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Physics Astrophysics

astro-ph Watch Astrophysics

Tuesday 7 April

Cosmology and Nongalactic Astrophysics · Cross-listed from cs.DC

JZ-Tree: GPU friendly neighbour search and friends-of-friends with dual tree walks in JAX plus CUDA

Jens Stücker, Oliver Hahn, Lukas Winkler et al. (+2 more)

Algorithms based on spatial tree traversal are widely regarded as among the most efficient and flexible approaches for many problems in CPU-based high-performance computing (HPC). However, directly transferring these algorithms to GPU architectures often yields substantially smaller performance gains than expected in light of the high computational throughput of modern GPUs. The branching nature of tree algorithms leads to thread divergence and irregular memory access patterns – both of which may severely limit GPU performance. To address these challenges, we propose a Morton (z-order) 'plane-based tree hierarchy' that is specifically designed for GPU architectures. The resulting flattened data layout enables efficient dual-tree traversal with collaborative execution across thread groups, leading to highly coalesced memory access patterns. Based on this framework we present implementations of two important spatial algorithms – exact $k$-nearest neighbour search and friends-of-friends (FoF) clustering. For both cases, we observe more than an order-of-magnitude performance improvement over the closest competing GPU libraries for large problem sizes ($N \gtrsim 10^7$), together with strong scaling to distributed multi-GPU systems. We provide an open-source implementation, 'JZ-Tree' (JAX z-order tree), which serves as a foundation for efficient GPU implementations of a broad class of tree-based algorithms.
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All authors Jens Stücker, Oliver Hahn, Lukas Winkler, Adrian Gutierrez Adame, Thomas Flöss

Solar and Stellar Astrophysics

Comments on "The impact of Solar magnetic field configurations on the production of gamma rays at the Solar disk” (arXiv:2512.01403)

M.N. Mazziotta

In this short comment, I discuss the relationship between the results presented in arXiv:2512.01403 and those previously published in Phys.~Rev.~D~101,~083011~(2020). The 2020 study provides a full Monte Carlo simulation of cosmic-ray interactions with the solar atmosphere using the FLUKA code, including realistic solar-atmosphere models, PFSS/Parker/BIFROST magnetic-field configurations, and predictions for gamma rays, electrons, positrons, neutrons, and neutrinos. Given the substantial scientific overlap – particularly in the modelling of hadronic interactions, magnetic-field effects, cascade development, and comparison with Fermi-LAT observations – a direct comparison is relevant to assess consistency and complementarity. Here I summarize the main points of agreement, highlight differences in modeling assumptions, and outline how the two approaches can jointly contribute to understanding high-energy emission from the solar disk.
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Cosmology and Nongalactic Astrophysics

Probing the Evolution of Dark Energy: A Joint Analysis of DESI DR2, Pantheon+, and Cosmic Chronometers

Chanchal Kumari and Dinesh Kumar

We investigate several phenomenological dark energy parameterizations using a joint analysis of late-time cosmological observations, including cosmic-chromatometer measurements of the Hubble parameter, DESI DR2 baryon acoustic oscillation data, and the Pantheon+ Type Ia supernova sample. Our results show that allowing for a time-varying dark energy equation of state significantly improves the overall fit compared to $\Lambda$CDM. The present-day equation-of-state parameter departs from the standard cosmological constant value. In contrast, the evolution parameter in two-parameter models tends to be negative, indicating a possible time dependence of dark energy. However, the constraints on the evolution remain moderate, and current data cannot clearly distinguish the specific functional form of dark energy. Model comparison using information criteria suggests that dynamical dark energy models are favored over $\Lambda$CDM, with the most straightforward one-parameter extension emerging as the most parsimonious scenario. These findings indicate a mild preference for dark energy evolution, though future high-precision observations will be required for definitive conclusions.
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Instrumentation and Methods for Astrophysics · Cross-listed from physics.ins-det

Noise budget of Cryogenic sub-Hz cROss torsion bar detector with quantum NOn-demolition Speed meter (CHRONOS)

Mario Juvenal S. Onglao III, Hsiang-Yu Huang, Yuki Inoue et al. (+2 more)

CHRONOS is a proposed gravitational-wave detector designed to operate in the sub-Hz frequency range (0.1 to 10 Hz), a largely unexplored band due to strong noise sources that hamper ground-based detectors. It employs cryogenic operation, a cross torsion-bar configuration, a triangular Sagnac interferometer, and a speed meter readout scheme to overcome key noise limitations, targeting a strain sensitivity of $h \sim 10^{-18} Hz^{-1/2}$ around 2 Hz and a stochastic gravitational wave background of $\Omega_{GW}$ approximately $2 \times 10^{-3}$ at 2 Hz. Using analytical and interferometric simulations with FINESSE3, we evaluate the noise budget of CHRONOS and characterize the relative contributions of quantum, thermal, and environmental noise sources. Our results demonstrate that CHRONOS achieves competitive sensitivity at low frequencies. The feasibility of using CHRONOS in an earthquake early-warning system by detecting prompt gravity-gradient signals is also investigated, and is predicted to be faster by approximately 2.92 to 6.90 seconds within 40 km. These findings highlight the scientific potential of CHRONOS, bridging gravitational-wave astronomy and geophysical monitoring, and motivating further development of low-frequency detector technologies.
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All authors Mario Juvenal S. Onglao III, Hsiang-Yu Huang, Yuki Inoue, Vivek Kumar, Daiki Tanabe

Cosmology and Nongalactic Astrophysics

Diagnostic Consistency Tests of the Concordance Cosmology

S. M. Koksbang and A. Heinesen

The $\Lambda$CDM cosmological model faces increasingly significant and robust tensions among independent cosmological probes, prompting renewed scrutiny of its foundational assumptions. While General Relativity and the nature of dark energy are now routinely tested with cosmological surveys, less progress has been made testing the space-time geometry at the largest scales, and in particular testing the assumption that observables (distances, redshifs, expansion of space, etc.) on the largest scales are described by a single Friedmann-Lemaître-Robertson-Walker (FLRW) metric. In order to enable such tests, we introduce a model-independent framework that combines successive derivatives of the angular diameter distance, $d_A(z)$, with the line-of-sight expansion rate, $\mathcal{H}(z)$, to expose the physical content of well-known FLRW consistency relations. This allows us to perform diagnostic tests of the large-scale geometry, that are free of assumptions about dark energy and the theory of gravity on large scales. In addition, we derive a new nonparametric estimator for the cosmic density field that is independent of the Friedmann equations. This enables qualitatively new, observationally accessible tests of the FLRW framework and provides a stringent, model-independent diagnostic for departures from standard cosmology using current and forthcoming distance and expansion rate measurements.
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Cosmology and Nongalactic Astrophysics

Forward analytical model for the optical selection bias on galaxy cluster lensing profiles

M. Costanzi, H. Y. Wu, J. H. Esteves et al. (+3 more)

Cluster catalogs selected by optical properties are subject to selection biases, primarily arising from unresolved systems along the line of sight. These biases affect key observables for cluster cosmology, such as the lensing signal and clustering statistics. In this work, we present a fully predictive forward analytical model to quantify the impact of optical-selection bias due to projection effects on cluster density profiles. This is achieved by introducing a scale-dependent parametrization of the optical cluster bias, whose small- and large-scale behaviour is set by the amplitude of projection effects, and by expressing the two-halo component of the density profile in terms of the contributions from off-axis halos along the line of sight. As a case study, we consider a DES Y3-like cluster catalog and validate our model against simulated samples. Our model successfully captures the dependence of the two-halo component on richness boosts induced by projections, as well as its evolution with richness and redshift. It also recovers the overall bias in the projected density profile relative to a randomly selected sample with the same mass distribution. The framework presented here provides a consistent methodology for modeling the impact of line-of-sight structures on the observed richness and density profiles of optically selected clusters, directly linking selection biases to the underlying cosmology and survey specifications.
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All authors M. Costanzi, H. Y. Wu, J. H. Esteves, S. Grandis, C. To, M. Aguena

Cosmology and Nongalactic Astrophysics

Model-independent constraints on generalized FLRW consistency relations with bootstrap-based symbolic regression

S. M. Koksbang and A. Heinesen

The standard $\Lambda$CDM cosmological model faces increasing tensions between key observations, motivating tests that probe its underlying assumptions. In a companion letter, we present a model-independent framework that combines derivatives of the angular diameter distance, $d_A(z)$, and the line-of-sight expansion rate, $\mathcal{H}(z)$, to clarify the physical content of FLRW consistency relations and to construct a general-spacetime estimator of the cosmic density field. Here, we apply these tests to data, introducing a non-parametric reconstruction method based on symbolic regression combined with bootstrapping to provide data-driven uncertainty estimates. Using supernova and BAO data, we reconstruct $d_A$, $\mathcal{H}$, and their derivatives, enabling model-independent evaluation of FLRW relations and recovery of the sky-averaged density field over $z \in [0.38, \sim 2]$. Current data are too sparse to tightly constrain $\mathcal{H}(z)$, and the reconstructed density is consistent with both Planck and SH0ES $\Lambda$CDM. Reconstructed FLRW consistency tests show mild to moderate deviations from FLRW expectations at the $\sim 2$-$4\sigma$ level, although their significance depends on data selection and reconstruction stability. If these indicated deviations from an FLRW geometry are real, it would signify that most of the cosmological solutions considered for solving the cosmological tensions (evolving/interacting dark energy, new types of matter/energy, modified gravity, etc., within the FLRW framework) are ruled out. These preliminary indications highlight the importance of future, denser distance and expansion rate measurements, as well as further work toward standardizing uncertainty estimation for symbolic-regression reconstructions.
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High Energy Astrophysical Phenomena

Unveiling axion signals in galactic supernovae with future MeV telescopes

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

Axion-like particles (ALPs) produced via the Primakoff process in the cores of Galactic core-collapse supernovae (SNe) could convert into MeV-energy gamma-rays through interactions with the Milky Way's magnetic field. To evaluate the detection prospects for such signals, we perform sensitivity projections for next-generation MeV telescopes by combining hypothetical instrument responses with realistic background estimates. Our analysis incorporates detailed simulations of the expected ALP flux from nearby SNe, the energy-dependent conversion probability in Galactic magnetic fields, and the telescope's angular/energy resolution based on advanced detector designs. Background components are modeled using data from current MeV missions and extrapolated to future sensitivity regimes. Our simulations demonstrate that next-generation telescopes with improved effective areas and energy resolution could achieve sensitivity to photon-ALP couplings as low as gagamma approx 1.61 x 10^-13 GeV^-1 for ALP masses ma < 10^-9 eV in Galactic Center. These results indicate that future MeV missions will probe unexplored regions of ALP parameter space, with conservative estimates suggesting they could constrain gagamma values two orders of magnitude below current astrophysical limits. Such observations would provide the most stringent tests to date for axion-like particles as a dark matter candidate in the ultra-light mass regime.
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All authors Zhen Xie, Jiahao Liu, Bing Liu, Ruizhi Yang

High Energy Astrophysical Phenomena

Strontium and helium in the kilonova AT2017gfo: Origin of the 1{\mu}m feature constrained via NLTE calculations

Aayush Arya, Rasmus Damgaard, Albert Sneppen et al. (+4 more)

Mergers of neutron stars are believed to be one of the primary sites for the synthesis of the universe's heavy elements via the rapid neutron capture process. AT2017gfo, the kilonova following GW170817 provided the first direct spectroscopic evidence of the $r$-process happening in the universe. A prominent line feature near $1\,\mu$m in its spectrum was attributed to strontium – a claim that has been independently recovered by several teams. However, in recent years it has been debated whether the feature arises instead from helium. Here, we present non–local thermodynamic equilibrium (NLTE) radiative transfer modelling of the observed kilonova spectra, including detailed radiation-matter interaction physics for both strontium and helium. We make use of freshly calculated strontium atomic data for e$^-$ impact collisions, photoionization, and recombination processes. Our strontium model self-consistently reproduces the temporal evolution of the $1\,\mu$m feature at early times, with its absence at $0.92\,$days to its clear emergence at $1.17\,$days. This transition mimics LTE, because at early epochs ($t\lesssim 1.5\,$days) the radiation field dominates the ionization state of the ejecta over thermal and non-thermal electron collisions. We further test if helium can form the feature under the same plasma conditions. The helium mass required at $1.17\,$days is comparable to the total ejecta mass, while a few percent by mass of helium suffices at 4.4 days. On the other hand, the strength of the strontium lines decrease with time, and may require a radially stratified abundance to consistently produce the feature. We conclude that strontium is required to explain the onset of the feature at early times, but helium can contribute to, or even dominate the feature at later epochs.
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All authors Aayush Arya, Rasmus Damgaard, Albert Sneppen, David J. Dougan, Stuart A. Sim, Connor P. Ballance, Darach Watson

Astrophysics of Galaxies · Cross-listed from physics.chem-ph

Valence and Rydberg excited state bond dissociation curves of CO2 from orbital-optimized density functional calculations

Darío Barreiro-Lage, Gianluca Levi, Hannes Jonssón et al. (+1 more)

Calculations of the lowest valence {\pi}* as well as the 3s and higher energy 3p{\sigma} Rydberg excited states of the CO2 molecule are carried out using density functionals with variational optimization of the orbitals, an approach involving relatively little computational effort. Five functionals with varying degree of exchange are used in combination with real or complex-valued orbitals that are optimized by finding saddle points on the electronic energy surface corresponding to the excited states. When the PBE functional is used in combination with complex orbitals, the calculated excitation energy is found to be within 0.3 eV of multireference configuration interaction reference values, and the results are further improved with hybrid functionals. In contrast, linear-response time-dependent density functional theory calculations give errors up to 1.9 eV for the most diffuse 3p{\sigma} excitation and exhibit stronger dependence on both the excitation character and the functional used. Calculated C-O dissociation curves using the PBE functional and the orbital-optimized approach compare remarkably well with the reported multireference configuration interaction and equation-of-motion coupled-cluster singles and doubles calculations. Thanks to the low computational cost, these results demonstrate that orbital-optimized density functional calculations can be a promising route for modelling photorelaxation in condensed-phase CO2, for example in the context of interstellar cosmic-ray radiation driven process involving high-energy Rydberg states.
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All authors Darío Barreiro-Lage, Gianluca Levi, Hannes Jonssón, Thanja Lamberts

Instrumentation and Methods for Astrophysics

Instrumental development for Cryogenic sub-Hz cROss torsion bar detector with quantum NOn-demolition Speed meter (CHRONOS)

Daiki Tanabe, Hsiang-Yu Huang, Yuki Inoue et al. (+2 more)

Gravitational waves from intermediate-mass black-hole (IMBH) binaries is a probe of strong-field gravity and black-hole evolution. Detection of IMBH is challenging because of their typically low frequency where the seismic noise, radiation pressure noise, and thermal noise dominate. The Cryogenic sub-Hz cROss torsion bar detector with quantum NOn-demolition Speed meter (CHRONOS) has been proposed to reach a strain sensitivity of $10^{-18} {\rm Hz}^{-1/2}$ at 2 Hz. It aims to detect GW from IMBH mergers with the mass of $\mathcal{O}(10^4)$ M$_{\odot}$ and to explore stochastic gravitational background of $\Omega_{\rm GW} \sim 2\times 10^{-3}$ at 2 Hz. We present the overview of the CHRONOS hardware which is designed to integrate key techniques for improving low frequency sensitivity; torsion bar, speed meter, and cryogenic mirror. As a demonstration of the interferometer operation, we also report the commissioning status of a Michelson interferometer in National Central University in Taiwan which has been assembled as a partial component of CHRONOS.
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All authors Daiki Tanabe, Hsiang-Yu Huang, Yuki Inoue, Mario Juvenal S. Onglao III, Ta-Chun Yu

Solar and Stellar Astrophysics · Cross-listed from physics.plasm-ph

Modeling complex plasma instabilities in space plasmas - Three-component electron formalism of heat-flux instabilities

Dustin L. Schröder, Marian Lazar, Horst Fichtner et al. (+2 more)

Despite the fact that electrons observed in situ in space plasmas have three major components-the quasi-thermal core, suprathermal halo, and strahl-the analysis of instabilities triggered by kinetic, velocity-space anisotropies (such as relative drifts and temperature anisotropy) generally considers only two. We demonstrate that realistic modeling with all three components is achievable in the present analysis focusing on heat-flux instabilities. In the absence of particle collisions, these instabilities regulate the heat flux carried mainly by suprathermal electrons. The velocity distributions were modeled according to in situ observations, with a Maxwellian core and Kappa-distributed halo and strahl. We exploited advanced numerical codes capable of solving the linear dispersion and stability properties of plasma systems with Maxwellian and Kappa distributions. The unstable solutions differ significantly from those obtained with simplified two-component models (such as core-strahl or core-beam). The growth rates predict the excitation and interplay of two unstable modes, whistler and/or firehose heat-flux instabilities. The numerical solver 'ALPS' was successfully applied to systems with regularized Kappa distributions, for which analytical derivation of dispersion relations is not straightforward. The two instabilities are triggered by the relative drifts, core-strahl and halo-strahl, and may have new consequences for heat-flux regulation. Particularly important are cases when the core-strahl instability is in competition with the instability driven by the halo-strahl drift, as well as when the two instabilities have the same nature and accumulate. Future studies are motivated to confirm these predictions in quasilinear theories and numerical simulations.
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All authors Dustin L. Schröder, Marian Lazar, Horst Fichtner, Rodrigo A. López, Stefaan Poedts

High Energy Astrophysical Phenomena

Non-LTE Ionization Modeling for Helium and Strontium in Neutron Star Merger Ejecta

Koya Chiba, Masaomi Tanaka, Shinya Wanajo et al. (+3 more)

The material ejected from a binary neutron star merger produces "kilonova," a radioactively powered emission at ultraviolet, optical, and infrared wavelengths. The early-phase spectra of the kilonova AT2017gfo, following the gravitational wave event GW170817, exhibit a strong absorption feature around $1\,\mathrm{\mu m}$. Helium (He) and strontium (Sr) have been proposed as the candidate elements contributing to this feature. However, due to the lack of consistent modeling including these two elements simultaneously, the exact contributions of each element to this feature remain unclear. In this study, we develop non-local thermodynamic equilibrium ionization models for He and Sr that take into account ionization by high-energy electrons, and estimate the abundances of each element required to reproduce the observed feature in the early-phase spectra of AT2017gfo. Our modeling indicates that about $1\, \%$ of He or $1\mathrm{-}10\, \%$ of Sr in mass fraction are present in the ejecta moving at $v \sim 0.15 \, c$. This Sr mass fraction nicely agrees with the mass fraction in the solar $r$-process pattern. Based on comparison with nucleosynthesis calculations, our constraints suggest that $r$-process nucleosynthesis in GW170817 occurs at relatively low electron fraction ($Y_{\rm e} \lesssim 0.35$) and low entropy ($s \lesssim 30 \, k_\mathrm{B}/\mathrm{nucleon}$) conditions. Generally, for $Y_{\rm e} \lesssim 0.15$, the observed feature can be reproduced by He at the mass fraction expected from the $\alpha$-decay of trans-Pb nuclei, and may therefore serve as an indirect signature for the production of elements beyond the third $r$-process peak in binary neutron star mergers.
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All authors Koya Chiba, Masaomi Tanaka, Shinya Wanajo, Sho Fujibayashi, Kyohei Kawaguchi, Kenta Hotokezaka

Astrophysics of Galaxies

Stellar Population Characterisations in nearby, dusty Early-Type Galaxies

Ron W. Savage, Anne E. Sansom and David H. W. Glass

Dust in Early-Type galaxies (ETGs) may originate from internal or external sources. In this paper we study the stellar populations of particularly dusty ETGs to search for evidence of the dust's origin. Using the Southern African Large Telescope (SALT), we obtained long-slit optical spectra within the effective radius (R_e), along the major axis of 15 nearby ETGs, selected from the GAMA and Herschel-ATLAS surveys for their high levels of interstellar dust. Using full spectrum fitting and Lick index fitting we analysed their major axis kinematics and stellar population characteristics. We used stellar population models from the newly developed sMILES library and from the empirical MILES library. Kinematic results show that most of our sample of dusty ETGs are rotationally supported and there are no detectable kinematic discontinuities. 12 of our sample of 15 dusty ETGs show evidence of young/intermediate age stellar population components suggesting ongoing/recent star formation. Using simulations, we show that these recent ($\approx$1~Gyr) populations are not artefacts of the fitting process or data. As a check with a control sample we use stacked SDSS spectra and find that dusty ETGs show a component with intermediate age, whereas non-dusty ETGs do not. Age, metallicity and $\alpha$-element abundance ratio increase with increasing central velocity dispersion in the SALT spectra, as seen in previous studies of ETGs, but with larger scatter in our sample. Given our stellar population findings, we discuss formation scenarios that might cause or rule out a high dust/molecular gas content.
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Astrophysics of Galaxies

Higher resolution optical spectra of $M_*<10^{10}~M_{\odot}$ galaxies reveal outflow signatures unresolved by the SDSS

B. Hagedorn, C. Cicone, C. Vignali et al. (+5 more)

Galactic outflows are predicted to be ubiquitous in low-mass galaxies, but observational evidence is lacking. Both a low signal-to-noise and a low spectral resolution can severely hamper the detection of galactic outflows, especially in small galaxies that have intrinsically narrow spectral lines. We obtained new, medium-high resolution (FWHM$_\mathrm{inst}\sim50-110$~km/s) optical spectra of 52 local star forming galaxies ($0.01 < z < 0.03$) with stellar masses $10^{8.5}<M_*/[M_{\odot}]<10^{10}$, using the TNG/DOLORES and NTT/EFOSC2 instruments. Our parent sample consists of SDSS galaxies with available heterodyne single-dish molecular (i.e., CO) line data. The targets of this study are selected among those that, based on the comparison between CO line widths, SDSS spectral resolution, and corresponding SDSS-based H$\alpha$ line widths, have a high chance of being unresolved by SDSS spectroscopy. Our new, spectra reveal overall narrower H$\alpha$ and [OIII]$\lambda5007$ lines, with signs of asymmetries and broad wings that are absent in the SDSS spectra of the same galaxies. This confirms that SDSS spectroscopy does not resolve the narrow emission lines of low-M$_*$ galaxies, which hinders the detection of outflows. We identify outflow signatures in $\sim30\%$ of our targets based on the H$\alpha$ line spectra. Assuming a typical bi-conical outflow geometry, this detection rate is consistent with theoretical predictions of ubiquitous outflows in the low-mass regime. The outflow incidence is enhanced ($\sim60\%$) for galaxies with above average star formation rates for the sample (SFR $>10^{-0.74}~\mathrm{M_{\odot}/yr}$). We estimate ionized gas mass outflow rates ranging from $\sim0.1-50\times10^{-3}~\mathrm{M_{\odot}/yr}$ (mean $\sim20\times10^{-3}~\mathrm{M_{\odot}/yr}$) and corresponding mass loading factors between 0.03 and 0.14 (mean $\sim0.07$) for the sample.
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All authors B. Hagedorn, C. Cicone, C. Vignali, P. Severgnini, M. Pedani, M. Sarzi, A. Saintonge, M. Romano

Astrophysics of Galaxies · Cross-listed from gr-qc

Twisted doughnuts: Thick disk torus around equatorial asymmetric black hole

Che-Yu Chen, Eva Hackmann and Audrey Trova

The Kerr black hole spacetime is symmetric with respect to a well-defined equatorial plane. When such a symmetry is broken, for instance, by some putative effects beyond general relativity, the Keplerian circular orbits around the black hole are distorted vertically away from the equatorial plane by an amount depending on the orbital radius. As a result, the Keplerian thin disk acquires a curved surface. In this work, we extend such results to thick tori configurations by considering non-self-gravitating Polish doughnut models. We show that due to the equatorial asymmetry of the spacetime, the centers and the cusps of tori are distorted away from the original equatorial plane toward the same direction as that experienced by the stable Keplerian orbits, and the entire tori configurations are twisted toward that direction as well. The shape of the distorted tori is demonstrated explicitly using a constant specific angular momentum profile $\ell(r,y)=\ell_0$ of the disk fluid. However, the result also applies to non-constant profiles of $\ell(r,y)$ generically in the sense that any asymmetric profile of $\ell(r,y)$ that attempts to produce a symmetric tori configuration either turns out to be ill-defined near the equatorial plane or suffers from fine-tuning issues.
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Astrophysics of Galaxies

The Sinking Statistics of Dark Matter Subhalos Across Hierarchical Levels

Wenkang Jiang, Jiaxin Han, Kun Xu et al. (+6 more)

We investigate the mergers among subhalos in a $\Lambda$CDM simulation, focusing on two fundamental aspects overlooked by previous studies: 1) how to identify mergers robustly; 2) the statistics of mergers across the subhalo hierarchy. To this end, we make use of the HBT+ subhalo finder that tracks subhalo evolution across hierarchy levels, identifying the coalescence of subhalo cores in phase space as a "sinking" event. This coalescence marks a distinct stalled phase in orbital decay, providing a physically motivated and natural definition of a resolved merger. Moreover, the phase transition occurs over a very short timescale, making the statistics robust to numerical resolutions. Our main findings are as follows. (1) More than 90% of sinking events occur between adjacent subhalo levels, while cross-level pathways arise from tidal stripping, group accretion, and numerical constraints. (2) Resolved sinking events are predominantly major mergers (mass ratios > 1/10), whereas the contribution from minor mergers decreases with the dynamical age of the host halo. (3) Although deep-level subhalos typically have low mass ratios relative to the host halo, their mass ratios relative to their direct parents are substantially larger, significantly enhancing their sinking probability. Consequently, the satellite-satellite sinking rate can rival or even exceed the central-satellite sinking rate at lower mass thresholds. (4) Satellite-satellite sinking events are spatially biased toward the outer regions of the host halo, suggesting that the central tidal field suppresses orbital decay between satellite systems.
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All authors Wenkang Jiang, Jiaxin Han, Kun Xu, Victor J. Forouhar Moreno, Feihong He, Zhaozhou Li, Chunyan Jiang, Yipeng Jing, Xiaohu Yang

High Energy Astrophysical Phenomena

Extreme Blazars Observed with MAGIC: Second Catalog Release

K. Abe, S. Abe, J. Abhir et al. (+353 more)

Extremely high-peaked BL Lac objects - also named extreme blazars - are among the most energetic and persistent extragalactic accelerators in the Universe, defined by a synchrotron emission peaking above $10^{17}$ Hz in X-rays. Such emission is then reprocessed and produces radiation extending deeply into very-high-energy (VHE, energy E>100 GeV) gamma rays. Observations in this energy band - optimally investigated by the Imaging Air-Shower Cherenkov telescopes - are crucial for probing the physical processes that drive their extreme behavior. This study extends our investigation of extreme blazars in the VHE gamma-ray range, providing a second new mini-catalog of sources observed by the MAGIC telescopes. We report on the monitoring of seven targets between 2017 and 2025, including four newly observed sources and three that have been part of long-term observation campaigns, for a total of approximately 338 hours of observations. The analysis of MAGIC data reveals two new VHE detections of extreme blazars, along with three additional sources showing hints of VHE emission. Joint observations of MAGIC and the first Large-Sized Telescope (LST-1) also confirmed a new VHE extreme blazar. Our results are complemented by simultaneous multiwavelength observations in other energy bands, including optical-UV, X-rays, and high-energy gamma rays (100 MeV<E<100 GeV). We confirm typical behavior of extreme blazars, such as a modest variability and a “harder-when-brighter” trend in X-rays across the sample. This new set increases the population of extreme blazars and their broadband analysis confirms the physical properties of these extreme sources.
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All authors K. Abe, S. Abe, J. Abhir, A. Abhishek, V. A. Acciari, F. Acero, A. Aguasca-Cabot, I. Agudo, C. Alispach, D. Ambrosino, F. Ambrosino, T. Aniello, S. Ansoldi, L. A. Antonelli, C. Aramo, A. Arbet-Engels, C. Arcaro, T.T.H. Arnesen, P. Aubert, A. Babić, C. Bakshi, A. Baktash, M. Balbo, A. Bamba, A. Baquero Larriva, U. Barres de Almeida, J. A. Barrio, L. Barrios Jiménez, I. Batkovic, J. Baxter, J. Becerra González, W. Bednarek, E. Bernardini, J. Bernete, A. Berti, C. Bigongiari, A. Biland, E. Bissaldi, O. Blanch, G. Bonnoli, P. Bordas, Ž. Bošnjak, A. Briscioli, E. Bronzini, G. Brunelli, J. Buces, A. Bulgarelli, I. Burelli, L. Burmistrov, A. Campoy-Ordaz, M. Cardillo, S. Caroff, A. Carosi, R. Carosi, R. Carraro, M. Carretero-Castrillo, F. Cassol, A. J. Castro-Tirado, D. Cerasole, G. Ceribella, A. Cerviño Cortínez, Y. Chai, G. Chon, L. Chytka, G. M. Cicciari, A. Cifuentes Santos, J. L. Contreras, J. Cortina, S. Covino, H. Costantini, M. Croisonnier, M. Dalchenko, G. D'Amico, P. Da Vela, F. Dazzi, A. De Angelis, M. de Bony de Lavergne, R. Del Burgo, M. Delfino, C. Delgado, J. Delgado Mengual, D. della Volpe, B. De Lotto, L. Del Peral, R. de Menezes, G. De Palma, V. de Souza, C. Díaz, L. Di Bella, A. Di Piano, F. Di Pierro, R. Di Tria, L. Di Venere, A. Dinesh, D. Dominis Prester, A. Donini, D. Dorner, M. Doro, L. Eisenberger, D. Elsässer, G. Emery, L. Feligioni, J. Escudero, L. Fariña, F. Ferrarotto, A. Fiasson, L. Foffano, L. Font, F. Frías García-Lago, S. Fröse, Y. Fukazawa, S. Gallozzi, R. Garcia López, S. Garcia Soto, C. Gasbarra, D. Gasparrini, S. Gasparyan, M. Gaug, J. Giesbrecht Paiva, N. Giglietto, F. Giordano, P. Gliwny, N. Godinovic, T. Gradetzke, R. Grau, J. Green, G. Grolleron, S. Gunji, P. Günther, J. Hackfeld, D. Hadasch, A. Hahn, G. Harutyunyan, M. Hashizume, T. Hassan, K. Hayashi, L. Heckmann, M. Heller, J. Herrera Llorente, N. Hiroshima, D. Hoffmann, D. Horns, J. Houles, D. Hrupec, R. Imazawa, T. Inada, S. Inoue, K. Ioka, M. Iori, D. Israyelyan, T. Itokawa, A. Iuliano, J. Jahanvi, I. Jimenez Martinez, J. Jimenez Quiles, I. Jorge Rodrigo, J. Jormanainen, J. Jurysek, M. Kagaya, S. Kankkunen, V. Karas, H. Katagiri, T. Kayanoki, D. Kerszberg, T. Kiyomoto, G. W. Kluge, Y. Kobayashi, K. Kohri, J. Konrad, P. Kornecki, P. M. Kouch, G. Koziol, H. Kubo, J. Kushida, B. Lacave, M. Lainez, A. Lamastra, L. Lemoigne, E. Lindfors, M. Linhoff, S. Lombardi, F. Longo, R. López-Coto, M. López-Moya, A. López-Oramas, S. Loporchio, J. Lozano Bahilo, F. Lucarelli, H. Luciani, L. Lulić, P. L. Luque-Escamilla, E. Lyard, P. Majumdar, M. Makariev, M. Mallamaci, D. Mandat, G. Maneva, M. Manganaro, S. Mangano, K. Mannheim, S. Marchesi, F. Marini, M. Mariotti, P. Marquez, G. Marsella, J. Martí, D. Martin, O. Martinez, G. Martínez, M. Martínez, M. Massa, P. Maruševec, D. Mazin, S. Menchiari, J. Méndez-Gallego, S. Menon, E. Mestre Guillen, D. Miceli, T. Miener, J. M. Miranda, R. Mirzoyan, M. Molero Gonzalez, E. Molina, H. A. Mondal, T. Montaruli, A. Moralejo, A. Morselli, V. Moya, A. L. Müller, H. Muraishi, S. Nagataki, T. Nakamori, C. Nanci, A. Negro, A. Neronov, V. Neustroev, D. Nieto Castaño, M. Nievas Rosillo, C. Nigro, L. Nikolic, K. Noda, V. Novotny, S. Nozaki, M. Ohishi, A. Okumura, R. Orito, L. Orsini, J. Otero-Santos, P. Ottanelli, S. Paiano, M. Palatiello, G. Panebianco, D. Paneque, R. Paoletti, J. M. Paredes, M. Pech, M. Pecimotika, M. Peresano, F. Perrotta, M. Persic, F. Pfeifle, M. Pihet, G. Pirola, C. Plard, F. Podobnik, M. Polo, C. Pozo-Gonzaléz, P. G. Prada Moroni, E. Prandini, S. Rainò, R. Rando, W. Rhode, M. Ribó, J. Rico, G. Rodriguez Fer dez, M. D. Rodríguez Frías, A. Roy, A. Ruina, E. Ruiz-Velasco, N. Sahakyan, T. Saito, S. Sakurai, D. A. Sanchez, H. Sano, E. Santos Moura, T. Šarić, Y. Sato, F. G. Saturni, V. Savchenko, F. Schiavone, K. Schmitz, F. Schmuckermaier, F. Schussler, T. Schweizer, M. Seglar Arroyo, A. Sciaccaluga, G. Silvestri, A. Simongini, J. Sitarek, V. Sliusar, I. Sofia, D. Sobczynska, A. Stamerra, J. Strišković, D. Strom, M. Strzys, Y. Suda, A. Sunny, H. Tajima, M. Takahashi, R. Takeishi, S. J. Tanaka, D. Tateishi, T. Tavernier, P. Temnikov, Y. Terada, K. Terauchi, T. Terzic, M. Teshima, M. Tluczykont, T. Tomura, D. F. Torres, F. Tramonti, P. Travnicek, G. Tripodo, A. Tutone, S. Ubach, M. Vacula, M. Vázquez Acosta, S. Ventura, G. Verna, I. Viale, A. Viana, A. Vigliano, C. F. Vigorito, E. Visentin, V. Vitale, G. Voutsinas, I. Vovk, T. Vuillaume, R. Walter, C. Walther, F. Wersig, M. Will, T. Yamamoto, R. Yamazaki, Y. Yao, P. K. H. Yeung, T. Yoshida, T. Yoshikoshi, W. Zhang, N. Zywucka, F. D'Ammando, V. Fallah Ramazani, D. Linder, F. Wierda

Earth and Planetary Astrophysics

Investigation of Transit Timing and an Optical Transmission Spectrum of the Hot Jupiter WASP-11 b

Napaporn A-thano, Supachai Awiphan, Eamonn Kerins et al. (+15 more)

WASP-11~b/HAT-P-10~b is an inflated hot Jupiter, which has a low density that makes it a good target for atmospheric studies using the transmission spectroscopy technique. In this work, we present 31 new transit light curves of WASP-11~b/HAT-P-10~b, obtained through the SPEARNET network. These data were analyzed along with previously published ground-based observations and space-based data from TESS. We refine the planetary parameters of WASP-11~b/HAT-P-10~b and perform a transit timing analysis using data spanning 16 years. The updated ($O-C$) diagram shows no significant evidence of orbital decay. The TTV analysis reveals no significant signals indicative of additional planets. Atmospheric analysis using multi-band optical observations indicates a strong Rayleigh scattering slope in the transmission spectra, which may originate from the planetary atmosphere itself or be influenced by contamination such as stellar activity or light from the companion star.
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All authors Napaporn A-thano, Supachai Awiphan, Eamonn Kerins, Akshay Priyadarshi, Iain McDonald, Orarik Tasuya, Ronnakrit Rattanamala, Ing-Guey Jiang, Yogesh C. Joshi, Fan Yang, Ida Janiak, Patcharawee Munsaket, Yasir Abdul Qadir, Smanchan Chandaiam, Boonyarit Choonhakit, Suwanit Wutsang, Boonrucksar Soonthornthum, Vik S Dhillon

Astrophysics of Galaxies

What can galaxy clustering really tell us about the galaxy-halo connections?

Xiaoju Xu, Xiaohu Yang, Zhongxu Zhai et al. (+6 more)

Subhalo abundance matching (SHAM) is a commonly used framework for modeling the galaxy-halo connection. Yet, its standard implementation has difficulty reproducing the observed galaxy clustering with high accuracy (e.g., $\chi^2/\mathrm{dof} \approx 1$). To overcome this issue, we propose a novel CS-SHAM framework, in which central and satellite galaxies are independently matched to main and satellite subhalos in simulations. Within this scheme, we introduce three free parameters to explicitly characterize the satellite fraction, $f_{\mathrm{sat}}$, as a function of stellar mass or absolute magnitude. To evaluate the performance of CS-SHAM, we apply it to two sets of mock galaxy catalogs built with the conventional SHAM method but using different subhalo mass proxies, $M_{\mathrm{peak}}$ and $V_{\mathrm{peak}}$, as well as two additional galaxy samples generated from a SAM and from TNG-300. We demonstrate that CS-SHAM reliably reproduces galaxy clustering whether $M_{\mathrm{peak}}$ or $V_{\mathrm{peak}}$ is used as the subhalo mass proxy. We also find that the models are unable to place robust constraints on $f_{\mathrm{sat}}$ if different mass proxies are employed. Indeed, within the CS-SHAM framework the halo occupation distribution (HOD) and conditional luminosity or stellar mass function (CLF/CSMF) are accurately recovered. Furthermore, we demonstrate for the first time that galaxy clustering constrains the HOD and CLF/CSMF primarily for relatively massive halos. Because the halo bias is nearly constant for low-mass halos, galaxy clustering is generally not very sensitive to the satellite population residing in these low-mass systems.
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All authors Xiaoju Xu, Xiaohu Yang, Zhongxu Zhai, Yiyang Guo, Yizhou Gu, Yirong Wang, Jiaxin Han, Zhenlin Tan, Junde Li

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

Cosmological collider signals of modular spontaneous CP breaking

Shuntaro Aoki and Alessandro Strumia

We consider a modular-invariant extension of the Standard Model. Assuming that the modulus is the inflaton, the CP-violating phases of the Yukawa couplings evolve during inflation. This dynamics favours a Higgs condensate, so that Standard Model fermions mediate a one-loop cosmological collider signal enhanced by chemical potentials. The effect appears too small for next-generation experiments. We provide precise expressions for Dirac fermions with chemical potentials in de Sitter.
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Astrophysics of Galaxies

WALLABY pilot survey: HI depletion times within the stellar discs of nearby galaxies

Seona Lee, Barbara Catinella, Tobias Westmeier et al. (+12 more)

Neutral atomic hydrogen (HI) reservoirs typically extend far beyond the inner star-forming regions of galaxies, and global HI measurements, which mix these distinct environments, limit our understanding of the gas-star formation cycle. In particular, global HI depletion times combine gas and star formation from different physical scales, contributing to long measured timescales (5-9 Gyr) and large scatter compared to molecular gas. Using 841 gas-rich galaxies from the Widefield ASKAP L-band Legacy All-sky Blind Survey (WALLABY) pilot observations, we investigate how HI depletion time and its scaling relations change when HI and star formation are both confined to the stellar disc (R25, the isophotal radius at 25 mag arcsec-2 in i-band). We find that depletion times within this region are on average 1.4 Gyr shorter than global values, though some remain very long, indicating that a substantial fraction of HI remains inactive for star formation. HI depletion times anti-correlate strongly with stellar surface density, and this trend becomes even tighter within the stellar disc. The Kennicutt-Schmidt relation further reveals an almost constant HI depletion time at fixed stellar surface density, similar to the behaviour seen for molecular gas, suggesting that HI and star formation are regulated by conditions that enable HI-to-H2 conversion, traced by stellar surface density. Beyond the stellar disc, HI depletion times are on average almost 10 Gyr longer than within R25, confirming extremely inefficient star formation in low-density outer regions. These results highlight the critical role of spatial location and local conditions for HI to serve as a fuel for star formation.
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All authors Seona Lee, Barbara Catinella, Tobias Westmeier, Luca Cortese, Lister Staveley-Smith, Federico Lelli, O. Ivy Wong, Yago Ascasibar, Alessandro Boselli, Toby Brown, Nathan Deg, Akhil Krishna R., Denis Leahy, Syed F. Rahman, Jonghwan Rhee

High Energy Astrophysical Phenomena

Remnant recoil and host environments of GWTC-4.0 binary black-hole mergers

Joan Llobera-Querol, Eleanor Hamilton, Neha Singh et al. (+8 more)

Determining the astrophysical origin of binary black holes and whether merger remnants are retained in their birth environments is essential for understanding hierarchical mergers and the growth of intermediate-mass black holes. We identified gravitational-wave events most consistent with dense-cluster origin and assessed whether their merger remnants are retained in globular clusters, nuclear star clusters, or galactic potentials. We considered 84 events consistent with binary-black-hole mergers from the first part of the fourth observing run (O4a) of the LIGO-Virgo-KAGRA detector network, and 3 selected events from the second part (O4b). We compared parameter-estimation posteriors with synthetic population models for field and cluster binaries using Bayes factors, accounting for the relative abundances of these formation channels. We computed recoil-velocity posteriors for all events using the IMRPhenomXPNR waveform model. We identified five events whose intrinsic parameters show preference for the adopted dense-cluster models over the considered field-binary populations, including the most massive O4a event GW231123_135430, while finding no robust preference for a dense-cluster origin for the high-spinning O4b event GW241011_233834. Typical recoil velocities are a few hundred km/s, with extended high-velocity tails. These kicks suggest merger remnants are likely ejected from typical globular clusters, while retention in nuclear star clusters remains possible but not guaranteed. Within the adopted models, efficient hierarchical growth may be challenging in typical globular clusters, whereas nuclear star clusters remain viable environments for repeated mergers. Although results depend on the adopted population models, this analysis highlights the importance of improved population models and higher-quality detections enabled by future GW detectors.
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All authors Joan Llobera-Querol, Eleanor Hamilton, Neha Singh, Marta Colleoni, Felip A. Ramis Vidal, Abbas Askar, Tomasz Bulik, Aleksandra Olejak, Sascha Husa, Yumeng Xu, Jorge Valencia

Solar and Stellar Astrophysics

Searching for Contact Binaries with LAMOST and TESS

Ting Wu, Jin-Zhong Liu, Senyu Qi et al. (+4 more)

Contact binaries (CBs) serve as fundamental laboratories for studying complex stellar interactions, including mass transfer, tidal effects, and angular momentum loss. In this work, we search for CB with high-precision light curves from the Transiting Exoplanet Survey Satellite (TESS) and large radial-velocity variation from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). We derive a sample of 1,281 CB candidates, among which 266 are newly reported. Our sample with both high-precision photometry and medium-resolution spectra may provide new constraints on the physical scales, luminosity calibration, and population distribution of CBs, offering valuable insights into their evolutionary role within the stellar population.
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All authors Ting Wu, Jin-Zhong Liu, Senyu Qi, Zhi-Xiang Zhang, Hubiao Niu, Ali Esamdin, Wei-Min Gu

Astrophysics of Galaxies

One sightline, many systems: a FLASH discovery of HI towards scintillating quasar PKS 0405-385

E.F. Kerrison, H. Yoon, E.M. Sadler et al. (+15 more)

We report the discovery of an intervening 21\,cm absorption line at z = 0.882 towards the z = 1.284 quasar PKS 0405-385, identified in the First Large Absorption Survey in HI (FLASH). This quasar once displayed the most rapid known intraday variability at radio frequencies, from which it earned the title of `the smallest radio quasar'. Although its size was revised upwards soon after based on updated scattering theory, PKS 0405-385 remains an important probe of Galactic plasma, and now also of intervening gas discovered through HI absorption. We present new long-slit spectroscopy spanning both PKS 0405-385 and the candidate host of the intervening HI gas. We identify MgII and FeII absorption lines in this spectrum consistent with the redshift of the intervening HI, as well as two additional, independent metal-line systems at z = 0.907 and z = 0.966, but we cannot accurately pinpoint the host(s) of this intervening gas in current data. We revisit the radio variability of PKS 0405-385 in light of advances in scintillation theory, as well as extended monitoring with the Australia Telescope Compact Array and the Australian SKA Pathfinder, and find a revised linear size >0.3 pc, but no new evidence of repeating intraday variability.
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All authors E.F. Kerrison, H. Yoon, E.M. Sadler, Y. Kang, P.G. Edwards, A. Tuntsov, J.P. Pritchard, V.A. Moss, E.K. Mahony, H. Bignall, J.N.H.S. Aditya, J.R. Allison, S. Curran, R.D. Ekers, M. Glowacki, J. Stevens, R. Su, M. Whiting

High Energy Astrophysical Phenomena

Multiquark clustering in neutron-star matter from color-spin molecular dynamics

Nobutoshi Yasutake, Yuta Mukobara, Aaron Park et al. (+2 more)

We study the equation of state of neutron-star matter with color-spin molecular dynamics. The calculation includes the internal color and spin degrees of freedom and their time evolution. The matter composition, including strangeness under $\beta$ equilibrium, is determined by energy minimization. We find two main trends. First, within the present color-spin molecular dynamics framework and under the adopted clustering criterion along the stable neutron-star branch, isolated quarklike configurations do not appear; instead, color-magnetic interactions favor the self-consistent formation of multiquark clusters. Within the same criterion, the cluster-size distribution is concentrated at quark numbers that are multiples of three, corresponding to integer baryon numbers. Second, relative to the conventional no-$K^*$ baseline, the interaction between strange and light quarks has a strong impact on neutron-star radii. This suggests that future radius measurements, together with phenomenological information on the strangeness-onset density, may help constrain flavor-sector interactions involving strangeness.
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All authors Nobutoshi Yasutake, Yuta Mukobara, Aaron Park, Su Houng Lee, Toshiki Maruyama

Astrophysics of Galaxies

Galactic-scale evolution of classical and complex radio galaxies. Impact of ambient morphology and jet geometry

Gourab Giri, Prajnadipt Ghosh, Ravi Joshi et al. (+9 more)

Extragalactic jets exhibit a wide range of propagation orientations relative to the host galaxy's principal axis. This study investigate the spatiotemporal evolution of jets as a function of their propagation direction within their triaxial hosts-introducing varying degrees of environmental hindrance-and as a function of internal jet properties (while maintaining identical jet power)-introducing varying collimation and thrust. Observational data on extended radio sources are re-analyzed to identify key traits arising from variations in jet orientation and intrinsic properties. These findings are then systematically tested using a suite of 3D RMHD simulations. When a jet propagates along host's major axis (path of maximal environmental resistance), it produces an X-shaped morphology with secondary lobe aligns along the minor axis, co-evolving actively alongside the active jet. At intermediate angles to the major axis, the jet morphology transitions into a double-boomerang structure with notably curved lobes. Such lobes are interestingly regenerative through both backflow and jet precession mechanisms, making it difficult to disentangle their origin. Jets propagating along the minor axis (path of minimal resistance) exhibit faster propagation, forming classical double-lobed sources. With increased thrust and improved collimation (keeping jet power constant), these jets advance even more rapidly, potentially evolving into giant radio galaxy candidates. Counterexample sources that deviate from these traits were also modeled. The spatial variation of internal turbulence shows significant fluctuations below 1 kpc, with stronger magnetic fields further suppressing these irregularities. Magnetic field plays a key role in the radiative appearance of these sources, modulating features like missing or one-sided (wing) lobe emission, filamentary structures, and warmspot versus hotspot formation.
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All authors Gourab Giri, Prajnadipt Ghosh, Ravi Joshi, Anderson Caproni, Paola Rossi, Gianluigi Bodo, Sayan Kundu, Kshitij Thorat, Swarna Chatterjee, Dario Borgogno, Valerio Vittorini, Marco Tavani

Cosmology and Nongalactic Astrophysics

Reconstructing a large-scale matter-density contrast profile to reconcile Pantheon+ supernovae with DESI DR2 BAO in an inhomogeneous universe

Toshifumi Futamase, Reiki Kojima and Masanori Tomonaga

The Hubble parameters measured by the DESI DR2 BAO observations show a significant discrepancy from the prediction of the standard cosmological model. This discrepancy, together with the long-discussed Hubble tension, may originate from large-scale inhomogeneities in the matter distribution. This interpretation is motivated by infrared galaxy surveys, which suggest that our galaxy resides within the $\sim300$ Mpc under-dense region known as the KBC void. In this study, we apply a linear order relation – relating the horizon-scale Hubble parameter inferred from CMB observations and the local-scale Hubble parameter – to the Pantheon+ Type Ia supernovae and the DESI DR2 BAO data. We show that a simple inhomogeneous cosmological model consisting of eight top-hat shells can consistently explain the Hubble parameters inferred from both observations. Based on the matter-density distribution, we also briefly discuss its possible impact on cosmological observables, including the magnitude–redshift relation, the kinematic Sunyaev–Zel'dovich effect, and the integrated Sachs–Wolfe effect.
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High Energy Astrophysical Phenomena

The NANOGrav 15 yr and 20 yr Datasets: Timing Events and Pulse Shape Changes

Ben Jacobson-Bell, James M. Cordes, Shami Chatterjee et al. (+61 more)

The average pulse shape of a pulsar is typically stable over decadal timescales, enabling estimation of pulse times of arrival to better than a small fraction of the pulse width using matched filtering techniques. However, in North American Nanohertz Observatory for Gravitational Waves (NANOGrav) observations of PSR J1713+0747, three discrete timing events that depart from the prevailing timing model have been seen in the last 20 yr. All three correspond to morphological changes in pulse shape. Using principal component analysis, we analyze the pulse profiles of nine NANOGrav pulsars, including seven with profiles from the 15 yr dataset and two with additional profiles from the forthcoming 20 yr dataset. We recover the three known pulse shape change events in PSR J1713+0747 and another previously known event in PSR J1643$-$1224. We implement a ranking metric for candidate events and address four highly ranked candidates in this nine-pulsar sample. We also recover known slow pulse shape variations in PSR J1643$-$1224, PSR J1903+0327, and PSR B1937+21 and report an unexpected recurrence after ~10 yr of one such variation in PSR B1937+21.
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All authors Ben Jacobson-Bell, James M. Cordes, Shami Chatterjee, Sashabaw Niedbalski, Gabriella Agazie, Akash Anumarlapudi, Anne M. Archibald, Zaven Arzoumanian, Jeremy G. Baier, Paul T. Baker, Paul R. Brook, H. Thankful Cromartie, Kathryn Crowter, Megan E. DeCesar, Paul B. Demorest, Lankeswar Dey, Timothy Dolch, Elizabeth C. Ferrara, William Fiore, Emmanuel Fonseca, Gabriel E. Freedman, Nate Garver-Daniels, Peter A. Gentile, Joseph Glaser, Deborah C. Good, Jeffrey S. Hazboun, Ross J. Jennings, Megan L. Jones, David L. Kaplan, Matthew Kerr, Michael T. Lam, Bjorn Larsen, Duncan R. Lorimer, Georgia A. Lowes, Jing Luo, Ryan S. Lynch, Ashley Martsen, Alexander McEwen, Maura A. McLaughlin, Natasha McMann, Bradley W. Meyers, Patrick M. Meyers, Cherry Ng, Mason Ng, David J. Nice, Shania Nichols, Daniel J. Oliver, Timothy T. Pennucci, Benetge B. P. Perera, Nihan S. Pol, Henri A. Radovan, Scott M. Ransom, Paul S. Ray, Alexander Saffer, Ann Schmiedekamp, Carl Schmiedekamp, Brent J. Shapiro-Albert, Ingrid H. Stairs, Kevin Stovall, Abhimanyu Susobhanan, Joseph K. Swiggum, Mercedes S. Thompson, Amir Tresnjic, Haley M. Wahl

High Energy Astrophysical Phenomena

Reconstruction of fast-rotating neutron star observables with the neural network

Wen Liu, Lingxiao Wang and Zhenyu Zhu

Rotation can significantly affect neutron-star (NS) properties, but accurate modeling of rapidly rotating NSs requires solving a two-dimensional, axially symmetric system, making traditional calculations too expensive for inference analyses that demand a large amount of model evaluations. We develop a causal convolutional neural networks that preserve the chronological-like dependence of NS properties on the equation of state (EoS) and rapidly reconstruct observables for static, Keplerian, and rotating configurations. Using RNS, we generate a dataset of NS observables and use it to train our networks. We validate our networks with three representative EoS (SFHo, SLy4, and DD2) and find that the they accurately reproduce the RNS results. The trained networks evaluate NS configurations for a single EoS in $\sim 50$ms, providing a substantial speedup over typical RNS runtimes of $\sim 30$ min and enabling efficient inference analyses involving rapidly rotating NSs.
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