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Physics Astrophysics

astro-ph Watch Astrophysics

Tuesday 18 November

Earth and Planetary Astrophysics

From Flash to Crater: Morphological and Spectral Analysis of the Brightest Lunar Impact on 11 September 2013 using LRO Data

J. L. Rizos, L. M. Lara, J. L. Ortiz et al. (+1 more)

We present a comprehensive morphological and spectrophotometric analysis of the lunar impact that occurred on September 11, 2013, based on pre- and post-event observations by the Lunar Reconnaissance Orbiter (LRO). The crater formed exhibits a rim-to-rim diameter of $35 \pm 0.7$ m, a depth of $4.9 \pm 0.4$ m, and an ejecta blanket extending over 2 km with an area of approximately $7 \times 10^{5}\,$m$^{2}$. The ejecta shows a pronounced asymmetry and, assuming uniform distribution, an average thickness limit of $\sim 2$ mm. Spectral analysis using WAC images reveals a consistent reddening of the central ejecta region, with an average 16.54 % increase in spectral slope between 321 nm and 643 nm, marking the first reported detection of color changes resulting from a lunar impact. We evaluated several scaling laws and found that the Gault et al. (1974) formulation most accurately reproduces the observed crater size. Furthermore, luminous efficiency values below $\eta = 2 \times 10^{-3}$ and higher projectile densities are most consistent with the morphology of the ejecta. The impact direction inferred from this pattern is not compatible with the radiant of the September $\varepsilon$-Perseids stream. Moreover, an independent probability analysis yields a greater than 96 % likelihood that the event was caused by a sporadic meteoroid. Our results also demonstrate the potential of WAC imagery for the automated detection of new lunar craters, which can improve statistical estimates of the current impact flux. This methodology offers a powerful complement to high-resolution imaging, with important implications for both lunar safety and planetary defense.
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All authors J. L. Rizos, L. M. Lara, J. L. Ortiz, J. M. Madiedo

High Energy Astrophysical Phenomena

Probing accretion dynamics and spin evolution in the X-ray pulsar RX J0520.5-6932 during its 2024 Outburst

Rahul Sharma, Aru Beri, Biswajit Paul et al. (+3 more)

After nearly a decade of quiescence, the transient Be/X-ray binary pulsar RX J0520.5-6932 underwent an outburst in 2024. We performed X-ray monitoring of the source with NICER and AstroSat near the peak of the event. Our primary objective is to investigate the energy and luminosity dependence of the pulsed emission, characterize the spin evolution, and study the broadband X-ray spectral properties of RX J0520.5-6932 during the outburst. The AstroSat/LAXPC and NICER light curves reveal pronounced short-duration flaring activity lasting ~400-700 s, with enhancements by a factor of ~2. The pulse profile exhibits a strong dependence on both energy and intensity, evolving from a simple single-peaked structure at low energies to complex multi-peaked shapes at intermediate energies, and reverting to simpler morphologies at higher energies. Pulse profiles during the flares differ significantly from those in the persistent state, indicating changes in the pulsed beam pattern with a change in the intensity on a short timescale. Broadband spectral analysis reveals a soft excess and an emission feature at ~1 keV, likely arising from reprocessed emission in the accretion disc and fluorescence from Ne K and Fe L ions. Continuous NICER monitoring over nearly one orbital cycle enabled us to track spin evolution with accretion-driven spin-up and spectral variability in the soft X-ray band. Additionally, a declining spin-up rate is observed during the outburst, likely due to a gradual reduction in mass accretion rate. Our results provide a comprehensive view of the complex accretion dynamics in RX J0520.5-6932 during its 2024 outburst. The strong variability in pulse shape and spin behaviour highlights rapid changes in the accretion geometry and torque as a function of accretion rate. [Abridged]
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All authors Rahul Sharma, Aru Beri, Biswajit Paul, Andrea Sanna, Chandreyee Maitra, Haonan Yang

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

Dark matter halos and transonic accretion flow

Avijit Chowdhury, Gargi Sen, Sayan Chakrabarti et al. (+1 more)

The interplay between supermassive black holes (SMBHs) and their surrounding environment is fundamental to understanding galactic evolution. This work investigates the influence of a cold dark matter (DM) halo on the dynamics of relativistic, low angular momentum, inviscid, and advective hot accretion flow onto a galactic SMBH. Modeling the spacetime geometry as a black hole embedded within various DM distributions, including those with a central density spike, we demonstrate that the presence of a DM halo, particularly one that is massive and compact, enhances the luminosity of the accretion disk. The dominant contribution to this luminosity originates from the inner regions of the flow, suggesting that luminosity measurements could serve as a valuable observational probe for the dense DM environments expected near galactic centers.
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All authors Avijit Chowdhury, Gargi Sen, Sayan Chakrabarti, Santabrata Das

Earth and Planetary Astrophysics

MINDS: The molecule-rich disc of the Herbig star HD 35929 revealed with JWST/MIRI

Till Kaeufer, Rens Waters, Danny Gasman et al. (+16 more)

Our knowledge of the chemical composition of the gas in the inner disc of intermediate-mass young stars is limited, due to the lack of suitable instrumentation. The launch of JWST has provided a significant improvement in our ability to probe gas in these inner discs. We analyse the gas composition and emitting conditions of the disc around HD 35929, a young intermediate-mass Herbig star, using MIRI/MRS data. Our goal is to constrain the chemistry and kinematics of the gas phase molecules detected in the inner disc. We use iSLAT to examine the observed molecular lines and DuCKLiNG to detect, fit, and analyse the molecular emission. We find gas phase H2O, CO, CO2, and OH in the disc, as well as HI recombination lines. Surprisingly, we also detect gas phase SiO in the fundamental v=1-0 vibrational band. We derive column densities and temperature ranges of the detected species, arising from the inner ~0.2 au, hinting towards a compact and very warm disc. The molecular column densities are much higher than found in lower mass T Tauri discs. In general, the molecular composition is consistent with an O-rich gas from which silicate-rich solids condense and the strong gas phase molecular line emission suggests a low dust opacity. The unexpected detection of gas phase SiO at the source velocity points to an incomplete condensation of rock forming elements in the disc, suggesting chemical disequilibrium and/or an underestimate of the gas kinetic temperature.
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All authors Till Kaeufer, Rens Waters, Danny Gasman, Milou Temmink, Hyerin Jang, Ewine F. van Dishoeck, Manuel Güdel, Thomas Henning, Alessio Caratti o Garatti, Inga Kamp, Aditya M. Arabhavi, Pacôme Esteve, Sierra L. Grant, Jayatee Kanwar, Nicolas T. Kurtovic, Giulia Perotti, Kamber Schwarz, Lucas M. Stapper, Benoît Tabone

Earth and Planetary Astrophysics

ExoClock Project IV: A homogeneous catalogue of 620 updated exoplanet ephemerides

A. Kokori, A. Tsiaras, G. Pantelidou et al. (+324 more)

The ExoClock project is an open platform aiming to monitor exoplanets by integrating observations from space and ground based telescopes. This study presents an updated catalogue of 620 exoplanet ephemerides, integrating 30000 measurements from ground-based telescopes (the ExoClock network), literature, and space telescopes (Kepler, K2 and TESS). The updated catalogue includes 277 planets from TESS which require special observing strategies due to their shallow transits or bright host stars. This study demonstrates that data from larger telescopes and the employment of new methodologies such as synchronous observations with small telescopes, are capable of monitoring special cases of planets. The new ephemerides show that 45% of the planets required an update while the results show an improvement of one order of magnitude in prediction uncertainty. The collective analysis also enabled the identification of new planets showing TTVs, highlighting the importance of extensive observing coverage. Developed in the context of the ESA's Ariel space mission, with the goal of delivering a catalogue with reliable ephemerides to increase the mission efficiency, ExoClock's scope and service have grown well beyond the remit of Ariel. The ExoClock project has been operating in the framework of open science, and all tools and products are accessible to everyone within academia and beyond, to support efficient scheduling of future exoplanet observations, especially from larger telescopes where the pressure for time allocation efficiency is higher (Ariel, JWST, VLT, ELT, Subaru etc). The inclusion of diverse audiences in the process and the collaborative mode not only foster democratisation of science but also enhance the quality of the results.
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All authors A. Kokori, A. Tsiaras, G. Pantelidou, A. Jones, A. Siakas, B. Edwards, G. Tinetti, A. Wünsche, Y. Jongen, F. Libotte, M. Correa, L. V. Mugnai, A. Bocchieri, A. R. Capildeo, E. Poultourtzidis, C. Sidiropoulos, L. Bewersdorff, G. Lekkas, G. Grivas, R. A. Buckland, S. R.-L. Futcher, P. Matassa, J.-P. Vignes, A. O. Kovacs, M. Raetz, B. E. Martin, A. Popowicz, D. Gakis, P. Batsela, V. Michalaki, A. Nastasi, C. Pereira, A. Iliadou, F. Walter, N. I. Paschalis, K. Vats, N. A-thano, R. Abraham, V. K. Agnihotri, M. Á. Álava-Amat, R. Albanesi, T. Alderweireldt, J. Alonso-Santiago, D. Q. Amat, L. Andrade, V. Anzallo, J. Aragones, E. Arce-Mansego, D. Arnot, R. A. Artola, C. Aumasson, M. Bachschmidt, R. Barberá-Córdoba, J.-F. Barrois, P. R. Barroy, M. Bastoni, V. Béjar, A. A. Belinski, A. Ben Lassoued, P. Bendjoya, B. Benei, D. Bennett, K. Bernacki, G. O. Bernard, L. Betti, G. Biesse, M. Billiani, P. Bosch-Cabot, V. Boucher, R. C. Boufleur, D. Boulakos, P. J.-M. Brandebourg, S. M. Brincat, X. Bros, A. Brosio, S. Brouillard, A.-M. Bruzzone, L. Cabona, C. Calamai, G. Calapai, Y. Calatayud-Borràs, M. Caló, F. Campos, A. Carbognani, F. Carretero, R. Casas, M. L. Castanheira, G. Catanzaro, L. Cavaglioni, C.-M. Chang, M. Chella, W.-H. Chen, P.-J. Chiu, R. Ciantini, J.-F. Coliac, J. Collins, F. Conti, G. Conzo, W. R. Cooney, Jr., L. N. Correa, S. P. Cosentino, N. Crouzet, M. V. Crow, B. V.-H.-V. da-Silva, A. Damonte, D. Daniel, S. Dawes, L. de Almeida, P. De Backer, A. de Melo, M. Deldem, D. Deligeorgopoulos, Y. Delisle, F. Denjean, F. Dias, S. Diaz Lopez, T. Dittadi, N. Dodd, S. Doman, G. Domènech-Rams, T. G. Dooley, S. Drapkin-Junyent, F. Dubois, A. Dustor, R. Dymock, T. Eenmäe, M. Emilio, E. Esparza-Borges, J. Estevez, C. Falco, R. G. Farfán, P. Farissier, G. Farrall, G. Fernandez Rodriguez, A. Ferretti, G. Ferrini, L. Fini, J. Fiołka, G. Fleerackers, J. Flores-Martín, g. follero, S. Foschino, L. Fossi, M. Fowler, A. Frasca, E. Frigeni, I. Fukuda, A. Fukui, G. Furlato, D. Gabellini, T. Gainey, P. Gajdoš, D. Galán-Diéguez, P. Gamache, E. García Navarro, N. A. Garcia, A. García-Sánchez, A. Garmash, T. Gesser, A. Ginard, I. Gkolias, E. Gomez, G. F. Gonçalves, J. González-Edo, J. González-Rodríguez, G. Gruntz, B. Guillet, T. Guillot, M. N. Günther, H. Hautecler, Y. Hayashi, E. Herrero, K. Hills, H. S. Hodkinson, G. Holtkamp, G. R. Hunt, N. Iannascoli, M. Iozzi, M. Irzyk, K. Isogai, K. Johnson, P. Jóźwik-Wabik, A. E. Kaeouach, S. Kartal, H. Kiiskinen, Ü. Kivila, U. Kolb, J. Korth, D. Kustrin, S.-P. Lai, S. Lasota, F. Le Rhun, Y. H. Lee, D. Lefoulon, F. Legrele, H. Leipold, A. Liberti, T. Lien, Y.-H. Lin, F. Linsalata, J. H. Livingston, C. Lopresti, S. Lora, E. R. Lorenz, D. Madison, M. Mannucci, A. Marchini, A. Marino, J.-C. Mario, E. Maris, J.-B. Marquette, N. A. Maslennikova, A. E. McGregor, A. Mengoudis, P. Meni, M. Mesarč, M. Michelagnoli, J. Michelet, J. Mieglitz, M. Mifsud, M. Miller, S. A. Mills, E. Miny, S. Miquel Romero, D. Molina, S. Montchaud, B. Monteleone, M. Monticelli, N. Montigiani, M. Morales-Aimar, G. Morello, L. Moretti, M. Mori, F. Mortari, M. Müller, D. Mura, F. Murgas, N. Narita, A. Nath, R. Nicollerat, V. Noce, P. Norridge, A. J. Norton, Y. Ogmen, Z. Orbanic, J. Owen-Lloyd-Walters, E. P. Pace, E. Pakštienė, A. F. Pala, E. Palle, C. Pantacchini, I. Parenti, D. Patterson, E. Pavoni, A. W. Pereira, I. Peretto, V. Perroud, S. W. Peterson, V. Pettina, M. Phillips, J. Philpot, D. Pica, P. Pintr, J.-B. Pioppa, T. J. Plunkett, T. G. Prado, A. Prasad, R. A. Prestes, A. Putz, F. Régembal, L. Ribe, D. F. Rocha, J. Rodrigues, R. Roth, L. Rousselot, N. Rozand, X. Rubia, N. Ruocco, M. Salisbury, T. Salomon, L. Sassaro, J. E.-G. Savage, T. Savin, F. Scaggiante, F.-X. Schmider, M. Serrau, I. D. Sharp, D. Shave-Wall, A. F. Silva, V. Školník, A. Solmaz, A. Sonka, M. Spiller, T. H. Sprecher, R. Stanga, M. Stefanini, D. Stouraitis, M. Stratigou-Psarra, O. Suarez, D. Suys, M. Szkudlarek, M. F. Talafha, A. N. Tarasenkov, G. Tartalo-Montardit, C. Titescu, A. Tomacelli, A. H. Triaud, S. Tsavdaridis, K. Tsiganis, M. A. van der Grijp, S. Vanaverbeke, j.-p. vergne, J. Verheyden, J. Vilalta, P. Vuylsteke, P. Wagner, D. Walliang, C. H. Wang, I. Weller, D. E. Wright, K. O. Xenos, R. Yorke, O. Zamora, J. Zapata, M. Zejmo, M. Zulian

2511.14407 · 18 Nov · 12 pages of text (104 in total, including the list of authors, acknowledgements, references and data tables), 7 figures, 8 tables. Submitted to ApJS (this version includes the first round of the reviewer's comments). The Data Release is available at: https://doi.org/10.17605/OSF.IO/WPJTN. Machine-readable versions of tables 7 and 8 are included the TeX Source

Abstract PDF $TSCP ×6$EXOP ×4$PLNT ×4$STAR ×1

Cosmology and Nongalactic Astrophysics

Magnetic Fields in the Shapley Supercluster Core with POSSUM: Challenging Model Predictions

D. Alonso-López, S. P. O'Sullivan, A. Bonafede et al. (+18 more)

Faraday Rotation Measure (RM) Grids provide a sensitive means to trace magnetized plasma across a wide range of cosmic environments. We study the RM signal from the Shapley Supercluster Core (SSC), in order to constrain the magnetic field properties of the gas. The SSC region consists of two galaxy clusters A3558 and A3562, and two galaxy groups between them, at $z\simeq 0.048$. We combine RM Grid data with thermal Sunyaev-Zeldovich effect data, obtained from the POSSUM pilot survey, and Planck, respectively. To robustly determine the gas density, its magnetic field properties, and their correlation, we study the RM scatter in the SSC region and its behavior as a function of distance to the nearest cluster/group. We compare observational results with semi-analytic Gaussian random field models and more realistic cosmological MHD simulations. With a sky-density of 36 RMs/deg$^{2}$, we detect an excess RM scatter of $30.5\pm 4.6 \, \mathrm{rad/m^2}$ in the SSC region. Comparing with models, we find an average magnetic field strength of 1-3 $\mu$G (in the groups and clusters). The RM scatter profile, derived from data ranging from 0.3-1.8 $r_{500}$ for all objects, is systematically flatter than expected compared to models, with $\eta<0.5$ being favored. Despite this discrepancy, we find that cosmological MHD simulations matched to the SSC structure most closely align with scenarios where the magnetic field is amplified by the turbulent velocity in the intercluster regions on scales $\lesssim 0.8\,r_{500}$. The dense RM grid and precision provided by POSSUM allows us to probe magnetized gas in the SSC clusters and groups on scales within and beyond their $r_{500}$. Flatter-than-expected RM scatter profiles reveal a significant challenge in reconciling observations with even the most realistic predictions from cosmological MHD simulations in the outskirts of interacting clusters.
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All authors D. Alonso-López, S. P. O'Sullivan, A. Bonafede, L. M. Böss, C. Stuardi, E. Osinga, C. S. Anderson, C. L. Van Eck, E. Carretti, J. L. West, T. Akahori, K. Dolag, S. Giacintucci, A. Khadir, Y. K. Ma, S. Malik, N. McClure-Griffiths, L. Rudnick, B. A. Seidel, S. Tiwari, T. Venturi

Solar and Stellar Astrophysics

The Formation of Solar Prominences: Plasma Origin and Mechanisms

Yuhao Zhou

Solar prominences, or solar filaments, are cool and dense plasma structures in the hot solar corona, whose formation mechanisms have remained a fundamental challenge in solar physics. This review provides a comprehensive overview of the current theoretical, numerical, and observational understanding of prominence formation, with a focus on the origin of the dense plasma component. We begin by summarizing the magnetic field configurations that enable prominence support, followed by a classification of four representative plasma formation mechanisms: injection, levitation, evaporation–condensation, and in-situ condensation. Each mechanism is analyzed in terms of its physical basis, numerical realizations, and observational diagnostics. A central focus is placed on the evaporation–condensation scenario, which has seen significant development over the past decade through numerical simulations. We also discuss recent progress in modeling in-situ condensation triggered by magnetic reconnection and levitation dynamics. Throughout, we emphasize the complementary nature of different mechanisms and their potential coexistence in forming and maintaining prominence mass. Observational constraints and recent high-resolution data are reviewed to assess the physical plausibility of each mechanism. We conclude by highlighting open questions and future directions in connecting multi-scale physical processes to the observed diversity of prominence behaviors.
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Solar and Stellar Astrophysics

Asteroseismic Imprints of Mass Transfer in Binary Stars: Probing the Interiors of Donors and Accretors with Gravity and Acoustic Modes

Tao Wu, Zhao Guo and Yan Li

Context. The synergy between close binary stars and asteroseismology enables constraints on mass-transfer episodes and their consequences for internal structure, rotation profiles, and oscillation modes. Aims. We investigate how mass accretion and donation in close binaries affects the internal structure and oscillation modes of main-sequence stars. Methods. Building on the established relation between the Brunt-Vaisala (buoyancy) glitch and the Fourier spectra of g-mode period spacings, we quantitatively explain the origins of the g-mode period-spacing differences between single-star and mass-accretion/donation models of intermediate-mass stars (M = 2.0, 3.0, and 4.5 Msun). In particular, the hydrogen mass fraction profiles X of the donor model show two chemical gradient regions, which results in a double-peaked Brunt-Vaisala profile. The presence of additional buoyancy glitches gives rise to further periodic modulations in the g-mode period spacings. Results. Mass-accretion induced changes in the chemical profile create sharp features in the buoyancy frequency, which modify both the amplitudes and frequencies of the g-mode period-spacing variations. This behavior resembles that produced by multiple chemical transition zones in compact pulsators such as white dwarfs and sub-dwarf B stars. Similarly, for acoustic modes in the M = 1 Msun solar-like models, we attribute the differences in frequency-separation ratios between single-star and mass-donor models to the variations in the internal sound-speed gradient (acoustic glitches). We discuss future prospects for using asteroseismology to discover the mass-transfer products and constrain the mass-transfer processes in binary star evolution.
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Astrophysics of Galaxies

QHSC: The Quasar Candidate Catalog for the Hyper Suprime-Cam Subaru Strategic Program

Rui Zhu, Xue-Bing Wu, Yuxuan Pang et al. (+1 more)

The Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) is a deep wide-field multi-band imaging survey consisting of three layers (Wide, Deep, and UltraDeep), with the Wide layer covering $\sim 1470$ deg$^2$ to a depth of $i \sim 26$ mag. We present the QHSC catalog, a machine-learning selected sample of quasar candidates with photometric redshifts in the Wide layer of the HSC-SSP survey (Public Data Release 3). The full QHSC catalog contains four distinct samples: a master sample with HSC-only photometry, an HSC+WISE sample, and two samples including near-infrared data from UKIDSS and VISTA, denoted as GoldenU and GoldenV. For each sample, an XGBoost classifier is trained and evaluated using independent spectroscopic test sets from HETDEX, VVDS, and zCOSMOS-bright. The numbers of quasar candidates in the QHSC catalog are 1,184,574 (master), 371,777 (HSC+WISE), 87,460 (GoldenU), and 120,572 (GoldenV), with respective completeness values of 85.3%, 92.7%, 89.8%, and 91.3%. We develop ensemble photometric redshift estimators based on bootstrap aggregating (bagging) of multiple XGBoost regressors, achieving outlier fractions of 21.7%, 13.1%, 9.5%, and 10.7% for these samples. The catalog provides quasar classification probabilities (p_QSO), enabling construction of purer subsamples via thresholding. This work offers a valuable resource for studies of quasars and cosmology, and highlights the effectiveness of machine learning for quasar selection in future wide and deep imaging surveys. The catalog is publicly available at https://doi.org/10.5281/zenodo.17515028.
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All authors Rui Zhu, Xue-Bing Wu, Yuxuan Pang, Yuming Fu

Astrophysics of Galaxies

Deep Andromeda JCMT-SCUBA2 Observations. The Submillimeter Maps and Giant Molecular Clouds

Sihan Jiao, Jingwen Wu, Hauyu Baobab Liu et al. (+23 more)

We have carried out unprecedentedly deep, nearly confusion-limited JCMT-SCUBA2 mapping observations on the nearest spiral galaxy, M31 (Andromeda). The 850 $\mu$m image with a $\sim$50 pc resolution yields a comprehensive catalog of 383 giant molecular clouds (GMCs) that are associated with the spiral arms. In addition, it unveiled a population of 189 compact inter-arm GMCs in M31, which are mostly unresolved or marginally resolved. The masses of all these GMCs are in the range of 2$\times$10$^4$ – 6$\times$10$^6$ $M_{\odot}$; the sizes are in the range of 30–130 pc. They follow a mass-size correlation, $M$ $\propto$ $R_{c}$$^{2.5}$. The inter-arm GMCs are systematically less massive, more diffuse, colder, and have lower star-forming efficiency (SFE) than on-arm GMCs. Moreover, within individual spatially resolved on-arm and off-arm M31 GMCs, the SFE is considerably lower than the SFE in molecular clouds in main sequence and green valley galaxies. Follow-up investigations on M31 GMCs may provide clues for how star formation may be quenched in galactic environments. Finally, we reconstrained the dust opacity spectral index $\beta$ in the M31 galaxy by combining our new JCMT observations with archival Herschel and Planck data and found that the radial variation of $\beta$ may not be as large as was proposed by previous studies.
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All authors Sihan Jiao, Jingwen Wu, Hauyu Baobab Liu, Chao-Wei Tsai, Yuxin Lin, Di Li, Zhi-Yu Zhang, Yu Cheng, Linjing Feng, Henrik Beuther, Junzhi Wang, Lihwai Lin, Jakob den Brok, Ludan Zhang, Fengwei Xu, Fanyi Meng, Zongnan Li, Ryan P. Keenan, Si-Yue Yu, Niankun Yu, Zheng Zheng, Junhao Liu, Yuxiang Liu, Hao Ruan, Fangyuan Deng, Yuanzhen Xiong

Cosmology and Nongalactic Astrophysics

The SRG/eROSITA all-sky survey: X-ray scaling relations of galaxy groups and clusters in the western Galactic hemisphere

M. E. Ramos-Ceja, L. Fiorino, E. Bulbul et al. (+19 more)

The soft X-ray telescope on board the SRG mission, eROSITA, has produced the largest sample to date of galaxy groups and clusters detected via their intracluster and intragroup medium emission. Scaling relations between the intrinsic properties of these systems provide valuable insight into their formation and evolution. In this work, we investigated the scaling relations between key physical properties, such as soft band X-ray luminosity, temperature, gas mass, and the low-scatter mass proxy $Y_{\rm X}$, for the galaxy groups and clusters detected in the first eROSITA All-Sky Survey (eRASS1). Our analysis fully accounts for selection effects and the redshift evolution of the observable distributions. We constructed a high-purity sample of $3061$ galaxy groups and clusters spanning the redshift range of $0.05<z<1.07$ and the mass range of $1.1\times10^{13}<M_{500}/$M$_{\odot}<1.6\times10^{15}$. This represents the largest sample to date used in scaling-relation analysis. The selection function, derived from state-of-the-art simulations of the eROSITA sky, is rigorously incorporated into our modeling. We report best-fit parameters – normalization, slope, redshift evolution, and intrinsic scatter – for a set of scaling relations: $L_{\mathrm{X}}-T$, $L_{\mathrm{X}}-M_{\rm gas}$, $L_{\mathrm{X}}-Y_{\rm X}$, as well as the $M_{\rm gas}-T$ relation. Our best-fit models indicate that the slopes of the scaling relations significantly deviate from self-similar expectations, while the redshift evolution remains consistent with the self-similar model. The fits exhibit small statistical uncertainties, likely owing to the large sample size. Our results are in good agreement with previous observational studies that account for selection effects. For clusters with $kT>3$~keV, our inferred $L_{\rm X}-T$ relation is consistent with simulation models that include strong or stronger AGN feedback.
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All authors M. E. Ramos-Ceja, L. Fiorino, E. Bulbul, V. Ghirardini, N. Clerc, A. Liu, J. S. Sanders, Y. E. Bahar, J. Dietl, M. Kluge, F. Pacaud, E. Artis, F. Balzer, J. Comparat, Z. Ding, N. Malavasi, A. Merloni, T. Mistele, K. Nandra, R. Seppi, S. Zelmer, X. Zhang

Astrophysics of Galaxies

Hubble Space Telescope proper motions of Large Magellanic Cloud star clusters – II. Kinematic structure of young and intermediate-age clusters

F. Niederhofer, L. Cullinane, D. Massari et al. (+14 more)

In this paper, we explore the kinematic properties of a sample of 19 young (<1 Gyr) and intermediate-age (1-2.5 Gyr) massive star clusters within the Large Magellanic Cloud (LMC). We analyse the proper motions of the clusters, which have been measured based on multi-epoch Hubble Space Telescope (HST) observations. Additionally, we infer from the HST data homogeneous and robust estimates for the distances, ages and metallicities of the clusters. This collection of information, in combination with literature line-of-sight velocities, allows us to investigate the full 3D dynamics of our sample of clusters within the frame of the LMC in a self-consistent way. While most young clusters orbit the LMC close to the stellar disc plane, NGC 1850 (~100 Myr old) depicts a peculiar case. Depending on the exact distance from the disc, it follows either a highly inclined, retrograde orbit or an eccentric orbit along the bar structure. The orbits of young clusters that formed North of the LMC centre show signs that might be connected to the resettling motion of the LMC bar structure. Based on the dynamic properties in combination with the positions of the clusters in the age-metallicity space, we find no clear-cut evidence for clusters in our sample that could have been stripped from the Small Magellanic Cloud (SMC) onto the LMC. We finally compare the kinematics of the intermediate-age clusters with a suite of simple numerical simulations of the Magellanic system to interpret the cluster motions. A possible interaction history of the LMC with the SMC, where the SMC had two past crossings of the LMC disc plane (about 300 and 900 Myr ago), in combination with the recent SMC pericentre passage, can qualitatively explain the observed kinematic structure of the clusters analysed in this work.
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All authors F. Niederhofer, L. Cullinane, D. Massari, N. Bastian, A. Bellini, F. Aguado-Agelet, S. Cassisi, D. Erkal, M. Libralato, N. Kacharov, I. Cabrera-Ziri, E. Ceccarelli, M.-R. L. Cioni, F. Dresbach, M. Häberle, S. Martocchia, S. Saracino

High Energy Astrophysical Phenomena · Cross-listed from physics.plasm-ph

Plasma oscillations within Israel-Stewart theory

Lorenzo Gavassino

It is well known that, at zero wavenumber, the non-hydrodynamic frequencies of uncharged kinetic theory are purely imaginary. On the other hand, it was recently shown that, in resistive magnetohydrodynamics, the interplay between the Israel-Stewart relaxation equation and the Ampère-Maxwell law can give rise to a pair of oscillating non-hydrodynamic modes. In this work, we analyze this phenomenon in detail. We first demonstrate that these oscillatory modes are exact solutions of the Drude model, corresponding to ordinary plasma oscillations. We then invoke the Onsager-Casimir principle to explain that their oscillatory nature reflects the distinct PT-transformation properties of the degrees of freedom: the distribution function is even, while the electric field is odd. Finally, we establish that, in a kinetic theory of charged particles, there can be at most one such pair of oscillatory modes per spatial dimension, while all other modes still must sit on the imaginary axis.
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High Energy Astrophysical Phenomena

Phase-Resolved Spectroscopy of the Polar V379 Vir with a Brown Dwarf

M.V. Suslikov, A.I. Kolbin and N.V. Borisov

The polar V379 Vir is a well-known magnetic cataclysmic variable with a brown dwarf donor. Despite numerous studies of this system across various spectral ranges, a detailed investigation of the orbital variability of its optical spectra has not been carried out. In this work, we present an analysis of spectroscopic observations of V379 Vir obtained with the 6-m telescope of the Special Astrophysical Observatory of the Russian Academy of Sciences. The orbital variability of the H$\alpha$ emission indicates that the line is most likely formed in the accretion stream near the Lagrangian point L$_1$, rather than on the donor's surface as previously assumed. The analysis of the rotational variability of the Zeeman splitting of hydrogen lines reveals a complex magnetic field topology of the white dwarf, which differs from a simple dipole configuration.
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Cosmology and Nongalactic Astrophysics

On the impact of the supernova subsamples in reducing the Hubble tension

Gonçalo Martins, Santiago González-Gaitán, João Duarte et al. (+1 more)

The persistent 4-6$\sigma$ difference between early- and late-time Hubble constant ($H_{0}$) measurements, known as the "Hubble tension", is a major problem in modern cosmology. We study how differences in colour ($c$), stretch ($x_{1}$), and host galaxy properties-stellar mass ($M$) and specific star formation rate (sSFR)-between calibration and Hubble Flow (HF) Type Ia supernova (SN Ia) samples used by SH0ES affect SN luminosity standardization and $H_{0}$ estimates. We generate subsamples from both, estimating $H_{0}$, $M_{B}$, $\alpha$, $\beta$, $\Delta_{host}$, and $\sigma_{int}$. We use Kolmogorov-Smirnov to assess the consistency between subsamples and reveal how parameter estimates change as sample matching improves. The calibration sample is not fully representative of the HF sample, especially in $M$ and sSFR. Improving sample consistency leads to changes in $H_{0}$, $M_{B}$ and $\sigma_{int}$, though overall values remain broadly stable. Better-matched subsamples tend to yield a mass step consistent with zero within 1$\sigma$. By disentangling SN subpopulations, we find persistent differences in $H_{0}$ ($\sim$2-3$\sigma$) and $M_{B}$ ($\sim2\sigma$) between low- and high-stretch SNe: $H_{0} = 75.27 \pm 1.18$ km s$^{-1}$ Mpc$^{-1}$ for low-stretch and $H_{0} = 71.25 \pm 1.59$ km s$^{-1}$ Mpc$^{-1}$ for high-stretch, resulting in Hubble tensions of 6.07$\sigma$ and 2.52$\sigma$. These differences suggest SNe Ia subpopulations with varying dust and intrinsic colour not captured by a single $\beta$, impacting cosmology. Estimating a single $H_{0}$ for both subpopulations yields $H_{0} = 73.78 \pm 2.17$ km s$^{-1}$ Mpc$^{-1}$, with a much larger uncertainty that lowers the Hubble tension from $5.87\sigma$ to $\sim2.86\sigma$. Our results suggest that the mass step may arise from an over-correction of more than one SN subpopulation associated to different environments.
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All authors Gonçalo Martins, Santiago González-Gaitán, João Duarte, Ana M. Mourão

Solar and Stellar Astrophysics

On the center-to-limb variations of the He I 10830 Å\ triplet

A.G.M. Pietrow, C. Kuckein, M. Verma et al. (+4 more)

We present high-resolution spectroscopic observations of the quiet-Sun center-to-limb variations (CLV) of the He I triplet at 10830 Å and the nearby Si I 10827 Å line, observed with GREGOR Infrared Spectrograph (GRIS) and the improved High-resolution Fast Imager (HiFI+). The observations cover the interval $\mu = [0.1,\, 1.0]$, where $\mu$ is the cosine of the heliocentric angle. At each $\mu$-position, the spectra are spatially averaged over 0.02 $\mu$, and the resulting CLVs are given both as these averaged data points and as smooth polynomial curves fitted across each wavelength point. The He I spectra were inverted using the HAnle and ZEeman Light (HAZEL) code, showing an increase in optical depth towards the limb and a reversed convective blueshift for the red component, while the blue component was entirely absent. In addition, we find a strong increase in the steepness of the He I CLV compared to that of the nearby continuum. The Si I showed a behavior more typical of photospheric lines, namely shallower CLV, a reduction in width and depth, and a more typical convective blueshift.
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All authors A.G.M. Pietrow, C. Kuckein, M. Verma, C. Denker, J.C. Trelles Arjona, R. Kamlah, K. Poppenhäger

Astrophysics of Galaxies

Chemical evolution in high-mass star-forming regions

Francesco Fontani, Maria Teresa Beltrán and Anton Vasyunin

Growing evidence shows that most stars in the Milky Way, including the Sun, are born in high-mass star-forming regions, but due to both observational and theoretical challenges, our understanding of their chemical evolution is much less clear than that of their low-mass counterparts. Thanks to the capabilities of new generation telescopes and computers, a growing amount of observational and theoretical results have been recently obtained, which have important implications not only for our understanding of the (still mysterious) formation process of high-mass stars, but also for the chemistry that the primordial Solar System might have inherited from its birth environment. In this review, we summarise the main observational and theoretical results achieved in the last decades in the study of chemistry evolution in high-mass star-forming regions, and in the identification of chemical evolutionary indicators. Emphasis is especially given to observational studies, for which most of the work has been carried out so far. A comparison with the chemical evolution occurring in other astrophysical environments, in particular in low-mass star-forming cores and extragalactic cores, is also briefly presented. Current open questions and future perspectives are discussed.
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Solar and Stellar Astrophysics

Solar carbon abundance from 3D non-LTE modelling of the diagnostic lines of the CH molecule

Richard Hoppe, Maria Bergemann, Philipp Eitner et al. (+5 more)

The spectral lines of the CH molecule are a key carbon (C) abundance diagnostic in FGKM-type stars. These lines are detectable in metal-rich and, in contrast to atomic C lines, also in metal-poor late-type stars. However, only 3D LTE analyses of the CH lines have been performed so far. We test the formation of CH lines in the solar spectrum, using for the first time, 3D Non-LTE (NLTE) models. We also aim to derive the solar photospheric abundance of C, using the diagnostic transitions in the optical (4218 - 4356 $\r{A}$) and infrared (33025 - 37944 $\r{A}$). We use the updated NLTE model molecule from Popa et al. 2023 and different solar 3D radiation-hydrodynamics model atmospheres. The models are contrasted against new spatially-resolved optical solar spectra, and the center-to-limb variation (CLV) of CH lines is studied. We find generally small ($\sim$0.01 dex) NLTE effects in the optical and IR diagnostic CH A-X lines in the solar atmosphere. Both 3D NLTE and 3D LTE spectral modelling yield an excellent fit to the solar intensity observations at all viewing angles. The 1D LTE and 1D NLTE models fail to describe the line CLV, and lead to underestimated solar C abundances. The 3D NLTE modelling of diagnostic lines in the optical and IR yields a carbon abundance of A(C)=8.52$\pm$0.07 dex. The estimate is in agreement with recent results based on neutrino fluxes measured by Borexino. 3D NLTE modelling and tests on spatially-resolved solar data are essential to derive robust solar abundances. The analysis presented here focuses on CH, but we expect that similar effects will be present for other molecules of astrophysical interest.
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All authors Richard Hoppe, Maria Bergemann, Philipp Eitner, Momo Ellwarth, Åke Nordlund, Jorrit Leenaarts, Bertrand Plez, Aldo Serenelli

Solar and Stellar Astrophysics

MHD waves with mixed properties / Alfvén waves with pressure variations: a review

Marcel Goossens, Iñigo Arregui, Roberto Soler et al. (+2 more)

Non-uniformity plays an important role for MHD waves. For a uniform plasma of infinite extent the MHD waves can be subdivided in two classes with distinct properties. The first class contains the Alfvén waves. The Alfvén waves are incompressible and propagate parallel vorticity. They do not have a parallel component of displacement, they do not cause variations in pressure and are driven by magnetic tension only. The second class contains the magneto-sonic waves. They are compressible and have a parallel component of displacement. They do not propagate parallel vorticity and are driven by pressure and magnetic tension. In non-uniform plasmas the situation can be very different. The clear division between Alfvén waves and magneto-sonic waves is no longer present. In a given part of the equilibrium an MHD wave can strongly resemble a magneto-sonic wave with little or no resemblance to Alfvén waves; while in another part of the equilibrium the MHD wave is practically an Alfvén wave, which has the amazing property of being accompanied by variations in pressure.
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All authors Marcel Goossens, Iñigo Arregui, Roberto Soler, Jaume Terradas, Tom Van Doorsselaere

High Energy Astrophysical Phenomena

Quarkyonic Neutron Stars as Candidates for the GW230529 Mass-Gap Object

Jeet Amrit Pattnaik and S. K. Patra

We examine whether quarkyonic equations of state (EOS) can account for compact objects in the $2.5$-$4.5\,M_\odot$ mass range reported for the GW230529 gravitational-wave event. The pressure-energy density and mass-radius (M-R) relations obtained from quarkyonic EOS models indicate a significant stiffening at high densities, allowing stable configurations beyond $2.5\,M_\odot$. The predicted M-R sequences extend into the GW230529 mass window while maintaining radii in the range of $\approx 13$-$15$~km, suggesting that quarkyonic stars can naturally populate the so-called compact object mass gap. These results imply that the heavier component of GW230529 could plausibly be a massive quarkyonic neutron star rather than a low-mass black hole.
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Astrophysics of Galaxies

Positive AGN feedback in the outskirts of nearby barred spiral galaxies?

Bannanje Ananthamoorthy, Debbijoy Bhattacharya and P. Sreekumar

Observational evidence regarding the impact of AGN feedback on star formation (SF) in non-jetted galaxies is limited. With the available high-resolution UV observations from AstroSat-UVIT, complemented by GALEX, we studied the SF properties in the outskirts ($>0.5R_{25}$) of six AGN-host galaxies and compared them with four non-AGN galaxies of similar morphology. We observed a higher SF rate density ($\Sigma_{\text{SFR}}$) for the UV knots in AGN-host galaxies, and it falls off less rapidly compared to non-AGN galaxies, suggesting positive AGN feedback in the outskirts of AGN-host galaxies. Additionally, FUV attenuation (A$_{\text{FUV}}$) is also enhanced in the outer regions and falls less rapidly in AGN-host compared to non-AGN, indicating that the feedback could be coupled with dust. We speculate that the radiation-pressure-driven and/or wind mode AGN feedback could be at play even in low-luminosity nearby AGN-host galaxies.
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Instrumentation and Methods for Astrophysics

Detection of Faint Sources by the UltraViolet Imaging Telescope Onboard AstroSat Using Poisson Distribution of Background

B. Ananthamoorthy, Debbijoy Bhattacharya, P. Sreekumar et al. (+1 more)

We present an improved approach for constructing the UV source catalogs using observations from the UltraViolet Imaging Telescope (UVIT) onboard AstroSat, by considering the Poisson distribution of the UV background. The method is tested extensively using fields that are not crowded, the Small Magellanic Cloud (SMC) and M31 (Field 13). The results are compared with previous studies that used UVIT observations. This approach is successful in detecting fainter sources and produces a large number of new sources ($\sim 15$ to $92\%$ more). Most of the newly discovered UV sources fall in the faint end of the source distribution (m $\gtrsim 22$). The counterparts at other wavelengths are identified for most sources. This approach is more efficient for source detection and provides an opportunity to explore new classes of UV sources.
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All authors B. Ananthamoorthy, Debbijoy Bhattacharya, P. Sreekumar, Swathi B

Astrophysics of Galaxies

Enhanced UV emission knot in the giant radio galaxy NGC 315: Hint of patchy star formation?

Bannanje Ananthamoorthy, Debbijoy Bhattacharya, Dipanjan Mukherjee et al. (+1 more)

High-resolution AstroSat-UltraViolet Imaging Telescope (UVIT) observations revealed a knot of UV emission, $\sim 1.7$ kpc away from the centre of NGC 315, a nearby elliptical galaxy hosting a giant (Mpc scale) radio source with a jet. We suggest that this patchy and spatially extended UV emission is likely due to ongoing star formation (SF) in the galaxy. The estimated SF rate (SFR) averaged over 100 Myr for the UV knot ($0.23\pm0.10$ M$_{\odot}$ yr$^{-1}$) is significantly higher compared to a typical elliptical galaxy. As the galaxy does not show the signatures of recent major mergers, the possible mechanisms for the triggered SF include AGN feedback or minor mergers. Hubble Space Telescope} (HST) observations reveal dust filaments that extend through a UV knot. The origin of dusty filaments, though not clear, could be associated with gas clouds as a result of a minor merger, cooled gas falling into the central BCG and/or condensing of the gas uplifted by AGN jet. No significant clumpy UV emission is observed in other regions along the dust filament. We speculate that mechanical feedback from the AGN jet could be playing a role in triggering SF in the UV knot.
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All authors Bannanje Ananthamoorthy, Debbijoy Bhattacharya, Dipanjan Mukherjee, P. Sreekumar

Solar and Stellar Astrophysics

Newborn jet in the symbiotic system R Aquarii

T. Liimets, D. P. K. Banerjee, M. Santander-García et al. (+12 more)

R Aquarii (R Aqr) is a well-known symbiotic binary that has attracted renewed interest during its recent periastron passage, an event that occurs only once every about 40 years. This passage marks the first to be observed with modern, state-of-the-art instruments. We investigate the inner, sub-arcsecond active region of R Aqr during this recent periastron passage, with the goal of gaining insight into the jet-launching mechanisms at work in this system. We analyse Ha speckle interferometric images obtained one month apart using Fourier techniques. These are complemented by high-resolution optical spectra in the same emission line. Our speckle imaging reveals a newborn two-sided jet orientated in the north-south direction. Its proper motion, 66 +- 19 mas per year, confirms that it was launched around 2020 Jan 7, at the onset of the periastron passage. Further analysis of the elongated central structure reveals a knot in the southern counterpart of the jet, moving away from the binary with a 27 +- 17 mas per year at a position angle of 187 degrees, and an ejection time around 2019 Oct 28. This interpretation is further supported by our high-resolution spectroscopic data. In addition, we update the expansion parallax distance of R Aqr to 260 pc.
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All authors T. Liimets, D. P. K. Banerjee, M. Santander-García, J. Alcolea, S. B. Howell, U. Munari, B. Deshev, C. E. Woodward, A. Evans, E. Furlan, T. Geballe, R. D. Gehrz, V. Joshi, N. Scott, S. Starrfield

Cosmology and Nongalactic Astrophysics

Spontaneous Symmetry Breaking as a Late-Time Trigger for Interacting Dark Energy

Pradosh Keshav MV, NS Kavya and Kenath Arun

Persistent tensions in the Hubble constant (H0) and the matter clustering parameter (S8) motivate late-time new physics that suppresses structure growth without significantly altering the background expansion history of the LambdaCDM model. We study a class of dark-sector dynamics in which a scalar dark energy field, governed by a Z2-symmetric quartic potential, interacts with dark matter through Yukawa and portal couplings. When the matter density drops below a critical threshold, a cosmological spontaneous symmetry breaking mechanism generates a time-dependent vacuum expectation value v(a) and activates an effective coupling eta(a). This creates a symmetric phase (a <= ac) identical to LambdaCDM at early times, and a broken phase (a > ac) in which eta(a) > 0 transfers energy from dark matter to dark energy, suppressing linear structure growth. Using RSD, BAO, cosmic chronometers, Pantheon+SH0ES supernovae, and compressed Planck distance priors, we compare a fixed LambdaCDM background with a self-consistent coupled-scalar evolution. The RSD-only analysis shows a strong shift: the dynamical background gives Omega_m ~ 0.31 +/- 0.10 and sigma8,0 ~ 0.59 +/- 0.01, while the fixed-background case gives Omega_m ~ 0.20 +/- 0.09 and sigma8,0 ~ 0.75 +/- 0.05. In the full joint fit, we obtain Omega_m = 0.29 +/- 0.01, H0 = 69.7 +/- 0.6 km s^-1 Mpc^-1, and sigma8,0 = 0.78 +/- 0.01. A late-time interaction triggered by spontaneous symmetry breaking can therefore damp structure growth and ease the S8 tension while leaving the expansion history and the inferred H0 essentially unchanged, suggesting distinct physical origins for the two tensions.
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Astrophysics of Galaxies

Unveiling the Sources of X-ray Luminosity in DESI Galaxy Groups: Insights from the SRG/eROSITA All-Sky Survey

YunLiang Zheng, Xiaohu Yang, Teng Liu et al. (+10 more)

We use the first eROSITA all-sky survey (eRASS1) to investigate the contributions of AGN and extended gas to the total X-ray luminosity ($L_X$) of galaxy groups with different halo masses ($M_h$) at different redshifts. The presence of AGN in their central galaxies is identified using multi-wavelength catalogs, including the X-ray counterparts, the ASKAP radio catalog, and the DESI spectroscopic measurements. We apply the stacking method to obtain sufficient statistics for the X-ray surface brightness profile and the $L_X$ for groups with different central AGN properties. We find that the X-ray groups exhibit the highest $L_X$, followed by groups with QSO, radio, BPT-AGN, and non-AGN centrals. Moreover, the $L_X$ of the $M_h \lesssim 10^{13}h^{-1}M_\odot$ groups is dominated by the central AGN, while the X-ray emission from extended gas tends to be more prominent in the $M_h \gtrsim 10^{13}h^{-1}M_\odot$ groups. In groups where the AGN play a major role in X-ray emission, the contribution from extended gas is minor, resulting in significant uncertainties concerning the extended X-ray emission. When the subset containing the X-ray detected counterparts is excluded, the extended gas component becomes easier to obtain. A correlation has been identified between the X-ray luminosity of the central AGN and extended gas. However, once we account for the positional offset, their correlation becomes less prominent. Currently, the results are not conclusive enough to confirm whether there is a connection between the AGN feedback and extended gas. However, they provide a new perspective on the feedback processes in the history of group assembly.
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All authors YunLiang Zheng, Xiaohu Yang, Teng Liu, Shijiang Chen, Esra Bulbul, Ang Liu, Yi Zhang, Dawei Li, Xi Kang, Yizhou Gu, Yirong Wang, Qingyang Li, Jiaqi Wang

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

Exotic compact objects in Einstein-scalar-Maxwell theories

Antonio De Felice and Shinji Tsujikawa

In k-essence theories within general relativity, where the matter Lagrangian depends on a real scalar field $\phi$ and its kinetic term $X$, static and spherically symmetric compact objects with a positive-definite energy density cannot exist without introducing ghosts. We show that this no-go theorem can be evaded when the k-essence Lagrangian is extended to include a dependence on the field strength $F$ of a $U(1)$ gauge field, taking the general form ${\cal L}(\phi, X, F)$. In Einstein-scalar-Maxwell theories with a scalar-vector coupling $\mu(\phi) F$, we demonstrate the existence of asymptotically flat, charged compact stars whose energy density and pressure vanish at the center. With an appropriate choice of the coupling function $\mu(\phi)$, we construct both electric and magnetic compact objects and derive their metric functions and scalar- and vector-field profiles analytically. We compute their masses and radii, showing that the compactness lies in the range ${\cal O}(0.01)<{\cal C}<{\cal O}(0.1)$. A linear perturbation analysis reveals that electric compact objects are free of strong coupling, ghost, and Laplacian instabilities at all radii for $\mu(\phi)>0$, while magnetic compact objects suffer from strong coupling near the center.
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Cosmology and Nongalactic Astrophysics

Numerical simulations of magnetic monopole evolution in an expanding universe

Mark Hindmarsh, Asier Lopez-Eiguren, Riikka Seppä et al. (+1 more)

Magnetic monopoles are an inevitable feature of post-inflation symmetry-breaking phase transitions in grand unified theories. Analytic estimates of their density indicate that they are compatible with standard cosmology only if their mass is less than $10^{11}$ GeV. We initiate a programme of numerical studies of monopole dynamics by simulating a gas of 't Hooft-Polyakov monopoles formed by the Kibble mechanism after a phase transition. In this paper we simulate monopoles in a radiation background, but without interactions with the radiation, in order to resolve differences between analytical models. We find that during the radiation era, the monopoles find each other and annihilate efficiently enough to keep their density fraction constant, which supports the modelling of Zel'dovich and Khlopov and Preskill in the epoch when plasma interactions can be neglected. In the matter era the density fraction decreases logarithmically. Further work is needed to quantify the effect of the thermal bath, which is expected to reduce the annihilation rate at later times.
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All authors Mark Hindmarsh, Asier Lopez-Eiguren, Riikka Seppä, David J. Weir

High Energy Astrophysical Phenomena

A nearby pulsar J1951+2837 observed by the LPA and FAST

T.V. Smirnova, D.J. Zhou, M.A. Kitaeva et al. (+5 more)

PSR J1951+2837 is a nearby pulsar with a period of 7.334 s and dispersion measure of DM = 2.9 $\pm$ 0.6 pc cm$^{-3}$, located about 200 or 300 pc from the Sun. It occasionally radiates bright pulses and has been observed by the Large Phased Array (LPA) radio telescope at 110 MHz and by the Five-hundred-meter Aperture Spherical radio Telescope (FAST) at 1250 MHz. We detected only 343 pulses in 228 LPA observation sessions and 5 bright pulses in two FAST sessions. Based on the times of arrival (TOAs) of these bright pulses, we determined the coherent timing solution for this pulsar at a frequency of 110 MHz. Based on flux densities (S) of these bright pulses at two frequencies ($\nu$), we found that it is probably one of the known pulsars with the lowest luminosities to date, with a spectral index of about $\alpha$ = (2.5 - 3.2) for S $\sim \nu^{-\alpha}$.
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All authors T.V. Smirnova, D.J. Zhou, M.A. Kitaeva, S.A. Andrianov, C. Wang, P.F. Wang, J.L. Han, S.A. Tyul'bashev

Earth and Planetary Astrophysics

The KPF SURFS-UP Survey I: Transmission Spectroscopy of WASP-76 b

Aaron Householder, Fei Dai, Aurora Kesseli et al. (+25 more)

We introduce the KPF SURFS-UP (Spectroscopy of the Upper-atmospheres and ReFractory Species in Ultra-hot Planets) Survey, a high-resolution survey to investigate the atmospheric composition and dynamics of a sample of ultra-hot Jupiters with the Keck Planet Finder (KPF). Due to the unique design of KPF, we developed a publicly available pipeline for KPF that performs blaze removal, continuum normalization, order stitching, science spectra combination, telluric correction, and atmospheric detection via cross-correlation. As a first demonstration, we applied this pipeline to a transit of WASP-76 b and achieved some of the highest signal-to-noise detections of refractory species in WASP-76 b to date (e.g., Fe I is detected at a SNR of 14.5). We confirm previous observations of an asymmetry in Fe I absorption, but find no measurable ingress-egress asymmetry in Na I and Ca II. Together, these results suggest variations within different layers of the atmosphere of WASP-76 b: neutral metals such as Fe I trace deeper regions with stronger asymmetries, while Na I and Ca II probe regions higher in the atmosphere where the ingress-egress asymmetries are weaker. Unlike some other ultra-hot Jupiters, our results are qualitatively consistent with GCM predictions of decreasing velocity asymmetry with altitude and do not require a high-altitude super-rotating jet that has been invoked for other planets (e.g., WASP-121 b). These results suggest that atmospheric circulation patterns in ultra-hot Jupiters may be more diverse than previously thought, highlighting the need for broader surveys to study how atmospheric dynamics depend on planetary and stellar properties.
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All authors Aaron Householder, Fei Dai, Aurora Kesseli, Andrew W. Howard, Samuel Halverson, Benjamin J. Fulton, Yapeng Zhang, Alex S. Polanski, Julie Inglis, Nick Tusay, Aaron Bello-Arufe, Ashley D. Baker, Kevin B. Burdge, Jerry Edelstein, Steven Giacalone, Steven R. Gibson, Gregory J. Gilbert, Luke B. Handley, Howard Isaacson, Russ R. Laher, Erik A. Petigura, Kodi Rider, Arpita Roy, Ryan A. Rubenzahl, Chris Smith, Andrew Vanderburg, Josh Walawender, Lauren M. Weiss