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Physics Astrophysics

astro-ph Watch Astrophysics

Saturday 13 December

Earth and Planetary Astrophysics

Measuring the Collisional Evolution of Debris Clusters in an Asteroid System

Yutian Wu, Xiaojing Zhang, Chenyang Huang et al. (+1 more)

Context. Rotational instability of rubble-pile asteroids can trigger mass shedding, forming transient debris clouds that may provide the initial conditions for secondary formation in binary systems. Aims. We investigate the dynamical and collisional evolution of a debris cloud numerically generated around a Didymos-like progenitor, as a representative case for the early formation of Dimorphos. The analysis focuses on the growth and structural properties of clusters composed of centimetre- to decimetre-scale particles. Methods. We perform full-scale simulations of debris evolution around a near-critically rotating asteroid using a cross-spatial-scale approach combined with the discrete element method (DEM). To overcome computational timescale limitations, an equivalent cluster-scale simulation framework is introduced to capture the essential collisional growth processes efficiently. These simulations quantify the efficiency of cluster growth and the structural evoution within the debris cloud. Results. Our simulations reveal that particles shed from a rotationally unstable asteroid exhibit a consistent migration pattern toward low-geopotential regions, which governs the mass distribution and dynamical structure of the debris cloud. The collisional velocity are well described by a Weibull distribution (lambda = 0.0642, k = 1.8349), where low-velocity impacts favor accretion. These collisions enable clusters to grow from centimeter-decimeter scales to meter-sized bodies, developing compact, moderately porous structures (Delta I \approx 0.8, phi \approx 0.52). Collisions between meter-sized clusters do not exhibit a bouncing barrier: low-velocity impacts yield Dinkinesh-like shapes, while moderate velocities promote plastic merging and continued growth.
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All authors Yutian Wu, Xiaojing Zhang, Chenyang Huang, Yang Yu

Solar and Stellar Astrophysics

Solar-cycle variations in meridional flows and rotational shear within the Sun's near-surface shear layer

Anisha Sen, S.P. Rajaguru, Abhinav Govindan Iyer et al. (+3 more)

Using solar-cycle long helioseismic measurements of meridional and zonal flows in the near-surface shear layer (NSSL) of the Sun, we study their spatio-temporal variations and connections to active regions. We find that near-surface inflows towards active latitudes are part of a local circulation with an outflow away from them at depths around 0.97 R, which is also the location where the deviations in the radial gradient of rotation change sign. These results, together with opposite-signed changes over latitude and depth in the above quantities observed during the solar minimum period, point to the action of the Coriolis force on large-scale flows as the primary cause of changes in the rotation gradient within the NSSL. We also find that such Coriolis force-mediated changes in near-surface flows towards active latitudes only marginally change the amplitude of zonal flow and hence are not likely to be its driving force. Our measurements typically achieve a high signal-to-noise ratio ($>$5$\sigma$) for near-surface flows but can drop to 3$\sigma$ near the base (0.95 R) of the NSSL. Close agreements between the depth profiles of changes in rotation gradient and in meridional flows measured from quite different global and local helioseismic techniques, respectively, show that the results are not dependent on the analysis techniques.
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All authors Anisha Sen, S.P. Rajaguru, Abhinav Govindan Iyer, Ruizhu Chen, Junwei Zhao, Shukur Kholikov

Solar and Stellar Astrophysics

A multi-viewpoint comparison of the velocity field of coronal propagating disturbances

Nina Stankovic, Huw Morgan, Marilena Mierla et al. (+3 more)

Small-scale propagating disturbances (PD) are ubiquitous in the solar corona. Time-Normalised Optical Flow (TNOF) is a method developed for mapping PD velocity fields in time series of Extreme-Ultraviolet (EUV) images. We show PD velocity fields of a quiet Sun (QS) region containing a small coronal hole (CH) and filament channel (FC) jointly observed by Extreme Ultraviolet Imager (EUI) aboard the Solar Orbiter and Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO). The QS observations acquired on 28 October 2023 in 174A channel of High Resolution EUV Imager (HRIEUV) of EUI and 171A channel of AIA are used. During the time of the observations, the separation angle between Solar Orbiter and SDO was approximately 26\de. A novel image alignment analysis shows that the dominant formation heights are 11.4Mm for HRIEUV and 4Mm for AIA. Despite this height difference, the PD velocity fields obtained from the observations from the two instruments are in good agreement across the region. In the QS the median PD speed is around 6.7 and 7.4\kms\ for HRIEUV and AIA respectively, with maximum speeds of around 40\kms. The small equatorial CH is a region dominated by a low temperature of $\approx$0.8MK and is host to high PD speeds, with a median speed of 17\kms. The velocity field bridges coherently across the CH from neighbouring QS regions from east to west, thus the CH must be overlaid by a system of long, low-lying closed magnetic loops. This unexpected configuration is supported by a potential field (PF) magnetic model and may be due to the longevity of the CH, allowing time for interchange reconnection with neighbouring closed-field regions. The FC is observed to be multithermal, with a narrow central strip of high emission at both low (0.8MK) and high (2.5MK) temperatures and low emission at warm (1.2MK) temperature. The FC has PD speeds similar to those of the QS.
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All authors Nina Stankovic, Huw Morgan, Marilena Mierla, Nancy Narang, Luciano Rodriguez, David Berghmans

Solar and Stellar Astrophysics

Hemispheric Magnetic Asymmetry and Cross-Equatorial Circulation Cells within the Sun's Near-Surface Shear Layer

Anisha Sen, S.P. Rajaguru, Ruizhu Chen et al. (+2 more)

Using time-distance helioseismic measurements of meridional flow in the near-surface shear layer over a period of 14 years, starting from May 2010, we probe the depth structure and evolution of its cross-equatorial part. We confirm that the hemispheric magnetic asymmetry determines the amplitude and direction of such flows. Additionally, we find that these flows turn over and change direction at depths below 0.97R, forming circulation cells with lifetimes dictated again by the hemispheric magnetic imbalance, which is dominated by the occurrences of large sunspots. We also examine connections between cross-equatorial magnetic flux plumes and the flows, and discuss their implications for the equatorial flux cancellation/submergence and the poleward transport of flux.
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All authors Anisha Sen, S.P. Rajaguru, Ruizhu Chen, Junwei Zhao, Shukur Kholikov

Cosmology and Nongalactic Astrophysics

Recovering Subtle Cosmological Information with the Zel'dovich-inspired Transform

Yun Wang, Hao-Ran Yu, Yu Yu et al. (+1 more)

Extracting cosmological information from nonlinear and non-Gaussian large-scale structure remains a major challenge. We introduce the Zel'dovich-inspired (ZI) transform, a simple one-parameter local nonlinear transform in which $\eta$ controls the weighting of higher-order information in the transformed density field. For $\eta\geq3$, the transform can substantially suppress gravitational non-Gaussianity. Using real-space matter density fields from the Quijote suite and Fisher analysis, we find that the joint data vector of three transformed-field power spectra with $\{\eta=\infty, 6, 3\}$, denoted $P_\mathrm{ZI}$, reduces marginalized errors for all parameters considered. The improvements range from several-fold for some $\Lambda$CDM parameters to factors of 290 for local primordial non-Gaussianity and 107 for the summed neutrino mass. Tests on independent fiducial simulations yield nearly unbiased parameter estimates. Compared with other state-of-the-art summary statistics, $P_\mathrm{ZI}$ provides tighter cosmological constraints.
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All authors Yun Wang, Hao-Ran Yu, Yu Yu, Ping He

High Energy Astrophysical Phenomena

The Effect of a Self-bound Equation of State on the Structure of Rotating Compact Stars

Andreas Konstantinou

This paper investigates how a self bound equation of state (EOS), which describes strange quark stars, affects the rotational properties of compact stars, focusing on deviations from universal relations governing gravitational mass and radius changes due to rotation. The analysis reveals significant deviations in stars with higher surface-to-center total energy-density ratios, $\frac{\epsilon_s}{\epsilon_c+c^2P_c}$, challenging the established universal relations. For Newtonian stars, hydrostatic equilibrium ensures that the difference between the gravitational potential at the center, $\Phi_c$, and at the poles, $\Phi_p$, remains constant within sequences of rotating neutron stars characterized by the same central and polar specific enthalpy ($\Phi_c - \Phi_p = -h_c +h_p$). Combined with the scaling $\Phi \propto R_e^2$, where $R_e$ denotes the equatorial radius, this condition naturally leads to a quasi-universal behavior in the rotational change of radius within these sequences. Similarly, in general relativistic stars, the hydrostatic equilibrium maintains that $\Phi^{GR}_{p} - \Phi^{GR}_{c}$ remains unchanged within these sequences, where $\Phi^{GR}$ is one of the metric potentials. Inspired by this theoretical framework, a toy model has been developed to capture the dependence of gravitational mass and radius deviations on the surface-to-central total energy density ratio. Subsequently, an improved set of empirical universal relations has been proposed, for accurately modeling rapidly rotating compact stars with self-bound EOSs.
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High Energy Astrophysical Phenomena

NICER Magnetar Burst Catalog

Che-Yen Chu, Chin-Ping Hu, Teruaki Enoto et al. (+13 more)

In this paper, we present a comprehensive catalog of short bursts from magnetars based on eight years of NICER observations. A total of 1130 bursts were identified from 14 sources, with the sample dominated by SGR 1935+2154, which accounts for 76% of all detected bursts. We analyzed burst durations, spectral properties, and their correlations across multiple sources. Bursts from SGR 1935+2154 exhibit significantly longer durations, with a distribution peak at 316 ms, compared to a peak of 23 ms for bursts from other magnetars. Two {\mu}s-scale bursts were detected for the first time, originating from 1E 1048.1-5937 and CXOU J010043.1-721134. Spectral analysis in the 0.5-8 keV range using both blackbody and power-law models shows that bursts with higher fluences have harder spectra. In contrast, correlations between burst duration and spectral parameters are weak or absent. This catalog provides a valuable dataset for studying magnetar short bursts, enabling future modeling efforts and improving our understanding of the diversity and physical mechanisms of magnetar bursts.
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All authors Che-Yen Chu, Chin-Ping Hu, Teruaki Enoto, George A. Younes, Andrea Sanna, Sebastien Guillot, Rachael Stewart, Zaven Arzoumanian, Matthew G. Baring, Marlon L. Bause, Tolga Güver, Wynn C. G. Ho, Chryssa Kouveliotou, Alex Van Kooten, Zorawar Wadiasingh, Keith C. Gendreau

Solar and Stellar Astrophysics

X-ray properties of RR Lyrae and Cepheid variables from eROSITA

Krystian Ilkiewicz and Henryka Netzel

We present a search for X-ray counterparts to RR Lyrae and Cepheid variables using data from the first eROSITA all-sky survey. We identify seven RR Lyrae and eight Cepheid variables with positional matches to X-ray sources. While most Cepheid associations appear reliable, the RR Lyrae matches are predominantly spurious. Only one source, OGLE-BLG-RRLYR-00252, appears to be a plausible RR Lyrae detection, potentially representing the first observational evidence of X-ray emission from a star of this type. Its inferred luminosity suggests that RR Lyrae stars are intrinsically at least two orders of magnitude fainter in X-rays than the brightest Cepheids. We also observe a tentative increase in X-ray luminosity with pulsation period among classical Cepheids, and higher luminosities in type II Cepheids at comparable periods. These trends may reflect intrinsic differences in atmospheric structure and shock efficiency, offering new insight into the mechanisms driving high-energy emission in pulsating stars.
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Earth and Planetary Astrophysics

A Comprehensive Sulfur Chemistry Network Including Excited S(1D) and SO(1{\Delta}) for the XODIAC Photochemical Model: Accounting for Missing Sulfur Processes in Venus and Exo-Venus Analogs

Priyankush Ghosh, Namrata Rani, Jeehyun Yang et al. (+3 more)

Sulfur chemistry plays a central role in controlling the atmospheric structure, cloud formation, and composition of Venus and Venus-like exoplanets. However, key reactions involving ground- and excited-state sulfur species remain poorly constrained, and existing photochemical models often rely on incomplete or uncertain kinetic data under high-temperature, CO2-rich conditions. In this work, we compute kinetic parameters for reactions of ground-state S(3P) and excited-state S(1D) with CO2 under Venus-like conditions, forming SO(3Sigma), SO(1Delta), and CO. We characterize the underlying potential energy surfaces, identify intermediate complexes, and derive temperature-dependent rate coefficients using a master-equation framework based on the chemically significant eigenvalue method. We also provide NASA 7-term polynomial coefficients for S and SO in both ground and excited states to enable consistent incorporation into photochemical models. Incorporating these reactions into the one-dimensional photochemical model XODIAC for Venus produces only minor effects above 60 km due to competing pathways. While the model reproduces most observed sulfur species, discrepancies remain for S3 and S4. Introducing a 1 ppm near-surface atomic sulfur source, representing unresolved deep-atmosphere or surface processes, enhances S3 and S4 abundances by 1-2 orders of magnitude and improves agreement with observations. For exo-Venus analogs, the updated chemistry produces modest changes under isothermal conditions. In contrast, in strongly irradiated atmospheres with a high-altitude isotherm and a near-surface sulfur source, it leads to pronounced changes in most sulfur-bearing species, along with significant enhancements in S(1D) and SO(1Delta). These results highlight missing sulfur pathways, including excited states and deep sources, and potential implications for shaping Venus and exo-Venus atmospheres.
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All authors Priyankush Ghosh, Namrata Rani, Jeehyun Yang, Karen Willacy, P. B. Rimmer, Liton Majumdar

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

New Massless Spectra from Cosmic String Cusps

Amelia Drew and Ivan Rybak

In the standard picture of cosmic strings, cusps are generic features of Nambu-Goto loops where the string momentarily reaches the speed of light. They have a characteristic sharp profile, following $y \sim x^{2/3}$ in the $(x,y)$ plane, and produce strong gravitational-wave (GW) bursts with waveform $\tilde\kappa(\omega) \propto \omega^{-4/3}$, making them key targets for GW searches. However, under certain conditions, this generic picture can differ. We identify novel cusp solutions with different, including smooth, shapes, and compute their massless GW and axion spectra. We derive a general expression for all possible Nambu-Goto cusp spectra with the asymptotic form $\tilde\kappa(\omega) \propto \omega^{-n/(2n-1)} \omega^{-m/(2m-1)}$ where $n, m\geq 2$. We calculate the effect on the waveform of realistic corrections to the Nambu-Goto description, such as those from backreaction and finite string width, which introduce a high frequency cutoff.
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High Energy Astrophysical Phenomena · Cross-listed from gr-qc

The macroscopic precession model: describing quasi-periodic oscillations including internal structures of test bodies

Gabriele Bianchini, Orlando Luongo and Marco Muccino

The relativistic precession model (RPM) is widely-considered as a benchmark framework to interpret quasi-periodic oscillations (QPOs), albeit several observational inconsistencies suggest that the model remains incomplete. The RPM ensures structureless test particles and attributes precession to geodesic motion alone. Here, we refine the RPM by incorporating the internal structure of rotating test bodies, while preserving the test particle approximation (TPA), and propose a macroscopic precession model (MPM) by means of the Mathisson-Papapetrou-Dixon (MPD) equations, applied to a Schwarzschild background, which introduces 1) a shift in the Keplerian frequency and 2) an effective spin correction to the radial epicyclic frequency that, once the spin tensor is modeled, reproduces a quasi-Schwarzschild-de Sitter (SdS) correction. We apply the MPM to eight neutron star low mass X-ray binaries (NS-LMXBs), performing Markov chain Monte Carlo (MCMC) fits to twin kHz QPOs and find observational and statistical evidence in favor of precise power law spin reconstructions. Further, our model accurately predicts the $3:2$ frequency clustering, the disk boundaries and the NS masses. From the MPM model, we thus conclude that complexity of QPOs can be fully-described including the test particle internal structure.
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High Energy Astrophysical Phenomena

The Merger Rate of Primordial Black Holes

Muhsin Aljaf and Ilias Cholis

The merger rate of primordial black hole (PBH) binaries can be used to understand the source population of the merging black hole binaries observable through gravitational-waves (GWs) and also to constrain the possible contribution of PBHs to dark matter. In the literature, the PBH merger rate is calculated analytically, assuming that PBH binaries stay in isolation (i.e. are unperturbed) and evolve solely via GW emission during their entire lifetime. However, if some or all of dark matter consists of PBHs, then as cosmic structures grow, PBH binaries and single PBHs fall inside dark matter halos. In those halos, the PBH binaries' interactions with their environment significantly affect the subsequent evolution of their orbital properties. In this paper, we present a numerical framework that accurately calculates the total PBH merger rate by combining the evolution of isolated binaries outside halos with the dynamics of binaries inside halos. In our work we have found that the isolated binary channel is suppressed at low redshifts and dynamical interactions in halos reshape the merger rate evolution with time, accelerating some mergers. At redshifts of $\lesssim 2$ the total merger rate is a factor of $\simeq 50 \%$ higher than the results assuming that all PBH binaries effectively stay unperturbed until their merger. Our simulations provide a definitive calculation on the total PBH merger rates, that are currently being probed and constrained from gravitational-wave observations. We make our merger rates publicly available at Zenodo
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Instrumentation and Methods for Astrophysics

Bibliometric benchmarking across astronomy journals: Knowledge-use cycle and PASJ in the global landscape

Hideaki Fujiwara

We present a comparative bibliometric analysis of eight astronomy journals over 1996–2024, including Publications of the Astronomical Society of Japan (PASJ). Using data from Scopus and SciVal, we extract annual indicators of publication activity and scholarly impact, analyze time series, citation distributions, and citation age profiles, and benchmark PASJ within this landscape. The age profiles reveal a characteristic knowledge-use cycle: citations rise over $\sim$2–4 years, approach saturation by $\sim$10–12 years, underscoring limits of short-window impact metrics. Journals published by European and North American astronomical organizations sustain higher impact, whereas PASJ generally lies below the world baseline. In parallel, PASJ shows episodic above-baseline impact through facility- or mission-driven special issues and features that, given the journal's modest annual volume, can materially shift year-level metrics. These patterns point to two potential avenues for PASJ: well-timed, thoughtfully organized special issues and features that highlight high-impact results, and continued strengthening of international collaboration.
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Solar and Stellar Astrophysics

Observational Properties of $\beta$ Cephei Stars: 88 new samples discovered Based on TESS and Gaia Data

Xiang-dong Shi, Sheng-bang Qian, Li-ying Zhu et al. (+5 more)

We present a systematic investigation of $\beta$ Cephei (BCEP) stars by integrating photometric data from the Transiting Exoplanet Survey Satellite (TESS) with astrometric parameters from Gaia Data Release 3. Utilizing TESS's short-cadence (SC) and full-frame image (FFI) photometry, along with Gaia parallaxes and temperatures derived from the Extended Stellar Parametrizer for Hot Stars (ESP-HS) pipeline, we identify 88 new BCEP stars and candidates–85 from SC data and 3 from SPOC-processed FFI observations. These targets exhibit visual magnitudes ranging from 8.0 to 12.0 mag, parallaxes between 0.11 and 1.74 mas, effective temperatures of 18,000 to 30,000 K, and luminosities from 1,500–38,000 $L_\odot$, consistent with previously cataloged BCEP populations, thereby demonstrating the robustness of our classification criteria. Key findings include: (1) a significant detection disparity between SC and FFI datasets, with 30% of SC targets exceeding 18,000 K compared to only 0.7% in FFI, reflecting observational biases toward high-luminosity, hotter stars in SC data; (2) four samples near the red edge of the theoretical instability strip, exhibiting sparse pulsation modes that are important samples for testing pulsation models under low-mass, low-temperature conditions; and (3) spatial clustering within the Galactic disk ($|b| < 20^\circ$), with two high-latitude outliers likely representing runaway stars ejected from disk environments. Our analysis underscores the critical role of space-based photometry in detecting low-amplitude pulsators and the transformative potential of multi-survey integration in the era of time-domain astronomy. These results provide new samples to constrain stellar pulsation theories of massive stars and to study Galactic dynamics.
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All authors Xiang-dong Shi, Sheng-bang Qian, Li-ying Zhu, Lin-jia Li, Er-gang Zhao, David Mkrtichian, Farkhodjon Khamrakulov, Wen-xu Lin

High Energy Astrophysical Phenomena

Constraining the dark matter origin of the halo-like 20 GeV $\gamma$-ray excess with the AMS-02 antiproton data

Xiao Wang and Kai-Kai Duan

Very recently, a significant $\sim 20$ GeV gamma-ray excess in the Milky Way halo has been reported and a dark matter origin has been suggested. The inferred dark matter parameters are $ m_\chi \sim 0.5-0.8 $ TeV and $ \langle \sigma v \rangle \sim (5-8) \times 10^{-25}~{\rm cm^3~s^{-1}}$ for the $ b\bar{b} $ channel. If correct, prominent antiproton emission is produced and can be directly tested by the AMS-02 data. In this work we calculate the corresponding antiproton emission and show that the expected flux at $\sim 100$ GeV is already above the AMS-02 observation. A proper treatment on the antiproton background resulting from the high energy cosmic ray propagation would suggest an annihilation cross section of $< 2\times 10^{-26}~{\rm cm^3~s^{-1}}$, which is a few$\times 10$ times lower than that needed to interpret the potential signal. We therefore conclude that the $\sim 20$ GeV gamma-ray excess in the Milky Way halo is not a viable dark matter signal.
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Astrophysics of Galaxies

AGN X-ray Reflection Spectroscopy with ML MYTORUS:Neural Posterior Estimation with Training on Observation-Driven Parameter Grids

Ingrid Vanessa Daza-Perilla, Panayiotis Tzanavaris, V. Madurga-Favieres et al. (+3 more)

X-ray spectroscopy of active galactic nuclei (AGN) reveals key information about circumnuclear geometry. Many AGN show a narrow Fe K-alpha line at 6.4 keV and associated Compton-scattered continua, produced by primary continuum scattering in cold, neutral material far from the central supermassive black hole. We present a novel approach based on Simulation-Based Inference with Neural Posterior Estimation (SBI-NPE) to train a machine-learning (ML) model using NuSTAR spectral fitting results from the literature, adopting the physically motivated MYTORUS-decoupled model, which separates line-of-sight and global equivalent hydrogen column densities (NH_Z and NH_S). To overcome limitations of traditional frequentist fitting such as local minima, limited automation, reproducibility, and computational cost, we employ normalizing flows and autoregressive networks to learn flexible posterior distributions from simulated spectra. From 34 NuSTAR spectral fits, we generate 34,000 synthetic spectra using uniform and Gaussian parameter distributions, showing that the latter is more strongly observationally driven. The network is trained to infer four MYTORUS parameters: NH_Z, NH_S, the photon index Gamma, and the relative normalization AS. Mutual information analysis identifies optimal spectral regions and motivates the inclusion of redshift, exposure time, and Galactic absorption. The observation-based grid significantly outperforms uniform sampling, achieving predictive accuracies above 90 percent for NH_S and AS, 89 percent for NH_Z, and 82 percent for Gamma within one sigma, with a joint accuracy of 70 percent for all parameters. We publicly release ML MYTORUS with a web interface enabling fast, reproducible inference from NuSTAR spectra. An application to NGC 4388 illustrates the promise of this approach.
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All authors Ingrid Vanessa Daza-Perilla, Panayiotis Tzanavaris, V. Madurga-Favieres, M. Yukita, A. Ptak, T. Yaqoob

High Energy Astrophysical Phenomena

Inference of Neutron Star Mass Distributions and the Dense Matter Equation of State from Multi-messenger Observations

Mahmudul Hasan Anik, Andrew W. Steiner and Richard O'Shaughnessy

We construct a combined model to incorporate neutron star (NS) mass measurements with electromagnetic mass-radius constraints and gravitational-wave observations using Bayesian inference. We use different mass distributions for three populations depending on the companion stars: double neutron stars, NS - white dwarfs, and low-mass X-ray binaries (LMXB). To observe the effects of different parametrizations, we use two equation of state (EoS) models: a piecewise polytrope and a fixed sound-speed model at high densities in combination with a low-density EoS. Our results show that the mass distributions of these NS populations are distinct and sensitive to the EoS prior choices. In addition, we show for the first time that using a uniform prior on the observable NS maximum mass, rather than a nuisance parameter in the unknown high-density EoS, shifts the posterior maximum mass to larger values. For polytropic EoSs, the maximum mass posterior changes from $M_\mathrm{max}=2.09_{-0.07}^{+0.18} M_\odot$ to $2.15_{-0.10}^{+0.19} M_\odot$ at 90% confidence level. This change in prior also impacts the shape of the mass distribution for NSs in LMXB, shifting the posterior for the population mean from $\mu_\mathrm{lmxb} = 1.51_{-0.13}^{+0.13} M_\odot$ to $1.62_{-0.12}^{+0.15} M_\odot$ at 68% confidence level.
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Instrumentation and Methods for Astrophysics · Cross-listed from hep-ph

Searching for axion dark matter with magnetic resonance force microscopy

Elham Kashi, Muhammad Hani Zaheer, Ryan Petery et al. (+1 more)

We propose a magnetic resonance force microscopy (MRFM) search for axion dark matter around 1 GHz. The experiment leverages the axion's derivative coupling to electrons, which induces an effective A.C. magnetic field on a sample of electron spins polarized by a D.C. magnetic field and a micromagnet. A second pump field at a nearby frequency enhances the signal, with the detuning matched to the resonant frequency of a magnet-loaded mechanical oscillator. The resulting spin-dependent force is detected with hih sensitivity via optical interferometry. Accounting for the relevant noise sources, we show that current technology can be used to put constraints competitive with those from laboratory experiments with just a minute of integration time. Furthermore, varying the pump field frequency and D.C. magnetic field allows one to scan the axion mass. Finally, we explore this setup's capability to put constraints on other dark matter - Standard Model couplings.
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All authors Elham Kashi, Muhammad Hani Zaheer, Ryan Petery, Swati Singh

Solar and Stellar Astrophysics

Binarity at LOw Metallicity (BLOeM): Projected rotational velocities

D. J. Lennon, S. R. Berlanas, A. Herrero et al. (+36 more)

The Binarity at LOw Metallicity (BLOeM) survey is an ESO large programme designed to obtain multi-epoch spectroscopy for 929 massive stars in the Small Magellanic Cloud (SMC). It will provide binary fractions and orbital configurations of binary systems, and search for dormant black-hole binary candidates (OB+BH). Here we present projected rotational velocities (vsini) of all sources and, using the multiplicity properties presented in previous papers, we derive the vsini distributions of apparent single stars, single lined spectroscopic (SB1) binaries, and SB2 systems. We identify a locus in the Hertzsprung-Russell diagram where rotational velocities decrease significantly; we interpret this feature as broadly corresponding to the terminal-age main sequence. The main sequence cohort is distinguished by a broad range of vsini values, but with a strong peak in the distribution in the range 30-60 km/s, close to the resolution limit of 30 km/s. Sources in this low vsini peak are distributed throughout the main sequence, and are also present in the SB1 sample, though less prominent than in the single star distribution. A preliminary analysis of the lowest vsini cohort, that includes SB1 systems, implies that roughly one third may be nitrogen rich and we speculate that this cohort is a mix of pristine single stars, long period binaries, and merger products. The SB2 systems appear to be mostly short period binaries in synchronous rotation and have vsini estimates distributed around a mean value of approximately 140 km/s . Higher vsini sources are also present in the single and SB1 systems, all of which have tail to higher vsini values, consistent with tidal and mass-transfer effects. The supergiants, with a few exceptions, have low vsini, the bulk of these systems being essentially unresolved at current spectral resolution.
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All authors D. J. Lennon, S. R. Berlanas, A. Herrero, N. Britavskiy, P. L. Dufton, N. Langer, H. Jin, A. Schootemeijer, A. Menon, J. Bestenlehner, P. Crowther, J. S. Vink, J. Bodensteiner, T. Shenar, K. Deshmukh, J. Villasenor, L. Patrick, F. Najarro, A. de Koter, L. Mahy, D. M. Bowman, A. Bobrick, C. J. Evans, M. Gull, G. Holgado, Z. Katabi, J. Kubat, P. Marchant, D. Pauli, M. Pawlak, M. Renzo, D. F. Rocha, A. A. C. Sander, T. Sayada, S. Simon-Diaz, M. Stoop, R. Valli, C. Wang, X.-T. Xu

Solar and Stellar Astrophysics

Identifying and Characterizing Very Low Mass Spectral Blend Binaries with Machine Learning Methods

Juan Diego Draxl Giannoni, Malina Desai, Adam J. Burgasser et al. (+5 more)

We present an approach to identifying and characterizing unresolved, very low mass spectral blend binaries composed of late-M, L, and T dwarfs using machine learning methodologies. We generated and evaluated a series of hierarchical random forest models to distinguish spectral blends from single very low-mass dwarfs, and to classify their primary and secondary components. Models were trained on a sample of single and synthesized binary templates generated from empirical spectra. We explored various aspects of the design of our models, and find that models trained on a full range of single and binary combinations have the best performance for identification and component classification. These models achieve binary identification recall and precision of $\gtrsim$85%, median component classification errors of $\lesssim$0.1 subtypes, and systematic classification uncertainties of $\lesssim$1 subtype, outperforming index-based methods in terms of fidelity, range, and speed. Optimal performance is achieved for binaries composed of L and T dwarf primaries and late-L and T dwarf secondaries. When applied to the spectra of previously confirmed very low-mass binaries, model performance is degraded due to the prevalence of systems with similar component types, but remains high in the optimal performance range. We propose potential improvements to these models, which can be used to explore binary populations among the thousands to millions of very low-mass stars and brown dwarfs anticipated with large-scale spectral surveys such as SPHEREx and Euclid.
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All authors Juan Diego Draxl Giannoni, Malina Desai, Adam J. Burgasser, A. Camille Dunning, Christian Aganze, Luke McDermott, Christopher A. Theissen, Daniella C. Bardalez Gagliuffi

Friday 12 December

High Energy Astrophysical Phenomena

Self-gravitating Superfluids: The Gross-Pitaevskii-Poisson Framework

Sanjay Shukla, Marc E. Brachet and Rahul Pandit

We provide an overview of the Gross-Pitaevskii-Poisson equation (GPPE) that is used to model self-gravitating superfluid systems, which include gravitationally collapsed boson and axion stars and dark-matter haloes. We outline how this framework can be used to develop minimal models for neutron stars and for pulsars and their glitches. We account not only for vortices in the neutron superfluid inside these stars, but also for the flux tubes in the proton-superconductor subsystem, using a coupled model with the neutron superfluid, proton superconductor, the Maxwell equations for the vector potential ${\bf A}$, and the Poisson equation for self-gravity.
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Instrumentation and Methods for Astrophysics

ESO Expanding Horizons White Paper: Electromagnetic characterisation of millihertz gravitational-wave sources in the Milky Way

James Munday, Valeriya Korol, Camilla Danielski et al. (+8 more)

The millihertz band is densely populated by continuous gravitational-wave signals from Galactic compact binaries, dominated by double white dwarfs (DWDs; binaries of two white dwarfs) with contributions from systems containing neutron stars and black holes (Amaro-Seoane et al. 2023). As these binaries inspiral due to gravitational-wave radiation, they can reach contact and begin mass transfer in the millihertz band. Gravitational-wave detectors like LISA will survey such compact binaries across the Milky Way, yielding samples numbering in the tens of thousands, with essentially complete sensitivity to orbital periods shorter than ~10-20 min (e.g. Lamberts et al. 2019). Assessing the nature of the binary components - and deriving masses, temperatures and compositions - requires systematic electromagnetic characterisation that breaks gravitational-wave degeneracies and enables full atmospheric and orbital solutions. At present, no dedicated facility or coordinated survey is planned to deliver electromagnetic follow-up at the scale necessary to maximise the science return of the millihertz gravitational-wave data; this white paper discusses the need and requirements of such a capability.
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All authors James Munday, Valeriya Korol, Camilla Danielski, Na'ama Hallakoun, Astrid Lamberts, Gijs Nelemans, Anna Pala, Steven Parsons, Ingrid Pelisoli, Alberto Rebassa Mansergas, Jan van Roestel

Solar and Stellar Astrophysics

X-ray Evolution of Young Stars: Early Dimming and Coronal Softening in Solar-Mass Stars with Implications for Planetary Atmospheres

Konstantin V. Getman, Eric D. Feigelson, Vladimir S. Airapetian et al. (+1 more)

X-ray and ultraviolet (XUV) emission from young stars plays a critical role in shaping the evolution of planetary atmospheres and the conditions for habitability. To assess the long-term impact of high-energy stellar radiation, it is essential to empirically trace how X-ray luminosities and spectral hardness evolve during the first ~<1 Gyr, when atmospheric loss and chemical processing are most active. This study extends the X-ray activity-mass-age analysis of <25 Myr stars by Getman et al. (2022) to ages up to 750 Myr, using Gaia-based cluster memberships, new Chandra observations of five rich open clusters (~45–100 Myr), and archival ROSAT and Chandra data for three older clusters (~220–750 Myr). We find a mass-dependent decay in X-ray luminosity: solar-mass stars undergo a far more rapid and sustained decline, accompanied by coronal softening and the disappearance of hot plasma by ~100 Myr, compared to their lower-mass siblings. These trends in solar-mass stars are likely linked to reduced magnetic dynamo efficiency and diminished ability to sustain large-scale, high-temperature coronal structures. The trends are significantly stronger than predicted by widely used XUV-rotation-age relations. The revised trends imply systematically lower rates of atmospheric mass loss and water photolysis, as well as altered ionization environments and chemical pathways relevant to the formation of prebiotic molecules, for planets in close orbits around solar analogs. These effects persist throughout at least the ~<750 Myr interval probed in this study.
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All authors Konstantin V. Getman, Eric D. Feigelson, Vladimir S. Airapetian, Gordon P. Garmire

Instrumentation and Methods for Astrophysics

Revisiting x-CTE in WFC3/UVIS

Jay Anderson

Most discussion of charge-transfer-efficiency (CTE) losses involves the parallel transfer of charge in the y-direction down the chip columns (y-CTE). Serial charge-transfer efficiency (x-CTE) refers to the horizontal transer of charge. Serial CTE losses were first assessed in WFC3/UVIS in 2014 (WFC3/ISR 2014-02), where it was found that bright stars were shifted by roughly 0.0015 pixel away from the readout amplifier. Now that the WFC3/UVIS CCD has spent more than three times as long in space, imperfect serial CTE should have three times the impact on the images, so we revisit the effect and characterize serial CTE in a similar manner to our models for parallel-CTE by using a combination of warm pixels, cosmic rays, saturated stars, and overscan pixels. Overall, serial CTE has a much smaller impact on images than does parallel CTE. As of 2023, parallel CTE can have a roughly 5 percent impact on bright sources and a greater than 50 percent impact on faint sources, and serial CTE can have a roughly 1% impact on bright sources and a roughly 3 percent impact on fainter sources. The first few pixels in the serial CTE trails are much sharper than the parallel trails, but there is a very faint component to the serial trails that extends much farther than the parallel trails, even wrapping around to the next row. We develop a pixel-based model for the trapping and release of charge in the serial register and release a stand-alone beta-version of this pixel-based serial-CTE correction. Most images are not significantly impacted by the x-CTE effect, however HST users that require high-precision astrometry could benefit from this correction. At the very least, curious users can quantify its potential impact on their science.
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Astrophysics of Galaxies

Measurement of the Half-Light Radius for the Tucana Dwarf Spheroidal Galaxy

Pei-Jun Huang, Ian Dell'Antonio, Philip LaDuca et al. (+2 more)

We present a new measurement of the half-light radius of the Tucana Dwarf galaxy, based on the combination of wider, deeper imaging conducted as part of the Local Volume Complete Cluster Survey (LoVoCCS) and HST archival images. We obtain a stellar density profile within the Tucana Dwarf field based on elliptical fitting. After background subtraction, we fit a Sérsic profile to the density profile to obtain the half-light radius. We measure the half-light radius to be $0.89_{-0.02}^{+0.06}$ arcmin, corresponding to a value of $R_{e} = 225.7_{-5.5}^{+14.4}$ pc (95% CL). Given the wider-field observations from LoVoCCS used in this analysis, our measurement of the half-light radius represents a $\sim 10 \%$ increased value from the previous results.
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All authors Pei-Jun Huang, Ian Dell'Antonio, Philip LaDuca, Zacharias Escalante, Anthony Englert

High Energy Astrophysical Phenomena

Direct measurement of $^{59}$Cu($p$,$\alpha$)$^{56}$Ni precludes a strong NiCu cycle in Type-I X-ray bursts

N. Bhathi, J. S. Randhawa, R. Kanungo et al. (+36 more)

Model-observation comparisons of type-I X-ray bursts (XRBs) can reveal the properties of accreting neutron star systems, including the neutron star compactness. XRBs are powered by nuclear burning and a handful of reactions have been shown to impact the model results. Reactions in the NiCu cycles, featuring a competition between $^{59}$Cu($p$,$\gamma$)$^{60}$Zn and $^{59}$Cu($p$,$\alpha$)$^{56}$Ni, have been shown to be among the most important reactions as they are a critical checkpoint in $rp$-process flow and significantly impact the light curves and burst ashes. We report a direct measurement of $^{59}$Cu($p$,$\alpha$)$^{56}$Ni bringing stringent constraints on this reaction rate. New results rule out a strong NiCu cycle in XRBs, with a negligible degree of recycling, $\leq$5% up to 1.5 GK. The new reaction rate, when varied within new uncertainty limits, shows no impact on one-zone XRB model light-curves tailored for clocked-burster $\tt{GS 1826-24}$, hence removing an important nuclear physics uncertainty in the model-observation comparison.
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All authors N. Bhathi, J. S. Randhawa, R. Kanungo, J. Refsgaard, M. Alcorta, T. Ahn, C. Andreoiu, D. Bardayan, S. S. Bhattacharjee, B. Davids, G. Christian, A. A. Chen, R. Coleman, P. E. Garrett, G. F. Grinyer, E. Gyabeng Fuakye, G. Hackman, R. Jain, K. Kapoor, R. Krucken, A. Laffoley, A. Lennarz, J. Liang, Z. Meisel, A. Psaltis, A. Radich, M. Rocchini, J.S. Rojo, N. Saei, M. Saxena, M. Singh, C. E. Svensson, P. Subramaniam, A. Talebitaher, S. Upadhyayula, C. Waterfield, J. Williams, M. Williams, M. A. Zubair

High Energy Astrophysical Phenomena

The maximum offsets of binary neutron star mergers from host galaxies

Ilya Mandel, Om Sharan Salafia, Andrew Levan et al. (+1 more)

We analytically derive, and illustrate with a population synthesis model, the maximum offset of binary neutron star mergers ejected from their host galaxies. This approximate maximum offset is 300 kpc $\times\ (v_\mathrm{esc} / 500\ \mathrm{km}\ \mathrm{s}^{-1})^{-7}$, where $v_\mathrm{esc}$ is the escape velocity from the host galaxy. Massive hosts with high escape velocities are unlikely to yield very large offsets. This maximum offset should inform the host associations of mergers that are not coincident with galaxies. We also discuss potential correlations between offsets and system masses, and possibly the duration of the gamma-ray burst accompanying the merger.
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All authors Ilya Mandel, Om Sharan Salafia, Andrew Levan, Paul Disberg

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

Born-Infeld signatures in AdS black hole thermodynamics and gravitational lensing

Ekrem Ayd{\i}ner, Tekin Dereli, İzzet Sakall{\i} et al. (+2 more)

We investigate the thermodynamic and optical properties of Einstein-Born-Infeld-Anti-de Sitter (EBI-AdS) black holes (BHs). Our study derives the Hawking temperature using standard surface gravity methods and examines quantum corrections through both the Generalized Uncertainty Principle (GUP) and exponential entropy modifications, showing enhanced thermal radiation and potential remnant formation scenarios. The gravitational redshift analysis separates contributions from mass, cosmological constant, electromagnetic charge, and Born-Infeld (BI) corrections, with the latter scaling as $a^4/r^6$ and thus confined to near-horizon regimes. Using the Gauss-Bonnet theorem, we calculate light deflection angles in both vacuum and plasma environments, demonstrating how dispersive media can either enhance or suppress nonlinear electrodynamic signatures depending on observational configurations. The thermodynamic analysis in extended phase space, where the BH mass corresponds to enthalpy, reveals phase structures with heat capacity transitions between positive and negative values, indicating regions of local stability and instability sensitive to parameter choices. We study BH heat engines operating in rectangular thermodynamic cycles, achieving efficiencies of $\eta \sim 0.11$–$0.21$ that reach 30–61% of the corresponding Carnot limits, consistent with other AdS BH systems. Comparison with Johnson's analysis confirms that BI corrections to heat engine efficiency are of order $10^{-12}$ for typical parameter ranges, though these effects become appreciable in the strong-field regime where $r_h \lesssim 1.5$ in Planck units. The plasma deflection analysis reveals frequency-dependent refractive modifications encoded in the plasma parameter, offering additional possible observational channels.
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All authors Ekrem Ayd{\i}ner, Tekin Dereli, İzzet Sakall{\i}, Erdem Sucu, Ece Seyma Yörük

Astrophysics of Galaxies

NGDEEP: A New Non-Parametric Measure of Local Star-Formation and Attenuation at Cosmic Noon

Grace M. Forrey, Raymond C. Simons, Jonathan R. Trump et al. (+6 more)

We introduce a new non-parametric technique to quantify the spatially-resolved relationship between the local star-formation rate (SFR) and dust attenuation. We then apply it to 14 star-forming galaxies at $1.0<z<2.5$ using JWST/NIRISS slitless spectroscopy from the NGDEEP survey. First, we construct spatially resolved ($\sim$1~kpc per pixel) Balmer decrement ($H\alpha/H\beta$) maps of these galaxies and derive their corresponding dust attenuation and intrinsic SFR maps. We then rank-order the map pixels by attenuation and construct a cumulative distribution curve of the total SFR as a function of increasing attenuation. We define $\mathrm{A}^{\mathrm{SFR}}_{10\%}$, $\mathrm{A}^{\mathrm{SFR}}_{50\%}$, and $\mathrm{A}^{\mathrm{SFR}}_{90\%}$ as the dust attenuation levels behind which 10%, 50%, and 90% of the total integrated SFR is screened, respectively. These metrics quantify the probability that a given star-forming region lies behind a given level of attenuation. Across the full sample, 50% of the local star formation occurs behind an attenuation of 3.41 mag or higher ($\mathrm{A}^{\mathrm{SFR}}_{50\%}$). This indicates that the bulk of star formation in these galaxies is significantly attenuated by dust. The value of $\mathrm{A}^{\mathrm{SFR}}_{10\%}$ equals 1.45 for the average profile, indicating that even the least attenuated star-forming regions are still highly attenuated. The globally measured attenuation more closely matches $\mathrm{A}^{\mathrm{SFR}}_{10\%}$ than $\mathrm{A}^{\mathrm{SFR}}_{50\%}$. This suggests that the global value is weighted toward the least dust-obscured star-forming regions and significantly underestimates the typical attenuation a star-forming region encounters. Our results demonstrate a new approach for understanding the extremely dusty local conditions of the star-forming interstellar medium in SF galaxies at cosmic noon.
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All authors Grace M. Forrey, Raymond C. Simons, Jonathan R. Trump, Lu Shen, Anton M. Koekemoer, Micaela B. Bagley, Steven L. Finkelstein, Casey Papovich, Nor Pirzkal

Instrumentation and Methods for Astrophysics · Cross-listed from eess.SY

Pivot-Only Azimuthal Control and Attitude Estimation of Balloon-borne Payloads

Philippe Voyer, Simon Tartakovsky, Steven J. Benton et al. (+1 more)

This paper presents an attitude estimation and yaw-rate control framework for balloon-borne payloads using pivot-only actuation, motivated by the Taurus experiment. Taurus is a long-duration balloon instrument designed for rapid azimuthal scanning at approximately 30 deg/s using a motorized pivot at the flight-train connection, without a reaction wheel. We model the gondola as a rigid body subject to realistic disturbances and sensing limitations, and implement a Multiplicative Extended Kalman Filter (MEKF) that estimates attitude and gyroscope bias by fusing inertial and vector-camera measurements. A simple PI controller uses the estimated states to regulate yaw rate. Numerical simulations incorporating representative disturbance and measurement noise levels are used to evaluate closed-loop control performance and MEKF behavior under flight-like conditions. Experimental tests on the Taurus gondola validate the pivot-only approach, demonstrating stable high-rate tracking under realistic hardware constraints. The close agreement between simulation and experiment indicates that the simplified rigid-body model captures the dominant dynamics relevant for controller design and integrated estimation-and-control development.
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All authors Philippe Voyer, Simon Tartakovsky, Steven J. Benton, William C. Jones