lenses with background quasars, all having spectroscopic redshifts. From this parent sample, we select 24 systems with high-quality ancillary data for joint analysis of strong lensing geometry and stellar kinematics. A key contribution is the derivation of new single-aperture stellar velocity dispersions for 11 lens galaxies via an iterative spectroscopic fitting procedure that mitigates quasar contamination, providing previously unavailable data. We model the total mass-density profile as a power law, $\rho \propto r^{-\gamma}$, and parameterise its logarithmic slope as $\gamma = \gamma_0 + \gamma_z \cdot z_l + \gamma_s \cdot \log \tilde{\Sigma}$, where $z_l$ is the lens redshift and $\tilde{\Sigma}$ the surface mass density. Within a flat $\Lambda$CDM framework and using DESI BAO measurements as a prior, we constrain the parameters via Monte Carlo nested sampling to $\gamma_0 = 1.62^{+0.11}_{-0.12}$, $\gamma_z = -0.35^{+0.08}_{-0.09}$, and $\gamma_s = 0.37^{+0.08}_{-0.07}$ ($68\%$ confidence intervals). Our results robustly demonstrate that $\gamma$ increases with surface mass density ($\gamma_s > 0$) and decreases with redshift ($\gamma_z < 0$). This implies that, at fixed redshift, galaxies with denser stellar cores have steeper mass profiles, while at fixed density, profiles become shallower at higher redshifts. By successfully applying the joint lensing–dynamics method to a substantial, independently acquired sample of lensed quasars, this work provides crucial validation of structural trends previously observed in galaxy–galaxy lensing systems, reinforcing the established evolutionary picture for massive ETGs and establishing lensed quasars as a potent probe of galaxy structure.
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All authors Ziyu Guo, Yun Chen, Yiping Shu, Jiaze Gao, Hui Li, Zizhao He, Jun Wang

Friday 13 February

High Energy Astrophysical Phenomena

Resonant Axion-Photon Conversion in the Early Inspiral of Neutron Star Binaries

D. Suárez-Fontanella, M. Ángeles Pérez-García and C. Albertus

We consider the early binary neutron star inspiral phase as a scenario to probe environmental axion–photon resonant conversion. For this we approximately model the merger site electromagnetic fields as the superposition of two rotating dipolar stellar magnetic fields at the thousand–km scale when both magnetospheres are not largely distorted. We capture the time-sliced near-zone magnetospheric geometry relevant for axion–photon mixing. Plasma effects are incorporated through an effective Goldreich–Julian charge density, used to determine the effective plasma frequency and the location of resonant conversion surfaces. Our results show that axion–photon resonant conversion in binary magnetospheres mostly occurs on extended peanut-shaped surfaces whose global geometry evolves as the binary inspiral evolves. As a consequence, the total electromagnetic power emitted through axion–photon conversion exhibits a characteristic dependence on axion mass and a slow temporal modulation correlated with the gravitational wave frequency emission. This feature is potentially detectable for $m_a \in [50,170] \,\rm \mu eV$ and set $g_{a \gamma} \lesssim 10^{-11}\rm \,GeV^{-1}$ as it lies within the sensitivity limits of current or planned radio observation missions. In light of our results we discuss the opportunity of binary neutron star inspirals as time-dependent, multimessenger probes of axion physics, and motivate coordinated searches combining gravitational wave observations with radio and millimeter wavelength electromagnetic measurements.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

May Negative Mass Objects exist in the sky?

Shin'ichi Nojiri and S.D. Odintsov

We conjecture the possibility of negative mass objects (NMOs) existing in the sky. It is shown that they may not be so exotic as usually expected. We show that NMOs appear as solutions of standard gravitational equations if we consider the system of a compact positive mass object, cosmological fluid and negative cosmological constant. We also construct models which generate such NMOs as solutions within the two-scalar theory and scalar-Einstein-Gauss-Bonnet gravity inspired by string theory. The orbits of the photon and massive particles are investigated in the background, where there is a negative mass object which realises a kind of effective anti-gravity. It is explicitly found that the bound system consisting of a positive mass object and a negative mass object can be formed in spite that a positive mass object suffers the repulsive force from the NMO. The possibility that such exotic objects might be observed is discussed. A simple conjecture about their possible masses is made, too. As an even more exotic object, we consider a non-trivial object with vanishing mass and investigate its properties.
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Solar and Stellar Astrophysics · Cross-listed from physics.space-ph

Leveling of MHD turbulence imbalance in shear flows

M. Kavtaradze, G. Mamatsashvili, G. Chagelishvili et al. (+1 more)

We investigate magnetohydrodynamic (MHD) turbulence in plane shear flows with a streamwise background magnetic field in the super-Alfvénic regime, i.e., when the flow velocity is larger than the local Alfvén speed. In this regime, turbulence is energetically supplied by large-scale shear of the flow via transient, or non-modal amplification of Alfvén waves, which are the building blocks of MHD turbulence, and streamwise-uniform, mostly nonmagnetic modes. We show that shear reduces turbulence imbalance, driving the system toward a balanced state – the energies of counter-propagating Alfvén waves become essentially equal, even for an initially perfectly imbalanced Alfvénic turbulence. This balancing occurs due to the shear-induced linear non-modal dynamics of Alfvén waves – their non-modal growth, resulting in over-reflection, and coupling between counter-propagating wave branches. Because of its linear origin, this process of balancing of MHD turbulence by shear is fundamentally different from the nonlinear processes operating in standard MHD turbulence in the absence of a mean shear flow. It can have direct implications for understanding the balanced/imbalanced nature of MHD turbulence in shear regions of the solar wind.
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All authors M. Kavtaradze, G. Mamatsashvili, G. Chagelishvili, E. Uchava

Cosmology and Nongalactic Astrophysics

The Cosmological Parameters (2025)

Marina Cortês, Ofer Lahav and Andrew R Liddle

This is a review article for The Review of Particle Physics 2026 (aka the Particle Data Book), appearing as Chapter 25. It forms a compact review of knowledge of the cosmological parameters near the end of 2025. Topics included are Parametrizing the Universe; Extensions to the standard model; Probes; Bringing observations together; Outlook for the future.
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High Energy Astrophysical Phenomena

Superorbital Phase Evolution and a Soft-Hard X-ray Phase Shift in LMC X-4

Yi Chou

The superorbital period of LMC X-4 is among the most stable known in Roche-lobe overflow, high-mass X-ray binaries. We analyzed 33 years of monitoring data from the Compton Gamma Ray Observatory Burst and Transient Source Experiment (CGRO BATSE), the Rossi X-ray Timing Explorer All-Sky Monitor (RXTE ASM), the Neil Gehrels Swift Burst Alert Telescope (Swift BAT), the Monitor of All-sky X-ray Image Gas Slit Camera (MAXI GSC), and the Fermi Gamma-ray Burst Monitor (Fermi GBM). The measured phases show a smooth long-term trend with superposed systematic fluctuations. Fits with cubic, quartic, and sinusoidal models indicate that the quartic and sinusoidal forms provide significantly better descriptions, with the sinusoidal model yielding an $8900^{+210}_{-230}$-day modulation. Such a long timescale is unlikely to arise from orbital motion around a tertiary companion. The fluctuations resemble stochastic, glitch-like events on several-hundred-day timescales. Their rms period variation exceeds that of the smooth trend, yet the total rms period variation over 33 years remains only 0.55%, demonstrating the exceptional stability of the superorbital period. During MJD 57000-60461, we detect a phase offset of 0.044$\pm$0.010 cycles between the soft and hard X-ray bands. This offset can be reproduced by including a higher-harmonic term in the azimuthal disk model, allowing a transition from antisymmetric to asymmetric structure. A contemporaneous decline in the hard X-ray flux suggests a partial obscuration of the emission region, similar to the anomalous low state in Her X-1. This evolving-disk scenario may also explain the superorbital phase shift previously reported in Her X-1.
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High Energy Astrophysical Phenomena

Searching for Neutron Star Mergers in the Absence of Gravitational Waves with Optical Afterglow Emission

Haille M. L. Perkins, Gautham Narayan, Brian D. Fields et al. (+2 more)

With the forth observing run of the LIGO-Virgo-KAGRA gravitational-wave network, which enabled the discovery of the kilonova (KN) counterpart to GW170817, ending with no new confirmed neutron star mergers, the intrinsic rate of these events must be even lower than previously estimated. As a result, building a sample of KNe will remain challenging even with continued GW observations, motivating complementary discovery strategies that do not rely on gravitational-wave triggers. In this work, we consider how leveraging bright short gamma-ray burst afterglows can aid in the discovery on KNe with the Rubin Observatory's upcoming Legacy Survey of Space and Time (LSST), whose unprecedented depth will make such detections feasible. We find that nearly on-axis (${\theta}_{\rm view} \leq 30{\deg}$) afterglows can enhance KN detection rates in the LSST $g$-band from $29^{+51}_{-21} \ \rm yr^{-1}$ to $91^{+160}_{-65} \ \rm yr^{-1}$. We further show how the colors of the observed events can be used to distinguish between neutron star merger counterparts with and without KN emission. This study demonstrates how critical multi-wavelength and multi-survey observations are for these rare events, especially without context from gravitational waves. Fortunately, detectable events will likely be discovered near peak with LSST, allowing for rapid follow-up and confirmation. We discuss key uncertainties in our study, particularly volume rate of merger events, and the degeneracy between the empirically determined explosion energy and ambient medium density.
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All authors Haille M. L. Perkins, Gautham Narayan, Brian D. Fields, Ved G. Shah, Genevieve Schroeder

Astrophysics of Galaxies

Surveying the Giant HII Regions of the Milky Way with SOFIA: VIII. W43 Main

James M. De Buizer, Wanggi Lim, James T. Radomski et al. (+1 more)

In this eighth paper of the SOFIA-FORCAST series on Milky Way GHII regions, we present an analysis of the massive star-forming complex W43 Main. We compared our 11 - 37 micron maps with multi-wavelength observations from the near-infrared to radio, and investigated the physical nature of compact sources and dust substructures. We applied SED fitting to constrain properties of the compact infrared objects, and examined the evolutionary states of the extended subregions. We identified 20 compact infrared objects, 16 (80%) of which we classify as massive young stellar objects (MYSOs) or candidate MYSOs. W43 Main resides at the junction of the Scutum spiral arm and the Galactic Bar, a location where enhanced turbulence is anticipated and has been proposed as a potential influence on star-formation activity. Nevertheless, our analysis shows that its Lyman continuum photon production rate, the mass of its most massive MYSO, and its MYSO density are all consistent with the survey-wide median values. We therefore conclude that, despite W43 Main's unique Galactic environment, its present star formation activity appears broadly consistent with that of an average Galactic GHII region.
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All authors James M. De Buizer, Wanggi Lim, James T. Radomski, Nicole Karnath

Earth and Planetary Astrophysics

Dust Morphology Under Changing Dust Mass Ratios in Protoplanetary Discs

Matthew Murray, Cassandra Hall, Hans Baehr et al. (+1 more)

Protoplanetary disc mass is one of the most fundamental properties of a planet-forming system, as it sets the total mass budget available for planet formation. However, obtaining disc mass measurements remain challenging, since it is not possible to directly detect H$_2$, and CO abundance ratios are poorly constrained. Dynamical measurements of the disc mass are now possible, but they are not suited to all discs since the measurements typically require well-behaved emission surfaces. A long-standing method is to obtain continuum flux measurements from the dust emission, and convert to a total disc mass by assumption of the dust-to-gas mass ratio, $\epsilon$. This quantity is poorly constrained in protoplanetary discs. % We investigate the impact of $\epsilon$ on the morphology of planet-containing hydrodynamical simulations of dusty protoplanetary accretion discs, and suggest that if a planet mass estimate can be obtained, then disc morphology could be used to constrain $\epsilon$ in observed systems relative to each other, improving the total disc mass estimates of protoplanetary discs.
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All authors Matthew Murray, Cassandra Hall, Hans Baehr, Jason Terry

Cosmology and Nongalactic Astrophysics

The Signature of Strong High-Redshift Radio Backgrounds on the Cosmic Dawn 21-cm Bispectrum

Sudipta Sikder, Rajesh Mondal, Rennan Barkana et al. (+1 more)

Measurements from the Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission 2 (ARCADE-2) reveal a strong radio background in the GHz frequency range. Since the cosmological 21-cm signal is measured relative to the background radiation temperature, the presence of a radio excess can significantly alter its characteristics. Previous studies have explored the impact of an inhomogeneous radio background on the global 21-cm signal and 21-cm power spectrum. This non-uniform radio background is also expected to introduce substantial non-Gaussianity. In this work, using the bispectrum, we analyze the non-Gaussianity in the 21-cm signal in the presence of an excess galactic radio background and investigate how line-of-sight radio fluctuations from early galaxies influence its nature. We find that even a moderate enhancement in radio efficiency in early galaxies significantly affects the small-scale 21-cm bispectrum. Furthermore, the delayed heating transition caused by a galactic radio background shifts the sign change in the squeezed-limit bispectrum to lower redshifts ($z\sim11$), providing a potential observational signature for distinguishing different radio background models. These results demonstrate that the 21-cm bispectrum, particularly in the squeezed limit, is highly sensitive to radio background fluctuations, making it a powerful tool for probing high-redshift radio-loud sources and the physics of the early cosmic epoch.
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All authors Sudipta Sikder, Rajesh Mondal, Rennan Barkana, Anastasia Fialkov

Instrumentation and Methods for Astrophysics

Updated Sensitivities of the Five STIS L-mode Gratings

Amy M. Jones, Svea Hernandez, Joleen K. Carlberg et al. (+1 more)

Re-derivation of the sensitivities of all of the Space Telescope Imaging Spectrograph (STIS) observing modes were required after major updates were introduced to the model atmospheres of the three primary standard stars. The new predicted continuum fluxes were up to 2-3% different from the models used to originally calibrate STIS. This work focuses on the re-derivation of spectral sensitivities for the five STIS low-resolution (L-mode) gratings: G140L, G230L, G230LB, G430L, and G750L, which span wavelengths from the far-ultraviolet through the near infrared. Updated photometric throughput tables were delivered to the Calibration Reference Data System (CRDS) on April 7, 2022 and April 14, 2023, which triggered a recalibration of all historical STIS datasets taken with these modes. The sensitivities derived from each of the standard stars typically agree with one another to better than 1%, though discrepancies as large as 1.5% are found in spectral regions most impacted by hydrogen absorption.
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All authors Amy M. Jones, Svea Hernandez, Joleen K. Carlberg, Daniel Welty

High Energy Astrophysical Phenomena

LHAASO observation of Mrk 421 during 2021 March - 2024 March: a comprehensive VHE catalog of multi-timescale outbursts and its time average behavior

The LHAASO Collaboration: Zhen Cao, F. Aharonian, Y.X. Bai et al. (+324 more)

The Large High Altitude Air Shower Observatory (LHAASO) monitors sources within its field of view for up to 7 hours daily, achieving a duty cycle exceeding 98% and an annual point-source sensitivity of 1.5% Crab Units (CU) in the very high energy (VHE) band. This unbiased sky-survey mode facilitates systematic monitoring and investigation of outburst phenomena. In this paper, we present results from an unprecedented three-year monitoring campaign (March 2021–March 2024) of Mrk421 using LHAASO, spanning energies from 0.4 TeV to 20 TeV. We find that the blazar stayed in a quiescent state in 2021 and became active starting in 2022 with a total of 23 VHE outburst events identified, where the highest observed daily significance reaches $20\,\sigma$ with a flux equivalent to approximately 3.3~CU. LHAASO's continuous monitoring suggests the flaring occupancy of Mrk~421 to be around 14%. During long-term monitoring, multiwavelength (MWL) variability and correlation analyses are conducted using complementary data from Fermi-LAT, MAXI-GSC, Swift-XRT, and ZTF. A significant correlation ($>3\,\sigma$) is observed between X-ray and VHE bands with no detectable time lag, while the correlation between GeV and TeV bands is weaker. The flux distribution of the TeV emission during the quiescent state is different from that in the active state, implying the existence of two modes of energy dissipation in the blazar jet. Using simultaneous MWL data, we also analyzed both the long-term and outburst-period SEDs, and discussed the possible origin of the outburst events.
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All authors The LHAASO Collaboration: Zhen Cao, F. Aharonian, Y.X. Bai, Y.W. Bao, D. Bastieri, X.J. Bi, Y.J. Bi, W. Bian, J. Blunier, A.V. Bukevich, C.M. Cai, Y.Y. Cai, W.Y. Cao, Zhe Cao, J. Chang, J.F. Chang, E.S. Chen, G.H. Chen, H.K. Chen, L.F. Chen, Liang Chen, Long Chen, M.J. Chen, M.L. Chen, Q.H. Chen, S. Chen, S.H. Chen, S.Z. Chen, T.L. Chen, X.B. Chen, X.J. Chen, X.P. Chen, Y. Chen, N. Cheng, Q.Y. Cheng, Y.D. Cheng, M.Y. Cui, S.W. Cui, X.H. Cui, Y.D. Cui, B.Z. Dai, H.L. Dai, Z.G. Dai, Danzengluobu, Y.X. Diao, A.J. Dong, X.Q. Dong, K.K. Duan, J.H. Fan, Y.Z. Fan, J. Fang, J.H. Fang, K. Fang, C.F. Feng, H. Feng, L. Feng, S.H. Feng, X.T. Feng, Y. Feng, Y.L. Feng, S. Gabici, B. Gao, Q. Gao, W. Gao, W.K. Gao, M.M. Ge, T.T. Ge, L.S. Geng, G. Giacinti, G.H. Gong, Q.B. Gou, M.H. Gu, F.L. Guo, J. Guo, K.J. Guo, X.L. Guo, Y.Q. Guo, Y.Y. Guo, R.P. Han, O.A. Hannuksela, M. Hasan, H.H. He, H.N. He, J.Y. He, X.Y. He, Y. He, S. Hernández-Cadena, B.W. Hou, C. Hou, X. Hou, H.B. Hu, S.C. Hu, C. Huang, D.H. Huang, J.J. Huang, X.L. Huang, X.T. Huang, X.Y. Huang, Y. Huang, Y.Y. Huang, A. Inventar, X.L. Ji, H.Y. Jia, K. Jia, H.B. Jiang, K. Jiang, X.W. Jiang, Z.J. Jiang, M. Jin, S. Kaci, M.M. Kang, I. Karpikov, D. Khangulyan, D. Kuleshov, K. Kurinov, Cheng Li, Cong Li, D. Li, F. Li, H.B. Li, H.C. Li, Jian Li, Jie Li, K. Li, L. Li, R.L. Li, S.D. Li, T.Y. Li, W.L. Li, X.R. Li, Y. Li, Zhe Li, Zhuo Li, E.W. Liang, Y.F. Liang, S.J. Lin, B. Liu, C. Liu, D. Liu, D.B. Liu, H. Liu, J. Liu, J.L. Liu, J.R. Liu, M.Y. Liu, R.Y. Liu, S.M. Liu, W. Liu, X. Liu, Y. Liu, Y. Liu, Y.N. Liu, Y.Q. Lou, Q. Luo, Y. Luo, H.K. Lv, B.Q. Ma, L.L. Ma, X.H. Ma, I.O. Maliy, J.R. Mao, Z. Min, W. Mitthumsiri, Y. Mizuno, G.B. Mou, A. Neronov, K.C.Y. Ng, M.Y. Ni, L. Nie, L.J. Ou, Z.W. Ou, P. Pattarakijwanich, Z.Y. Pei, D.Y. Peng, J.C. Qi, M.Y. Qi, J.J. Qin, D. Qu, A. Raza, C.Y. Ren, D. Ruffolo, A. Sáiz, D. Savchenko, D. Semikoz, L. Shao, O. Shchegolev, Y.Z. Shen, X.D. Sheng, Z.D. Shi, F.W. Shu, H.C. Song, Yu.V. Stenkin, Y. Su, D.X. Sun, H. Sun, J.X. Sun, Q.N. Sun, X.N. Sun, Z.B. Sun, N.H. Tabasam, J. Takata, P.H.T. Tam, H.B. Tan, Q.W. Tang, R. Tang, Z.B. Tang, W.W. Tian, C.N. Tong, L.H. Wan, C. Wang, D.H. Wang, G.W. Wang, H.G. Wang, J.C. Wang, K. Wang, Kai Wang, Kai Wang, L.P. Wang, L.Y. Wang, L.Y. Wang, R. Wang, W. Wang, X.G. Wang, X.J. Wang, X.Y. Wang, Y. Wang, Y.D. Wang, Z.H. Wang, Z.X. Wang, Zheng Wang, D.M. Wei, J.J. Wei, Y.J. Wei, T. Wen, S.S. Weng, C.Y. Wu, H.R. Wu, Q.W. Wu, S. Wu, X.F. Wu, Y.S. Wu, S.Q. Xi, J. Xia, J.J. Xia, G.M. Xiang, D.X. Xiao, G. Xiao, Y.F. Xiao, Y.L. Xin, H.D. Xing, Y. Xing, D.R. Xiong, B.N. Xu, C.Y. Xu, D.L. Xu, R.F. Xu, R.X. Xu, S.S. Xu, W.L. Xu, L. Xue, D.H. Yan, T. Yan, C.W. Yang, C.Y. Yang, F.F. Yang, L.L. Yang, M.J. Yang, R.Z. Yang, W.X. Yang, Z.H. Yang, Z.G. Yao, X.A. Ye, L.Q. Yin, N. Yin, X.H. You, Z.Y. You, Q. Yuan, H. Yue, H.D. Zeng, T.X. Zeng, W. Zeng, X.T. Zeng, M. Zha, B.B. Zhang, B.T. Zhang, C. Zhang, H. Zhang, H.M. Zhang, H.Y. Zhang, J.L. Zhang, J.Y. Zhang, Li Zhang, P.F. Zhang, R. Zhang, S.R. Zhang, S.S. Zhang, S.Y. Zhang, W. Zhang, W.Y. Zhang, X. Zhang, X.P. Zhang, Yi Zhang, Yong Zhang, Z.P. Zhang, J. Zhao, L. Zhao, L.Z. Zhao, S.P. Zhao, X.H. Zhao, Z.H. Zhao, F. Zheng, T.C. Zheng, B. Zhou, H. Zhou, J.N. Zhou, M. Zhou, P. Zhou, R. Zhou, X.X. Zhou, X.X. Zhou, B.Y. Zhu, C.G. Zhu, F.R. Zhu, H. Zhu, K.J. Zhu, Y.C. Zou, X. Zuo

Earth and Planetary Astrophysics

The Interplanetary Habitable Zone

Caleb Scharf

The concept of a system-wide measure of the sustainment of life (habitability) for space-faring interplanetary species is introduced and explored. Although largely agnostic to the details of how interplanetary life might operate (e.g., via technology or by utilizing organism traits that are, as of now, unknown to us), some assumptions must be made about energy harvesting, orbital mobility costs, radiation risks, and resource requirements. A multi-modal figure of merit is developed for evaluating an interplanetary habitable zone (IHZ). An agent-based model is also developed to simulate the dispersal of interplanetary life in a planetary system and characterize the IHZ. For the solar system, resource weightings between planetary bodies dictate many overall behaviors, including the sequence of migration from Earth to the Moon, Mars, and asteroid belt. Comparisons with the Trappist-1 exoplanetary system also point to critical sensitivities in the balance between resource availability and risk or cost factors (e.g., radiation risks and orbital Delta-v costs) that determine the structure of an IHZ. Results suggest that our solar system may have an inherent, and significant, advantage for a space-faring species over a system like Trappist-1. This modeling approach may also have application to emerging space economies in our own solar system.
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Astrophysics of Galaxies

Revising the Milky Way Cepheid Calibration: Quantifying and Correcting for Previously Undetected Distance Modulus Errors in the Gaia-based Multi-Wavelength Period-Luminosity Relations

Barry F. Madore and Wendy L. Freedman

We examine the multi-wavelength period-luminosity-color relations for Cepheid variables in the Large and Small magellanic Clouds and the Milky Way. From first-principles stellar physics, the luminosity of a Cepheid is determined by its radius and surface temperature, yielding a fundamental PLC relation whose observational proxies are pulsation period and intrinsic color. Using Cepheids in the Magellanic Clouds, we show that the PLC relation recovers the known geometries and line-of-sight tilts of their disks, confirming its ability to detect true distance-modulus variations that are achromatic and consistent across all filters. Surprisingly, for Milky Way Cepheids with individually determined reddenings and HST and Gaia parallaxes, the residuals from multi-wavelength PL fits are also found to be achromatic, identical in sign and amplitude across all passbands, in this case indicating that parallax errors are the dominant source of scatter. Applying bandpass-averaged corrections to individual Cepheids recovers the theoretically expected wavelength-dependent narrowing of the instability strip, and results in revised parallaxes with a median improvement in precision of roughly a factor of two. In addition, they show no statistically significant correlation with metallicity over the range -0.2 < Fe/H < 0.05 dex. The final extinction- and reddening-corrected PLC relation yields an rms scatter of 0.04 mag, corresponding to 2 percent precision in distance per star. Use of a physically grounded PLC will provide a more robust foundation for the Cepheid-based extragalactic distance scale and the determination of the Hubble constant.
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Astrophysics of Galaxies

MeerKAT discovery of a high-redshift strongly-lensed hydroxyl gigamaser

Thato E. Manamela, Roger P. Deane, Tariq Blecher et al. (+3 more)

At low redshifts, hydroxyl megamasers (OHMs) have been shown to trace galaxy mergers, obscured starbursts, high molecular gas densities, and candidate dual supermassive black hole systems. Given this astrophysical utility, exploring these sources at larger cosmological look-back times is therefore of key interest. While previous OHM surveys have been limited to redshifts of $z \lesssim 0.25$, the ability to expand the OHM frontier is significantly enhanced with new high-sensitivity radio facilities such as MeerKAT. In this Letter, we report the discovery of an OHM in the gravitational lens system HATLAS J142935.3-002836 at $z = 1.027$, the most distant OHM source yet detected. The spectrum has blended 1667 and 1665 MHz emission and exhibits a highly complex profile, with spectral components ranging in widths of $<8$ km s$^{-1}$ to $\sim300$ km s$^{-1}$. The integrated (magnification uncorrected) luminosity of log($L_{\rm OH} / L_{\odot}$) = 5.51 $\pm$ 0.67 makes this the most apparently luminous OHM known to date. In the same wide-band dataset, we have also detected a previously unknown ${\rm H I}$ absorption line. The signal-to-noise ratio of over 150 with just a 4.7 h observation highlights the potential that MeerKAT and the future Square Kilometre Array mid-frequency array offer to explore the high-redshift OHM universe.
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All authors Thato E. Manamela, Roger P. Deane, Tariq Blecher, Ian Heywood, Athol J. Kemball, Danail Obreschkow

Astrophysics of Galaxies

ARCHITECTS II: Impact of subgrid physics on the observable properties of the circumgalactic medium

Maxime Rey, Jérémy Blaizot, Taysun Kimm et al. (+3 more)

Galaxy evolution is driven by star formation and stellar feedback on scales unresolved by current high-resolution cosmological simulations, requiring robust subgrid models. However, these models remain degenerate, often calibrated primarily to match observed stellar masses. To explore these degeneracies, we conduct three state-of-the-art cosmological zoom-in simulations of the same galaxy, each incorporating different subgrid models: mechanical feedback, a combination of mechanical and thermal feedback, and delayed cooling. We compare their circumgalactic media (CGM) through quasar absorption sightlines of HI, MgII, CIV, and OVI. Our findings demonstrate that despite producing galaxies with the same stellar masses, the models lead to distinct feedback modes and CGM properties. Column densities and covering fractions serve as effective diagnostics of subgrid models, with all four ions providing strong constraints as they trace diverse gas phases, exhibit complementary spatial distributions, and originate from different mechanisms. Although all simulations bracket observed column density distributions, direct comparisons are limited by scarce detections and significant scatter in absorption strengths. Covering fractions of weak absorbers provides the most robust constraints. All models fail to reproduce HI and MgII covering fractions, and delayed cooling overproduces OVI covering fractions, while the other models underproduce them. The simulation including mechanical feedback reproduces the observed CIV covering fractions well, whereas the other models show slight offsets. We argue that this discrepancy is likely driven by unresolved thermal structures for HI and MgII, and insufficient metals for CIV and OVI, arising from missing physics such as AGNs or cosmic rays.
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All authors Maxime Rey, Jérémy Blaizot, Taysun Kimm, Joakim Rosdahl, Léo Michel-Dansac, Valentin Mauerhofer

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-th

Holographic Dark Matter

Sylvain Fichet, Eugenio Megias and Mariano Quiros

Cold dark matter may be a fluid (or plasma) residing in a strongly-interacting hidden sector, rather than a population of weakly-coupled particles. Such a scenario admits a holographic description in terms of a cosmological braneworld embedded in the linear dilaton five-dimensional (5D) spacetime. In this framework, dark matter originates from the linear dilaton bulk black hole, whose phase we show to be thermodynamically favored at all temperatures. We present a natural freeze-in mechanism for the production of holographic dark matter, in which the bulk black hole is fed by energy leaking from the brane after inflation. Our model is characterized by two free parameters, one of which, the position of the black hole horizon, is fixed by the observed dark matter abundance. The remaining parameter, the 5D Planck scale $M_5$, is consistent with all current experimental bounds provided that $M_5\gtrsim 3\times 10^5$ TeV.
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Astrophysics of Galaxies

ARCHITECTS I: Impact of subgrid physics on the simulated properties of the circumgalactic medium

Maxime Rey, Jérémy Blaizot, Taysun Kimm et al. (+2 more)

Galaxy evolution is shaped by star formation and stellar feedback at scales unresolved by current high-resolution cosmological simulations. Precise subgrid models are thus necessary, and different approaches have been developed. However, they are degenerate and often primarily calibrated to reproduce stellar masses from observations. To explore these degeneracies, we perform three cosmological zoom-in radiation-hydrodynamics simulations of the same galaxy within a $5\times10^{11}\rm\ M_\odot$ dark matter halo at $z\sim1$, each with a different subgrid model: mechanical feedback, a combination of mechanical feedback and thermal feedback, and delayed cooling. We calibrate the simulations to match in stellar mass, isolating the effect of the models on the circumgalactic medium (CGM). Our findings demonstrate that despite producing galaxies with comparable stellar masses, the three models lead to distinct feedback modes, resulting in notable variations in the CGM properties. The delayed cooling run is dominated by ejective feedback and exhibits high burstiness, whereas mechanical and the hybrid models primarily feature preventive feedback, respectively acting at the galaxy and halo scales. Delayed cooling reduces the baryon mass to half the universal baryon fraction while mechanical feedback retains most baryons, with the hybrid model standing in between. Delayed cooling also ejects significantly more metals into the CGM than both other models. While for delayed cooling and mechanical feedback metals are almost evenly distributed in the CGM, they are concentrated around satellites in the hybrid model. These discrepancies emphasize the need to design an appropriate subgrid model to understand how stellar feedback regulates galaxy growth.
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All authors Maxime Rey, Jérémy Blaizot, Taysun Kimm, Joakim Rosdahl, Léo Michel-Dansac

High Energy Astrophysical Phenomena

Constraining Binary Neutron Star Populations using Short Gamma-Ray Burst Observations

Alessio Ludovico De Santis, Samuele Ronchini, Filippo Santoliquido et al. (+1 more)

The landmark multi-messenger observations of the binary neutron star (BNS) merger GW170817 provided firm evidence that such mergers can produce short gamma-ray bursts (sGRBs). However, the limited number of BNS detections by current gravitational-wave (GW) observatories raises the question of whether BNS mergers alone can account for the full observed sGRB population. We analyze a comprehensive set of 64 BNS population synthesis models with a Monte Carlo-based framework to reproduce the properties of sGRBs detected by Fermi-GBM over the past 16 years. We consider three jet geometry scenarios: a universal structured jet calibrated to GW170817, a universal top-hat jet, and a non-universal top-hat jet with distributions of core opening angles. Our results show that models characterized by low local BNS merger rates ($R_{BNS}(0) \lesssim 50$ Gpc$^{-3}$ yr$^{-1}$) predict too few observable sGRBs to reproduce the Fermi-GBM population, effectively disfavoring them as sole progenitors. Even when relaxing assumptions on jet geometry, low-rate models remain viable only for wide jets ($\theta_c \ge 15^\circ$), in tension with the narrow jet cores ($\theta_c \approx 6^\circ$) inferred from sGRB afterglow observations. In contrast, models with local merger rates of order $R_{BNS}(0) \approx 100$ Gpc$^{-3}$ yr$^{-1}$ successfully reproduce the observed sGRB population, assuming a plausible fraction of BNS mergers launch relativistic jets and realistic jet geometries. This analysis highlights the power of combining GW observations of BNS mergers with electromagnetic observations of sGRBs to place robust constraints on the BNS merger population and to assess their role as progenitors of sGRBs.
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All authors Alessio Ludovico De Santis, Samuele Ronchini, Filippo Santoliquido, Marica Branchesi