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Physics Astrophysics

astro-ph Watch Astrophysics

Monday 10 August

Instrumentation and Methods for Astrophysics

NASA ASTRA Initiative White Paper: Space-Based Mission for Ultrahigh Energy Particles

Mauricio Bustamante, Johannes Eser, Ke Fang et al. (+9 more)

Ultra-high-energy cosmic rays ($E_{\rm CR} \gtrsim 1$ EeV) are the highest-energy particles known, signaling extreme particle processes at work in the universe. However, many aspects of their nature remain largely unknown, even after more than a century of study. Very-high-energy ($E_\nu \gtrsim 1$ PeV neutrinos associated with cosmic-ray interactions, both during the acceleration process and propagation, would provide new insight into these extreme particles, as we have seen at lower energies with the dawn of TeV neutrino astronomy. Nevertheless, only a handful of such neutrinos have been observed thus far. A space-based observatory dedicated to studying cosmic rays, neutrinos, and photons would provide an unprecedented platform for observations of these extreme-energy messengers.
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All authors Mauricio Bustamante, Johannes Eser, Ke Fang, Claire Guépin, John Krizmanic, Eric Mayotte, Keith McBride, Kohta Murase, Mary Hall Reno, Frank Schroeder, Tonia M. Venters, Stephanie Wissel

Astrophysics of Galaxies

An emerging baryon cycle in a galaxy 500 million years after the Big Bang

Shengzhe Wang, Xin Wang, Hang Zhou et al. (+17 more)

The emergence of stellar feedback as a regulator of galaxy growth marks a fundamental transition in cosmic history. At early times, rapid gas accretion and collapse may induce intense star formation before feedback becomes effective, producing feedback-free starbursts. When and how such bursts subsequently develop into self-regulated baryon cycles remain observationally unknown. Here we show that Gz9p3, a merging galaxy at $z=9.311$, is caught in this transition only 500 million years after the Big Bang. Deep JWST spectroscopy reveals a substantial neutral-gas reservoir along its merger-driven tidal structure and a multiphase outflow. Fine-structure absorption provides the first direct measurement of the electron density of the cool outflowing gas at high redshift ($\approx\,17\,{\rm cm^{-3}}$), yielding a mass-loading factor among the highest yet measured for galaxies of comparable stellar mass. The emergence of such efficient feedback after an intense burst is consistent with the delayed onset of feedback expected in feedback-free starburst models. The cool outflowing gas is unlikely to escape the host halo, implying that much of this metal-enriched material may remain available for future recycling through the circumgalactic medium. Gz9p3 therefore provides an early view of a baryon cycle being established through the interplay of merger-driven gas redistribution, bursty star formation and stellar feedback, suggesting that feedback-regulated recycling was already shaping galaxy growth during the epoch of reionization.
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All authors Shengzhe Wang, Xin Wang, Hang Zhou, Zhijie Qu, Zhaozhou Li, Yuxuan Pang, Qianqiao Zhou, Shouyi Wang, Yangyao Chen, Yuguang Chen, Karl Glazebrook, Glenn G. Kacprzak, Nicha Leethochawalit, Houjun Mo, Themiya Nanayakkara, Huiyuan Wang, Weida Hu, Xunda Sun, Chao-Wei Tsai, Hu Zhan

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

Probing ultralight bosons with LISA observations of spinning black hole mergers and follow-up searches of merger remnants

Ifigeneia Giannakoudi, Maxence Corman and William E. East

Ultralight bosons can trigger superradiant instabilities around rotating black holes, extracting angular momentum and leading in some cases to observable gravitational signatures. When the associated spin-down timescale is shorter than the black hole lifetimes and the spin-up timescales due to, e.g. accretion, this process imposes an upper limit on black hole spins. In addition, the formation and subsequent dissipation of boson clouds generates quasi-continuous gravitational wave emission. In this work, we explore the prospects for constraining and detecting ultralight bosons with observations of massive black hole binary mergers with the space-based LISA observatory. We consider two complementary approaches: measurements of black hole spins from merging binaries and follow-up gravitational wave searches targeting massive black hole binary merger remnants. We consider three population models for massive black holes, based on either heavy or light seeds, and forecast the exclusion and detection probabilities for both scalar and vector bosons. We find that black hole spin measurements can constrain scalar masses in the range $[5\times10^{-18},10^{-14}]$ eV and vector masses in the range $[6\times10^{-19},2\times10^{-14}]$ eV, with the exact range depending on the model. In contrast, restricting to vector bosons, follow-up gravitational wave searches are sensitive to a narrower vector boson mass range of $\sim[3\times10^{-17},3\times10^{-15}]$ eV, with the specific values again depending on the model. If a vector boson with a mass in the range $[10^{-16},2\times10^{-15}]$ eV existed, the probability of having an event that the follow-up searches would be sensitive to ranges from very small to near unity depending on the astrophysical model.
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Instrumentation and Methods for Astrophysics

SGNAX: a unified matched-filter and excess-power pipeline for gravitational-wave detector characterization

Zach Yarbrough, Olivia Godwin, Derek Davis et al. (+1 more)

We present SGNAX, an open-source pipeline for gravitational-wave detector characterization that delivers matched-filter and excess-power transient triggers from a single streaming dataflow graph. Built on the Stream Graph Navigator (sgn) framework, SGNAX unifies the multi-rate sine-Gaussian matched-filter search of snax and the multi-resolution Q-transform search of omicron in one Python-native package. Auxiliary channels from an interferometer are analyzed as parallel branches sharing data-read and whitening stages, reducing per-channel processing cost as channels are added. A full day of 16 kHz strain is analyzed in 14 minutes, and Q-transform processing is 2.8 times more efficient per channel at 32 channels than at one. Matched-filter correlations use PyTorch and run on CPU or GPU. Data sources include offline frame caches, shared-memory buffers, and the arrakis distribution service, with the same configuration supporting offline and online operation. The matched filter delivers triggers at about five seconds end-to-end latency, while the Q-transform operates at latencies of tens of seconds. Injection campaigns recover 99.4% of recoverable sine-Gaussian injections with parameters within the expected template mismatch and show broadband white-noise-burst recovery consistent with established event-trigger generators. On 24 hours of archival LIGO strain, SGNAX reproduces the omicron trigger population at 10–100 Hz, with trigger rates and SNRs agreeing to a few percent. On production auxiliary channels, it recovers the snax loud-feature population with 80% per-bin coincidence. The injection-calibrated reimplementation also reveals a multiband amplitude error in production snax that inflates reported SNRs below 25.6 Hz by factors of $\sqrt{2}$–2, for which we identify the mechanism and correction.
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All authors Zach Yarbrough, Olivia Godwin, Derek Davis, Gabriela González

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

Thermal Origin of Black Hole Quasinormal Modes

D. Giataganas, G.F. Giudice, A. Kehagias et al. (+2 more)

When a black hole rings after a merger, it emits gravitational waves at characteristic frequencies known as quasinormal modes (QNMs). In the eikonal limit, these modes are governed by the unstable circular light orbits that form the photon ring. In this work, we demonstrate that the ringing of a black hole has a precise thermal interpretation. A probe string propagating in the near-ring geometry acquires an induced Rindler horizon on its worldsheet, with a temperature set by the Lyapunov exponent of the photon ring. Out of this structure, the black hole QNMs emerge as thermal excitations, so that the characteristic ringing of a black hole is the retarded response of a thermal system living on the photon ring. We explicitly derive the QNM spectrum from two complementary perspectives: microscopically, via unstable transverse worldsheet fluctuations, and macroscopically, through the pole structure of the causal response function of an open thermal quantum system.
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All authors D. Giataganas, G.F. Giudice, A. Kehagias, F. Quevedo, A. Riotto

Instrumentation and Methods for Astrophysics

Quasi-automatic software support for Gaia ground based optical tracking

S. Bouquillon, C. Barache, T. Carlucci et al. (+6 more)

The ESA Gaia satellite mission will create a catalog of 1 billion stars with unprecedented astrometric precision. To achieve its aim in terms of astrometric precision, a ground based optical tracking campaign (GBOT) of the satellite itself is necessary during the five years of the mission. We present an overview of the GBOT project as a whole in another contribution (Altmann et al. in SPIE category "observatory operations"). The present paper will focus more specifically on the software solutions developed by the GBOT group.
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All authors S. Bouquillon, C. Barache, T. Carlucci, F. Taris, M. Altmann, A. H. Andrei, R. Smart, I. A. Steele, S. G. Els

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

Adiabatic Perturbations in GW170817-Compatible Einstein-Gauss-Bonnet Inflation

S.D. Odintsov and V.K. Oikonomou

We study the adiabaticity of the cosmological perturbations in the context of inflationary Einstein-Gauss-Bonnet theories. We focus on viable inflationary Einstein-Gauss-Bonnet theories which are compatible with the current Cosmic Microwave Background radiation experiments and also are compatible with the GW170817 observations. We derive the effects of the adiabaticity requirement on the Einstein-Gauss-Bonnet physical parameters and we show that the sound speed of the scalar perturbations and the propagation speed of the tensor perturbations are constrained. We consider two classes of inflationary viable and GW170817-compatible theories, and in the first class the adiabaticity is not violated during inflation, while in the second class the adiabaticity is violated only at the end of inflation. We discuss the effects of the adiabaticity violation in the second class of models. From our analysis, it seems that only one class of viable EGB inflationary theories, which is also compatible with the GW170817 event, is free from adiabaticity pathologies.
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Instrumentation and Methods for Astrophysics

Pulsar Timing Array Sensitivity to Anisotropy: Empirical Sensitivity Curves, Scaling Relations, and the Multi-Resolution Pixel Basis

Taha T. Moursy, Nihan S. Pol, Gabriella Agazie et al. (+115 more)

We quantify pulsar timing array (PTA) sensitivity to anisotropy in the gravitational wave background using the cross-correlation based Fisher information matrix in the pixel and spherical harmonic bases. We use a set of simulations to empirically determine scaling relations of a PTA's sensitivity to anisotropy with the number of pulsars $N_\mathrm{psr}$ in the array, the error $\delta t$ on the times of arrival, the frequency $f_\mathrm{GW}$ of the gravitational waves, and the angular scale $\Delta\Omega$ of the anisotropy. The sensitivity scales approximately as $N_\mathrm{psr}^{0.8}$, $\delta t^{-0.08}$, and $\Delta\Omega^{1.6}-\Delta\Omega^{2.1}$ (depending on the ranges of $\ell$ and $m$ under consideration). In addition, we use realistic simulations to project the NANOGrav PTA sensitivity to a 30-year baseline and quantify the growth in sensitivity at several timeslices. Except at the lowest frequencies, we find negligible effect on sensitivity through increasing the observation duration only. Finally, we introduce a multi-resolution pixel basis motivated by the large dependence of the sensitivity on sky location, and demonstrate the operation of the basis through a set of injections and recoveries.
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All authors Taha T. Moursy, Nihan S. Pol, Gabriella Agazie, Nikita Agarwal, Akash Anumarlapudi, Anne M. Archibald, Zaven Arzoumanian, Anjana Ashok, Jeremy G. Baier, Paul T. Baker, Bence Bécsy, Laura Blecha, Adam Brazier, Paul R. Brook, Sarah Burke-Spolaor, Rand Burnette, Robin Case, J. Andrew Casey-Clyde, Maria Charisi, Shami Chatterjee, Tyler Cohen, James M. Cordes, Neil J. Cornish, Fronefield Crawford, H. Thankful Cromartie, Kathryn Crowter, Megan E. DeCesar, Paul B. Demorest, Heling Deng, Lankeswar Dey, Timothy Dolch, Graham M. Doskoch, Elizabeth C. Ferrara, William Fiore, Emmanuel Fonseca, Gabriel E. Freedman, Emiko C. Gardiner, Nate Garver-Daniels, Peter A. Gentile, Kyle A. Gersbach, Joseph Glaser, Deborah C. Good, Kayhan Gültekin, Aiden Gundersen, C. J. Harris, Jeffrey S. Hazboun, Ross J. Jennings, Aaron D. Johnson, Megan L. Jones, David L. Kaplan, Anala K. Sreekumar, Luke Zoltan Kelley, Matthew Kerr, Joey S. Key, Nima Laal, Michael T. Lam, William G. Lamb, Bjorn Larsen, T. Joseph W. Lazio, Natalia Lewandowska, Tingting Liu, Duncan R. Lorimer, Jing Luo, Ryan S. Lynch, Chung-Pei Ma, Dustin R. Madison, Ashley Martsen, Cayenne Matt, Alexander McEwen, James W. McKee, Maura A. McLaughlin, Natasha McMann, Bradley W. Meyers, Patrick M. Meyers, Matthew T. Miles, Chiara M. F. Mingarelli, Andrea Mitridate, Cherry Ng, David J. Nice, Shania A. Nichols, Stella Koch Ocker, Daniel J. Oliver, Ken D. Olum, Timothy T. Pennucci, Benetge B. P. Perera, Polina Petrov, Henri A. Radovan, Scott M. Ransom, Paul S. Ray, Joseph D. Romano, Jessie C. Runnoe, Alexander Saffer, Shashwat C. Sardesai, Ann Schmiedekamp, Carl Schmiedekamp, Kai Schmitz, Levi Schult, Brent J. Shapiro-Albert, Xavier Siemens, Joseph Simon, Sophia V. Sosa Fiscella, Ingrid H. Stairs, Daniel R. Stinebring, Kevin Stovall, Abhimanyu Susobhanan, Joseph K. Swiggum, Jacob Taylor, Stephen R. Taylor, Mercedes S. Thompson, Jacob E. Turner, Michele Vallisneri, Rutger van Haasteren, Sarah J. Vigeland, Haley M. Wahl, Kevin P. Wilson, Caitlin A. Witt, David Wright, Olivia Young

Cosmology and Nongalactic Astrophysics

Not R Kurvature: Beating Large-Scale White Noise

Wayne Hu

Kurvature, a recently identified curvature invariant, has been argued to acquire superhorizon, or large-scale, white noise from hard-hard momentum coupling even when matter nonlinearities are small. If kurvature were related directly to cosmological curvature perturbations R through a Poisson equation, this white noise would cause an infrared-divergent variance sensitive to ultraviolet hard-mode physics. However, this relation does not generically hold. Kurvature is not intrinsic 3-curvature: on comoving slices it contains extrinsic-curvature terms, and intrinsic curvature is not related to R by a Poisson equation beyond linear order. We test this inference with second-order perturbation theory in radiation domination, relevant to CMB observables. Quadratic hard-hard composites do generate large-scale white noise in the kurvature density, but the Hamiltonian constraint separates it into intrinsic curvature and extrinsic shear, or equivalently density and expansion. Only the extrinsic terms carry the growing dimensionless kurvature density that mimics an ordinary density fluctuation above the horizon. The direct hard-hard curvature power is ultraviolet convergent, dominated by horizon-scale modes at evaluation, and leaves no IR relic in R from purely ultraviolet modes. By contrast, the Poisson construction of a curvature potential from kurvature is infrared divergent and cutoff sensitive; its white noise arises from extrinsic curvature associated with nonlinear acoustic beat modes in a radiation fluid.
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High Energy Astrophysical Phenomena

Exploring the multi-wavelength properties of the high energetic event ZTF20abbiixp/GRB 200524A: from prompt emission to afterglow

A. Ghosh, Dimple, K. Misra et al. (+32 more)

We conducted a comprehensive multi-wavelength analysis of a high energetic long-duration ZTF20abbiixp / GRB~200524A detected by Fermi Gamma Ray Burst Monitor (GBM). Our study combines extended high-energy observations from multiple space-based observatories including Fermi with broadband afterglow data spanning X-ray to radio wavelengths, complemented by extensive photometric and spectroscopic follow-up from several ground-based optical facilities worldwide like 3.6-m Devasthal Optical Telescope (DOT). ZTF20abbiixp / GRB~200524A exhibits almost negligible spectral lag, likely arising from the presence of multiple overlapping emission episodes, a property uncommon among long-duration bursts. The burst additionally shows a clear intensity-tracking evolution of the prompt-emission spectral parameters. The broadband afterglow light curve best fits with a broken powerlaw with a break at $10^{5}$ s since the GBM trigger. The electron powerlaw index (p) calculated from the temporal and spectral slopes fail to distinguish between a interstellar medium and a wind environment. Our custom-developed afterglow model fits the panchromatic data well, combining forward shock (FS) and reverse shock (RS) emission. The RS contribution required to fit the early time optical data. The inferred afterglow model parameters suggest that ZTF20abbiixp / GRB~200524A is a high energetic burst expanding into a dense ISM environment, with a relatively large value of the fraction of energy going to accelerating electron and magnetic field ($\epsilon_B$).
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All authors A. Ghosh, Dimple, K. Misra, P. Yu. Minaev, Y. Yao, D. A. Kann, M. Blazek, A. S. Pozanenko, S. Belkin, L. Izzo, H. Kumar, A. de Ugarte Postigo, A. Rossi, G. C. Anupama, V. Bhalerao, D. Bhattacharya, N. K. Chakradhari, S. Chandra, R. Gupta, K. M. Jayasurya, A. Kumar, B. Kumar, T. S. Kumar, A. Moskvitin, S. B. Pandey, A. Omar, A. R. Rao, L. Resmi, V. Rumyantsev, P. Sanwal, A.V. Volnova, A.O. Novichonok, M. Krugov, S.A. Ehgamberdiev, A.E. Volvach

Cosmology and Nongalactic Astrophysics

Cross-frequency SGWB anisotropy from compact topology: CMB B-mode covariance as a transfer probe

Li-E Qiang and Peng Xu

Compact spatial topology restricts the eigenmodes of primordial tensor perturbations, and the resulting discreteness can render the primordial stochastic gravitational-wave background (SGWB) anisotropic. Here we treat the CMB tensor $B$-mode covariance as a transfer-filtered measurement of that ultra-low-frequency anisotropy. Writing the normalized angular tensor-power measure as $F(k,\hat k)=1+Q(k,\hat k)$ and its nonmonopole moments as $q_{LM}(k)$, we obtain an explicit kernel that maps $q_{LM}(k)$ onto the off-diagonal covariance $\delta C^{BB}_{\ell m,\ell' m'}$. The kernel factorizes into tensor transfer functions and a spin-weighted Gaunt coefficient and obeys the parity rule $L+\ell+\ell'$ even for $BB$ and odd for $TB/EB$. It is an exact source–response representation of the full compact covariance rather than an additional observable. For a cubic three-torus the geometry pins down a common cubic angular subspace and orientation across frequency bands, although the amplitudes of the allowed multipoles still depend on the radial shell and source spectrum. The same topology-restricted template can therefore be read out either through the CMB $B$-mode kernel or through the anisotropy response of PTA/LISA/Taiji/TianQin searches. Using CAMB transfer functions and an invariant anisotropic-template statistic, we contrast this tensor channel with the scalar $T/E$ covariance. Independent direct angular-shell sums and $q_{LM}$–Gaunt contractions agree at $L_q^{\max}=2\ell_{\max}$ to relative Frobenius residuals of $1.4\times10^{-14}$–$3.0\times10^{-14}$. The scalar sector holds most of the practical CMB topology information; a fixed-template scan places the combined full-sky $S/N=1$ transition between $L/\chi_*=2.34$ and $2.36$, while the $B$-mode channel remains subthreshold but isolates the primordial SGWB contribution.
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Earth and Planetary Astrophysics

TOI-7475 spectroscopic follow up - detection of a massive hot Jupiter on an eccentric orbit

Joanna Pietrucha, Jakub Jerzy Tokarek, Mateusz Witczak et al. (+1 more)

We present the first spectroscopic follow-up for TOI-7475, and report the detection of a planetary-mass companion. Transits with a period of 3.25 days were observed by TESS. The dips in brightness are 0.006 mag and last approximately 4.5 hours. The host star is a spectral type F5 with a mass of approximately 1.48 M$_{\odot}$. We collected 24 high resolution echelle spectra using the PST1 telescope. Analysis of the TESS photometric data and our radial velocities was performed using the Wilson-Devinney method. We obtained a planetary mass of the companion of 12.0$\pm$1.0 M$_{\mathrm{jup}}$. The small semi-major axis and short orbital period classify the planet as a Hot Jupiter. Its orbit is elliptical with an eccentricity of 0.16. The ellipticity is evident in the spectroscopic data and could indicates the young age of the system.
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All authors Joanna Pietrucha, Jakub Jerzy Tokarek, Mateusz Witczak, Wojciech Dimitrov

Solar and Stellar Astrophysics · Cross-listed from nucl-th

A Gaussian Process framework for constraining the nuclear equation of state from microscopic calculations with correlated uncertainties

Y. G. Lee, J. Kim, T. Zhao et al. (+1 more)

We present constraints on the nuclear equation of state (EOS) from microscopic asymmetric matter calculations at zero temperature based on chiral nucleon-nucleon and three-nucleon interactions. The constraints include the saturation point, the isospin dependence of the incompressibility, and the symmetry energy, as well as the crust-core transition density of neutron-star matter. To quantify and propagate correlated uncertainties from noisy many-body calculations to derived observables, we introduce GPDiff, an efficient JAX-based Python package for multivariate Gaussian process (GP) regression with automatic differentiation. After training, GPDiff enables joint predictions of the EOS and derivatives of arbitrary order with respect to the input variables, including mixed partial derivatives. In this initial application, we analyze recent high-order many-body perturbation theory calculations of asymmetric matter up to about twice saturation density and explore nonstationary change-surface kernels, a class of input-dependent kernels, for modeling the EOS. GPDiff is broadly applicable to microscopic nuclear EOS calculations at zero and finite temperature and provides a versatile package for GP-based uncertainty quantification and inference of the nuclear EOS.
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All authors Y. G. Lee, J. Kim, T. Zhao, C. Drischler

High Energy Astrophysical Phenomena

Recoiling Black Holes I. Burst of Observables

Erwan Hochart and Simon Portegies Zwart

We aim to investigate the tidal disruption and gravitational wave events shortly after a massive black hole binary merges in the galactic centre and whose remnant black hole is ejected from the galaxy. Using computational methods, black holes of mass $M_{\bullet}=10^{5}$ M$_\odot$ and $4\times10^{5}$ M$_\odot$ embedded in a nuclear star cluster are kicked at velocities of $v_k=300$ and $600$ km s$^{-1}$. Systems are integrated for $0.1$ Myr using a $4$th-order Hermite scheme. The kick instantaneously repopulates the loss cone, producing a strong burst of tidal disruption events and gravitational wave mergers. The anisotropy in the apsidal orientation of bound stars prolongs this burst phase. Rates increase for lower $v_k$, larger $M_{\bullet}$ and for steeper nuclear star cluster density profiles at moment of merger. Assuming binary black holes scour a Bahcall-Wolf density profile during coalescence, ejected remnants with mass between $10^{5}\leq M_{\bullet}$ [M$_\odot] \leq 4\times10^{5}$ generate observable offset events at a forecasted rate of $\dot{N}\lesssim290$ yr$^{-1}$ up to redshift $z=3$. If, at the moment of merger, the milliparsec scales of the nuclear star cluster are described by a shallow density profile ($\gamma=1$), this decreases to $\dot{N}\lesssim30$ yr$^{-1}$. The strong dependence on the initial density profile and recoil kick makes observables powerful probes of the nuclear star cluster post-massive black hole binary coalescence, and provides test for numerical relativity.
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Instrumentation and Methods for Astrophysics

Wigner interferometry

Vladimir Lenok

Aims. This work aims to introduce a new method of interferometric measurements based on correlation of Wigner functions constructed for the fields from a distant source. Methods. This work presents theoretical studies of correlation of the Wigner functions. Numerical simulations support the findings. Results. It is shown that in comparison to the correlation of the fields, a correlation of their Wigner functions samples twice higher spatial frequencies of the source intensity distribution and has about twice smaller scale of the spatial pattern. This opens a fundamental possibility to improve the angular resolution of interferometric measurements by a factor of two.
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Solar and Stellar Astrophysics

HXI-DLA2: A Physics-Constrained Deep Learning Algorithm for the ASO-S Hard X-ray Imager

Zou SiZhong, Liu Hui, Su Yang et al. (+5 more)

Solar flare hard X-ray imaging is a key diagnostic of flare energy release and electron acceleration. The Hard X-ray Imager (HXI) aboard ASO-S compresses the two-dimensional source distribution into counts measured by 91 sub-collimators, making image reconstruction an inherently underdetermined inverse problem. Conventional algorithms such as CLEAN rely on point-source priors and manual tuning, whereas recent deep-learning methods offer no guarantee that their reconstructions obey the instrument's modulation-sampling forward equation. In this work we show that the counts decompose into two nearly decoupled quantities—the counts average energy, which tracks the total source flux, and the normalized counts distribution, which encodes the source spatial structure—and we exploit this property to construct a physics-constrained network, the Hard X-ray Imager Deep Learning Algorithm 2 (HXI-DLA2). Non-negativity and exact counts-average-energy closure are enforced at the network output, while a distribution-consistency loss aligns the re-projected counts with the measurement, so that the reconstruction satisfies the forward equation by construction. Tests on simulated Gaussian sources, observed soft X-ray morphologies, and a real HXI flare event show two main improvements over existing methods: the limiting resolvable dynamic range of double sources is pushed well beyond that of conventional imaging algorithms and our previous method; and complex morphologies on which prior reconstructions degrade, such as ring-like and diffuse structures, are reliably reconstructed, with the real-event result consistent with contemporaneous SDO/AIA imaging. Embedding the instrumental forward equation as a hard constraint while learning source priors from data offers a general inversion framework for modulation imaging.
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All authors Zou SiZhong, Liu Hui, Su Yang, Hong JunChao, Bin Wang, Chen Wei, KaiFan Ji, ZhenYu Jin

Instrumentation and Methods for Astrophysics

Unsupervised Domain Adaptation for Multitask Image Analysis in Realistic Context with Extreme Label Shift; Application to the CTAO first Large Sized Telescope

Michaël Dell'aiera, Thomas Vuillaume and Alexandre Benoit

Unsupervised domain adaptation is a widespread set of methods that leverages the knowledge of a labeled source domain to train a model to perform well on a related unlabeled target domain. They generally introduce an auxiliary adaptation-related task that can be integrated into the multitask paradigm, which aims to merge multiple single-task models into a unified architecture. In this paper, we propose to associate domain adaptation and multitask balancing in the realistic context of an extreme class imbalance. Therefore, we propose a combined framework to cover and validate these approaches, and evaluate its performance in the physics-based context of the Cherenkov Telescope Array Observatory (CTAO). Along with a comparative study of some relevant adaptation techniques, we highlight the impact of extreme label shift and extend the investigations on importance weighting to rectify it. The complete code and results are published and available as open-source resources on Zenodo.
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Astrophysics of Galaxies

A Chemical Inventory of the Disk around the Class 0 Protostar L1527 IRS with ALMA

Merel L.R. van 't Hoff, Łukasz Tychoniec, John J. Tobin et al. (+1 more)

Planet formation starts in disks that are still embedded within their natal envelopes. Here, we compile an extensive inventory of the chemical composition of the disk and envelope ($<$ 3500 au) around the Class 0 protostar L1527 IRS. Using all publicly available ALMA (Atacama Large Millimeter/submillimeter Array) data, we report the detection of 40 molecules, including isotopologues. Of these, 23 are different molecular species and 29 are reported here for the first time toward L1527 in ALMA observations. CH$_3$OH is the only complex organic molecule detected, while the hydrocarbon CH$_3$CCH is the largest molecule detected. Overall, only a few programs are sensitive enough to detect emission unambiguously originating from the disk based on the kinematics. Nitrogen-bearing molecules are predominantly detected on more extended scales, while hydrocarbons show a distinct tail roughly along the southeastern outflow cavity wall, probably due to a stronger UV field in the eastern outflow lobe. The L1527 IRS protostellar system is not rich in sulfur-bearing molecules, with only strong emission observed for CS and SO. Overall, the envelope appears dominated by a carbon-rich chemistry, which seems to transition into an oxygen-rich chemistry in the disk. We calculate column densities of all detected species, providing a starting point to quantify the chemical diversity among young disks and the chemical evolution of the planet-forming material.
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All authors Merel L.R. van 't Hoff, Łukasz Tychoniec, John J. Tobin, Daniel Harsono

Astrophysics of Galaxies

Ubiquitous Interstellar Neutral Helium Detected with JWST

Jane R. Rigby, D. Koutroumpa, M. Galeazzi et al. (+8 more)

We report the discovery of ubiquitous neutral helium emission in sky spectra taken with JWST's NIRSpec instrument. The emission, with a wavelength of 1.0833 micron, resembles one of the "sky lines" that are seen by ground-based observatories. We examine this emission in all suitable NIRSpec spectra in the public archive, totaling 22 days of exposure time. We find that this He I emission is almost always present: it is well-detected in 80 percent of the observations, and in 53 percent of the individual exposures. The emission is highly time-variable: at a given pointing, the line intensity can vary by factors of several over the course of a day. The He I emission is strongest when JWST crosses through the cone of interstellar neutral helium that is gravitationally focused by the sun; intensity during the cone crossing is anti-correlated with solar activity. The low redshift and narrow velocity width of the He I line, and the elevated intensity when JWST crosses through the focusing cone, together indicate that origin of the He I emission is cold Milky Way gas passing through our solar system. JWST provides a new way to study this interstellar gas, revealing new insights such as extreme variability on timescales of hours to days, which has not been previously reported.
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All authors Jane R. Rigby, D. Koutroumpa, M. Galeazzi, T. Hutchison, K. D. Kuntz, Rosalia O'Brien, Marshall Perrin, F. S. Porter, Yu. Ralchenko, B. M. Walsh, Brian Welch

Solar and Stellar Astrophysics

Sector-based morphological analysis of four planetary nebulae (J 320, NGC 2610, A 6672 and PRTM 1) observed with UVIT/ASTROSAT

Anisha Hazra, Ranjan Kumar, Sonika Piridi et al. (+1 more)

Four planetary nebulae (PNe), Jonckheere 320, NGC 2610, A 6672, and PRTM 1, have been imaged in the far-ultraviolet (FUV) filter F148W ($\lambda_{\mathrm {eff}} = 1481\, \mathring{A} $) using the Ultraviolet Imaging Telescope (UVIT) onboard ASTROSAT. The FUV images reveal faint extended emission structures surrounding the bright central star. A novel sector-based structural analysis technique was employed to examine the detailed FUV morphologies of PNe. In this method, sector strengths were calculated for each nebula and used to classify their structures. Our results show that Jonckheere 320 exhibits a polypolar morphology, while NGC 2610 and PRTM 1 display spherical structures. In contrast, A 6672 shows irregular or elliptical features in the FUV.
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All authors Anisha Hazra, Ranjan Kumar, Sonika Piridi, Ananta C. Pradhan

Astrophysics of Galaxies

Searching for low-surface-brightness galaxies with compact neural networks A parameter-efficient approach to first-pass selection of diffuse galaxy in HSC-SSP imaging

Günther K. Heemann, Henri Cecatka and Dominik J. Bomans

Low-surface-brightness galaxies (LSBGs) trace a diffuse and observationally challenging regime of galaxy formation that remains highly susceptible to selection effects in optical surveys. We present a hybrid LSBG detection pipeline that integrates compact convolutional neural networks (cCNs) as a morphological validation stage within a multi-step detection framework applied to HSC-SSP imaging. Permissive low-threshold source detection with SEP is followed by cCN-based morphological filtering, physically motivated consistency checks, and parametric surface-brightness modelling with galfitm. The cCN is deliberately constrained to ${\sim}10^4$ trainable parameters to match the spatial scales of diffuse emission and ensure computational efficiency at survey scale. The cCN reduces the initial detection set of ${\sim}77\times10^6$ objects by more than four orders of magnitude while recovering essentially all literature LSBGs that pass the detection stage. The resulting Gold catalog of 5156 candidates occupies the characteristic loci of LSBGs in colour-colour and structural parameter space, in close agreement with previously published HSC-SSP based samples. Cross-matching with SDSS and DESI spectroscopic redshifts confirms that the pipeline identifies genuine nearby diffuse galaxies. Compact neural networks provide a robust and computationally scalable morphological filter for LSBG searches, effectively bridging classical detection pipelines and large general-purpose deep architectures. The pipeline is detection-limited rather than selection-limited, identifying the initial source extraction stage as the primary target for future improvement.
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Astrophysics of Galaxies

Dust production in the harsh environment of Sgr A* - MIRI/JWST observation of the O-rich asymptotic giant branch star IRS~3

F. Peißker, M. García Marín, A. Eckart et al. (+18 more)

Studies of the interstellar medium (ISM) have frequently revealed signatures of the dust produced in the envelopes of asymptotic giant branch (AGB) stars, demonstrating a connection between the dust composition of the ISM and that of AGB stellar envelopes. Investigating this relationship in the extreme, radiation-dominated environment surrounding Sgr A*, the center of our own galaxy, reveals how such conditions might influence dust composition and the recycling of material in galactic centers. IRS 3, the brightest L band source in the Galactic center and most prominent AGB star within the inner parsec of the Milky Way, is embedded in a dusty envelope with an estimated radius of $\sim$10000 AU. We aim to conduct a comprehensive spectral analysis to more tightly constrain the dust composition and line-emitting species within the envelope of IRS 3 in the immediate vicinity of Sgr A*. In 2025, we observed the inner parsec of the Milky Way with the Mid-Infrared Instrument (MIRI) on board the James Webb Space Telescope (JWST) as part of the guaranteed time observations (GTO) program Mid-Infrared Characterisation of Nearby Iconic galaxy Centres (MICONIC). We used the MIRI Medium Resolution Spectrometer (MRS) to study the spectroscopic characteristics of the AGB star IRS 3, located about 0.17 parsecs in projection from Sgr A*.
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All authors F. Peißker, M. García Marín, A. Eckart, G. Wright, O. C. Jones, D. Dicken, A. Alonso Herrero, D. Rouan, D. Law, T. Böker, T. Henning, M. Baes, A. Labiano, L. Pantoni, L. Hermosa Muñoz, P.O. Lagage, P. van der Werf, G. Östlin, J. A. D. L. Blommaert, M. Güdel, P. Guillard

High Energy Astrophysical Phenomena

Global simulations of accretion flows onto perturbers embedded in magnetized disks -I. MRI and jet formation in ideal MHD

Raúl O. Chametla, F. J. Sánchez-Salcedo, Martin E. Pessah et al. (+1 more)

We present the highest resolution global MHD simulations to date of gas flow around a low mass a perturber with mass ratio $q\in[10^{-4},10^{-3}]$, embedded in an accretion disk around a massive central object. We find that gas flow onto the secondary self-consistently forms a turbulent, magnetized mini-accretion disk. The mini-accretion disk sustains a large-scale magnetic field generated by the dynamo effect of the MRI and the accretion flow into the perturber. Simultaneously, a bipolar, collimated, magnetized outflow is launched, extending beyond the perturber's Hill sphere. The bipolar outflows are driven by the combined action of magnetic pressure, in the innermost regions of the mini-accretion disk, and the magnetocentrifugal acceleration of gas, which may attain speeds comparable to the escape velocity from the massive central object. Our results establish an important conceptual connection in accretion disk physics across a wide range of astrophysical systems -from mini-accretion disks to circumstellar and black hole accretion disks-by demonstrating that no fine-tuning is required for small-scale disks to naturally enter an outflow-launching regime. Beyond identifying the physical mechanism responsible for launching small-scale outflows, our framework lays the groundwork for developing more sophisticated physical models of mini-accretion disks around embedded low-mass perturbers.
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All authors Raúl O. Chametla, F. J. Sánchez-Salcedo, Martin E. Pessah, Mauricio Reyes-Ruiz

Cosmology and Nongalactic Astrophysics

CMB Spectral Distortion Anisotropies from Acoustic Damping with primordial non-Gaussianity

Jens Chluba, Atsuhisa Ota and Nicola Bartolo

In this paper, we evaluate the precise distortion source and transfer functions caused by mixing of blackbodies of different temperatures using the recently developed frequency hierarchy (FH) treatment of CosmoTherm. With this we are able to evaluate the effects of primordial non-Gaussianity (PNG) on the $\mu T$, $\mu E$, $y T$ and $y E$ cross-power spectra including the coupled spectro-spatial evolution and important photon-transport effects retained by the FH treatment. For local-type PNG, we compare our results with those from previous works, illustrating new aspects that were previously not captured. We then demonstrate how the $\mu T$ and $\mu E$ signals change in the presence of enhanced curvature perturbations at small scales. For a nearly scale-invariant primordial spectrum, our results agree broadly with previous estimates on large angular scales but exhibit additional small-scale damping and modified $y$-distortion correlations arising from the scale dependence of the heating source and the distinct transport of distortion perturbations. Tight-coupling and monopole-source approximations accurately reproduce the $\mu$-distortion spectra, while the $y$-distortion signals remain more sensitive to the detailed source evolution. For enhanced small-scale power, anisotropies generated by propagation of the distorted average spectrum can become comparable to those from anisotropic dissipation. Their different angular dependences and parameter scalings principally allow the small-scale power amplitude and primordial non-Gaussianity to be constrained separately. The results presented here thus pave the path for studying PNG in new regimes using existing and upcoming high precision CMB anisotropy data to measure primordial distortion correlations.
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Astrophysics of Galaxies

The Environmental Dependence of Star Cluster Demographics

Jianling Tang, Kathryn Grasha, Mark R. Krumholz et al. (+1 more)

Both the star cluster mass function and the lifetimes of clusters may vary with galactic environment, but measuring this variation is challenging because in observational surveys real features of cluster demographics are invariably entangled with catalogue incompleteness. Here we analyse $\approx$ 8300 star clusters in 12 galaxies drawn from the LEGUS survey using the slug Bayesian forward modelling framework coupled to our new c-4 neural network-based completeness estimator, which allows us to incorporate realistic catalogue-inclusion probabilities directly into the likelihood and compensate for these biases. We show that this approach allows us to fit observed cluster luminosity functions with excellent fidelity at both galactic and sub-galactic scales. We find that mass function slopes are relatively universal and broadly consistent with a power law $M^{-2}$ form, but high mass truncations vary by orders of magnitude both between and within galaxies. Our fits also strongly favour models where cluster disruption is mass-independent, but the time at which disruption begins again shows wide environmental variations. Our results demonstrate that young cluster demographics are environmentally dependent, with the clearest signal appearing at the upper end of the cluster mass function, but that these variations are not well-explained by any of the models currently in the literature, and do not correlate straightforwardly with properties such as star formation rate per unit area or strength of shear.
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All authors Jianling Tang, Kathryn Grasha, Mark R. Krumholz, Tomasz Różański

Astrophysics of Galaxies

A Partial Lyman Limit Absorber in the Halo of a Galaxy Pair: A Possible Signature of Gas Inflow

Sumukha R. Bharadwaj, Anand Narayanan, Sowgat Muzahid et al. (+2 more)

We present an analysis of a partial Lyman limit system at z = 0.87641 detected in the HST/COS spectrum of the background quasar LBQS 0107-0235. The absorber exhibits a simple kinematic structure, with the metal-lines and the H I Lyman-series absorption well described by a single component. Photoionization modeling yields a gas metallicity of one-tenth solar and a hydrogen number density of n_H \approx 8.5 \times 10^{-4} cm^{-3} (log_{10}(n_H/cm^{-3}) \approx -3.1). At the absorber redshift, the VLT/MUSE data show two galaxies (G1 and G2) at normalized impact parameters of \rho/R_{vir} \approx 0.9 and velocity separations of |\Delta v| = 18 and 99 km s^{-1}, respectively, from the absorber. Both galaxies have rotating disks with stellar masses of M_* \approx 6 \times 10^9 and \approx 2.2 \times 10^{10} M_{\odot}. Their 100-Myr-averaged star formation rates are \approx 2.5 and \approx 2.2 M_{\odot} yr^{-1}, though their instantaneous rates place G2 on the star-forming main sequence and G1 above it, which is actively star-forming at this redshift. The absorber is positioned very close to the projected major axis of both galaxies. The absorber's orientation, kinematics, and sub-solar metallicity (log_{10}(Z/Z_{\odot}) = -1.05) are consistent with the absorption tracing a sub-solar metallicity inflowing stream, though a galaxy-galaxy interaction origin cannot be excluded. We discuss these scenarios in the context of cosmological simulations of cold-mode accretion and CGM gas flows around galaxies with halos of mass M_h \lesssim 10^{12} M_{\odot}.
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All authors Sumukha R. Bharadwaj, Anand Narayanan, Sowgat Muzahid, Jane C. Charlton, Sebastiano Cantalupo

High Energy Astrophysical Phenomena

Hyperaccreting Magnetised Neutron Stars inside Rotating Massive Envelopes: Low-Power Jets and Precursor Flares

Patrick Chi-Kit Cheong, Christopher L. Fryer and David Radice

The engulfment of a neutron star (NS) by a massive companion initiates a highly dynamic common-envelope (CE) evolution phase. As the NS spirals into the dense stellar core, it is subjected to hypercritical accretion rates that threaten to rapidly collapse the NS into a black hole (BH). However, if the infalling envelope possesses sufficient angular momentum and magnetic fields, the NS might survive longer and launch feedback-driving jets. To investigate this, we perform fully coupled, axisymmetric General Relativistic Magnetohydrodynamic (GRMHD) simulations of hyperaccreting NSs, featuring energy-integrated two-moment neutrino transport and a 13-isotope nuclear reaction network. We systematically vary the envelope rotation profile and the magnetic field strength of the NS surface ($B_{\rm surf} \sim 5 \times 10^{10} - 5 \times 10^{13}$~G). In non-magnetised models, we find that envelope rotation naturally forms a centrifugal barrier and a geometrically thick accretion disk, which suppresses the mass accretion rate and lowers the neutrino luminosity; conversely, the intrinsic spin of the NS has a negligible global impact. In magnetised models, the differential rotation of the accretion flow vigorously amplifies the toroidal magnetic field via the $\Omega$-effect, driving the expansion of magnetic towers. Crucially, for strong initial surface magnetic fields ($B_{\rm surf} \gtrsim 2.3 \times 10^{13}$~G), the intense magnetic pressure could completely halt the accretion flow at the NS surface and evacuates a low-density polar funnel. We conclude that while this highly magnetised NS engine successfully delays prompt BH formation and may launch low-power precursor jets (with powers up to ${\sim} 10^{46}~{\rm erg/s}$) capable of generating observable X-ray flares, it lacks the energy budget to unbind the massive envelope, potentially setting the stage for a subsequent BH-driven explosion.
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Cosmology and Nongalactic Astrophysics

Big-Bang Nucleosynthesis and WIMP Dark Matter Freeze-Out as Probes of Yukawa Cosmology

Ava Shahbazi Sooraki and Ahmad Sheykhi

We investigate Big-Bang Nucleosynthesis (BBN) in the context of Yukawa cosmology. We first derive the modified Friedmann equations by starting from the first law of thermodynamics on the apparent horizon. Using observational data on \(^4\mathrm{He}\), deuterium, and \(^7\mathrm{Li}\) abundances, we place stringent bounds on the Yukawa coupling \(\alpha\). The \(^4\mathrm{He}\) and deuterium constraints are mutually consistent (\(-0.24 \lesssim \alpha \lesssim 0.12\)), while \(^7\mathrm{Li}\) requires $\alpha \in [-0.76,\,-0.72]$. This indicate that Yukawa cosmology cannot resolve the Lithium Problem. We then extend our analysis to WIMP freeze-out, and show that the modified Hubble parameter alters the relic abundance, yielding an independent constraint \(-0.017 \lesssim \alpha \lesssim 0.018\) from \(\Omega_{\mathrm{CDM}}h^2 = 0.120 \pm 0.001\). We also derive the modified time-temperature relation, and show that the positive \(\alpha\) raises the early Universe temperature. Our analysis demonstrates that BBN and dark matter relic abundance serve as complementary probes of modified gravity. Our studies confirm that Yukawa cosmology is a testable framework for early-Universe physics.
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Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc

Observational constraints on fractional holographic dark energy in the light of DESI DR2

Qihong Huang, Yuchen Zhang, Bing Xu et al. (+1 more)

Based on the fractional entropy from fractional quantum mechanics, fractional holographic dark energy (FHDE) has been proposed with the Hubble horizon as the IR cutoff (FHDEH). We extend this framework by adopting the future event horizon and the particle horizon as the IR cutoff, proposing the FHDEF and FHDEP models. Using the SN+OHD+DESI DR2 dataset to constrain these models, we find that all three models provide a marginally lower $\chi^{2}_{min}$ compared to $\Lambda$CDM but without significant preference according to AIC and BIC. When CMB distance priors are included, the FHDEH and FHDEP models are strongly ruled out. We further analyze the cosmological evolution for these models, and find that only the FHDEF model predicts nearly identical evolutions of $\Omega_{m}$ and $\Omega_{de}$ to those of the $\Lambda$CDM model across cosmic history, but its deceleration parameter $q$ deviate from the $\Lambda$CDM model in the future, indicating richer late time dynamics beyond the standard $\Lambda$CDM cosmology.
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All authors Qihong Huang, Yuchen Zhang, Bing Xu, Kaituo Zhang

Earth and Planetary Astrophysics

A Machine Learning Based Search for Lunar Anomalies

Cameron Kelahan, Daniel Angerhausen, Adam Lesnikowski et al. (+1 more)

The Lunar Reconnaissance Orbiter (LRO) has been collecting high-resolution images (at around 0.5-2 meters per pixel linearly with its Narrow Angle Camera) of the Moon since 2009, amassing a large dataset of images and offering researchers the opportunity to study the surface of the Moon at unprecedented scale. Here, we aim to test the abilities of the Beta-Variational Autoencoder (VAE) created by Lesnikowski et al. (2024), an unsupervised learning model which identifies anomalous features across the Moon's surface, locating not only scientifically useful geologic formations such as rockfall deposits, fresh impact craters, irregular mare patches, or volcanic pits/collapsed lava tubes, but also artificial objects such as landed spacecraft. This investigation further gauged the model's ability to locate anomalous surface features, successfully recovering two places of interest (Plaskett Crater and Paracelsus C Crater) and numerous landed technological assets at a statistically significant rate.
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All authors Cameron Kelahan, Daniel Angerhausen, Adam Lesnikowski, Valentin T. Bickel