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Physics Astrophysics

astro-ph Watch Astrophysics

Saturday 15 August

Astrophysics of Galaxies

Improved constraints on the Milky Way potential using the M68 stream and DESI spectroscopic data

Carles G. Palau, Wenting Wang, Jiaxin Han et al. (+41 more)

We present a selection of stars belonging to the stellar stream of the M68 (NGC 4590) globular cluster, also known as Fjörm. This star selection is an improvement on previous ones that used only Gaia data, as it incorporates spectroscopic measurements from the DESI survey and photometric data from the DESI Legacy Surveys. The selection contains 96 stars, each with five phase-space parameters from Gaia-DR3 and radial velocity from DESI, covering the entire observed section of the stream. This constitutes the largest selection of M68 stream stars with measured radial velocities to date. The observed stream is wider than expected from N-body simulations, and the stars farthest from the centre of the stream appear to be correlated in radial velocity space. This suggests that these stars cannot have been stripped from the cluster in a static axisymmetric potential. By modelling a mock sample of stream stars created using an N-body simulation, we found that we could reliably constrain the disc mass $M_{\rm d}$ and the dark matter halo axis ratio $q_{\rm h}$ of the Milky Way. This is because the stream flows close to and almost parallel to the disc. Using the 44 stars that are consistent with having been stripped from the cluster, combined with measurements of the Milky Way's rotation curve, we constrain the Galactic potential, obtaining $M_{\rm d} = 5.34 \pm 0.57 \times 10^{10}$ M$_{\rm sun}$ and an oblate halo of $q_{\rm h} = 0.83^{+0.06}_{-0.05}$. Additionally, by fitting the stream track, we estimate the Heliocentric distance of M68 to be $r=10.55\pm0.09$ kpc.
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All authors Carles G. Palau, Wenting Wang, Jiaxin Han, J. Aguilar, S. Ahlen, F. Beutler, D. Bianchi, D. Brooks, A. Carnero Rosell, F. J. Castander, T. Claybaugh, A. Cuceu, A. de la Macorra, J. E. Forero-Romero, E. Gaztañaga, Satya Gontcho A Gontcho, G. Gutierrez, J. Guy, D. Kirkby, A. Kremin, M. Landriau, L. Le Guillou, A. Leauthaud, G. E. Medina, A. Meisner, R. Miquel, S. Nadathur, H. E. Noriega, E. Paillas, N. Palanque-Delabrouille, W. J. Percival, F. Prada, I. Pérez-Ràfols, C. Ravoux, G. Rossi, R. Ruggeri, E. Sanchez, C. Saulder, D. Schlegel, M. Schubnell, M. Siudek, G. Tarlé, B. A. Weaver, H. Zou

Solar and Stellar Astrophysics

Stability of circumbinary orbits in misaligned triple star systems

Stephen Lepp and Rebecca G. Martin

We investigate the stability of circumbinary orbits in hierarchical triple star systems, focusing on the effects of a misaligned outer companion star. Test particles are subject to competing gravitational torques from the inner binary and the outer binary companion. With secular theory we estimate the outer radius of particle stability, where the torques balance. We find good agreement with $n$-body simulations across a wide range of triple star configurations. Stable circumbinary orbits can exist even in strongly misaligned triples. Polar and highly inclined orbits with respect to the inner binary can remain stable over a substantial radial range, which is insensitive to the triple star misalignment. Orbits that are close to coplanar or retrograde coplanar to the inner binary are more susceptible to instability when the mutual inclination between the binaries is large. These findings indicate that misaligned and polar circumbinary disks and planets can survive in triple star systems under a broad set of conditions. The analytic criterion identifies where stable material may exist, with implications for the formation and detection of circumbinary planets in multiple-star systems.
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Cosmology and Nongalactic Astrophysics

Prospects for Direct Detection of Ultralight Dark Matter candidates in deci-Hz Band with IndIGO-D

Md. Emanuel Hoque, Andrew L. Miller and Arunava Mukherjee

We investigate the sensitivity of IndIGO-D, a proposed space-based decihertz gravitational-wave interferometer, to different classes of ultralight dark matter. IndIGO-D will probe the $\sim0.01$–$10~\mathrm{Hz}$ frequency band between those accessible to current ground- and future space-based gravitational-wave interferometers, providing access to ultralight dark-matter masses beyond the reach of existing instruments. We consider two complementary signatures: interferometric displacements induced by coherently oscillating scalar (dilaton), vector (dark-photon, $U(1)_B$ and $U(1)_{B-L}$ gauge groups), and tensor fields with masses $m_{\rm DM}\sim10^{-17}$–$10^{-14}~\mathrm{eV}$; and changes in laser polarization induced by pseudoscalar axion dark matter at higher masses, around $m_a\sim10^{-12}~\mathrm{eV}$. For the dilatons, dark photons and tensors, we compute the expected sensitivities using two pipelines – cross-correlation and BSD excess-power – assuming L-shaped and triangular interferometer layouts and three representative noise power spectral densities (S1, S2, S3), each for two years of continuous observation. We find that the projected sensitivities agree to within a factor of order unity across the search pipelines and interferometer geometries. In particular, we show that IndIGO-D could open previously unconstrained coupling parameter space for vector and tensor dark matter across $m_{\rm DM}\sim10^{-16}$–$10^{-14}~\mathrm{eV}$, bridging the sensitivity of space- and ground-based experiments. For axion dark matter, we demonstrate that a complementary detection for laser light polarization shifts, limited primarily by photon shot noise, could probe the axion-photon coupling $g_{a\gamma}$ at masses around $m_a\sim10^{-12}~\mathrm{eV}$ at a level potentially better than that of other future experiments without degrading sensitivity to gravitational waves.
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Earth and Planetary Astrophysics · Cross-listed from hep-ex

Deep Earth imaging through neutrino and seismic tomography

Sanjib Kumar Agarwalla, Arjun Datta, Amol Dighe et al. (+2 more)

This article is a report on the Deep Earth Neutrino + Seismic Imaging and TomographY (DENSITY 2026) mini-workshop, held on 23–24 February 2026 in the Department of Earth and Climate Science at the Indian Institute of Science Education and Research (IISER), Pune. The workshop was jointly organised by IISER Pune and the Institute of Physics (IOP), Bhubaneswar. Researchers from Earth Sciences and Neutrino Physics participated in the workshop to explore multipronged approaches for studying the deep interior of the Earth. Since the participants came from diverse scientific disciplines (seismology, geochemistry, mineral physics, and neutrino physics), the programme featured a series of overview talks introducing all participants to the basic concepts of each field and highlighting how these concepts may be applied to the study of the deep Earth.
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All authors Sanjib Kumar Agarwalla, Arjun Datta, Amol Dighe, Vinod Kumar Gaur, Anuj Kumar Upadhyay

Solar and Stellar Astrophysics

A self-consistent solar coronal heating model by Alfvenic waves

Hidetaka Kuniyoshi and Richard J. Morton

Alfvenic waves are prevalent throughout the solar atmosphere and are believed to play an essential role in coronal heating, classified as alternating current (AC) heating in contrast to direct current (DC) heating associated with quasi-static magnetic field line braiding. The relative importance of AC versus DC heating depends on the details of the photospheric driver and on the configuration of the magnetic field. Moreover, even if AC heating prevails, several wave dissipation mechanisms have been proposed, and which of them dominates remains unclear, as its efficiency depends on plasma compressibility and density inhomogeneity. We address these issues by performing three-dimensional radiative magnetohydrodynamic (MHD) simulations of a coronal loop spanning from the upper convection zone to the corona, which self-consistently capture many relevant physical processes. We find that the corona is predominantly heated by AC heating, with Alfven wave turbulence providing the primary contribution, accounting for at least 80% of the entire coronal heating in the present simulation. Our results strongly support the use of Alfven wave turbulence-based models employed in space weather and stellar activity research, such as the Alfven Wave Solar Model (AWSoM) and the Magnetohydrodynamic Algorithm outside a Sphere (MAS).
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Instrumentation and Methods for Astrophysics

Design and Realization of the LST Main Structure for the Cherenkov Telescope Array

T. Schweizer, J. Eder, H. Wetteskind et al. (+12 more)

The 23 m diameter Large Size Cherenkov Telescope (LST) for CTA, located at 2250 m a.s.l. on the Canary Island of La Palma, is the next-generation Cherenkov telescope following MAGIC, H.E.S.S., and VERITAS. To enable rapid repositioning (180{\deg} in 18 s) for gamma-ray burst observations, the mechanical structure was designed to be ultra- lightweight (110 tons). The space-frame structure consists of slender struts made of carbon fibre, aluminium (dish and camera mast), and steel. The telescope is designed to withstand extreme environmental conditions at the ORM observatory on La Palma, including wind speeds up to 200 km/h, uplift forces, and ice loads of up to 30 tons. We present the structural design developed to meet these functional and environmental requirements. MPP Munich is responsible for the telescope's mechanical structure together with partner institutes in France (LAPP) and Spain (IFAE). The prototype, LST-1, has been operational since 2019, and three additional LSTs are curre1ntly under construction.
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All authors T. Schweizer, J. Eder, H. Wetteskind, C. Jablonski, R. Stadler, R. Mirzoyan, D. Paneque, T. Masahiro, A. Fiasson, N. Geffroy, G. Deleglise, O. Blanch, J. Mundet, R. Garcia, A. J. Penuela Lopez

Instrumentation and Methods for Astrophysics

Adapting the 23m LST-North mechanical structure design for the strong Chile seismic environment

Thomas Schweizer, Josef Eder, Teshima Masahiro et al. (+2 more)

The 23-meter-diameter Large-Sized Telescope (LST) is the largest size telescope of the next generation Cherenkov Telescope Array (CTA). The first telescope, LST-1, was installed at the Roque de los Muchachos Observatory (ORM) on La Palma at an altitude of 2,250 m in 2018 and has been in operation since 2019. Its ultra-lightweight structure (110 tons) enables extremely rapid repositioning (180{\deg} in 18 seconds) and has been designed to withstand extreme environmental conditions, including storms and winds exceeding speed up to 200 km/h. To deploy the same solid telescope design at the CTA Southern Observatory in Chile, the structure must be adapted to the significantly higher seismic demands of the site. To address this challenge, the Max Planck Institute for Physics (MPP) has proposed the integration of a seismic isolation system with the proven LST-1 structural design. This approach substantially reduces seismic loads and dynamic amplification, thereby avoiding extensive structural modifications and enabling the existing telescope design to be transferred to the Chilean site with only minor adaptations. In this contribution, we present the proposed seismic isolation concept and its feasibility studies. MPP is responsible for the mechanical structure of the LST and has validated the concept through detailed finite-element analyses and long-term structural lifetime assessments.
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All authors Thomas Schweizer, Josef Eder, Teshima Masahiro, Holger Wetteskind, Razmik Mirzoyan

Cosmology and Nongalactic Astrophysics

Testing a Sign-Switch Cosmological Model with Curvature through Latest Planck 2018, DESI DR2 and PantheonPlus&SH0ES Observational Data

Archana Dixit, Manish Yadav, Anirudh Pradhan et al. (+1 more)

We investigate the spatial geometry of the Universe within the framework of a sign-switch dark energy scenario by extending the recently proposed $\Lambda_{\rm s}$CDM model to include a free curvature parameter $\Omega_k$.In this framework, the effective cosmological constant undergoes a transition from a negative to a positive value at a characteristic redshift $z_{\dagger}$. Using the latest Planck 2018 cosmic microwave background (CMB) data, DESI DR2 baryon acoustic oscillation (BAO) measurements, and the PantheonPlus&SH0ES Type Ia supernova sample, we derive joint constraints on the spatial curvature parameter $\Omega_k$ and other cosmological parameters. We find that Planck data itself slightly favors a closed universe within both the $\Lambda_{\rm s}$CDM$+\Omega_k$ and $\Lambda$CDM$+\Omega_k$ frameworks, although spatial flatness remains well within the allowed uncertainties. When low-redshift probes were included, the curvature constraints were significantly tightened. In particular, the full Pk18+DR2+PP&SH0ES dataset yields $\Omega_k = 0.0001 \pm 0.0014$ for the $\Lambda_{\rm s}$CDM model, indicating a universe that is remarkably consistent with spatial flatness. We further analyzed the correlations between $\Omega_k$, $H_0$, and $S_8$, finding that the inclusion of curvature and a sign-switch dark energy component helps stabilize cosmological parameter estimates while remaining compatible with current observational constraints. Model comparison using AIC and Bayesian evidence shows that the $\Lambda_{\rm s}$CDM model receives inconclusive/weak observational support relative to $\Lambda$CDM.
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All authors Archana Dixit, Manish Yadav, Anirudh Pradhan, M. S. Barak

Instrumentation and Methods for Astrophysics

Stress-Testing DANTE under Detector Domain Shift: a Representation-Coherent Reanalysis of LIGO O4a

Luca Cirfeta

This sixth version of the Domain-Adaptive Network for Transient Evaluation (DANTE) preprint stress-tests an unsupervised transient-noise pipeline under representation mismatch and observing-run adaptation. We reanalyse 10,429 detector-time strain candidates from 42 LIGO O4a sessions using frozen DINOv2 patch embeddings and a Top-k multiple-instance score. Candidate and native-background Q-transforms share Q in [4,64], and detector-specific thresholds are calibrated from 5,000 run-native windows by temporal-block bootstrap. The coherent analysis yields 6,365 ROBUST, 1,275 AMBIGUOUS, and 2,789 BACKGROUND statistical dispositions; 4,676 of 10,372 paired historical dispositions differ from the cross-representation v5 analysis. Direct controls resolve an O3b-O4a score shift and reduction after native adaptation for H1, but not L1, while known-glitch separation is detector- and morphology-dependent. Replicated studies quantify population-dependent sensitivity to background draw, clustering seed, dictionary size, and whitening, demonstrate native-index absorption, and identify conditional low-Q blindness. A conservative H1-L1 max-shift screen yields 13/8,806 values above threshold, but its on-source values and pooled per-event null maxima are not exchangeable. The primary two-null PEM endpoint shows no resolved ROBUST-BACKGROUND enrichment (p=1.000), and two catalogue overlaps are consistent with a circular-shift coverage proxy (p=0.651). Simulation-only compact-binary controls show detector- and distance-dependent disagreement between novelty, native disposition, and physical coincidence. We withdraw the v5 discovery, rate-limit, catalogue-recall, and survey-wide stability interpretations. The supported result is a measured set of failure modes and validity conditions for unsupervised detector characterization, not a new glitch class or an astrophysical search.
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2608.15166 · 15 Aug · 12 pages, 10 figures, 1 table. Sixth version: representation-coherent O4a reanalysis, detector-aware catalogue reconstruction, replicated robustness and failure-mode validation, physical and catalogue null controls, and withdrawal of unsupported v5 discovery, rate-limit, catalogue-recall, and survey-wide stability interpretations

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Instrumentation and Methods for Astrophysics

Parameter estimation in differential equations: Mathematical foundations for satellite gravimetry, review and perspectives

Peiliang Xu

Satellite gravimetry has become essential in many areas of earth science. However, the resolution of satellite gravitational models remains low at scales of a few hundreds km and no gravity recovery methods can take full advantages of unprecedented high accuracy of satellite tracking measurements. We first provide a unified theoretical framework of parameter estimation in differential equations for satellite gravimetry and then briefly review the mathematical methods to compute the gravity field of the Earth from satellite tracking. We focus on the collocation method, Kaula linear perturbations, two-point boundary value problems and orbit-energy-based methods. The numerical integration method is also included in this review, though it has been proved to be mathematically incorrect and physically not permitted. The reason is that it has become the standard method to routinely produce global gravitational models from satellite tracking data, which have been widely applied in many different areas of earth science. Because it is not clear how the incorrect foundation would affect gravity products from satellite tracking, we do not review any applications of these products. We then present a measurement-based perturbation theory to estimate the gravity field of the Earth, which can fully utilize both precise satellite orbits of arbitrary length and unprecedented high accuracy of satellite and inter-satellite tracking. The method is theoretically free of modeling errors, is capable of extracting any small forces from satellite and inter-satellite tracking data and provides a guarantee for high-precision and high-resolution global gravity models. Finally, we assume a reference gravity model and derive local solutions to the Newton's nonlinear governing differential equations of satellite motion for scattered tracking data that can still be important in some applications.
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Cosmology and Nongalactic Astrophysics

Improved Cosmological Constraints from Morphology-Based Marked Correlation Functions

Xu Xiao, Zhao Chen, Yu Yu et al. (+2 more)

The cosmic web contains morphology-dependent information that is not fully captured by standard two-point statistics. We construct morphology-based marked correlation functions (MCFs) by assigning marks to halos according to the cosmic-web morphology identified with the Nexus algorithm. Using the Kun simulation suite, which spans 129 $w_0w_a$CDM cosmologies, we build Gaussian-process emulators for the MCFs as functions of cosmological parameters and tracer bias. We then apply the emulators to mock halo catalogues from the independent Jiutian simulation and perform a joint likelihood analysis to quantify the resulting cosmological constraints. We consider two marker choices: a discrete morphology marker and a continuous morphology strength marker. The continuous marker improves the Figure of Merit (FoM) by a factor of $\sim 8.6$ relative to the standard 2PCF and reduces the $1\sigma$ uncertainty on $\sigma_8$ by a factor of $\sim 5$. The discrete marker gives a more modest FoM improvement of $\sim 17\%$. We further test the impact of tracer selection by varying the halo mass threshold by a factor of $\sim 4.5$. Even for the lowest mass threshold, the continuous marker remains unbiased and achieves a FoM about $\sim 3.4$ times higher than that of the 2PCF alone. These results show that morphology-based MCFs, combined with simulation-based emulation, provide a useful framework for extracting additional cosmological information from large-scale structure surveys.
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All authors Xu Xiao, Zhao Chen, Yu Yu, Xiao-Dong Li, Le Zhang

Earth and Planetary Astrophysics

Scaling of microcraters with molten rims derived from laser-induced cratering experiments

S. Sato, H. Shibayama, K. Nagai et al. (+1 more)

Microcraters with molten rims are widely observed in returned samples from the Moon and asteroids. These features reflect the conditions of small-scale impact events, but the impact velocities required for their formation are not well understood. In this study, we use well-controlled laser irradiation on rock surfaces as an experimental analog to investigate the formation of these molten-rim craters. Specifically, we derive a scaling relation between crater volume, total irradiation energy, and energy loss associated with thermal diffusion. The experimental results indicate that molten-rim structures of microcraters can be formed in the range of $10^2$–$10^3$~m/s impact velocity. This value is consistent with some previous studies which suggested that the origin of microcraters is secondary impact events. These findings provide experimental constraints on the formation mechanisms of molten-rim microcraters and offer a new perspective on impact processes recorded on planetary surfaces. The estimated result is also consistent with the impact velocity required to produce the observed wavy rim protrusions due to a Rayleigh-Taylor hydrodynamic instability ($\sim 10^2$~m/s).
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All authors S. Sato, H. Shibayama, K. Nagai, H. Katsuragi

Solar and Stellar Astrophysics

Panchromatic JWST Observations and Models of the Dim Type Iax Supernova 2024vjm at 200 days

E Baron, J. M. DerKacy, C. Ashall et al. (+23 more)

We report JWST spectra and photometry of the underluminous SN Iax 2024vjm obtained 202.8 restframe days post-explosion. The spectrum exhibits a rich set of forbidden lines from low-ionization, intermediate-mass, and iron-group elements, notably the [Ni II] 6.64 micron resonance line, which is a direct indicator of stable nickel. Strong CO and SiO emission is detected alongside a warm dust continuum; the spectral properties are consistent with pre-existing rather than newly formed dust. Synthetic spectra were computed with the generalized stellar atmospheres code PHOENIX/1D using simplified ejecta models. The models reproduce the overall spectral energy distribution and the molecular emission features reasonably well, but substantially underestimate the strength of the mid-infrared atomic forbidden lines, leaving the synthetic spectrum dominated by molecular emission. Experiments in which the molecular opacity is suppressed do not recover the forbidden lines; instead, the emission peak migrates to Co and Fe transitions near 2 microns. We attribute this discrepancy to poorly constrained collisional rates and possibly to an excess of iron-group material in the current ejecta models. A prominent feature at 12.8 microns is not well accounted for by the [Ne II] 12.81 micron line, indicating that the 12.8 micron feature may be largely due to [Fe III]. The presence of CO, SiO, and stable nickel together with the non-detection of neon places tight constraints on the total ejecta mass and the nucleosynthetic yields of SNe Iax progenitor systems.
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All authors E Baron, J. M. DerKacy, C. Ashall, M. Shahbandeh, Peter H. Hauschildt, T. Barman, J. P. Aufdenberg, C. R. Burns, N. Morrell, M. D. Stritzinger, P. Hoeflich, K. Medler, E. Fereidouni, C. M. Pfeffer, T. Mera, W. B. Hoogendam, S. Shiber, P. J. Brown, Divya Mishra, Inma Dominguez, L. Galbany, Paolo Mazzali, E. Y. Hsiao, Huangfei Xiao, T. de Jaeger, S. Kumar

Astrophysics of Galaxies

Aromatics and Aliphatics in Local Star-Forming Galaxies as Probed by AKARI

Junhao Peng, Xuejuan Yang and Aigen Li

Polycyclic aromatic hydrocarbon (PAH) molecules are abundant and widespread in galaxies and their infrared (IR) emission traces star formation. PAH molecules in astronomical environments often have aliphatic contents as revealed by the detection of the 3.4 micron aliphatic C–H stretch, a weak satellite feature accompanying the 3.3 micron aromatic C–H stretch. Here, we selected 102 local star-forming galaxies from the AKARI archive, including 66 galaxies each of which hosts an active galactic nucleus (AGN). We analyzed their AKARI near-IR spectra, which exhibit pronounced 3.3 micron aromatic and 3.4 micron aliphatic C–H emission. We also compiled their multi-wavelength photometric data and performed a decompositional analysis of their spectral energy distributions (SEDs) from the ultraviolet (UV) to the far-IR to derive the star formation rates (SFRs), stellar masses, metallicities, and luminosity of the galaxies. We explored the 3.3 micron PAH emission luminosity ($L_{3.3}$) as a calibrator of the SFR and found a close agreement with previous studies. We also found that $L_{3.3}/L_{\rm IR}$ and $L_{3.4}/L_{\rm IR}$ exhibit a strong dependence on metallicity, but remain nearly constant above 12+log(O/H)$\sim\,$8.5, where $L_{\rm IR}$ is the total luminosity emitted by dust, and $L_{3.4}$ is the luminosity of the 3.4 micron aliphatic emission. We derived from $L_{3.4}/L_{3.3}$ the PAH aliphatic fractions, defined as the fractions of carbon atoms in aliphatic units, to be in the range of $\sim\,$0.38%–6.8%, with a median fraction of $\sim\,$3.1%. The PAH aliphatic fractions are lower in AGN hosts and show a weak negative correlation with the SFR and $L_{\rm IR}$, suggesting that UV photons in regions with AGN or strong star formation activities may photodissociate the aliphatic structures associated with PAH molecules.
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High Energy Astrophysical Phenomena

An ALMA view of the Jet-Arc CO clouds toward the TeV $\gamma$-ray source HESS J1023-575 and Westerlund 2; Evidence for the footprints of microquasar jets, the very powerful cosmic-ray accelerator in the Galactic disk

Yasuo Fukui, Kisetsu Tsuge, Hidetoshi Sano et al. (+7 more)

The TeV $\gamma$-ray source HESS J1023-575 (HESSJ 1023 hereafter) is one of the brightest H.E.S.S. sources near the young massive cluster Westerlund 2. HESS J1023 shows a remarkable positional alignment with the Jet and Arc CO clouds on its eastern and western sides over 170 pc length. We have carried out sub-pc scale observations of the CO clouds with ALMA and have discovered that the clouds consist of numerous thin filamentary features of $\sim$0.5 pc width and 10–20 pc length at distance of 7.5 kpc, which are well aligned with the Jet-Arc axis. Based on the magneto-hydrodynamical model of microquasar jets launched from {the center of the $\gamma$-ray source} HESS J1023-575, we present an interpretation that the thin filamentary clouds are the footprints of the microquasar jets on the HI gas. The model also explains the dissimilar Jet vs. Arc clouds in terms of HI density difference on each side. By using the density of the CO and HI gas and the $\gamma$-ray luminosity, we have calculated the cosmic ray proton energy $W_{\rm p}$ to be 7$\times$10$^{48}$ erg under the hadronic scheme, which is ten times larger than those derived in the TeV $\gamma$-ray SNRs RX J1713.7-3946 and RX J0852.0-4622. It is likely that HESS~J1023 has been active over 1-10 Myr, which is significantly longer than the duration of cosmic ray acceleration of the SNRs. HESS~J1023 is therefore an outstanding source of cosmic rays equivalent to at least 1000 SNRs, and is possibly the most powerful CR accelerator in the Galactic disk. A high energy compact source in HESS~J1023, which is likely a Myr-old black hole or neutron star, remains veiled due to heavy extinction.
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All authors Yasuo Fukui, Kisetsu Tsuge, Hidetoshi Sano, G. R. Bhuvana, Rin I. Yamada, Ryoji Matsumoto, Yuta Asahina, Tsuyoshi Inoue, Tim Lukas Holch, Emma de Oña Wilhelmi

Astrophysics of Galaxies

Detection of Aliphatically Deuterated Aromatic Hydrocarbons in the Large Magellanic Cloud 30 Doradus Star-Forming Complex

Junhao Peng, Xuejuan Yang and Aigen Li

The unidentified infrared (IR) emission (UIE) bands at 3.3, 6.2, 7.7, 8.6, 11.3 and 12.7 micron are ubiquitously seen in a wide variety of astrophysical environments. While the exact assignment of these UIE bands remains controversial, they are generally ascribed to C–H and C–C stretching and bending vibrations of aromatic hydrocarbon molecules. Here, based on observations made with the Near Infrared Spectrograph (NIRSpec) and the Mid Infrared Instrument (MIRI) aboard the James Webb Space Telescope (JWST), we report that the UIE emitters in the 30 Doradus star-forming complex in the Large Magellanic Cloud (LMC) are deuterated and have an appreciable amount of aliphatic content. The spatially resolved NIRSpec and MIRI spectra of 30 Doradus reveal a widespread detection of the 3.4 and 6.85 micron emission features attributed to aliphatic C–H stretch and deformation, respectively, as well as the 4.65 micron feature attributed to aliphatic C–D stretch. Notably, the 6.85 micron feature exhibits three complex substructures at ~6.83, 6.86 and 6.88 micron that have never been reported before.
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Astrophysics of Galaxies

Infrared Spectroscopy of Cyanonaphthalenes under Interstellar Relevant Conditions and Their Potential Connection with Astronomical Aromatic Infrared Bands

Jiaqi Xin, Jianzhi Xu, Piero Ferrari et al. (+1 more)

Context. Aromatic infrared bands (AIBs) are widely observed in diverse astrophysical environments and are generally attributed to vibrational emission from polycyclic aromatic hydrocarbons (PAHs). The recent interstellar detection of 1-cyanonaphthalene (1-CNN) and 2-cyanonaphthalene (2-CNN) has motivated detailed infrared spectroscopic studies of cyano-substituted PAHs. Aims. We aim to characterize the infrared spectra and vibrational modes of neutral 1-CNN and 2-CNN under cold and gas-phase conditions and to assess their possible spectroscopic relevance to the astronomical AIBs. Methods. The gas-phase infrared spectra of neutral 1-CNN and 2-CNN were measured in a cold molecular beam using ion-dip spectroscopy. The observed bands were assigned with the aid of harmonic and anharmonic calculations at the B3LYP/N07D level. Infrared emission spectra were subsequently simulated from the experimental spectra within a single-photon approximation framework. Results. We report the infrared spectra of neutral 1-CNN and 2-CNN measured under cold and gas-phase conditions relevant to the interstellar medium. Their vibrational features were assigned in detail, including fundamental vibrations as well as overtone and combination bands. The simulated emission spectra exhibit features in several wavelength regions associated with prominent AIBs, including the aromatic CH stretching region near 3.3 micron, the CC stretching region near 6.2 micron, the mixed CH in-plane bending and CC stretching region at 8.6-8.9 microns, and the CH out-of-plane bending region between 10 and 15 microns. Conclusions. The present spectra provide laboratory reference data for small cyano-substituted PAHs and offer useful clues for interpreting selected AIB regions. These results suggest that cyanonaphthalene molecules are promising contributors to the aromatic infrared bands.
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All authors Jiaqi Xin, Jianzhi Xu, Piero Ferrari, Gao-Lei Hou

Friday 14 August

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

Area-product universality in multi-horizon black hole entropy

Francisco Tello-Ortiz, Y. Gómez-Leyton, Jean Báez Cuevas et al. (+1 more)

Black-hole entropy and multi-horizon area-product relations represent two apparently distinct manifestations of universality, arising respectively from microscopic statistics and classical geometry. We show that these structures are unexpectedly connected. Extending a minimum-assumptions statistical discretization to multiple Killing horizons, with distinct horizon sectors treated as statistically independent, we derive a general area-product rule. In particular, while the leading Bekenstein-Hawking entropy probes the sum of the horizon areas, the logarithmic correction probes their product. Consequently, whenever the classical area product is mass independent, the logarithmic entropy automatically inherits this universality. We demonstrate this for Reissner-Nordström and, under an area-based extension to rotating horizons, Kerr-Newman black holes. However, Reissner-Nordström-de Sitter provides a crucial three-horizon counterexample, for which the area-product rule survives while mass independence is generically lost for the physical horizons. Thus, statistical area-product selection and classical universality are distinct properties. Our results uncover a structural connection between microscopic entropy counting and classical multi-horizon geometry that is invisible at the level of the leading area law, suggesting that logarithmic corrections encode distinctive information about the global horizon structure.
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All authors Francisco Tello-Ortiz, Y. Gómez-Leyton, Jean Báez Cuevas, Emmanuel N. Saridakis

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

Singlet Extended Mirror Standard Model World as Dark Matter and Gravitational Waves Imprints of a High Scale Mirror Phase Transitions

Asterios T. Papadopoulos and V.K. Oikonomou

We study a mirror Standard Model world which contains a high scale duplicate of the Standard Model, and includes a singlet mirror scalar extension coupled to the mirror Higgs particle. Among the interactions of the mirror Higgs to the mirror singlet scalar, we include dimension-six non-renormalizable operators. We examine the electroweak phase transition of this mirror singlet extended world and we show that the phase transition is a strong first order phase transition, the bubble collision of which can be detectable by LISA, the BBO and the DECIGO gravitational wave experiments. We also provide a rough estimate of the abundance of the mirror singlet and we show that the whole dark matter in the Universe may be comprised by mirror particles and atoms.
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High Energy Astrophysical Phenomena

Controlling artificial surface heating in neutron star simulations: Application to hybrid equations of state

Georgios Doulis

The treatment of the stellar surface in binary neutron star simulations is crucial for the accuracy of the numerical evolution and the physical reliability of the predicted observables. Numerical artifacts associated with the treatment of steep gradients near the stellar surface can produce spurious heating during the inspiral, leading to an artificial increase of the internal energy and an unphysical expansion of the neutron star. In this work, we investigate the effectiveness of the entropy-based flux-limiting (EFL) scheme in mitigating these numerical effects within the finite-difference code BAM. We perform simulations of both isolated neutron stars and binary neutron star inspirals employing a representative set of hybrid equations of state. We show that the EFL scheme significantly reduces artificial surface heating. This reduction is observed consistently across all stellar models and binary configurations considered, demonstrating that the reduction of numerical heating is a robust feature of the EFL method.
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Astrophysics of Galaxies

Local Interstellar Flow Parameters from the First Intersection of IMAP-Lo's Parameter Tubes

Nathan A. Schwadron, Mitchell M. Shen, Fatemeh Rahmanifard et al. (+24 more)

The Sun's motion through the interstellar medium creates a flow of interstellar neutral (ISN) atoms through the heliosphere. ISN He, due to its high universal abundance and relatively low ionization rate, is the most abundant of the interstellar species near 1 au and ideal for flow parameter determination. The Interstellar Boundary Explorer (IBEX) measurements of ISN He flow parameters (speed, temperature, and direction) yielded a tube in 4D parameter space – narrow in cross-section but highly extended along one parameter axis (e.g., ecliptic longitude direction). This “4D parameter tube” results in large systematic uncertainties, a direct consequence of IBEX-Lo's fixed viewing orientation on the spacecraft. On the Interstellar Mapping and Acceleration Probe (IMAP), the articulation of the IMAP-Lo boresight using its pivot platform enables multiple viewing orientations of the ISN flow for significant systematic uncertainty reduction. We provide first results that definitively intersect ISN parameter tubes for elongation angles $79^\circ$, 94$^\circ$, and 109$^\circ$, resulting in precise interstellar parameters: speed $26.37 \pm 0.82$ km s$^{-1}$, ecliptic longitude direction $74.85^\circ \pm 0.96^\circ$, ecliptic latitude direction $-5.212^\circ \pm 0.035^\circ$, and temperature $7740^{+770}_{-730}$ K. The inferred flow of the Very Local Interstellar Medium is not consistent with either the Local Interstellar Cloud or the G-Cloud, but rather an intermediate state. IMAP is now positioned to study the detailed physics of this complex, nearby interstellar region. By resolving and understanding its physics, we determine how the heliosphere responds to the local interstellar flow, and how it may evolve in time
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All authors Nathan A. Schwadron, Mitchell M. Shen, Fatemeh Rahmanifard, Eberhard Moebius, Hafijul Islam, Jonathan S. Bower, Maciej Bzowski, Eric R. Christian, Ken Fairchild, Herbert O. Funsten, Stephen A. Fuselier, Andre Galli, Jonathan Gasser, Matina Gkioulidou, David Heirtzler, Izabela Kowalska-Leszczyska, Marzena A. Kubiak, David J. McComas, Jonathan T. Niehof, Jamie S. Rankin, Justyna Sokol, Pawel Swaczyna, Jamey R. Szalay, Carol Weaver, Peter Wurz, Gary P. Zank, Eric J. Zirnstein

High Energy Astrophysical Phenomena

4U 1538-52 in a Heartbeat: Broadband X-ray Spectral Properties from XMM-Newton and NuSTAR

C. M. Diez, S. Dupourqué, A.-L. Doherty et al. (+8 more)

Galactic high-mass X-ray binaries (HMXBs) are important systems for studying accretion mechanisms onto compact objects and for investigating the complex stellar winds of massive stars. In particular, HMXBs hosting a neutron star allow us to reveal the structure of the accreted material in X-ray pulsars and consequently to investigate how matter behaves under extreme conditions of pressure and density. These are major scientific goals for XRISM and NewAthena. Here we report on the first out-of-eclipse XMM-Newton observation of the HMXB 4U 1538-52, complemented by NuSTAR coverage. Our campaign aimed to investigate stellar-wind variability and continuum changes with high-resolution spectroscopy at a critical orbital phase: when the neutron star is in inferior conjunction. Thanks to simultaneous observations covering both soft and hard X-rays, we obtain the most detailed X-ray view of the accreted material in 4U 1538-52 to date. In particular, we perform time-resolved spectroscopy down to the pulse period of the neutron star to highlight wind clumping properties and accretion structures. In this dataset, we observe a bright flare reaching $\sim$10$^{37}\,\rm{erg\,s^{-1}}$ probably induced by the accretion of a $10^{20}\,\rm{g}$ clump, followed by a luminosity dip forming a heartbeat-like episode. This event is followed by three local absorption peaks with local variability of the order of the pulse period, and a gradual hardening of the underlying spectrum throughout the observation. This could indicate the presence of both small-scale and large-scale overdense structures in the vicinity of the neutron star, which can be attributed to clumps and filamentary structures embedded in the accretion wake. These observational evidences are further supported and reproduced by 3D hydrodynamic simulations.
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All authors C. M. Diez, S. Dupourqué, A.-L. Doherty, D. Dickson, A. Zainab, S. Martínez-Núñez, J. M. Torrejón, S. Guillot, A. Rouco Escorial, F. Fürst, P. Kretschmar

Astrophysics of Galaxies

VAPOLA - A multiyear, multiband polarization survey of AGNs and Sgr A* at millimeter wavelengths with ALMA II. Spectropolarimetric properties and their evolution from 2017 to 2023

Douglas Carlos, Ciriaco Goddi, Alejandro Mus et al. (+5 more)

We present a systematic analysis of the spectropolarimetric properties of a sample of 39 active galactic nuclei and Sagittarius A* observed with the Atacama Large Millimeter/submillimeter Array during five VLBI campaigns between 2017 and 2023. We characterize the compact cores in total intensity and polarization, focusing on the behavior or the linear polarization fraction (LP), electric vector position angle (EVPA), and Faraday rotation measure (RM) over time and spectral domains. We investigate both individual objects–such as M87, Sgr A*, 3C273, and 3C279–and ensemble properties of different source classes, including flat-spectrum radio quasars, BLLac objects, and other active galaxies. While total intensity and spectral index are generally stable on weekly timescales, polarization properties often exhibit strong variability, with significant day-to-day changes in LP, EVPA, and RM. Several sources display large EVPA rotations accompanied by variations in LP and RM, in some cases coinciding with flaring activity. We observe that the magnitude of RM increases with observing frequency for all sources for which we have reliable multi-band measurements, consistent with Faraday rotation arising in a magnetized sheath surrounding the relativistic jet, although an origin in the accretion flow–particularly in the case of Sgr A*–cannot be ruled out.
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All authors Douglas Carlos, Ciriaco Goddi, Alejandro Mus, Nicola Marchili, Kazi L.J. Rygl, Ezequiel Albentosa-Ruíz, Iván Martí-Vidal, The Event Horizon Telescope Collaboration

Astrophysics of Galaxies

High-spectral-resolution Observations of the [S II] Emission-line Doublet in the Filamentary Nebula Surrounding NGC 1275

Benjamin Vigneron, Julie Hlavacek-Larrondo, Carter Lee Rhea et al. (+10 more)

We analyze new high-spectral resolution SITELLE observations (R = $\lambda/\Delta\lambda$ = 7000) of the filamentary nebula surrounding NGC 1275, central galaxy of the Perseus cluster. We present here analysis of the \sii$\lambda6716$ and \sii$\lambda6731$ emission line doublet, using its ratio to determine the electron density of the optically emitting filaments. We compare these measurements with electron densities derived from deep Chandra X-ray observations of the intra-cluster medium (ICM) to determine if any correlations in density can be found. We report the detection of a clear dichotomy between the outer filaments, displaying on average lower \sii\text{ }emission line ratio of $\sim 1.1$ and the inner filaments displaying higher ratios of $\sim 1.3$. These results indicate that most of the gaseous filaments lie close to the low-density threshold for the density measurement of $\sim 10^2\text{ cm}^{-3}$. Using radial profiles, we find that the inner filaments have a roughly constant density, whereas the ICM density decreases with radius. In the outer filaments, we observe hints of local connections between the densities of the ICM and optical filaments, but no clear correlation seems to be observed overall. We also combined these density measurements with cold molecular CO gas observations to derive a relationship between temperature, density and pressure for the multiphase environment surrounding NGC 1275. Finally, we investigated potential models to explain the observed density measurements and explored similar studies of filamentary nebula around other central galaxies of cool-core galaxy clusters.
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All authors Benjamin Vigneron, Julie Hlavacek-Larrondo, Carter Lee Rhea, Christoph Pfrommer, Greg L. Bryan, Megan Donahue, Alastair Edge, Andrew Fabian, Michael McDonald, Annabelle Richard-Lafferrière, Laurie Rousseau-Nepton, G. Mark Voit, Norbert Werner

Instrumentation and Methods for Astrophysics

Sub-Pixel Calibration of CMOS Sensors for Precision Astrometry

M. Shao and I. Hahn

Many sources of systematic error are important to centroid the position of a star below the level of $10^{-4}$ of the FWHM of the stellar image. One of the more important sources of centroiding error is the imperfect position of the pixels in a focal plane array. In this paper, we discuss the calibration of pixel position of multiple commercial CMOS detectors. Focal plane arrays are semiconductor devices fabricated with 10's nanometer precision. However, the effective location of a pixel can be biased if there's a QE gradient across the pixel. We typically see pixel position variations of 1–3% of a pixel in most CMOS imagers. This paper describes how we measure the position of each pixel below the $10^{-3}$ pixel level. We also describe how this information might be used in a least square fitting of an airy spot to obtain a higher accuracy position of the centroid of the PSF.
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Instrumentation and Methods for Astrophysics

Enabling Quantitative Polarimetry for Keck/NIRC2: Preliminary Mueller Matrix Model Calibration

Manxuan Zhang, Briley L. Lewis, Maxwell A. Millar-Blanchaer et al. (+27 more)

The Keck/NIRC2 infrared imager was upgraded in 2025 with dual-beam polarimetric observing modes spanning approximately 1.1–4.1 microns (JHKL' bands). We present a preliminary JHK calibration of NIRC2 Polarimetry using a wavelength-dependent Mueller matrix model of the Keck tertiary mirror (M3), half-wave plate (HWP), image rotator (IMR), downstream optics, and Wollaston prism. We constrain the model downstream of M3 using dome flat sequences spanning ten HWP and nine IMR angles in each band. Although the model reproduces the dominant modulation, the residuals show structure dependent on HWP and IMR angle. Measurement matrix inversion of unpolarized standard star observations gives M3 diattenuations of 0.0119+/-0.0009, 0.0098+/-0.0004, and 0.0068+/-0.0005 in J, H, and Kp, substantially closer to Fresnel predictions for aluminum than the values derived from dome flats. The larger dome flat modulation may indicate polarization in the incident dome illumination or Mueller matrix model inaccuracies. These results establish an initial calibration framework while motivating improved input polarization constraints, fixed HWP parameters from previous laboratory measurements, model validation with polarized standard stars, and extension to L'.
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All authors Manxuan Zhang, Briley L. Lewis, Maxwell A. Millar-Blanchaer, Eduardo Marin, Jayke S. Nguyen, William Melby, Carlos Alvarez, Jaren N. Ashcraft, Mahawa Cisse, Charles-Antoine Claveau, Jacques-Robert Delorme, Greg Doppmann, Michael P. Fitzgerald, Matthew Freeman, Percy Gomez, Trisha Hammen, Ryan Hersey, Nemanja Jovanovic, Marc Kassis, Scott Lilley, Jessica Lu, James E. Lyke, Keith Matthews, Dimitri Mawet, Thomas McIntosh, Max Service, Lauren Simmons, Jacob Taylor, Rob G. van Holstein, Ed Wetherell

Instrumentation and Methods for Astrophysics

An open-source data processing pipeline for Keck / NIRC2-Polarimetry

Briley L. Lewis, Maxwell A. Millar-Blanchaer, Rebecca Zhang et al. (+3 more)

The Keck/NIRC2 infrared imager was recently upgraded with a new suite of polarimetric observing modes. This polarimetry upgrade (referred to as NIRC2-Pol) will open up a wide range of new astronomical studies, including investigations of exoplanets, the Galactic center, active galactic nuclei and the solar system. Astronomical polarimeters require sophisticated data reduction, especially for quantitative polarimetry requiring the use of a Mueller Matrix model for instrumental polarization calibration. This work presents the design of a flexible, user-friendly, open-source data processing pipeline intended for use with NIRC2-Pol, summarizing its key steps and details of its ongoing implementation.
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All authors Briley L. Lewis, Maxwell A. Millar-Blanchaer, Rebecca Zhang, Jayke Nguyen, Max Brodheim, Ashish Uhlmann

High Energy Astrophysical Phenomena

X-ray thread/Nonthermal Radio Filament associations: Evidence for Interstellar Magnetic Reconnection

Q. Daniel Wang

Nonthermal radio filaments (NTFs), first discovered at 20-centimeter wavelength more than four decades ago, are among the most enigmatic structures at the Galactic Center. They still defy a clear explanation. These striking narrow features trace intense magnetic fields and often stand in bold contrast to the Galactic plane. Recent discoveries have revealed surprising associations: some NTFs align well with X-ray threads that seem to exhibit Fe He-$\alpha$ emission. Here, I present preliminary results from an ongoing, collaborative, multi-wavelength study aimed at understanding the origins of these filaments, focusing on testing the magnetic reconnection scenario of these associations and shedding new light on the high-energy processes and magnetic phenomena operating under extreme conditions at the heart of our Galaxy.
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Earth and Planetary Astrophysics

The Enceladian crater production function

E. W. Wong, S. C. Werner, M. R. Kirchoff et al. (+1 more)

Interpreting Enceladus's past and present surface history and interior state remains challenging, owing to uncertain prescription of its impact bombardment history and limited interpretation of its crater statistics. Further progress in understanding its evolutionary history can be achieved with an improved crater chronology model and a thorough assessment of Enceladus's surface. Here we present the first step in the form of a comprehensive, global crater catalogue with geomorphology survey for Enceladus. From our dataset we build the crater production function (CPF), which is the underlying, unmodified crater size-frequency distribution of the satellite surface, assuming no subsequent modification. We obtained the CPF with a data-driven approach; therefore it makes no assumptions about the impactor source population or planet evolution models or the timing of impact. We fit the CPF with a high-order polynomial as is customary for the Moon and Mars, capturing the slope variations across different crater diameter ranges. The Enceladian CPF generally has a steeper cumulative slope than that of the Moon and Mars for small crater diameters D_cr < 10 km, as well as that of the size-frequency distribution of trans-Neptunian objects. This CPF serves as a critical observational input for an Enceladian crater chronology model, enabling the conversion of crater densities into absolute surface ages. Extending the crater cataloguing and CPF derivation of this study to other Saturnian satellites will determine whether the Enceladian CPF is unique; a shared CPF would indicate a common impactor population, providing observational constraints on the size-frequency distribution of small bodies in the outer Solar System.
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All authors E. W. Wong, S. C. Werner, M. R. Kirchoff, R. Brasser

Astrophysics of Galaxies

Mixing stochasticity relinquishes evidence for magnetorotational hypernovae

Anmol Aggarwal and Ralph Schoenrich

A recent work claimed by fitting the observed elemental abundance pattern of a halo star with the total yields from single super-/hypernova events that only a magnetorotational hypernova event (a very energetic supernova event that also produces r-process elements) could be the source of the observed abundances. Here, we show that the star's peculiar abundance pattern is better fitted within the framework of mixing stochasticity with yields from a normal core collapse supernova (ccSN; Energy$_{\rm exp}$ $\sim 10^{51}$ erg.) and a neutron star merger (NSM). The stochastic mixing model outperforms the hypernova fitting significantly, (r.m.s 0.24 vs 0.44) i.e., favours the composition from common events (ccSN + NSM) over the magnetorotational hypernova scenario. We also discuss the origin of the star and the possibility of enrichment of its birth cloud by both a ccSN and a NSM.
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