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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 30 March

High Energy Astrophysical Phenomena

Single vs. Binary Origin: The Diversity of Stripped-Envelope Supernova Remnants

Gaku Kawashima, Shiu-Hang Lee, Keiichi Maeda et al. (+1 more)

Core-collapse supernova remnants (CCSNRs) are crucial for understanding the final stages of massive star evolution, as they reflect the imprints of their progenitors' pre-explosion activities. However, the evolution of CCSNRs, particularly those originating from progenitors with high mass-loss rates – known as stripped-envelope SNRs (SESNRs) – remains poorly understood. This is largely due to the lack of comprehensive numerical models connecting progenitor stars to their remnants, especially in the context of binarity. In this study, we perform self-consistent simulations of CCSNRs from both single and binary progenitors, utilizing mass-loss histories and supernova ejecta profiles directly derived from stellar evolution and explosion calculations. Our models reveal significant differences in the circumstellar medium (CSM) structures between single and binary progenitors, which drive distinct SNR dynamics and spectral characteristics. We find that binary-stripped progenitors tend to produce SNRs with more monotonic CSM profiles, resulting in smoother shock dynamics and less pronounced X-ray luminosity peaks compared to their single-star counterparts. Additionally, we introduce a new characteristic timescale, $t_{\rm CSM}$, defined by the total mass lost by the progenitor. This timescale effectively scales the evolutionary phases of CCSNRs in complex CSM environments, thereby facilitating the comparison of SESNRs. Given that observed elemental abundances in SNRs reflect the nucleosynthesis yields of the progenitor, our results highlight the importance of considering the dynamical state of SNRs when interpreting observed abundances. This work provides a fiducial framework for future observational and theoretical studies of CCSNRs, particularly regarding the impact of binary evolution.
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All authors Gaku Kawashima, Shiu-Hang Lee, Keiichi Maeda, Daniel Patnaude

Astrophysics of Galaxies

The complex relationships between AGN, bars and bulges

Izzy L. Garland, Henry Best, Lucy F. Fortson et al. (+9 more)

Context. Via scaling relations, it is well-known that active galactic nuclei (AGN) and bulges are linked. This link was thought to be driven by mergers, but recent studies show that secular processes are the dominant mechanism of supermassive black hole growth. One such secular mechanism is gas inflow driven by large-scale bars. Since bulges can also grow via these bars, there is likely some common process between these three features. Aims. We investigate whether the observed correlation between AGN and bars is real or arises as a result of correlations between bars and bulges. Methods. Using a catalogue of AGN identifications and galaxy morphologies in the DESI Legacy Survey at $z\leq0.1$, we control for mass and colour and investigate the AGN fraction variation with bulge prominence and bar strength. Results. We first show that the variation in AGN fraction between strongly barred, weakly barred and unbarred galaxies does not qualitatively change if we additionally control for bulge prominence. Second, we find that in fixed bins of bulge prominence, the AGN fraction increases with increasing bar strength. In subsamples split by bar strength, the AGN fraction increases with bulge prominence, indicating that AGN presence correlates with both bar strength and bulge prominence simultaneously.
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All authors Izzy L. Garland, Henry Best, Lucy F. Fortson, Tobias Géron, Chris J. Lintott, David O'Ryan, Brooke D. Simmons, Rebecca J. Smethurst, Monika Viskotová, Mika Walmsley, Norbert Werner, Michal Zajaček

Solar and Stellar Astrophysics

Statistics of transition-region loop brightenings and their heating implication

Xiuhui Zuo, Zhenghua Huang, Maria S. Madjarska et al. (+4 more)

Transition-region loops are a type of critical magnetic structure in the solar atmosphere, yet their physical properties and evolutionary characteristics remain statistically poorly constrained. We aim to statistically characterize the physical properties of propagating brightening events in transition-region loops and to explore the underlying heating mechanism responsible for these brightenings.Using coordinated observations from the Extreme Ultraviolet Imager onboard the Solar Orbiter and the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory, we analyze 42 propagating brightening events in loops that are unambiguously detected in both instrument data. Each of these events evolve simultaneously in the AIA 94, 131, 171, 193, 211, 304, and 335 passband images, suggesting that they are in the transition-region or low-coronal temperature range. Our analyses show that these brightenings are impulsive, with an average brightening time of 118.4 s and a mean intensity decreasing time of 159.4 s. The propagating brightenings are predominantly subsonic, with velocities in the range of 0-90 km/s and an average of 51.3 km/s. The lengths of brightenings range from 3 to 11 Mm, with an average and standard deviation of 6.3 Mm, which are closely related to the propagation velocity and the lifetime. The initial brightening sites are predominantly located near the footpoints of these loops, and the number of brightening events decreases systematically with increasing of loop height. Our results are consistent with an energizing mechanism regulated by enthalpy flows and radiative cooling.
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All authors Xiuhui Zuo, Zhenghua Huang, Maria S. Madjarska, Hui Fu, Hengyuan Wei, Xinzheng Shi, Lidong Xia

Instrumentation and Methods for Astrophysics

Weak polarized lines of the second solar spectrum (Na, Al, H, He, Ti, Li, Sc, C2 and MgH) observed at the Pic du Midi turret dome

Jean-Marie Malherbe

The second solar spectrum is the solar spectrum of Stokes parameter Q observed in linear polarization close to the solar limb. It differs significantly of the usual intensity spectrum (Stokes parameter I). The second solar spectrum contains in the visible range a few polarized lines with Q/I > 1% (such as CaI, SrI, SrII, BaII), but most lines exhibit weak or very faint polarization rates (Q/I < 0.3%). This paper presents unpublished observations made in 2004-2006 of weak polarized lines performed with the Pic du Midi Turret Dome spectropolarimeter, such as atomic lines of Na, Al, H, He, Ti, Li, Sc as well as C2 and MgH molecules.
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High Energy Astrophysical Phenomena

Probing burst-disc interaction and disc reflection in SAX J1808.4$-$3658 with NICER, XMM-Newton, and NuSTAR

Manoj Mandal, Sachindra Naik and Birendra Chhotaray

We performed a comprehensive study of thermonuclear bursts from the millisecond X-ray pulsar SAX J1808.4$-$3658 with XMM-Newton and NICER. We report the results from the analysis of an intense burst with NICER using a self-consistent and physically motivated disc reflection modeling approach and investigate the burst-disc interaction. The dynamic evolution of the spectral parameters suggested evidence of photospheric radius expansion (PRE) of the neutron star using the disc reflection modeling approach, which indicates a maximum expansion of the photosphere up to 14.8$\pm$0.7 km. The corresponding blackbody temperature drops to a minimum of 1.9 keV. In addition, an emission line at 1 keV is observed, possibly originating from the Ne or Fe L-band transition as a result of the reprocessing of burst photons by cold gas in the accretion disc. The 1 keV emission line flux is found to be strongly correlated with the flux of the reflection component. We also investigated a thermonuclear burst observed with XMM-Newton EPIC-PN from SAX J1808.4$-$3658 using the variable persistent emission method and the disc reflection modeling approach. The X-ray reflection feature is also investigated in persistent emission using a NuSTAR observation. The best-fitting results provide an inner disc radius of $14_{-5.9}^{+9.7}$ $R_g$ and an inclination of $ 38^\circ-60^\circ$ during the NuSTAR observation. The magnetic field is estimated to be $\simeq$3.7 $\times$10$^8$ G at the poles of the neutron star.
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Earth and Planetary Astrophysics

Planet-star interactions with precise transit timing. V. Tidal decay of hot Jupiters through wave breaking

J. Golonka and G. Maciejewski

Tidal interactions shape the evolution of close-in giant planets and internal gravity-wave breaking offers an efficient pathway for dynamical-tide dissipation, although its population-wide impact remains poorly constrained. We aim to quantify wave-breaking tidal dissipation for 550 hot Jupiters, accounting for stellar-parameter uncertainties. We also aim to identify the most promising systems for detecting orbital decay through transit timing.\\ Stellar masses, radii, and ages were homogeneously redetermined from spectroscopic and photometric data using an isochrone fitting. For each system, these parameters were propagated through a dedicated MESA model grid to calculate the tidal quality factor, wave-breaking probability, orbital decay rate, transit-timing diagnostics and destruction timescales.\\ Wave breaking is predicted to be largely inactive in pre-intermediate-age main sequence (pre-IAMS) stars. The tidal quality factor for systems undergoing wave breaking peaks between $10^6$ and $10^7$, consistent with population-level inferences. About 43% of planets, primarily with periods $\lesssim3.5$~d, are expected to inspiral on the main sequence, providing a physical explanation for the observed tendency of hot Jupiters to orbit younger stars. A further 41% inspiral during post-main-sequence evolution within the stages considered. Systems with periods $\lesssim 1$~d, which could in principle experience the strongest tidal forcing, are unlikely to trigger wave breaking, leaving planets on stable orbits. Conversely, the most rapidly inspiralling systems with high wave-breaking probability might display measurable orbital-period shortening only over multi-decade baselines, eluding immediate detection. In contrast, the demographic imprint of wave breaking on occurrence rates should emerge more readily, with the first signs already visible in current population statistics.
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Earth and Planetary Astrophysics

Shape, regolith size and thickness, SMFe^0 content, and spectral type of Tianwen-2 target asteroid (469219) Kamo'oalewa

Pengfei Zhang, Guozheng Zhang, Yongxiong Zhang et al. (+13 more)

China's Tianwen-2 spacecraft will return samples from the near-Earth asteroid (469219) Kamo'oalewa. We previously reported that Kamo'oalewa develops an LL-chondrite-compositional, highly space-weathered surface. This study aims to estimate Kamo'oalewa's shape, regolith grain size and thickness, sub-micrometer iron (SMFe0) content, and spectral type. Using the lightcurve data and the Cellinoid model, we modeled Kamo'oalewa's shape, rotation period, and pole orientation. We then estimated its global distribution of regolith critical size using the balance method of gravity, cohesive force, and centrifugal force. Furthermore, in the temperature range of 253.15 to 473.15 K, we measured the thermal parameters of laser-irradiated LL chondrite powder that best matches Kamo'oalewa's spectrum, estimating Kamo'oalewa's thermal inertia and skin depth (lower limit of regolith thickness). Using the radiative transfer mixing model, we also estimated the content of SMFe0 in Kamo'oalewa's regolith. Finally, using the MIT online spectral classification tool for the laser-irradiated LL chondrite powder, we obtained a virtual spectral type of Kamo'oalewa. Our model gives a size of 68 m x 46 m x 39 m, a rotation period of 27.66 minutes, and a pole orientation of 134.7 degrees longitude and -11.4 degrees latitude for Kamo'oalewa. Regolith grains with a size <2 cm can remain stable over 93.8% of the global surface area of Kamo'oalewa. Laser-irradiated LL chondrite powder shows a low thermal inertia (95.5 to 135.1 J m^-2 K^-1 s^-1/2), corresponding to a thermal skin depth of 3 to 3.5 mm on Kamo'oalewa. An SMFe0 content of 0.29 +- 0.05 wt.% is required to match Kamo'oalewa's spectrum. The virtual spectral type of Kamo'oalewa is given as "Sqw".
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All authors Pengfei Zhang, Guozheng Zhang, Yongxiong Zhang, Marco Fenucci, Pierre Vernazza, Jin Zhao, Yunbo Niu, Xuejin Lu, Xing Wu, Honglei Lin, Edward Cloutis, Xiaoran Yan, Xiaoping Lu, Xiaobin Wang, Xiaoping Zhang, Yang Li

Earth and Planetary Astrophysics

Tianwen-2 target asteroid (469219) Kamo'oalewa probably develops an Itokawa-compositional but ultra-highly space-weathered surface

Pengfei Zhang, Guozheng Zhang, Zichen Wei et al. (+45 more)

China's Tianwen-2 mission plans to return samples from a small, rapidly spinning Earth quasi-satellite (469219) Kamo'oalewa. Previous studies linked Kamo'oalewa to lunar composition and origin. Here, we propose another scenario. We reanalyzed the reflectance spectrum of Kamo'oalewa and obtained an absorption band center at 1.001+-0.028 um (error is 1sigma), consistent with LL chondrites. We then conducted space weathering (SW) experiments on meteorites and found that highly space-weathered LL chondrite powder (but not slab) successfully reproduced the reflectance spectrum of Kamo'oalewa. We further traced the dynamical origin of Kamo'oalewa and found that it probably originated from the v6 secular resonance, and more specifically, the Flora family. Kamo'oalewa exhibits a similar composition to Itokawa and 7 objects in the Flora family, but with a higher degree of space weathering. We, therefore, proposed that Kamo'oalewa probably originated from the Flora family and developed an Itokawa-compositional, highly space-weathered, fine-regolith-dominated surface.
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All authors Pengfei Zhang, Guozheng Zhang, Zichen Wei, Mikael Granvik, Xiaoran Yan, Pengyue Wang, Qinwei Zhang, Ronghua Pang, Wen-Han Zhou, Te Jiang, Pierre Vernazza, Takahiro Hiroi, Edward Cloutis, Francesca DeMeo, Pierre Beck, Wing-Huen Ip, Marco Fenucci, Yongxiong Zhang, Michael Marsset, Yunbo Niu, Xuejin Lu, Xing Wu, Honglei Lin, Shoucun Hu, Bin Cheng, Haibin Zhao, Xiaobin Wang, Xiaoping Lu, Yonglong Zhang, Zongcheng Ling, Jiang Zhang, Sizhe Zhao, Cateline Lantz, Jooyeon Geem, Zhiping He, Juntao Wang, Liyong Zhou, Xiliang Zhang, Shijei Li, Sen Hu, Wei Yang, Xiongyao Li, Xiaoping Zhang, Jiahui Liu, Peng Zhang, Guang Zhang, Yangting Lin, Yang Li

Earth and Planetary Astrophysics

Developing and characterizing a new-generation regolith simulant "IGCAS-AST01" for the Tianwen-2 target asteroid (469219) Kamo'oalewa

Pengfei Zhang, Zichen Wei, Takahiro Hiroi et al. (+12 more)

China plans to return samples from the near-Earth asteroid (469219) Kamo'oalewa, which we previously identified as an LL-chondrite-compositional, highly space-weathered object with fine-grained regolith. In this study, we developed 10 mL of Kamo'oalewa regolith simulant, designated "IGCAS-AST01", by irradiating LL5/6 chondrite (Kheneg Ljou^ad) powder with a high-energy pulsed laser. We then analyzed the composition, grain size distribution, density, porosity, visible to near-infrared reflectance spectrum, thermal emission spectrum, thermal diffusivity, specific heat capacity, and microstructural features of both the fresh (unirradiated) powder and IGCAS-AST01. IGCAS-AST01 is composed of 57.8 vol.% olivine, 19.9 vol.% orthopyroxene, 5.6 vol.% diopside, 12.2 vol.% plagioclase, 2.6 vol.% troilite, and minor amounts of other phases. It has a mean size of 26.99 um, a median size of 23.19 um, a density of 700 kg m^-3, and a porosity of 79.1%. Additionally, IGCAS-AST01 exhibits a low reflectance of 0.1 at 0.55 um and an extremely steep spectral slope. In the temperature range of 253.15-473.15 K, its thermal diffusivity and specific heat capacity range from 3.6-4.7 x 10^-6 m^2 s^-1 and 718.43-890.20 J kg^-1 K^-1, respectively. Furthermore, thick amorphous rims and abundant nanophase metallic iron particles are observed in olivine and pyroxene grains of IGCAS-AST01. These results could support the Tianwen-2 mission's payload calibration, sampling operations, on-orbit scientific data interpretation, and future sample analysis.
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All authors Pengfei Zhang, Zichen Wei, Takahiro Hiroi, Jin Zhao, Edward Cloutis, Guozheng Zhang, Marco Fenucci, Rui Li, Xiaojing Zhang, Xiaoping Zhang, Zhiping He, Yan Su, Yangting Lin, He Zhang, Yang Li

Instrumentation and Methods for Astrophysics

KMTNet Synoptic Survey of Southern Sky III: The First Data Release

Seo-Won Chang, Myungshin Im, Mankeun Jeong et al. (+13 more)

We present the first public data release (DR1) of the KMTNet Synoptic Survey of Southern Sky (KS4). This deep, wide-field imaging survey covers a southern footprint of -85$^{\circ}$ < Decl. < -28.8$^{\circ}$ in the $B$, $V$, $R$, and $I$ bands using a network of three 1.6-m telescopes. Although primarily designed to secure reference imaging for gravitational wave counterpart identification, DR1 delivers science-ready data for $\sim$4,000 deg$^{2}$ to enable a broad range of astrophysical research. The release includes deep co-added images reaching median 5$\sigma$ depths of 22.0-23.5 AB mag. It is accompanied by two source catalogs containing over 200 million sources with SNR $>5$: an $I$-band-selected forced-photometry catalog optimized for consistent colors, and a band-merged catalog offering enhanced completeness. Validation demonstrates robust data quality, characterized by mean astrometric offsets of $+0.054 \pm 0.129$ arcsec in RA and $-0.015 \pm 0.120$ arcsec in Dec relative to Gaia DR3. {\refbf Photometric uniformity for point sources is maintained within $\pm 0.03$ mag relative to Gaia XP for 97.5–99.8% of the footprint across all four bands.} A key advantage of KS4 is its uniform and contiguous spatial coverage. It extends to fainter magnitudes than other uniform surveys while filling irregular gaps in existing deep datasets. All data products are publicly available via the CDS and NOIRLab's Astro Data Lab.
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All authors Seo-Won Chang, Myungshin Im, Mankeun Jeong, Joonho Kim, Bomi Park, Jaewon Lee, David A. H. Buckley, Jeff Cooke, Sungho Jung, Dong-Jin Kim, Ji Hoon Kim, Yongjung Kim, Chung-Uk Lee, Seong-Kook Lee, Gregory S. H. Paek, Jiseop Shin

Astrophysics of Galaxies

A Wide and Deep Exploration of Radio-detected Active Galactic Nuclei with Subaru HSC (WERGS). XIII. High-z Radio Quasar Selection from HSC–VLASS over $\sim1200$ deg$^2$

Youwen Kong, Kohei Ichikawa, Hisakazu Uchiyama et al. (+12 more)

We report the results of $g-$, $r-$, $i-$, and $z-$dropout selections based on optical identifications of Very Large Array Sky Survey (VLASS) radio sources using the Hyper Suprime-Cam Subaru Strategic Program survey (HSC–SSP). By positional crossmatching within $1.''5$ between the VLASS Epoch~2 catalog and the HSC–SSP Wide-layer catalog ($i \lesssim 26$), we obtain $\sim$400 high-redshift radio AGN candidates at $z \gtrsim 4$ over a $\approx1200~\mathrm{deg}^2$ survey footprint, extending optimistically to $z \sim 7$. Their $i$-band AB magnitudes range from $i_\mathrm{AB} \simeq 24$–26, placing most below the SDSS detection limit. By further crossmatching the HSC–VLASS dropout catalog with VLA Faint Images of the Radio Sky at Twenty-centimeters (FIRST) at 1.4~GHz, the LOFAR Two-metre Sky Survey (LoTSS) at 144~MHz, and the TIFR GMRT Sky Survey (TGSS) at 150~MHz, we obtain multi-frequency radio measurements for the majority of the sample. Approximately 85% of the sources have three radio detections. The majority of the high-$z$ candidates show flat to moderately steep radio spectra ($-1 \lesssim \alpha \lesssim 0$, with $f_\nu \propto \nu^\alpha$), while some also exhibit turnover radio spectra, demonstrating a broad diversity of radio spectral properties among the dropout-selected candidates. SED fitting yields typical AGN bolometric luminosities of $\log(L_{\rm bol}/{\rm erg\,s^{-1}})\sim46.5$–47.5. We also find that the comoving number density declines from the $g$-dropout to the $z$-dropout regimes, with substantial decreases toward higher redshift, suggesting fewer luminous radio AGN candidates toward reionization.
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All authors Youwen Kong, Kohei Ichikawa, Hisakazu Uchiyama, Yuxing Zhong, Xiaoyang Chen, Kotaro Kohno, Tohru Nagao, Kianhong Lee, Bovornpratch Vijarnwannaluk, Yoshiki Matsuoka, Yoshiki Toba, Itsna Khoirul Fitriana, Sakiko Obuchi, Yuta Ishikawa, Victor Kadri

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

Study of neutrinophilic low-mass dark matter mediated by pseudoscalar

Zhuo Zhang, Lian-Bao Jia and Reyes J.F. Eduardo

In this work, we investigate a neutrinophilic low-mass dark matter model mediated by a pseudoscalar particle. Since dark matter lacks Standard Model gauge charges, new interactions are required to connect it to the visible sector. Traditional indirect detection searches for annihilation products, such as cosmic rays, become ineffective when the annihilation predominantly yields invisible neutrinos. In our model, the present-day annihilation cross section into neutrinos (manifesting as a neutrino line) falls below current indirect detection limits. We therefore constrain the model using complementary probes: the Lyman-$\alpha$ forest, high-energy astrophysical neutrinos from active galactic nuclei and supernovae, direct detection via nucleon and electron scattering, and invisible Higgs decays. These observables provide stringent and multifaceted constraints on neutrinophilic dark matter interactions in the low-mass regime. Our results indicate that searches for the neutrino line from dark matter annihilations, neutrino self-interactions from supernovae and collider signatures, and invisible Higgs decays offer critical tests for the model's parameter space.
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Cosmology and Nongalactic Astrophysics

Bayesian Model Comparison of $R_h=ct$ versus $\Lambda$CDM using HII galaxy Hubble diagram

Yuva Himanshu Pallam and Shantanu Desai

We complement a recent analysis comparing $R_\mathrm{h}=ct$ with $\Lambda$CDM/$w$CDM using HII galaxies and giant extragalactic HII regions, by carrying out Bayesian model comparison. For this purpose, we calculate the Bayes factors for $R_\mathrm{h}=ct$ compared to flat $\Lambda$CDM/$w$CDM using the same dataset. When we use uniform priors on cosmological parameters, we find that the Bayes factors are close to 1, implying that $R_\mathrm{h}=ct$ is equally favored compared to $\Lambda$CDM/$w$CDM. However, when we use normal priors on cosmological parameters based on Planck cosmology, we find that $R_\mathrm{h}=ct$ is strongly favored over flat $\Lambda$CDM, while $R_\mathrm{h}=ct$ is marginally favored over flat $w$CDM.
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Astrophysics of Galaxies

Modeling the Accretion of High-Velocity Clouds from a Rotating Halo

Izumi Seno, Shu-ichiro Inutsuka and Jiro Shimoda

High-Velocity Clouds (HVCs) are a major fuel reservoir for star formation in the Galactic disk. Determining their origin and kinematics is thus crucial for understanding Galactic evolution. In this paper, we employ simple test-particle simulations to model HVC kinematics, generating line-of-sight velocity maps and probability density functions (PDFs) for comparison with observational results. We find that models assuming low angular momentum and an initial scale of tens of kiloparsecs (kpc) successfully reproduce the observed kinematic trends for both blue-shifted and red-shifted components. This consistency may support the dominance of intermediate-halo dynamics (tens of kpc scale) in regulating Galactic evolution, consistent with HVC formation via thermal instability in metal-polluted gas in the halo. Furthermore, by considering the entire bulk mass involved in the continuous accretion process – including diffuse or ionized components that often escape direct observation – our theoretical estimates yield a total mass accretion rate of several solar masses per year. This indicates that HVC accretion has the potential to supply a sufficient amount of gas to the Galactic disk to sustain ongoing star formation over several Gyr. Our findings suggest that the Galactic baryon cycle and disk evolution are governed by dynamics within the intermediate halo, providing key kinematic constraints for future magnetohydrodynamical simulations that resolve spatial structures of high velocity clouds.
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Cosmology and Nongalactic Astrophysics

Euclid preparation. Galaxy power spectrum and bispectrum modelling

Euclid Collaboration: K. Pardede, A. Eggemeier, D. Alkhanishvili et al. (+305 more)

Higher-order correlation functions of the large-scale galaxy distribution offer access to information beyond that contained in standard 2-point statistics such as the power spectrum. In this work we assess this potential for the $\textit{Euclid}$ mission using synthetic catalogues of H$\alpha$ galaxies based on the 54 $\, h^{-3} \, {\rm Gpc}^3$ Flagship I simulation, designed to reproduce the $\textit{Euclid}$ spectroscopic sample. We comprehensively validate the one-loop galaxy power spectrum and tree-level bispectrum predictions from perturbation theory in both real and redshift space. Assuming scale cuts consistent with our previous power spectrum study on the same catalogues, this modelling yields unbiased cosmological constraints for the bispectrum up to $k_{\rm max} = 0.15\,\, h \, {\rm Mpc}^{-1}$ in real space and $0.08 \, (0.1)\,\, h \, {\rm Mpc}^{-1}$ at the lowest (highest) redshift, corresponding to $z=0.9$ ($z=1.8$), for the monopole and quadrupole in redshift space using statistical uncertainties corresponding to the full simulation volume. With these scale cuts, adding bispectrum information to the power spectrum improves constraints on the amplitude of scalar perturbations and the matter density by up to 30 %, increasing the overall figure of merit for key cosmological parameters by a factor of about 2.5. Similar conclusions hold when statistical uncertainties are rescaled to a $\textit{Euclid}$-like volume, highlighting the importance of the bispectrum for fully exploiting the forthcoming $\textit{Euclid}$ data. Our analysis also provides the first detailed characterisation of the nonlinear bias model of H$\alpha$ emitters, showing that bias relations calibrated on low-resolution N-body simulations do not adequately describe the clustering of H$\alpha$ galaxies at low redshift, whereas excursion-set and co-evolution relations for tidal biases remain accurate.
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All authors Euclid Collaboration: K. Pardede, A. Eggemeier, D. Alkhanishvili, E. Sefusatti, A. Moradinezhad Dizgah, L. Christoph, A. Chudaykin, M. Kärcher, D. Linde, M. Marinucci, C. Porciani, A. Veropalumbo, M. Crocce, M. S. Cagliari, B. Camacho Quevedo, L. Castiblanco, E. Castorina, G. D'Amico, V. Desjacques, A. Farina, G. Gambardella, M. Guidi, F. Janssen, J. Lesgourgues, C. Moretti, A. Pezzotta, A. Pugno, J. Salvalaggio, B. Altieri, S. Andreon, N. Auricchio, M. Baldi, S. Bardelli, P. Battaglia, A. Biviano, M. Brescia, S. Camera, G. Cañas-Herrera, V. Capobianco, C. Carbone, V. F. Cardone, J. Carretero, S. Casas, M. Castellano, G. Castignani, S. Cavuoti, K. C. Chambers, A. Cimatti, C. Colodro-Conde, G. Congedo, C. J. Conselice, L. Conversi, Y. Copin, F. Courbin, H. M. Courtois, A. Da Silva, H. Degaudenzi, S. de la Torre, G. De Lucia, H. Dole, F. Dubath, X. Dupac, S. Escoffier, M. Farina, R. Farinelli, F. Faustini, S. Ferriol, F. Finelli, P. Fosalba, S. Fotopoulou, N. Fourmanoit, M. Frailis, E. Franceschi, M. Fumana, S. Galeotta, K. George, B. Gillis, C. Giocoli, J. Gracia-Carpio, A. Grazian, F. Grupp, S. V. H. Haugan, W. Holmes, F. Hormuth, A. Hornstrup, K. Jahnke, M. Jhabvala, B. Joachimi, S. Kermiche, A. Kiessling, B. Kubik, M. Kunz, H. Kurki-Suonio, A. M. C. Le Brun, S. Ligori, P. B. Lilje, V. Lindholm, I. Lloro, G. Mainetti, D. Maino, E. Maiorano, O. Mansutti, S. Marcin, O. Marggraf, K. Markovic, M. Martinelli, N. Martinet, F. Marulli, R. J. Massey, E. Medinaceli, S. Mei, M. Melchior, Y. Mellier, M. Meneghetti, E. Merlin, G. Meylan, A. Mora, M. Moresco, L. Moscardini, C. Neissner, S.-M. Niemi, J. W. Nightingale, C. Padilla, S. Paltani, F. Pasian, K. Pedersen, W. J. Percival, V. Pettorino, S. Pires, G. Polenta, M. Poncet, L. A. Popa, F. Raison, A. Renzi, J. Rhodes, G. Riccio, E. Romelli, M. Roncarelli, R. Saglia, Z. Sakr, A. G. Sánchez, D. Sapone, B. Sartoris, P. Schneider, A. Secroun, G. Seidel, S. Serrano, E. Sihvola, P. Simon, C. Sirignano, G. Sirri, A. Spurio Mancini, L. Stanco, J. Steinwagner, P. Tallada-Crespí, I. Tereno, N. Tessore, S. Toft, R. Toledo-Moreo, F. Torradeflot, I. Tutusaus, J. Valiviita, T. Vassallo, G. Verdoes Kleijn, Y. Wang, J. Weller, G. Zamorani, F. M. Zerbi, E. Zucca, V. Allevato, M. Ballardini, A. Boucaud, E. Bozzo, C. Burigana, R. Cabanac, M. Calabrese, A. Cappi, T. Castro, J. A. Escartin Vigo, L. Gabarra, J. García-Bellido, V. Gautard, S. Hemmati, J. Macias-Perez, R. Maoli, J. Martín-Fleitas, N. Mauri, R. B. Metcalf, P. Monaco, M. Pöntinen, I. Risso, V. Scottez, M. Sereno, M. Tenti, M. Tucci, M. Viel, M. Wiesmann, Y. Akrami, I. T. Andika, G. Angora, S. Anselmi, M. Archidiacono, F. Atrio-Barandela, E. Aubourg, L. Bazzanini, J. Bel, D. Bertacca, M. Bethermin, F. Beutler, A. Blanchard, L. Blot, M. Bonici, S. Borgani, M. L. Brown, S. Bruton, A. Calabro, F. Caro, C. S. Carvalho, F. Cogato, S. Conseil, A. R. Cooray, S. Davini, G. Desprez, A. Díaz-Sánchez, S. Di Domizio, J. M. Diego, V. Duret, M. Y. Elkhashab, A. Enia, Y. Fang, A. Finoguenov, A. Fontana, F. Fontanot, A. Franco, K. Ganga, T. Gasparetto, E. Gaztanaga, F. Giacomini, F. Gianotti, G. Gozaliasl, A. Gruppuso, C. M. Gutierrez, A. Hall, C. Hernández-Monteagudo, H. Hildebrandt, J. Hjorth, J. J. E. Kajava, Y. Kang, V. Kansal, D. Karagiannis, K. Kiiveri, J. Kim, C. C. Kirkpatrick, S. Kruk, M. Lattanzi, L. Legrand, M. Lembo, F. Lepori, G. Leroy, G. F. Lesci, T. I. Liaudat, S. J. Liu, M. Magliocchetti, C. J. A. P. Martins, L. Maurin, M. Miluzio, G. Morgante, S. Nadathur, K. Naidoo, P. Natoli, A. Navarro-Alsina, S. Nesseris, L. Pagano, D. Paoletti, F. Passalacqua, K. Paterson, L. Patrizii, R. Paviot, A. Pisani, D. Potter, G. W. Pratt, S. Quai, M. Radovich, K. Rojas, W. Roster, S. Sacquegna, M. Sahlén, D. B. Sanders, E. Sarpa, A. Schneider, D. Sciotti, E. Sellentin, L. C. Smith, J. G. Sorce, K. Tanidis, C. Tao, F. Tarsitano, G. Testera, R. Teyssier, S. Tosi, A. Troja, D. Vergani, F. Vernizzi, G. Verza, P. Vielzeuf, S. Vinciguerra, N. A. Walton, A. H. Wright

Astrophysics of Galaxies

A Wide and Deep Exploration of Radio-detected Active Galactic Nuclei with Subaru HSC (WERGS). XII. Final Optical Identification of VLASS Radio Sources from the Subaru/HSC-SSP Wide Survey Over 1200 deg$^2$

Hisakazu Uchiyama, Kohei Ichikawa, Youwen Kong et al. (+11 more)

We present a wide-area and deep optical identification catalog for radio sources based on the VLASS Epoch 2 catalog at 3 GHz. Optical counterparts are identified using the final-year internal processing of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) Wide layer (DR S23B), which provides deep imaging over ~1200 deg$^2$ in $grizy$ with $i$-band depth of $i_\mathrm{AB}\sim26$. Starting from a 1.0 arcsec nearest-neighbor match between VLASS and HSC, we construct a quality-controlled primary catalog (Clean VLASS-HSC) of 22,773 sources by requiring S/N$>5$ in at least one HSC band. We further provide ancillary nearest-neighbor associations to FIRST (1.4 GHz) and LoTSS DR3 (150 MHz) within 2.5 arcsec, resulting in 18,444 FIRST-matched sources, 16,167 LoTSS-matched sources, and a 14,206-source subset matched to both surveys. The catalog contains approximately six times more optically identified radio sources than the first WERGS optical-identification effort based on the early HSC-SSP S16B data and positional cross-matching with FIRST (Yamashita et al. 2018). The VLASS Epoch 2 resolution yields more precise optical associations (median 0.199 arcsec) and, together with uniform FIRST/LoTSS matches, enables robust multi-frequency radio SED constraints. Compared to UNIONS-based VLASS identifications (Zhong et al. 2025), the deeper HSC imaging improves sensitivity to optically faint and even morphologically resolved hosts at $z\gtrsim1$. Our catalog preferentially highlights host-dominated AGN candidates, potentially including a substantial fraction of obscured systems.
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All authors Hisakazu Uchiyama, Kohei Ichikawa, Youwen Kong, Yuxing Zhong, Xiaoyang Chen, Tohru Nagao, Kianhong Lee, Kotaro Kohno, Bovornpratch Vijarnwannaluk, Masayuki Akiyama, Yen-Ting Lin, Yoshiki Toba, Sakiko Obuchi, Itsna Khoirul Fitriana

High Energy Astrophysical Phenomena

The Environmental Effects on Inspiraling Binary Black Hole Systems in the Centers of the LMC and M31

Meng Xu, Zhijin Li, Xiao Guo et al. (+1 more)

Binary black hole (BBH) systems residing in the centers of galaxies evolve within complex astrophysical environments. These environments, comprising dark matter (DM) halos and baryonic accretion disks, can significantly alter the orbital dynamics of the binaries and their resulting gravitational wave (GW) emission. In this study, we investigate the dynamical evolution and GW waveforms of BBH systems embedded in the centers of the Large Magellanic Cloud (LMC) and the Andromeda Galaxy (M31). We construct a comprehensive analytical framework that jointly incorporates GW radiation reaction, DM spike effects (including dynamical friction and accretion, derived from the Navarro-Frenk-White profile), and accretion disk perturbations. Using this framework, we track the long-term evolution of the binary's semi-latus rectum $p$ and orbital eccentricity $e$. Our simulations reveal that the coexistence of a DM spike and an accretion disk significantly accelerates the inspiral process compared to pure DM or vacuum scenarios. Crucially, to assess the observability of these environmental effects, we calculate the Signal-to-Noise Ratio (SNR) and waveform Mismatch for future Pulsar Timing Arrays (PTAs). Our analysis demonstrates that these systems can achieve robust detectability thresholds ($\text{SNR} \ge 8$) within specific parameter spaces. Furthermore, the substantial Mismatch (reaching $\sim 0.7$ over a 20-year observation in the LMC scenario) indicates that the phase deviations induced by these environmental effects are highly distinguishable from vacuum templates. These findings predict the prospect of using future GW detections to probe complex galactic environments.
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All authors Meng Xu, Zhijin Li, Xiao Guo, Yun-Long Zhang

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

Secular evolution of orbital parameters for general bound orbits in Kerr spacetime

Norichika Sago, Ryuichi Fujita, Soichiro Isoyama et al. (+1 more)

We analytically derive the secular changes of the orbital parameters, i.e., energy, angular momentum, and Carter constant, for general bound orbits in Kerr spacetime, at leading order in the mass ratio, through the 6th post-Newtonian (6PN) order and the 16th order in orbital eccentricity. We validate the formulas against high-precision numerical Teukolsky results and quantify how eccentricity affects both the achievable accuracy and the PN convergence. We then construct and test a simple “hybrid” approximation that combines different PN and eccentricity truncations to retain accuracy at reduced computational cost. We also assess the performance of exponential resummation at higher PN orders. These results provide building blocks for fast, (analytic) adiabatic inspiral and waveform models for extreme mass ratio inspirals relevant to space-based detectors such as the Laser Interferometer Space Antenna (LISA).
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All authors Norichika Sago, Ryuichi Fujita, Soichiro Isoyama, Hiroyuki Nakano

Sunday 29 March

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

Cherenkov plasmons emission by primordial neutrinos

Maxim Dvornikov

We study the emission of Cherenkov plasmons by the gas of neutrinos with a nonzero temperature and a chemical potential. The background plasma, consisting of charged leptons, is taken to be nonrelativistic. The energy emission rate is obtained for longitudinal plasmons. To get the neutrino emissivity we average quantum field theory matrix element over the distribution functions of incoming and outgoing particles. Our results are applied for the description of the cooling down of a neutrino cluster formed in the early universe. Such clusters can exist owing to the neutrino interaction with a hypothetical light scalar boson. Using particular cluster parameters, we demonstrate that the considered cooling mechanism is efficient for some clusters. We find the temperature range where the proposed cooling channel is valid. Some useful calculations of the polarization tensor, as well as the plasmon form factors and their dispersion relations are also provided.
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Instrumentation and Methods for Astrophysics

The Impact of Computing Data Centres Orbiting Earth

Geoffrey W. Marcy

Artificial intelligence is projected to increase U.S. data centre power demand beyond 100 gigawatt by 2035 and global demand toward 1 terrawatt. In response, companies and governments have proposed placing computing infrastructure in sun-synchronous low-Earth orbit, where continuous sunlight could supply electrical power. Generating 5 GW would require solar arrays 4 x 4 kilometers in size. Although technically feasible, such structures at roughly 500 km altitude would dramatically alter both the night and daytime sky. A 4 x 4 km array in low earth orbit would span about 0.4 degrees, comparable to the Moon, and reflected sunlight would make it shine at magnitude g = -5 to -7 mag, 100 times brighter than the brightest stars. Dozens of these structures would appear as a north-to-south chain of industrial objects across the sky, visible for about 1 1/2 hours after sunset and 1 1/2 hours before sunrise. They would block stars, planets, and deep-sky objects for minutes at a time, while increasing the likelihood of collisions that could trigger runaway debris production. These orbiting computing facilities therefore pose serious astronomical, technical, and cultural concerns.
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High Energy Astrophysical Phenomena · Cross-listed from hep-ph

Rotation of the polarization plane in axion fields: application to neutron star polar cap regions

Iver H. Brevik, Moshe M. Chaichian, Tiberiu Harko et al. (+1 more)

We study observable manifestations of an axion field, focusing on possible polarizational effects for electromagnetic wave propagating in such a special magnetoelectric medium. The corresponding analysis is based on a geometric model of the Casimir type, in the framework of which the rotation angle of the polarization plane is derived to the lowest order. The results obtained are discussed for astrophysical conditions of a neutron star, where an existence of a locally inhomogeneous axion region is predicted in the polar cap.
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All authors Iver H. Brevik, Moshe M. Chaichian, Tiberiu Harko, Yuri N. Obukhov

High Energy Astrophysical Phenomena

Similar ratios of rise timescale to decline timescale of optical light curves in common tidal disruption events

Zhang XueGuang

Totally similar physical process in tidal disruption events (TDEs) basically indicates that there should be potential parameter to distinguish variability properties of TDEs from the other transient events having different physical processes. Here, we try to report such a parameter, the timescale ratio $R_{2/1,rd}$ of rise timescale $t_{1/2,r}$ (from half-max to maximum) to decline timescale $t_{1/2,d}$ (from maximum to half-max), especially based on the 34 optical TDEs with reported $t_{1/2,r}$ and $t_{1/2,d}$. Among the 34 optical TDEs, AT2020wey is an outlier with $R_{2/1,rd}\sim2.7$ which is 4.5 times larger than the mean value 0.6 of the other optical TDEs. However, after considering similar but more flexible model functions, the re-determined $R_{2/1,rd}$ is $\sim$0.9 in AT2020wey, totally similar as the values of the other optical TDEs. Therefore, the parameter $R_{1/2,rd}\sim0.6$ could be a potential classification parameter for optical TDEs. Furthermore, $R_{1/2,rd}$ have been checked in the unique optical transients of AT2019avd, PS1-10adi, SDSS J0946+3512 and J2334+1457. We can find that the second flare with $R_{1/2,rd}\sim11$ in AT2019avd should be very different from the other optical TDEs, but PS1-10adi, SDSS J0946+3512, J2334+1457 and the first flare in AT2019avd should be similar as the other optical TDEs. In the near future, properties of $R_{1/2,rd}$ through large sample of optical transients could provide further clues to support whether $R_{1/2,rd}$ could be a better classification parameter to distinguish TDEs and the other transient events.
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Earth and Planetary Astrophysics · Cross-listed from cs.DC

jaxsgp4: GPU-accelerated mega-constellation propagation with batch parallelism

Charlotte Priestley and Will Handley

As the population of anthropogenic space objects transitions from sparse clusters to mega-constellations exceeding 100,000 satellites, traditional orbital propagation techniques face a critical bottleneck. Standard CPU-bound implementations of the Simplified General Perturbations 4 (SGP4) algorithm are less well suited to handle the requisite scale of collision avoidance and Space Situational Awareness (SSA) tasks. This paper introduces jaxsgp4, an open-source high-performance reimplementation of SGP4 utilising the JAX library. JAX has gained traction in the landscape of computational research, offering an easy mechanism for Just-In-Time (JIT) compilation, automatic vectorisation and automatic optimisation of code for CPU, GPU and TPU hardware modalities. By refactoring the algorithm into a pure functional paradigm, we leverage these transformations to execute massively parallel propagations on modern GPUs. We demonstrate that jaxsgp4 can propagate the entire Starlink constellation (9,341 satellites) each to 1,000 future time steps in under 4 ms on a single A100 GPU, representing a speedup of $1500\times$ over traditional C++ baselines. Furthermore, we argue that the use of 32-bit precision for SGP4 propagation tasks offers a principled trade-off, sacrificing negligible precision loss for a substantial gain in throughput on hardware accelerators.
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Solar and Stellar Astrophysics

On the collimation properties of jets with finite Poynting flux launched from Keplerian accretion discs

Thomas Jannaud, Jonathan Ferreira and Claudio Zanni

It is generally accepted that the launching of astrophysical jets requires a large-scale magnetic field threading a central object (black hole or star) and/or its surrounding accretion disc. However, the collimation mechanism far away from the central object has not yet been fully understood. In a previous work we investigated a mechanism in which the jet is self-collimated due to a dominant hoop stress. We ran numerical simulations in which a Jet-Emitting disc (JED) spans the entire lower computational boundary. Those were the first of their kind to showcase the steady recollimation shocks predicted by steady-state analytical studies of jets. However, the huge size of the JED prevented a complete study of the connection between the accelerating and asymptotic electric circuits, as well as the influence of the outer medium. We performed a set of axisymmetric ideal MagnetoHydroDynamics (MHD) non-relativistic jet simulations. In those, only the innermost region of the accretion disc is a jet-launching zone. The jets of finite radial extent in those simulations also produce steady recollimation shocks at large distances from the central object. Standing recollimation shocks are not a bias of self-similarity, but a generic feature of jets emitted from magnetized Keplerian accretion discs. They may produce observable features, such as a standing emission knots, a decrease of the rotation rate or a change in polarisation. We also recover previous results on the influence of external pressure on jet confinement, such as the relation between pressure profile and jet shape, and jet acceleration efficiency.
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High Energy Astrophysical Phenomena

The counterjet dominates the production of PeV photons from Cyg X-3

Andrzej A. Zdziarski, Anton Dmytriiev and Karri I. I. Koljonen

We study the physical mechanisms underlying the production of orbitally-modulated PeV photons from Cyg X-3, recently discovered by the LHAASO collaboration. Our key findings are as follows. Helium nuclei are accelerated in a compact and strongly magnetized region within the jet, but they then quickly advect downstream to regions with a weaker field, allowing them to diffuse out of the jet, where they produce pions in hadronic collisions with both the stellar photons and the stellar wind of the Wolf-Rayet donor. The optical depths across the binary are $\lesssim$1 for both types of interactions, implying that their rates are proportional to the column densities along the particle paths. Given the low viewing angle of Cyg X-3 ($i\approx26^\circ$–$28^\circ$), most of the observed photons are produced by the relativistic hadrons accelerated in the counterjet (for which the column densities toward the observer are much longer than for the jet). This also explains the peak of the phase-folded PeV photon flux to be on the opposite side of the superior conjunction than that for the (also orbitally-modulated) GeV photons, which are produced by collisions of relativistic electrons with stellar photons in the optically thick regime. This then implies that the GeV emission is produced in the approaching jet.
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High Energy Astrophysical Phenomena

Self-Consistent Modelling of Neutrino Production in Turbulent Black Hole Coronae

Sébastien Le Bihan, Martin Lemoine and Frank Rieger

Stochastic particle acceleration in magnetized turbulent plasmas has emerged as a key mechanism to explain multi-messenger signals from compact astrophysical environments. Self-consistent modelling remains challenging because it requires to treat simultaneously several non-linear kinetic processes, especially turbulence-driven acceleration and its feedback on the turbulent cascade, as well as the radiative and hadronic losses, including the reprocessing of electromagnetic radiation in radiatively dense environments. The present paper introduces the hybrid numerical code Turb-AM3 designed to this effect. This hybrid numerical code couples the state-of-the-art time-dependent lepto-hadronic radiative solver AM3 with a stochastic acceleration module that incorporates recent theoretical advances in turbulent acceleration and accounts for the dynamical damping of turbulence by accelerated particles. In the second part of the paper, we use this code to provide self-consistent time-dependent models of proton acceleration in the turbulent black hole corona of NGC~1068. We find that the IceCube neutrino signal is well reproduced for a standard set of physical parameters describing the black hole corona. The same template model accounts in a satisfactory way for IceCube observations of other active galactic nuclei. Furthermore, our exploration of parameter space allows us to predict detailed template spectral shapes for the TeV neutrino spectrum, which in turn help understand how future neutrino observations can constrain the properties of turbulent AGN coronae and the underlying acceleration mechanism. This Turb-AM3 framework provides a powerful tool to model multi-messenger emission in a broad variety of compact astrophysical environments.
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Astrophysics of Galaxies

Segmenting Superbubbles in a Simulated Multiphase Interstellar Medium using Computer Vision

Jing-Wen Chen, Alex S. Hill, Anna Ordog et al. (+2 more)

We developed a computer vision-based methodology to achieve precise 3D segmentation and tracking of superbubbles within magnetohydrodynamic simulations of the supernova-driven interstellar medium. Leveraging advanced 3D transformer models, our approach effectively captures the complex morphology and dynamic evolution of these astrophysical structures. To demonstrate the technique, we specifically focused on a superbubble exhibiting interesting interactions with its surrounding medium, driven by a series of successive supernova explosions. Our model successfully generated detailed 3D segmentation masks, enabling us to visualize and analyze the bubble's structural evolution over time. The results reveal insights into the superbubble's growth patterns, energy retention, and interactions with surrounding interstellar matter. This interdisciplinary approach not only enhances our understanding of superbubble dynamics but also offers a robust framework for investigating other complex phenomena in the cosmos.
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All authors Jing-Wen Chen, Alex S. Hill, Anna Ordog, Rebecca A. Booth, Mohamed S. Shehata

Earth and Planetary Astrophysics

Low-Energy Round-Trip Trajectories to Near-Earth Objects using Low Thrust

Alessandro Beolchi, Mauro Pontani, Kathleen Howell et al. (+3 more)

Near-Earth Objects (NEOs) are attractive exploration targets due to their accessibility, scientific value, and resources. Although trajectory design has revealed efficient pathways to these bodies, systematic strategies for Earth-NEO transfers, especially with low thrust, remain limited. This work presents a streamlined methodology that blends the Sun-Earth circular restricted three-body problem (CR3BP) with the heliocentric two-body problem (2BP) to design low-energy round-trip trajectories. The current planar implementation enables efficient large-scale exploration of near-Earth space. Three-body manifold trajectories and transit orbits provide natural pathways for Earth departure and return through the L1 and L2 libration points, while the 2BP framework identifies spacecraft-NEO encounters through intersections of their elliptical orbits. This hybrid structure supports generating large collections of round-trip trajectories without heavy optimization, enabling rapid preliminary mission design across broad NEO populations. Rendezvous and takeoff maneuvers are first modeled as impulsive, then translated into low-thrust arcs to improve propellant efficiency. Round-trip transfers are assembled by combining compatible outbound and inbound branches under simple mission constraints. This modular approach is well suited for complex mission architectures that conventional patched-conics methods cannot systematically uncover. Applied to a representative NEO population, the method yields a large ensemble of round-trip trajectories with low launch and return energies, broad temporal flexibility, and competitive rendezvous and departure impulses compared to existing 2BP solutions.
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All authors Alessandro Beolchi, Mauro Pontani, Kathleen Howell, Chiara Pozzi, Sean Swei, Elena Fantino

High Energy Astrophysical Phenomena

Toward More Realistic Machine-Learning Inference of the Dense-Matter Equation of State from Supernova Gravitational Waves

Almat Akhmetali, Y. Sultan Abylkairov, Marat Zaidyn et al. (+6 more)

Gravitational waves from core-collapse supernovae offer a unique probe of the equation of state (EOS) of dense nuclear matter. For rapidly rotating stars, previous machine-learning studies demonstrated promising EOS classification accuracy. However, these analyses relied on several simplifying assumptions. In this work, we relax three key assumptions. First, we include real detector noise. Second, we expand the analysis from a single progenitor model to four models spanning 12 to 40 solar masses, and for each mass we consider multiple rotational configurations, from slow to rapid. Third, we introduce uncertainty in the core bounce time of up to 20 ms, rather than assuming it is known precisely. We find that none of these effects significantly degrades EOS classification performance. Instead, the larger dataset associated with multiple progenitor models and noise realizations improves training and classification accuracy. This study is a step in a broader effort to progressively incorporate more realistic conditions into gravitational-wave inference for core-collapse supernovae.
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All authors Almat Akhmetali, Y. Sultan Abylkairov, Marat Zaidyn, Aknur Sakan, Alisher Zhunuskanov, Nurzhan Ussipov, José Antonio Font, Alejandro Torres-Forné, Ernazar Abdikamalov

Cosmology and Nongalactic Astrophysics

Avoiding recollapse in an open-AdS universe via a self-tuning-like mechanism

Yupeng Zhang, Shuxun Tian and Zhengxiang Li

We study whether an open FLRW universe with a negative cosmological constant can evade the eventual recollapse characteristic of an AdS-type universe. Within a power-law realization of Fab-Four theory, we solve the background equations numerically and analyze the asymptotic dynamics. For the representative branch and parameter choice studied here, we find that the scalar sector provides a self-tuning-like compensation for the negative {\Lambda}, while the curvature term remains unscreened. As a result, the universe can continue expanding instead of recollapsing. Instead, the universe evolves toward a curvature-dominated linear-expansion regime, a {\propto} t. To probe the underlying compensation mechanism, we further analyze an auxiliary zero-curvature subsystem using Poincaré compactification. In the {\Lambda}<0 domain, there exist background trajectories that approach a critical point at infinity. Near this point, the compensating scalar-{\Lambda} sector becomes stiff-like, w_{{\phi}+{\Lambda}} {\to} 1, so that the system effective energy density redshifts faster than curvature (w_k = -1/3). Although this auxiliary analysis does not cover the full curved cosmology, it is consistent with and qualitatively supports the numerical finding that the net {\phi}+{\Lambda} contribution becomes subdominant to curvature, thereby preventing recollapse despite {\Lambda}<0. This extends the application of the self-tuning mechanism to the AdS region and offers a possibility for the AdS Universe predicted by string theory to become a reality.
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