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Physics Astrophysics

astro-ph Watch Astrophysics

Thursday 8 January

Astrophysics of Galaxies

Detection of time delay between UV and X-ray variability in Mrk 1044 using AstroSat observations

M. Reshma, C. S. Stalin, Amit Kumar Mandal et al. (+3 more)

Active galactic nuclei are known to exhibit flux variations across the entire electromagnetic spectrum. Among these, correlations between UV/optical and X-ray flux variations serve as a key diagnostics for understanding the physical connection between the accretion disk and the corona. In this work, we present the results of analysis of ultraviolet (UV) and X-ray flux variations in the narrow line Seyfert 1 galaxy Mrk 1044. Simultaneous observations in the far-UV band (FUV: 1300$-$1800 Å) and the X-ray band (0.5$-$7 keV) obtained during 31 August $-$ 8 September 2018 with the Ultraviolet Imaging Telescope and the Soft X-ray Telescope onboard AstroSat were used for this study. Significant flux variability was detected in both FUV and X-ray bands. The fractional root mean square variability amplitude ($F_{\rm var}$) was found to be 0.036 $\pm$ 0.001 in the FUV band and 0.384 $\pm$ 0.004 in the X-ray band. To explore potential time lag between the two bands, cross-correlation analysis was performed using both the interpolated cross-correlation function (ICCF) and just another vehicle for estimating lags in nuclei (JAVELIN) methods. Results from both approaches are consistent within 2$\sigma$ uncertainty, indicating that X-ray variations lead the FUV variations, with measured lags of 2.25$\pm$0.05 days (ICCF) and $2.35_{-0.01}^{+0.02}$ days (JAVELIN). This is the first detection of a time delay between UV and X-ray variations in Mrk 1044. The observed UV lag supports the disk reprocessing scenario, wherein X-ray emission from the corona irradiates the accretion disk, driving the observed UV variability.
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All authors M. Reshma, C. S. Stalin, Amit Kumar Mandal, Abhijit Kayal, S. B. Gudennavar, Prajwel Joseph

High Energy Astrophysical Phenomena

Multigroup Radiation Diffusion on a Moving Mesh: Implementation in RICH and Application to Tidal Disruption Events

Itamar Giron, Menahem Krief, Nicholas C. Stone et al. (+1 more)

Radiation-hydrodynamics (RHD) determines the bulk evolution and observable emission in a wide variety of high-energy astrophysical phenomena. Due to their complexity, RHD problems must usually be studied through numerical simulation. We have extended the publicly available RICH code, which previously solved the equations of RHD in the limit of grey flux-limited diffusion (FLD), to operate with a multigroup FLD solver. RICH is a semi-Lagrangian code that solves the equations of RHD on an unstructured moving mesh, and is the first multigroup RHD moving mesh code, making it uniquely applicable to problems with extreme dynamic range and dynamically important radiation forces. We validate our multigroup module against multiple analytic benchmarks, including a novel test of the RHD Doppler term. The computational efficiency of the code is aided by a novel scheme to accelerate convergence in optically thick cells by limiting the absorption coefficients. Finally, we apply multigroup rich in a pilot three dimensional study of a stellar tidal disruption event (TDE), using a $10^4 M_\odot$ intermediate-mass black hole. Our simulations self-consistently produce a bright early-time X-ray flash prior to peak optical/UV light, in qualitative agreement with post-processing of (grey) RICH simulations of supermassive black hole TDEs, as well as X-ray observations of the TDE AT 2022dsb.
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All authors Itamar Giron, Menahem Krief, Nicholas C. Stone, Elad Steinberg

Earth and Planetary Astrophysics

Surveying exogenous species in Saturn with ALMA I. Detecting and Mapping CO

Deborah Bardet, Thierry Fouchet, Thibault Cavalié et al. (+5 more)

The origin of carbon monoxide (CO) in Saturn's stratosphere remains uncertain, with proposed sources including internal thermochemical production, cometary impacts, and exogenic material from the rings and icy moons (i.e. Enceladus). We aim to constrain the vertical and meridional distribution of stratospheric CO and assess the relative contributions of these potential sources. Here, we analysed high-spectral-resolution ALMA observations of the CO (J=3-2) line obtained on 25 May 2018, sampling Saturn's limb from 20{\deg}S to 69{\deg}N. CO vertical profiles were retrieved using a line-by-line radiative transfer model combined with spectral inversion techniques, testing multiple prior scenarios representative of different source hypotheses. CO is confined to a narrow layer between 0.1 and 1 mbar, with a robust negative vertical gradient and mean abundances of (3.7+/- 0.8) x 10$^{-8}$ at 0.1 mbar and (7.2 +/- 0.9) x 10$^{-8}$ at 1 mbar. The meridional distribution is statistically homogeneous, with a marginal enhancement near 60{\deg} N plausibly related to Enceladus. No significant equatorial enhancement is detected. The absence of a strong equatorial enhancement rules out a long-lived steady source associated with ring infall. The observations are most consistent with a relatively recent ($\approx$200-year-old or younger) cometary impact whose material has since been horizontally mixed, while any Cassini Grand Finale ring influx was either too recent or inefficient to affect CO abundances at the probed pressure levels.
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All authors Deborah Bardet, Thierry Fouchet, Thibault Cavalié, Raphaël Moreno, Emmanuel Lellouch, Camille Lefour, Bilal Benmahi, Sandrine Guerlet

Cosmology and Nongalactic Astrophysics

Constraining the Primordial Black Hole Abundance with Space-Based Detectors

Wencong Hong, Shi Pi, Ao Wang et al. (+1 more)

Overdense regions can collapse into primordial black holes (PBHs) in the early universe, which are a compelling candidate for dark matter. Current constraints leave the asteroid-mass window the only possible one for PBH to account for all the dark matter, which can only be probed indirectly by the scalar-induced gravitational waves (GWs) sourced by the curvature perturbation which forms PBH. In this work, we explore the capabilities of future space-based gravitational wave detectors, including LISA, Taiji, and TianQin, to constrain such induced GWs as well as the PBH abundance. We systematically account for the width of the primordial curvature power spectrum, and find that the asteroid-mass window can be fully probed by all three space-based interferometers. If PBHs constitute the majority of dark matter, the induced GW leaves a strong signal in the mHz band with a signal-to-noise ratio of $10^3$–$10^4$.
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All authors Wencong Hong, Shi Pi, Ao Wang, Zhenyu Zhang

Solar and Stellar Astrophysics

Energetic particles accelerated via turbulent magnetic reconnection in protoplanetary discs – I. Ionisation rates

Valentin Brunn, Fulvia Pucci, Alexandre Marcowith et al. (+3 more)

Context. Ionisation controls the chemistry, thermal balance, and magnetic coupling in protoplanetary discs. However, standard ionisation vectors such as stellar UV, X-rays, Galactic cosmic rays (GCRs) might not be efficient enough, as UV/X-rays are attenuated rapidly with depth, while GCRs are modulated. Turbulence-induced magnetic reconnection in disc atmospheric layers offers a physically motivated, in situ source of energetic particles (EPs) that has never been considered. Aims. We quantify the ionisation and heating produced by EPs accelerated by turbulent reconnection, identify where they dominate over X-rays and GCRs, and determine energetic thresholds for their relevance. We provide scalable diagnostics tied to the local energy budget. Methods. We adopt a Fermi-like acceleration model with parameters linked to a turbulent reconnection geometry trigger by the magneto-rotational instability, yielding a steady-state energy distribution of the EP forming a power-law of index $p=2.5$. We propagate electrons and protons through the disc and compute primary and secondary ionisation and associated heating on a fiducial T Tauri disc model background. The non-thermal normalisation is set by the fraction of local viscous accretion energy dissipation channelled to EPs, parametrised by $\kappa$. Results. For $\kappa\gtrsim 0.4\%$, EPs ionisation overpass standard ionisation sources in the disc atmosphere and intermediate/deep layers out to radii of a few tens of astronomical units. Even at $\kappa\sim 0.025\%$, EPs contribute at the few-percent level, thus are chemically and dynamically relevant. These results identify EPs accelerated by turbulence-induced magnetic reconnection as a rather robust, disc-internal ionisation channel that should be included in thermo-chemical models of protoplanetary discs.
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All authors Valentin Brunn, Fulvia Pucci, Alexandre Marcowith, Marco Padovani, Christian Rab, Christophe Sauty

High Energy Astrophysical Phenomena

Jet launching from the Kerr black hole magnetosphere: An electrogeodesic approach

Jibril Ben Achour, Ileyk El Mellah and Eric Gourgoulhon

The launch of relativistic jets of plasma on astrophysical to cosmological scales is observed in a variety of astrophysical sources, from active galactic nuclei to X-ray binaries. While these jets can be reproduced by general relativistic magneto-hydrodynamics (GRMHD) and particle-in-cells (GRPIC) simulations of the dynamical Kerr magnetosphere, the development of analytic models to describe the physics of the jets has remained limited. A key challenge is to analytically describe the individual trajectories of accelerated charged particles, which ultimately build up the jet and emit radiation. In this work, we provide a first simple but fully analytical model of jet launching from the Kerr magnetosphere based on the motion of charged particles. To that end, we use the integrability of electrogeodesic motion in the Kerr monopole magnetosphere to study the ejection of charged particles near the poles. This enables us to derive (i) a criterion for the rotation axis to constitute a stable latitudinal equilibrium position, thereby representing an idealized jet, (ii) the expression for the magnetic frame-dragging effect, and (iii) the condition for an asymptotic observer to measure blueshifted particles emanating from the black hole surroundings. Our study reveals that particles can be accelerated only in a specific region whose maximal radius depends on the spin and magnetization of the black hole. Alongside these results, we provide a detailed review of the construction of test magnetospheres from (explicit and hidden) symmetries of the Kerr geometry and the condition for the separability of the electrogeodesic motion in a test magnetosphere, which serves as a basis for the model studied in this work.
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Solar and Stellar Astrophysics

Mutual Orbit Alignment in Resolved Triple Systems

Andrei Tokovinin

A sample of 278 triple systems with outer separations under 300 au and resolved inner pairs is studied, focusing on the mutual alignment between inner and outer orbits. The degree of alignment increases with (i) decreasing outer separation, (ii) decreasing ratio of outer and inner separations, (iii) decreasing mass of the inner primary component, and (iv) increasing inner mass ratio. There is no dependence on the outer mass ratio. The average mutual inclination is ~40deg for the full sample and ~10deg for 38 triples with primary components less massive than 1 solar and outer separations below 50 au. Inner eccentricities in aligned triples are smaller compared to misaligned ones. In another sample of 371 hierarchies with known outer orbits and inner eclipsing subsystems, only 22% show mutual alignment within 20deg, while the rest are aligned randomly. These findings match qualitatively current understanding of the formation of hierarchical systems, where the N-body dynamics dominates at large scales, while the accretion and migration shape systems closer than $\sim$100 au. Fragmentation of isolated cores apparently produces approximately aligned low-mass hierarchies.
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High Energy Astrophysical Phenomena

Probing millisecond magnetar formation in binary neutron star mergers through X-ray follow-up of gravitational wave alerts

Clara Plasse, Alexis Reboul-Salze, Jérome Guilet et al. (+5 more)

The nature of the remnant of a binary neutron star (BNS) merger is uncertain. Though certainly a black hole (BH) in the cases of the most massive BNSs, X-ray lightcurves from gamma-ray burst (GRB) afterglows suggest a neutron star (NS) as a viable candidate for both the merger remnant as well as the central engine of these transients. When jointly observed with gravitational waves (GWs), X-ray lightcurves from BNS merger events could provide critical constraints on the remnant's nature. We aim to assess the current and future capabilities to detect a NS remnant through X-ray observations following GW detections. To this end, we simulate GW signals from BNS mergers and the subsequent X-ray emission from newborn millisecond magnetars. The GW detectability is modeled for both current and next-generation interferometers, while the X-ray emission is reproduced using a dedicated numerical code that models magnetar spin-down and ejecta dynamics informed by numerical-relativity simulations. In our simulations, 2% - 16% of BNS mergers form millisecond magnetars. Among these, up to 70% could be detectable, amounting to up to 1 millisecond magnetar detection per year with SVOM/MXT-like instruments during the LIGO Virgo KAGRA LIGO India (LVKI) O5 run, with optimal detectability occurring about 2 hours post-merger. For next-generation GW interferometers, this rate could increase by up to three orders of magnitude, with peak detectability 3 to 4 hours post-merger. We also explore how the magnetar's magnetic field strength and observer viewing angle affect detectability and discuss optimized observational strategies. Although more likely with upcoming GW interferometers, detecting the spin-down emission of a millisecond magnetar may already be within reach, warranting sustained theoretical and observational efforts given the profound implications for mergers, GRBs, and NS physics of a single detection.
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All authors Clara Plasse, Alexis Reboul-Salze, Jérome Guilet, Diego Götz, Nicolas Leroy, Raphaël. Raynaud, Matteo Bugli, Tito Dal Canton

Astrophysics of Galaxies

Through Thick and Thin: The Cosmic Evolution of Disk Scale Height

Si-Yue Yu, Luis C. Ho, Takafumi Tsukui et al. (+16 more)

To investigate the formation and evolution of vertical structures in disk galaxies, we measure global $\operatorname{sech}^2$ scale heights, averaging thin and thick components when present, for 2631 edge-on disk galaxies with $M_*>10^{10} M_\odot$ at $0<z<3.5$ from the JWST COSMOS-Web survey. We show that dust extinction systematically overestimates scale heights at shorter rest-frame wavelengths, and therefore adopt a fixed rest-frame wavelength of 1 $\mu$m. After further correcting for projection-induced bias using a new accurate method, we find that the median disk scale height increases from $0.56\pm0.03$ kpc at $z=3.25$ to $0.84\pm0.04$ kpc at $z=1.25$, and subsequently decreases to $0.67\pm0.06$ kpc at $z=0.25$. The bias-corrected disk scale-length-to-height ratio remains constant at $2.7\pm0.2$ for $z>1.5$, but rises to $4.0\pm0.4$ at $z=0.25$. These results imply that the high-redshift progenitors of present-day thick disks were of intermediate thickness, neither thin nor thick, yet dynamically hot and dense. The observed radial variation of scale height is consistent with the artificial flaring expected from observational effects, disfavoring minor mergers as the primary mechanism of disk thickening. Instead, we suggest that the high-redshift intermediate-thickness disks were single-component systems that increased their vertical scale height through decreasing surface mass density and/or violent gravitational instabilities, eventually producing thick disks. Thin-disk growth begins at $z\approx2$ and dominates at $z\lesssim1$, yielding a vertically more compact system with decreasing scale heights from $z\approx1$ to $0$. The inferred thin-disk mass fraction increases from $0.1\pm0.03$ at $z=1$ to $0.6\pm0.1$ at $z=0$. Together, these findings reveal a continuous evolutionary link between high-redshift single-component disks and present-day thick thin disk systems.
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All authors Si-Yue Yu, Luis C. Ho, Takafumi Tsukui, John D. Silverman, Marc Huertas-Company, Anton M. Koekemoer, Maximilien Franco, Richard Massey, Lilan Yang, Rafael C. Arango-Toro, Andreas L. Faisst, Ghassem Gozaliasl, Kartik Sheth, Jeyhan S. Kartaltepe, Can Xu, Aryana Haghjoo, Xuheng Ding, Zhaoxuan Liu, Jacqueline McCleary

Astrophysics of Galaxies

Overmassive black holes and little red dots naturally form in simulations

Sunmyon Chon, Shingo Hirano, Tomoaki Ishiyama et al. (+2 more)

The origin of supermassive black holes (SMBHs) remains a long-standing problem in astrophysics. Recent JWST observations reveal an unexpectedly abundant population of overmassive black holes at $z>4$–$6$, where the BH masses lie far above local scaling relations and are not reproduced by current cosmological models. How such overmassive black holes form and rapidly grow within young galaxies has remained unclear. Here we present fully cosmological radiation-hydrodynamic simulations that self-consistently follow the birth, early growth, and emergent observable signatures of SMBHs in proto-cluster environments. We find that heavy seeds of order $10^{6}\,M_\odot$ naturally form, exceeding typical theoretical expectations by an order of magnitude. These seeds rapidly develop dense, optically thick disks whose strong electron scattering produces broad H$\alpha$ emission comparable to that seen in little red dots (LRDs). Sustained super-Eddington accretion then drives fast growth to $\sim3\times10^{7}\,M_\odot$ by $z\simeq 8$. This is the first demonstration that unifies LRDs to a short-lived, enshrouded phase of heavy-seed formation, which naturally evolve into the overmassive quasars detected by JWST and ultimately the progenitors of today's SMBHs.
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All authors Sunmyon Chon, Shingo Hirano, Tomoaki Ishiyama, Seok-Jun Chang, Volker Springel

High Energy Astrophysical Phenomena

Triaxial Magnetars as Sources of Fast Radio Bursts

J. I. Katz

Some of the mysterious temporal properties of Fast Radio Bursts (FRB) may be explained if they are produced by dynamically triaxial magnetars. If the bursts are narrowly collimated along open field lines, then observed repeating FRB are those few whose rotation axis, open field lines and infrequent radiation (analogous to pulsar giant pulses) point nearly to the observer. In apparently non-repeating FRB these are misaligned and the directions of the open field lines and infrequent radiation wander across the sky as they rotate, reducing their observed duty factors by several orders of magnitude. In repeaters a triaxial moment tensor moves the radiation pattern into or out of the line of sight on long (precessional) time scales, explaining periods of greater or lesser (or absent) activity. The dynamics of triaxial bodies may thwart the coherent integration of gravitational signals from rotating neutron stars.
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Instrumentation and Methods for Astrophysics

Multi-Messenger Studies with High-Energy Neutrinos and Gamma Rays: The WST Opportunity

Fabian Schüssler, Sofia Bisero, Bernardo Cornejo et al. (+5 more)

The search for the sources of ultra-high-energy cosmic rays (UHECRs) using high-energy neutrinos represents a frontier in high-energy astrophysics. However, a critical bottleneck remains: the ability to rapidly survey the sizable sky areas defined by the localization uncertainties of neutrino detectors and to provide rapid spectroscopic classification of the multitude of optical transients found within them. By deploying a large field-of-view with high-multiplex Multi-Object Spectroscopy (MOS) on a large aperture telescope, one can instantaneously cover neutrino error circles, thus providing crucial spectroscopic classifications of potential counterparts discovered, for example, by the Vera C. Rubin Observatory (LSST) with unprecedented efficiency. Furthermore, simultaneous operation of a giant panoramic central Integral Field Spectrograph (IFS) would allow for detailed kinematic and environmental characterization of primary candidates. This facility would unlock deep synergies between next-generation neutrino telescopes (IceCube-Gen2, KM3NeT) and gamma-ray observatories (CTAO), transforming unique multi-messenger alerts into a comprehensive physical understanding.
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All authors Fabian Schüssler, Sofia Bisero, Bernardo Cornejo, Filippo D'Ammando, Richard I. Anderson, Ilja Jaroschewski, Silvia Piranomonte, Fatemeh Zahra Majid

Solar and Stellar Astrophysics

Three-equation turbulent convection models in classical variables

Gábor B. Kovács, Róbert Szabó and János Nuspl

Context. Turbulent convection models in nonlinear radial stellar pulsation models rely on an extra equation for turbulent kinetic energy and fail to adequately explain mode-selection problems. Since multidimensional calculations are computationally expensive, it is reasonable to search for generalizations of physically grounded 1D models that approximate multidimensional results with sufficient accuracy, at least in a given parameter range. A natural way of progressing from one-equation models is to use additional nonlocal equations. While these types of models also exist in the literature, they have not been adopted for this type of object. Aims. We aim to adapt the three-equation turbulent convection model from Kuhfuss to radial stellar pulsation modeling. Methods. We use a Reynolds-stress one-point closure approach to derive our extensions alongside the model, while using additional models from the literature to close the anisotropy and dissipation terms. Results. We provide five extensions to the original model. These include an enhanced dissipation correction to the mixing length, a local anisotropy model replacing eddy viscosity, a second-order correction for turbulent ion transport in the atmosphere (alongside opacity effects), and turbulent damping of entropy fluctuations and convective flux.
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High Energy Astrophysical Phenomena

Temporal Variations in Pulsar Spectro-Polarimetry: Findings from millisecond pulsar J2144-5237 using Parkes UWL receiver

Rahul Sharan, Bhaswati Bhattacharyya, Simon Johnston et al. (+2 more)

While the temporal variations of the spectro-polarimetric nature of pulsars remains unexplored, this investigation offers significant potential for uncovering key insights into pulsar emission mechanisms, magnetic field geometry, and propagation effects within the magnetosphere. We developed a package for investigating time-varying spectral behavior for full Stokes parameters and demonstrate it on a millisecond pulsar (MSP) J2144-5237 in a binary system (orbital period ~10 days) using the Parkes UWL receiver. In this study we report rotation measure (RM) variation with orbital phase. We find that the temporal variations in the spectra of Stokes I, Q, and V are generally correlated throughout the orbit, while Stokes U exhibits intervals of both correlation and anticorrelation with Stokes I, depending on the orbital phase. We also provide a Poincare sphere representation of the polarization properties of J2144-5237, demonstrating a systematic temporal change of Poincare sphere location for the main component with orbital phase. To our knowledge, this is the first investigation of time-varying properties of the spectro-polarimetric nature of any pulsars or MSPs. Extending this study to probe the spectro-temporal nature of full Stokes data on a larger sample of MSPs or pulsars has the potential to provide vital information on emission mechanisms inside the magnetosphere, interstellar propagation effects, and binary interactions.
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All authors Rahul Sharan, Bhaswati Bhattacharyya, Simon Johnston, Patrick Weltevrede, Jayanta Roy

High Energy Astrophysical Phenomena

Tidal encounters of close white dwarf binaries with spinning black holes

Aryabrat Mahapatra, Adarsh Pandey, Pritam Banerjee et al. (+1 more)

When a stellar binary encounters a spinning black hole, interesting phenomena might result due to the mutual interaction between the binary spin, orbital angular momentum and the black hole spin. Here we consider such encounters between an intermediate mass spinning black hole and a close identical white dwarf binary system whose center of mass follows a parabolic trajectory. After studying a corresponding three-body problem in the point particle approximation, we perform a suite of smoothed particle hydrodynamics based numerical simulations of such scenarios. For this, we integrate the geodesic equations for the spinning black hole, while considering the hydrodynamics and the self and mutual gravitational interactions of the stars in a Newtonian approximation, an approach justified by the choice of parameters in the theory. We consider various initial configurations of the binary center of mass leading to equatorial and off-equatorial orbits, as also various initial inclinations between the binary's initial spin angular momentum and its initial orbital angular momentum. We find that the effects of black hole spin manifest clearly in the tidal dynamics of the binary components, while the observables of tidal encounters such as mass fallback rates are strongly dependent on the initial inclination angle. We show that the influence of the black hole spin emerges in distinct ways for different initial configurations of the binary's spin alignment. We establish that within the ambits of the Hills mechanism, in certain cases, the fallback rate may show a three-hump structure, due to interactions between tidal debris of the individual stars.
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All authors Aryabrat Mahapatra, Adarsh Pandey, Pritam Banerjee, Tapobrata Sarkar

High Energy Astrophysical Phenomena

Long-term evolution of cyclotron resonant scattering features in the accreting pulsar Vela X-1: A pulse-to-pulse approach

Yu-Jia Du, Peng-Ju Wang, Lorenzo Ducci et al. (+5 more)

We investigated the long-term evolution of the cyclotron line energy, as well as the relationship between cyclotron line energy and luminosity in the high-mass X-ray binary Vela X-1, based on archival Swift/BAT monitoring from 2005 to 2024 and pulse-to-pulse analysis of nine NuSTAR observations from 2012 to 2024. Our results provide the first confirmation that the long-term decay of the harmonic line energy ($E_{\rm cyc,H}$) in Vela X-1 has ended. We further report the first detection of a transient increase in $E_{\rm cyc,H}$ between 2020 and 2023, which suggests a sudden and significant change in the magnetic field configuration or accretion geometry. In addition, $E_{\rm cyc,H}$ shows slightly lower values at low luminosities and tends to flatten at higher luminosities, in the range of $(0.13\text{--}1.21) \times10^{37} $erg $\rm{s}^{-1}$. The fundamental line energy ($E_{\rm cyc,F}$) exhibits no significant variation with time or luminosity, remaining stable at approximately 25 keV.
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All authors Yu-Jia Du, Peng-Ju Wang, Lorenzo Ducci, Long Ji, Ling-Da Kong, Qing-Cui Bu, Chirag Mehrotra, Andrea Santangelo

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

Braneworld Baryogenesis and QCD-Era Magnetogenesis: A Predictive Link

Michaël Sarrazin

We demonstrate that primordial magnetic fields (PMF) play a decisive role in the braneworld baryogenesis scenario of [Phys. Rev. D $\textbf{110}$, 023520 (2024)], where C/CP violation arises from the coupling of visible and hidden matter-antimatter sectors through a pseudo-scalar field. Although this mechanism generates baryon number efficiently only after the quark-hadron transition, by incorporating a realistic stochastic PMF within a semi-analytical framework, we find that matching the observed baryon-antibaryon asymmetry robustly requires PMF strengths of order $10^{10}$ T right after the transition, in agreement with causal QCD-era magnetogenesis. We further reveal that magnetic fluctuations drive the baryon-density spectrum to white noise on large scales, yielding an isocurvature component compatible with Cosmic Microwave Background (CMB) bounds. This establishes a predictive link between the braneworld baryogenesis model and realistic early-Universe magnetic fields.
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Earth and Planetary Astrophysics

A change of the rotation period of asteroid (65803) Didymos caused by the DART impact

Josef Durech, Petr Pravec, Masatoshi Hirabayashi et al. (+3 more)

On 26 September 2022, the NASA Double Asteroid Redirection Test (DART) spacecraft impacted Dimorphos, the secondary component of the binary asteroid (65803)~Didymos. This experiment tested the Kinetic Impactor technology for diverting dangerous asteroids. Due to the impact, the binary system's angular momentum has changed, resulting in a significant change in the orbital period of Dimorphos. Precise values of the pre- and post-impact orbital periods were derived from a large set of photometric light curves measured for the Didymos-Dimorphos system during six apparitions from 2003 to 2023. We used these data to detect a possible change in the rotation period of the primary as a consequence of the impact. We analyzed the binary system's light curves using the binary asteroid light curve decomposition method. We selected parts of the light curves covering orbital phases outside mutual events, which represent the primary rotational light curves. We applied the light curve inversion method to construct a convex shape model of Didymos and determine its rotation period before and after the impact. These two periods were treated as independent free parameters of the modeling. We found a value of 2.2603891 +/- 0.0000002 h for the pre-impact period and 2.260440 +/- 0.000008 h for the post-impact period. Their difference 0.18 +/- 0.03 s is small yet significant, indicating that the rotation of Didymos became slower after the DART impact. The most plausible physical explanation is Didymos's post-impact reshaping, making its shape more oblate.
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All authors Josef Durech, Petr Pravec, Masatoshi Hirabayashi, Derek C. Richardson, Harrison Agrusa, Ryota Nakano

Cosmology and Nongalactic Astrophysics

Euclid preparation. Galaxy 2-point correlation function modelling in redshift space

Euclid Collaboration: M. Kärcher, M.-A. Breton, S. de la Torre et al. (+308 more)

The Euclid satellite will measure spectroscopic redshifts for tens of millions of emission-line galaxies. In the context of Stage-IV surveys, the 3-dimensional clustering of galaxies plays a key role in providing cosmological constraints. In this paper, we conduct a model comparison for the multipole moments of the galaxy 2-point correlation function (2PCF) in redshift space. We test state-of-the-art models, in particular the effective field theory of large-scale structure (EFT), one based on the velocity difference generating function (VDG$_{\infty}$), and different variants of Lagrangian perturbation theory (LPT) models, such as convolutional LPT (CLPT) and its effective-field-theory extension (CLEFT). We analyse the first three even multipoles of the 2PCF in the Flagship 1 simulation, which consists of four snapshots at $z\in\{0.9,1.2,1.5,1.8\}$. We study both template-fitting and full-shape approaches and find that with the template-fitting approach, only the VDG$_{\infty}$ model is able to reach a minimum fitting scale of $s_{\rm min}=20\,h^{-1}\,{\rm Mpc}$ at $z=0.9$ without biasing the recovered parameters. Indeed, the EFT model becomes inaccurate already at $s_{\rm min}=30\,h^{-1}\,{\rm Mpc}$. Conversely, in the full-shape analysis, the CLEFT and VDG$_{\infty}$ models perform similarly well, but only the CLEFT model can reach $s_{\rm min}=20\,h^{-1}\,{\rm Mpc}$ while the VDG$_{\infty}$ model is unbiased down to $s_{\rm min}=25\,h^{-1}\,{\rm Mpc}$ at the lowest redshift. Overall, in order to achieve the accuracy required by Euclid, non-perturbative modelling such as in the VDG$_{\infty}$ or CLEFT models should be considered. At $z=1.8$, the CLPT model is sufficient to describe the data with high figure of merit. This comparison selects baseline models that perform best in ideal conditions and sets the stage for an optimal analysis of Euclid data in configuration space.
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All authors Euclid Collaboration: M. Kärcher, M.-A. Breton, S. de la Torre, A. Veropalumbo, A. Eggemeier, M. Crocce, E. Sefusatti, E. Sarpa, R. E. Angulo, B. Camacho Quevedo, L. Castiblanco, E. Castorina, A. Chudaykin, V. Desjacques, A. Farina, G. Gambardella, M. Guidi, D. Linde, F. Marulli, A. Moradinezhad Dizgah, M. Moresco, C. Moretti, K. Pardede, A. Pezzotta, M. Pellejero Ibañez, C. Porciani, A. Pugno, M. Zennaro, N. Aghanim, B. Altieri, L. Amendola, S. Andreon, N. Auricchio, C. Baccigalupi, M. Baldi, S. Bardelli, A. Biviano, E. Branchini, M. Brescia, S. Camera, G. Cañas-Herrera, V. Capobianco, C. Carbone, V. F. Cardone, J. Carretero, M. Castellano, G. Castignani, S. Cavuoti, K. C. Chambers, A. Cimatti, C. Colodro-Conde, G. Congedo, L. Conversi, Y. Copin, F. Courbin, H. M. Courtois, H. Degaudenzi, G. De Lucia, H. Dole, F. Dubath, X. Dupac, S. Dusini, A. Ealet, S. Escoffier, M. Farina, R. Farinelli, F. Faustini, S. Ferriol, F. Finelli, P. Fosalba, N. Fourmanoit, M. Frailis, E. Franceschi, M. Fumana, S. Galeotta, K. George, W. Gillard, B. Gillis, C. Giocoli, J. Gracia-Carpio, A. Grazian, F. Grupp, L. Guzzo, S. V. H. Haugan, W. Holmes, F. Hormuth, A. Hornstrup, K. Jahnke, M. Jhabvala, B. Joachimi, E. Keihänen, S. Kermiche, A. Kiessling, B. Kubik, M. Kümmel, M. Kunz, H. Kurki-Suonio, A. M. C. Le Brun, S. Ligori, P. B. Lilje, V. Lindholm, I. Lloro, G. Mainetti, D. Maino, E. Maiorano, O. Mansutti, S. Marcin, O. Marggraf, M. Martinelli, N. Martinet, R. J. Massey, E. Medinaceli, S. Mei, M. Melchior, Y. Mellier, M. Meneghetti, E. Merlin, G. Meylan, A. Mora, L. Moscardini, C. Neissner, S.-M. Niemi, C. Padilla, F. Pasian, J. A. Peacock, K. Pedersen, W. J. Percival, V. Pettorino, S. Pires, G. Polenta, M. Poncet, L. A. Popa, F. Raison, G. Riccio, E. Romelli, M. Roncarelli, C. Rosset, R. Saglia, Z. Sakr, A. G. Sánchez, D. Sapone, B. Sartoris, P. Schneider, T. Schrabback, A. Secroun, G. Seidel, S. Serrano, P. Simon, C. Sirignano, G. Sirri, L. Stanco, J. Steinwagner, P. Tallada-Crespí, A. N. Taylor, I. Tereno, N. Tessore, S. Toft, R. Toledo-Moreo, F. Torradeflot, I. Tutusaus, J. Valiviita, T. Vassallo, Y. Wang, J. Weller, G. Zamorani, F. M. Zerbi, E. Zucca, V. Allevato, M. Ballardini, M. Bolzonella, A. Boucaud, E. Bozzo, C. Burigana, R. Cabanac, M. Calabrese, A. Cappi, T. Castro, J. A. Escartin Vigo, L. Gabarra, J. García-Bellido, V. Gautard, J. Macias-Perez, R. Maoli, J. Martín-Fleitas, M. Maturi, N. Mauri, R. B. Metcalf, P. Monaco, M. Pöntinen, I. Risso, V. Scottez, M. Sereno, M. Tenti, M. Tucci, M. Viel, M. Wiesmann, Y. Akrami, I. T. Andika, G. Angora, M. Archidiacono, F. Atrio-Barandela, E. Aubourg, L. Bazzanini, J. Bel, D. Bertacca, M. Bethermin, F. Beutler, L. Blot, M. Bonici, S. Borgani, M. L. Brown, S. Bruton, A. Calabro, F. Caro, C. S. Carvalho, F. Cogato, S. Conseil, A. R. Cooray, S. Davini, G. Desprez, A. Díaz-Sánchez, S. Di Domizio, J. M. Diego, V. Duret, M. Y. Elkhashab, A. Enia, Y. Fang, A. G. Ferrari, P. G. Ferreira, A. Finoguenov, A. Fontana, F. Fontanot, A. Franco, K. Ganga, T. Gasparetto, E. Gaztanaga, F. Giacomini, F. Gianotti, G. Gozaliasl, A. Gruppuso, C. M. Gutierrez, A. Hall, H. Hildebrandt, J. Hjorth, S. Joudaki, J. J. E. Kajava, Y. Kang, V. Kansal, D. Karagiannis, K. Kiiveri, J. Kim, C. C. Kirkpatrick, S. Kruk, M. Lattanzi, J. Le Graet, L. Legrand, M. Lembo, F. Lepori, G. Leroy, G. F. Lesci, J. Lesgourgues, T. I. Liaudat, M. Magliocchetti, A. Manjón-García, F. Mannucci, C. J. A. P. Martins, L. Maurin, M. Migliaccio, M. Miluzio, A. Montoro, G. Morgante, S. Nadathur, K. Naidoo, P. Natoli, A. Navarro-Alsina, S. Nesseris, L. Pagano, D. Paoletti, F. Passalacqua, K. Paterson, L. Patrizii, R. Paviot, A. Pisani, D. Potter, G. W. Pratt, S. Quai, M. Radovich, K. Rojas, W. Roster, S. Sacquegna, M. Sahlén, D. B. Sanders, A. Schneider, D. Sciotti, E. Sellentin, L. C. Smith, J. G. Sorce, K. Tanidis, C. Tao, F. Tarsitano, G. Testera, R. Teyssier, S. Tosi, A. Troja, A. Venhola, D. Vergani, F. Vernizzi, G. Verza, S. Vinciguerra, N. A. Walton, A. H. Wright

Cosmology and Nongalactic Astrophysics

First measurement of the Hubble constant from a combined weak lensing and gravitational-wave standard siren analysis

Felipe Andrade-Oliveira, David Sanchez-Cid, Danny Laghi et al. (+1 more)

We present a new measurement of the Hubble constant ($H_0$) resulting from the first joint analysis of standard sirens with weak gravitational lensing and galaxy clustering observables comprising three two-point correlation functions (3$\times$2pt). For the 3$\times$2pt component of the analysis, we use data from the Dark Energy Survey (DES) Year 3 release. For the standard sirens component, we use data from the Gravitational-Wave Transient Catalog 4.0 released by the LIGO-Virgo-KAGRA (LVK) Collaboration. For GW170817, the only standard siren for which extensive electromagnetic follow-up observations exist, we also use measurements of the host galaxy redshift and inclination angle estimates derived from observations of a superluminal jet from its remnant. Our joint analysis yields $H_0 = 67.9^{+4.4}_{-4.3}$~km~s$^{-1}$~Mpc$^{-1}$, a $6.4\%$ measurement, while improving the DES constraint on the total abundance of matter $\Omega_m$ by $22\%$. Removing the jet information degrades the $H_0$ precision to $9.9\%$. The measurement of $H_0$ remains a central problem in cosmology with a multitude of approaches being vigorously pursued in the community aiming to reconcile significantly discrepant measurements at the percent-level. In light of the impending new data releases from DES and LVK, and anticipating much more constraining power from 3$\times$2pt observables using newly commissioned survey instruments, we demonstrate that incorporating standard sirens into the cosmology framework of large cosmic surveys is a viable route towards that goal.
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All authors Felipe Andrade-Oliveira, David Sanchez-Cid, Danny Laghi, Marcelle Soares-Santos

Astrophysics of Galaxies

Optimization of Deep Learning Models for Radio Galaxy Classification

Philipp Denzel, Manuel Weiss, Elena Gavagnin et al. (+1 more)

Modern radio telescope surveys, capable of detecting billions of galaxies in wide-field surveys, have made manual morphological classification impracticable. This applies in particular when the Square Kilometre Array Observatory (SKAO) becomes operable in 2027, which is expected to close an important gap in our understanding of the Epoch of Reionization (EoR) and other areas of astrophysics. To this end, foreground objects, contaminants of the 21-cm signal, need to be identified and subtracted. Source finding and identification is thus an important albeit challenging task. We investigate the ability of AI and deep learning (DL) methods that have been previously trained on other data domains to localize and classify radio galaxies with minimal changes to their architectures. Various well-known pretrained neural network architectures for image classification and object detection are trained and fine-tuned and their performance is evaluated on a public radio galaxy dataset derived from the Radio Galaxy Zoo. A comparison between convolutional neural network (CNN)- and transformer-based algorithms is performed. The best performing architecture is systematically optimized and an uncertainty estimation is performed by means of an ensemble analysis. Radio source classification performance nearly comparable to the current leading customized models can be obtained using existing standard pretrained DL architectures, without modification and increase in complexity of the model architectures but rather adaptation of the data, by combining various transformations on replicated image channels. Using an ensemble of models can also further improve performance to over 90% accuracy, on par with top-performing models in the literature. The results can be transferred to other survey data, e.g. from the Murchison Wide-field Array (MWA), and in the future be used to study the EoR with the SKAO.
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All authors Philipp Denzel, Manuel Weiss, Elena Gavagnin, Frank-Peter Schilling

Solar and Stellar Astrophysics

The effect of metallicity on the Leavitt Law using phase-dependent properties of classical Cepheids

Gautam Bhuyan, Shashi Kanbur, Sukanta Deb et al. (+5 more)

The absolute calibration of period-luminosity (PL) relations of Cepheids in the Milky Way (MW) and its nearby galaxies has been a cornerstone in determining extragalactic distances and the current local expansion rate of the Universe. However, the universality of PL relations is still debated; particularly, the metallicity effect on the Cepheid PL relation. Due to the HIF-stellar photosphere interactions in Cepheids, different period-color (PC) relations at different phases can influence the corresponding PL relations at those phases.We have considered the PL relations at multiple pulsation phases as they capture the ensemble radiation hydrodynamic properties at those phases. We investigate the effect of metallicity on PL relations based on multiphase analysis of classical Cepheid light curves in the MW, Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC). Multiphase metallicity coefficients $(\gamma)$ are derived in five different photometric bands ($V$, $I$, $G$, $G_{\rm BP}$, $G_{\rm RP}$) and two Wesenheit indices ($W_{VI}$, $W_{G}$). We show that the coefficients of multiphase period-luminosity-metallicity (PLZ) relations vary dynamically as functions of Cepheid pulsation phases over a complete pulsation cycle. We find significant differences in the $\gamma_{\lambda}$ values between the short- $(0.4 \leq \log{P} < 1)$ and long-period $(1 \leq \log{P} < 2)$ Cepheids at multiple phases, in two bands, $G_{\rm RP}$ and $W_{G}$. The weighted averages of the multiphase $\gamma_{\lambda}$ values are found to be in good agreement with the latest results published in the literature. Our methods and results provide new insights into the metallicity effect on the Leavitt law, which can be useful in constraining pulsation models. Additionally, this study shows that the metallicity effect on mean-light PL relations can be recovered from its phase-dependent nature found in this study.
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All authors Gautam Bhuyan, Shashi Kanbur, Sukanta Deb, Louise Breuval, Anupam Bhardwaj, Mami Deka, Earl P. Bellinger, Kerdaris Kurbah

Cosmology and Nongalactic Astrophysics

Probing Trans-Planckian Signatures in the Early Universe: A Bayesian Analysis of the Generalized Sasaki-Mukhanov Equation

Mahdieh Eskandari Merajin

We present a rigorous and comprehensive investigation of a generalized inflationary perturbation theory designed to address persistent large-scale anomalies in the Cosmic Microwave Background (CMB). Motivated by the Trans-Planckian problem and potential non-canonical dynamics in the early Universe, we introduce a generalized Sasaki-Mukhanov equation characterized by a time-dependent correction term, parameterized by a coupling constant f. Unlike the standard slow-roll approximation, we derive the exact analytical solutions for the mode functions in terms of Whittaker functions, ensuring a precise treatment of the mode evolution across the horizon. We compute the resulting primordial scalar power spectrum, which exhibits scale-dependent oscillatory modulations and a distinct suppression of power at low multipoles. We numerically implement this modified framework within the Cobaya Bayesian inference engine. Utilizing the latest Planck 2018 temperature and polarization likelihoods combined with high-resolution data from the Atacama Cosmology Telescope (ACT) DR6, we perform a robust Monte Carlo Markov Chain (MCMC) analysis. Our results place stringent constraints on the modification parameter, |f| <= 10^-4, at a 95% confidence level. However, we find intriguing hints that the generalized model provides a better fit to the low-l CMB spectrum compared to the standard LambdaCDM model, effectively alleviating the low-quadrupole anomaly without compromising the fit at smaller scales. We discuss the implications of these findings for the energy scale of inflation and the validity of the effective field theory description during the inflationary epoch.
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Instrumentation and Methods for Astrophysics

sidmkit: A Reproducible Toolkit for SIDM Phenomenology and Galaxy Rotation-Curve Modeling

Nalin Dhiman

Self-interacting dark matter (SIDM) is a well-motivated extension of cold dark matter that can modify halo structure on galactic and group scales while remaining consistent with large-scale structure. However, practical SIDM work often requires bridging several layers, including microphysical scattering models, velocity-dependent effective cross sections, phenomenological astrophysical constraints, and (separately) data-driven halo fits, such as rotation curves. In this paper, we describe sidmkit, a transparent and reproducible Python package designed to support SIDM “micro$\rightarrow$macro” calculations and to provide a robust batch pipeline for fitting rotation curves in the SPARC data. On the SIDM side, sidmkit implements velocity-dependent momentum-transfer cross sections for a Yukawa interaction using standard analytic approximations (Born, classical, and Hulthén-based) with a numerical partial-wave option for spot checks. It also provides consistent velocity-moment averaging for Maxwellian relative speeds, scattering-rate utilities, and curated literature summary constraints for regression tests and exploratory scans. On the rotation-curve side, we implement bounded non-linear least squares fits of NFW and Burkert halo models to SPARC baryonic decompositions, with optional mass-to-light priors and information-criterion summaries (AIC/BIC). For the demonstration dataset, we process 191 rotmod galaxies (LTG+ETG bundles) and fit both NFW and Burkert models (382 total fits). We find that Burkert is preferred by $\Delta \mathrm{BIC} > 0$ for $65.4\%$ of galaxies, with “strong” preference ($\Delta \mathrm{BIC}>6$) in $32.5\%$ of galaxies;
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Solar and Stellar Astrophysics

Spectroscopy of a sample of RV Tauri stars without IR excess

Karlis Pukitis and Karina Korenika

We observed high-resolution optical spectra of 11 RV Tauri stars without IR excess, with the primary goal of searching for chemical depletion patterns. Using equivalent widths of absorption lines, we calculated photospheric parameters and chemical element abundances for five stars in the sample: HD 172810, V399 Cyg, AA Ari, V457 Cyg, and V894 Per. Only the abundance pattern of V457 Cyg suggests depletion. In the spectrum of this star, TiO lines are also observed in emission in addition to metal emissions. V457 Cyg is likely a binary system that was once surrounded by a circumbinary disc. In the spectrum of V894 Per, we find a set of spectral lines that appear to belong to another star, corroborating that it is an eclipsing variable rather than an RV Tauri star. The high overabundance of sodium may result from mass transfer within the binary system.
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Solar and Stellar Astrophysics

Empirical Evidence of Planetary Group Configurations Modulating Solar Activity

Jeff A Hansen and Shaun David Brocus Fell

Our prior research found that a $90^{\circ}$ configuration of two planetary groups were temporally associated with significant changes in global electromagnetic standing waves (Schumann resonances) during and after the three $90^{\circ}$ configuration events occurring in late 2017 and early 2018. Specifically noted were reductions in variability moving into an event and level changes immediately after a event. Because global standing-wave data have a short history and no $90^{\circ}$ events have occurred since that period, we examine here whether these geometric configuration events correspond to similar signatures in the long sunspot count record. Using daily sunspot data from January 1935 through December 2024, we conducted empirical studies assessing variance changes, post-event level shifts, and potential intrinsic oscillatory structure. In Study A, a variance-ratio test showed that sunspot variability was systematically lower during the events than in the preceding period, with 21 of 26 events since 1935 exhibiting reduced variance (binomial $p=0.0025$). In Study B, solar activity level declined roughly 21 days after events ended, with 21 of 26 events showing negative changes (binomial $p=0.0025$). In Study C, wavelet and filtering analyses revealed no internal solar oscillations at comparable timescales. These findings provide empirical evidence that the configuration events are associated with shifts in solar activity. The next three configuration events in mid- and late-2026 offer an opportunity to assess these patterns in real time.
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Instrumentation and Methods for Astrophysics

Explainable machine learning classification of Chandra X-ray sources: SHAP analysis of multi-wavelength features

Shivam Kumaran, Samir Mandal and Sudip Bhattacharyya

Extensive astronomical surveys, like those conducted with the Chandra X-ray Observatory, detect hundreds of thousands of unidentified cosmic sources. Machine learning (ML) methods offer an efficient, probabilistic approach to classify them, which can be useful for making discoveries and conducting deeper studies. In earlier work, we applied the LightGBM (ML model) to classify 277,069 Chandra point sources into eight categories: active galactic nuclei (AGN), X-ray emitting stars, young stellar objects (YSO), high-mass X-ray binaries, low-mass X-ray binaries, ultraluminous X-ray sources, cataclysmic variables, and pulsars. In this work, we present the classification table of 54,770 robustly classified sources (over $3\sigma$ confidence), including 14,066 sources at $>4\sigma$ significance. To ensure classification reliability and gain a deeper insight, we investigate the multiwavelength feature relationships learned by the LightGBM model, focusing on AGNs, Stars, and YSOs. We employ Explainable Artificial Intelligence (XAI) techniques, specifically, SHapley Additive exPlanations (SHAP), to quantify the contribution of individual features and their interactions to the predicted classification probabilities. Among other things, we find infrared-optical and X-ray decision boundaries for separating AGN/Stars, and infrared-X-ray boundaries for YSOs. These results are crucial for estimating object classes even with limited multiwavelength data. This study represents one of the earliest applications of XAI to large-scale astronomical datasets, demonstrating ML models' potential for uncovering physically meaningful patterns in data in addition to classification. Finally, our publicly available, extensive, and interactive catalogue will be helpful to explore the contributions of features and their combinations in greater detail in the future.
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Astrophysics of Galaxies

Dual AGNs on 100 kpc Scales from the Million Quasar Catalog

Zhuojun Deng, Cheng Xiang, Qihang Chen et al. (+3 more)

Research on dual active galactic nuclei (AGNs) is crucial for understanding the coevolution of galaxies and supermassive black holes. However, the current number of dual AGNs remains scarce. In this work, we selected 173 new dual AGNs, 4 AGN triplets, and 1 AGN quadruplet from the Million Quasars Catalog, all with low redshift ($z < 0.5$), a projected distance ($r_p$) of no more than 100 kpc, and a line-of-sight velocity difference ($|\Delta v|$) of less than 600 km s$^{-1}$, thus supplementing existing low-redshift dual AGNs demographics. Visual inspection of the optical images from the Dark Energy Spectroscopic Instrument Legacy Survey was performed for each pair, revealing that $\sim$16% of pairs exhibit tidal features. Statistical analyses show an increasing number of dual AGNs with decreasing redshift, with velocity difference primarily at $|\Delta v| < $ 300 km s$^{-1}$, which is likely an artifact of our selection strategy. The tidal sample peaks as having 13 pairs at 5-20$h^{-1}_{70}$ kpc, but drops to 1 pair $> 55\,h^{-1}_{70}$ kpc. Our study also explores thewide separation ($r_p>10$ kpc) dual AGNs, finding 165 such systems, with 25 displaying clear tidal features. Furthermore, some extra galaxies, AGNs, and/or their candidates were found in the same regions of the pairs or multiplets forming interacting systems with these pairs or multiplets.
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All authors Zhuojun Deng, Cheng Xiang, Qihang Chen, Liang Jing, Xingyu Zhu, Jianghua Wu

High Energy Astrophysical Phenomena

The X-ray properties and structure of A3571 up to $R_{500}$

X. Zheng, H. Yu, S. Jia et al. (+22 more)

Abell 3571 is a nearby, X-ray bright galaxy cluster located in the Shapley Supercluster. Although it appears morphologically relaxed in X-ray images, multiwavelength observations reveal subtle indications of residual dynamical activity, likely associated with past merger events. Using wide-field ($1^{\circ} \times 1^{\circ}$) data from the Einstein Probe Follow-up X-ray Telescope (EP-FXT), we extend measurements of the cluster's properties beyond its $R_{500}$ radius. We detect surface-brightness excesses on both the northern and southern sides, consistent with previous XMM-Newton results. The temperature, pressure, and entropy in the northern excess region are lower than the average values, whereas those on the southern side are slightly higher. However, we find no evidence for cold fronts or shocks. These features can be interpreted as sloshing motions triggered by an off-center minor merger. Our findings suggest that, despite its symmetric appearance, A3571 is still recovering from a minor merger and is currently in a post-merger phase. This work also demonstrates the excellent capability of EP-FXT for probing the outskirts of galaxy clusters.
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All authors X. Zheng, H. Yu, S. Jia, C. Li, X. Hou, A. Liu, Y. Chen, H. Feng, L. Song, C. Liu, F. Lu, S. Zhang, W. Yuan, J. Sanders, J. Wang, K. Nandra, W. Cui, J. Guan, D. Han, C. Jin, Y. Liu, J. Xu, J. Zhang, H. Zhao, X. Zhao

Earth and Planetary Astrophysics

Investigating the High-energy Radiation Environment of Planets in Sun-like Binary Systems

Patrick R. Behr, Kevin France, Nicholas Kruczek et al. (+6 more)

Far-ultraviolet (FUV) radiation is a driving source of photochemistry in planetary atmospheres. Proper interpretation of atmospheric observations requires a full understanding of the radiation environment that a planet is exposed to. Using the Suborbital Imaging Spectrograph for Transition-region Irradiance from Nearby Exoplanet host stars (SISTINE) rocket-borne spectrograph, we observed the Sun-like binary system $\alpha$ Centauri AB and captured the FUV spectrum of both stars simultaneously. Our spectra cover 980–1570 Å, providing the broadest FUV wavelength coverage taken in a single exposure and spanning several key stellar emission features which are important photochemical drivers. Combining the SISTINE spectrum with archival observations, model spectra, and a novel stellar activity model, we have created spectral energy distributions (SEDs) spanning 5 Å–1 mm for both $\alpha$ Centauri A and B. We use the SEDs to estimate the total high-energy flux (X-ray–UV) incident on a hypothetical exoplanet orbiting $\alpha$ Centauri A. Because the incident flux varies over time due to the orbit of the stellar companion and the activity level of each star, we use the VULCAN photochemical kinetics code to estimate atmospheric chemical abundances in the case of minimum and maximum flux exposure. Our results indicate that enhanced atmospheric mass loss due to stellar binarity will likely not be an issue for future exoplanet-hunting missions such as the Habitable Worlds Observatory when searching for Earth-like planets around Sun-like stars.
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All authors Patrick R. Behr, Kevin France, Nicholas Kruczek, Nicholas Nell, Brian Fleming, Stefan Ulrich, Girish M. Duvvuri, Amy Louca, Yamila Miguel