Cosmology and Nongalactic Astrophysics · Cross-listed from hep-lat
Revisiting the sphaleron and axion production rates in QCD at high temperatures
Sayak Guin and Sayantan Sharma
We report our new
lattice results for the sphaleron rate calculated within a thermal effective field theory of soft SU(N)
gluons whose momenta are below the
magnetic scale, where $N=2,3$, for a wide range of temperatures spanning from $0.6$ to $10^{15}$ GeV at sufficiently large volumes. Comparing these results with sphaleron rates in a nonthermal SU(N)
plasma where the infrared
gluons are overoccupied, we estimate the typical thermalization time for these ultrasoft
gluons during the early stages of reheating after inflation. We also calculate the thermal production rate of relativistic
axions due to these non-perturbatively interacting soft
gluons which shows a significant deviation from its perturbative estimate even at the electroweak scale.
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Cosmology and Nongalactic Astrophysics
Observational Tests for Distinguishing Classes of Cosmological Models
Asta Heinesen and Timothy Clifton
We investigate observational tests that can be used to distinguish between broad classes of cosmological models. This is achieved using
curvature-consistency tests of the Friedmann-Lemaître-Robertson-Walker (FLRW) models, which we investigate in two scenarios where they can be violated; (i) when the optical properties of the cosmology deviate from the expectations of FLRW, and also (ii) when the large-scale expansion of the cosmology is different from FLRW. We identify useful ways to determine the properties of these alternative scenarios in terms of the violation of the
curvature-consistency tests, and propose a new null test that can be used to isolate cosmologies with non-FLRW observational relations. The characteristic signatures we find can be used, together with the results of recent and upcoming cosmological observations, to probe and/or rule out large classes of cosmological models. This becomes an increasingly important task as the number of proposals in the literature increases, as cosmologists attempt to explain tensions, anomalies, and the dark sector of the Universe. Our approach provides a clear route for telling apart these different proposals, and offers a new opportunity for using precision cosmological data to efficiently discriminate between cosmological models.
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Earth and Planetary Astrophysics
Panchromatic View of the Frigid Jovian Exoplanet COCONUTS-2 b
Matthieu Ravet, Mickaël Bonnefoy, Gaël Chauvin et al. (+24 more)
We use a high signal-to-noise MIRI-LRS spectrum (5.45 - 11 $\mu$m, R$_\lambda$ $\sim100$) of COCONUTS-2~b revealing prominent molecular features of H$_2$O, CH$_4$ and NH$_3$. This
dataset is combined with spectra from Gemini/FLAMINGOS-2 and JWST/NIRSpec (G395H), as well as photometry from WISE and Spitzer, resulting in almost continuous wavelength coverage from 1 to 15 $\mu$m. We analyze the data using five grids of self-consistent atmospheric models, spanning a wide range of T$_\text{eff}$, log(g), and [M/H]. We also investigate the use of Gaussian Processes to account for correlated noise either caused by the spectrograph or by systematic departures of models in the inversion framework. All models manage to fit the overall combined observations but predict fainter flux in Y- and N-bands. Classical model comparison suggests that the ATMO2020++ synthetic specra (with and without PH$_3$) are statistically preferred. Fitting for the correlated noise of the three spectroscopic instruments, ATMO2020++ models yields constraints consistent with previous studies and evolutionary models predictions: T$_\text{eff}$ $=496^{+5}_{-3}$ K, log(g) $=4.30^{+0.04}_{-0.02}$ dex, [M/H] $=-0.02^{+0.03}_{-0.02}$ dex, and R $=1.03^{+0.01}_{-0.02}$ R$_\text{jup}$. The extended wavelength coverage provided by MIRI (accounting for 41% of the bolometric flux) completes the SED, yielding a precise luminosity estimation of log(L/L$_{\odot}$) $=-6.166\pm0.002$ dex. Combined with a previous estimate of the system age ($414\pm23$ Myr), cooling models predict a mass of M $=7.3\pm0.3$ M$_\text{jup}$.
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All authors Matthieu Ravet, Mickaël Bonnefoy, Gaël Chauvin, Zhoujian Zhang, Jacqueline K. Faherty, Maël Voyer, Mark W. Phillips, Pascal Tremblin, Rocio Kiman, Jessica Copeland, James J. Mang, Caroline V. Morley, Helena Kühnle, Benjamin Charnay, Sam de Regt, Paul Mollière, Simon Petrus, Allan Denis, Alice Radcliffe, Paulina Palma-Bifani, Arthur Vigan, Mathilde Mâlin, Gabriel-Dominique Marleau, Elena Manjavacas, Kevin Hoy, Elisabeth C. Matthews, Thomas K. Henning
Astrophysics of Galaxies
The Way We Tally Becomes the Tale: the Impact of Selection Strategies on the Inferred Evolution of Little Red Dots Across Cosmic Time
Pierluigi Rinaldi, Kevin Hainline, Francesco D'Eugenio et al. (+27 more)
Little Red Dots (LRDs) have emerged as a key population linked to early black hole growth, yet photometric selections have predominantly targeted only the most extreme red systems, thereby shaping our current understanding of this new population of objects. In this work, we deliberately explore a broad range of optical redness while enforcing stringent compactness and visual inspection to ensure robustness and minimize contamination. Leveraging the depth and multiwavelength coverage of the JWST Advanced Deep Extragalactic Survey (JADES) data in the GOODS-North and GOODS-South fields, we construct the largest photometric census of LRDs to date in these fields, comprising 412 sources over $z\approx2\text{--}11$ across $\approx349.6$ arcmin$^2$. We show that classic extreme color cuts isolate only a minor fraction of this population ($\lesssim25\%$), while the majority of LRDs span a broader, largely unexplored parameter space. We quantify how selection strategies impact UV and optical luminosity functions and number density
evolution, finding that current demographic trends of LRDs are strongly driven by selection biases and further limited by incomplete identification at both high and low
redshift. Spectroscopically confirmed LRDs reveal a continuous range of spectral shapes, consistent with varying Active
Galactic Nucleus (AGN) and host contributions in agreement with recent findings. Our results demonstrate that commonly adopted, purity-driven selections bias current demographic constraints toward the most extreme systems, potentially misrepresenting the diversity and
evolution of the LRD population. Accounting for these selection effects is essential for interpreting LRDs and their role in early black hole growth.
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All authors Pierluigi Rinaldi, Kevin Hainline, Francesco D'Eugenio, Pablo G. Pérez-González, Daniel J. Eisenstein, Christopher N. A. Willmer, Courtney Carreira, Brant Robertson, Benjamin D. Johnson, Stacey Alberts, William M. Baker, Andrew J. Bunker, Stefano Carniani, Eiichi Egami, Jakob M. Helton, Zhiyuan Ji, Ignas Juodžbalis, Xiaojing Lin, Jianwei Lyu, Zheng Ma, Roberto Maiolino, Eleonora Parlanti, Jan Scholtz, Yang Sun, Sandro Tacchella, Giacomo Venturi, Christina C. Williams, Chris Willott, Joris Witstok, Zihao Wu
Instrumentation and Methods for Astrophysics
LightCurveLynx: Forward Modeling of Time-Domain Surveys with Application to ZTF SN Ia DR2
Mi Dai, Jeremy Kubica, Konstantin Malanchev et al. (+5 more)
We present LightCurveLynx, a flexible and extensible software framework for end-to-end forward modeling time-domain light curves. Given the growing need for realistic simulations in the time-domain astronomy community, LightCurveLynx is designed to support a wide range of applications, including the development and validation of analysis pipelines, the optimization of survey strategies, and simulation-based inference studies. Realistic simulations can be generated from real survey metadata, forecasted survey plans, or user-defined mock survey strategies. We demonstrate the functionality of LightCurveLynx by generating a realistic simulation of Type Ia
supernovae that is representative of the ZTF SN Ia Data Release 2
dataset and perform extensive comparisons between the simulated and observed samples to validate the software. The simulation shows excellent agreement with the data in parameter distributions (with the Kullback-Leibler divergence values around 0.01-0.02) and in noise properties. The Hubble diagram generated from the simulation also indicates that the sample is complete up to
redshift 0.06, which is consistent with previous studies. Our results confirm that LightCurveLynx is robust, accurate, and ready for community use and contribution.
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All authors Mi Dai, Jeremy Kubica, Konstantin Malanchev, Alex I. Malz, Olivia Lynn, Andrew Connolly, Rachel Mandelbaum, W.M. Wood-Vasey
Astrophysics of Galaxies
VST-SMASH: VST Survey of Mass Assembly and Structural Hierarchy I. Survey presentation and deep photometry of IC 5332: tracing the mass assembly in the challenging faintest-end regime
R. Ragusa, C. Tortora, L. Hunt et al. (+9 more)
Understanding the formation and
evolution of late type
galaxies (LTG) requires deep imaging for tracing the faintest
stellar components in their outskirts. Despite their crucial role in the buildup of
stellar mass, these low surface brightness (LSB) features remain largely unexplored due to observational limitations. The VST-SMASH is designed to fill this gap, providing deep, wide field optical imaging for a volume limited sample of nearby LTG, overlapping with the Euclid Wide Survey in the South. This paper aims to introduce the VST-SMASH survey and showcase its scientific potential through the analysis of IC 5332, a LTG observed in the g, r, and i bands. The main goal is to demonstrate the depth, quality, and diagnostic power of the
dataset in tracing LSB features and structural components in
galactic outskirts. We carried out detailed surface photometry of IC 5332 to extract radial surface brightness and color profiles down to LSB regime. We performed multicomponent Sersic decompositions and constructed
stellar mass surface density profiles. We identified and characterized faint
stellar streams, estimating their colors and comparing them with adjacent
galactic regions. While the internal (1Reff) negative colour gradients can be explained by dissipative collapses and SN
outflows, the color profiles at larger radii reveal a significant gradient toward redder colors, consistent with the presence of accreted populations in the outskirts. We also find bluer r - i, which could be explained by strong Ha emission. These findings support a scenario of ongoing
stellar mass assembly through
accretion and highlight the capability of VST-SMASH to uncover faint structures in nearby
galaxies.(abridged)
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All authors R. Ragusa, C. Tortora, L. Hunt, M. Spavone, M. Baes, Abdurro uf, M. Gatto, F. Annibali, A. Mercurio, N. Bellucco, A. Unni, E. Schinnerer
Astrophysics of Galaxies
Metal Mayhem at z~7-10: Diversity and Evolution of Gas-Phase Metallicity Gradients
Maria Koller, Roberto Maiolino, Hannah Übler et al. (+16 more)
We present a JWST/NIRSpec Integral Field Unit (IFU) study of
metallicity gradients in seven low-
metallicity systems at $z=7.2-9.5$. The main sample spans
stellar masses of $\rm \log(M_*/M_{\odot}) \sim 7.8-9.5$,
star formation rates (SFRs) of $\rm \log(\text{SFR} / M_{\odot} \text{yr}^{-1}) \sim 0.5-2.5$, and gas-phase
metallicities of $4\%-13 \%~Z_\odot$. Within our sample, we also identify three low-
metallicity satellite
galaxies associated with two of our sources, providing a rare view of early-epoch interactions. The three satellites exhibit even more
primordial properties, with
metallicity $3\% -4\% ~Z_\odot$ and low
star-formation activity ($\rm \log(\text{SFR} / M_{\odot} \text{yr}^{-1}) \sim -0.5$ to $-0.9$). We find that our
galaxies, and especially the satellites, are significantly offset from the local Fundamental
Metallicity Relation (FMR), with deviations reaching $\Delta \text{FMR} \approx -1.0$ dex. This indicates that these
galaxies are likely experiencing strong
accretion of pristine gas. Overall, we observe a large scatter in radial
metallicity gradients, ranging from positive to negative with an average
metallicity gradient of $\rm -0.03 \pm 0.04 \ dex \ kpc^{-1}$. Flat gradients are found in systems with confirmed satellites, suggesting that
tidal interactions and mergers drive the radial mixing necessary to homogenise the interstellar medium. The (tentative) presence of an AGN in two of our sources suggests that strong feedback may also be responsible for the observed flat gradients. Conversely, the detection of a positive gradient in one source points toward a direct funnelling of metal-poor gas inflow into the central region of the
galaxy. These results show that
galaxies in the first billion years grow through diverse, episodic processes, suggesting that early
evolution is characterised by structural variety rather than a single, predictable path.
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All authors Maria Koller, Roberto Maiolino, Hannah Übler, Qiao Duan, Jan Scholtz, Santiago Arribas, William M. Baker, Stefano Carniani, Stephane Charlot, Mirko Curti, Luca Graziani, Gareth Jones, William McClymont, Michele Perna, Bruno Rodríguez Del Pino, Sandro Tacchella, Alessandra Venditti, Giacomo Venturi, Joris Witstok
Earth and Planetary Astrophysics
An astrometric search for planets in debris disk systems
Elisabeth M. Penderghast, Benjamin C. Bromley, Scott J. Kenyon et al. (+1 more)
Debris disks are likely created and sculpted by planetary bodies in the orbital space they share. The properties of these disks, including mass, orbital extent, and morphology, can be indicators of their planetary shepherds. Recently, T. D. Pearce and collaborators placed limits on the masses and orbits of hypothetical
planets around 178
stars with debris disks. Here, we consider 176 of these
stars, all objects that have astrometric data in the
Gaia Data Release 3 archive, to assess
planet detection from astrometry. Our analysis begins with a set of
stellar hosts of known
exoplanets, selected to have parallax, apparent magnitude, and color similar to the 176 debris disk systems. We confirm that
Gaia's ruwe parameter, a measure of the quality of astrometric fitting to a linear drift model, is sensitive to the presence of massive companions, even planetary ones. We also train a machine-learning model with a range of
planet host properties from
Gaia, considering more detailed astrometric data beyond ruwe that might indicate orbital motion. In addition, the model incorporates
Gaia photometry to inform how brightness and
stellar type affect detectability, with the risk that selection bias in the training set may affect reliability. Guided by ruwe and predictions of the machine-learning model, we identify
stars with debris disks that may host as-yet-undiscovered
planets. Overall, the model predictions, ruwe, and the mass limits from debris disk morphology do not show strong trends. Nonetheless, our top candidates with high ruwe and high planethood probability from the machine learning model will be compelling subjects for time-series analyses with
Gaia Data Release 4.
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All authors Elisabeth M. Penderghast, Benjamin C. Bromley, Scott J. Kenyon, Joan R. Najita
Astrophysics of Galaxies
Clues for the accretion regulated dust torus in the changing-look AGN SDSS J101152.98+544206.4
Zhang XueGuang
Dust torus plays the key role in determining active
galactic nuclei (AGN) observational appearance. Here, the scenario of
accretion regulated central
dust torus is tested for the first time in the individual changing-look AGN (CLAGN) SDSS J1011+5442. Through the dependence of broad H$\alpha$ luminosity on continuum luminosity, the scenario of moving
dust clouds can be ruled out in SDSS J1011+5442. Meanwhile, virial BH mass in the bright state is consistent with the M-sigma relation determined mass, indicating the virialization assumptions efficient in central BLRs. However, the virial BH mass determined in the dim state is 60 times smaller than the M-sigma relation determined value. The contrary properties of broad H$\alpha$ in different states can be naturally explained by the scenario of
accretion regulated
dust torus. Below a critical Eddington ratio, opening angle of
dust torus declines with increasing
accretion rate, leading to only outer part of central BLRs for broad H$\alpha$ with smaller line widths detected in the dim state but all the BLRs detected in the bright state. The results in this manuscript not only indicate properties of central
dust torus having apparent effects on variability properties of CLAGN, but also indicate that studying CLAGN could provide further clues to check dynamical evolving models for
dust torus in AGN.
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Astrophysics of Galaxies
Large Interstellar Polarisation Survey. III. Observational constraints on the structure of grains
Ralf Siebenmorgen, Stefano Bagnulo, Lapo Fanciullo et al. (+2 more)
Dust in the diffuse interstellar medium remains incompletely understood with regard to the structure, composition, size distribution, and
alignment properties of the grains. Joint observations of reddening, starlight polarisation spectra, and polarised
dust emission for individual sightlines provide essential constraints on such properties. We study a far-UV selected sample of 96 reddening curves, for which optical linear polarisation spectra were obtained with FORS at the VLT as part of the Large Interstellar Polarisation Survey (LIPS). Starlight polarisation spectra for 60
stars are presented in this work. These data are combined with
Gaia distance estimates and Planck thermal
dust emission. A three-component
dust model is made publicly available. It consists of nanoparticles, amorphous grains, and micrometre-sized
dust agglomerates, varying axial ratios, porosities, sizes, element abundances, and
alignment efficiencies to match the observations. The diversity of reddening and polarisation spectra is well reproduced by prolate grains with typical axial ratios of two, a porosity of 10%, and high
alignment efficiencies. Such efficiencies can be achieved with radiative torque
alignment theory (RAT), but not with imperfect Davis-Greenstein (IDG)
alignment, except when adjusting the
magnetic-field orientation to maximise the polarisation. Micrometre-sized
dust contributes wavelength-independent grey extinction in the optical, accounts for about one-third of the visual extinction, and carries one-third of the
dust mass. A follow-up submillimetre survey with high-resolution polarimetry will further constrain grain shapes and
alignment physics.
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All authors Ralf Siebenmorgen, Stefano Bagnulo, Lapo Fanciullo, Thomas Vannieuwenhuyse, Vincent Guillet
Astrophysics of Galaxies
Extinction Distributions in Nearby Star-resolved Galaxies. II. M33
Yuxi Wang, Yi Ren, Jian Gao et al. (+2 more)
Extinction maps are essential for tracing interstellar
dust and enabling accurate
stellar population studies in
galaxies. Here, a high-resolution extinction distribution of nearby
galaxy M33 is constructed by fitting multiband color indexes of the individually resolved red
giant branch (RGB)
stars from the Panchromatic Hubble Andromeda Treasury: Triangulum Extended Region (PHATTER) survey. Achieving an angular resolution of approximately 6$^{\prime\prime}$ ($\sim$ 24.4 pc), the extinction map reveals the intricate and heterogeneous distribution of
dust throughout the entire disk of M33, with distinct delineation of spiral arms, inter-arm regions, and compact
dust clouds. In addition, it exhibits strong spatial correspondence with the distributions of total hydrogen, H I, and CO, underscoring the reliability of the extinction map for tracing both diffuse and dense components of the interstellar medium. The derived $V$-band extinction reaches up to 2.5 mag per pixel, with a mean value of about 1.05 mag. Beyond providing new insights into the
dust structure of M33, the extinction map offers a robust foundation for accurate extinction corrections and will support future studies, including upcoming observations with the Chinese Space Station
Telescope.
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All authors Yuxi Wang, Yi Ren, Jian Gao, Bingqiu Chen, Ying Li
Astrophysics of Galaxies
Galaxy discs regulate the growth of supermassive black holes
Ryan J. Roberts, Jonathan J. Davies and Robert A. Crain
We examine the relationship between the mass of present-day central supermassive black holes (SMBHs, $M_{\rm BH}$), and the
stellar mass ($M_{\star}$) and
halo mass ($M_{200}$) of their host
galaxies in the EAGLE simulation, and find that scatter about these relations correlates with both
halo structure and
galaxy morphology. EAGLE reproduces the observed $M_{\rm BH}$-$M_{\star}$ relation, including (qualitatively) its dependence on morphology: at fixed $M_{\star}$, disc-dominated
galaxies host less massive SMBHs than ellipticals. We show that $M_{\rm BH}$ correlates with $M_{200}$, as expected if SMBHs are regulated by processes acting on the scale of the host dark matter
halo, but exhibits a tighter correlation with the
halo binding energy ($E_{\rm bind}$), signalling that this quantity, which encodes information about both
halo mass and
halo structure, is more fundamental to $M_{\rm BH}$. As with $M_{\rm BH}$-$M_{\star}$, scatter about the $M_{\rm BH}$-$E_{\rm bind}$ relation is strongly correlated with morphology. Gas in the central few parsecs of
galaxies with present-day discs retains strong rotational support as the
galaxy grows, inhibiting inward transport and precluding periods of rapid SMBH growth by gas
accretion. In
galaxies destined to be present-day ellipticals, however, this rotational support is disrupted, enabling gas to be funnelled onto the central SMBH, triggering rapid growth.
Evolution of the mass fraction of
stars formed ex-situ indicates that this disruption is caused by
galaxy-
galaxy interactions and mergers. Our findings corroborate the conclusion of recent studies, based on controlled simulations of an ~$L^{\star}$
galaxy, that prolonged secular
galaxy evolution inhibits central SMBH growth.
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Earth and Planetary Astrophysics
D. Revilla, P.J. Amado, R. Luque et al. (+17 more)
Theory predicts that a
planet with a sufficiently strong
magnetic field orbiting close to its host
star could induce
star-
planet magnetic interactions. This is potentially observable as an optical or
radio signal synchronised with the orbital period. We analyze 18 years of high-resolution optical spectroscopy of GJ 436, a low mass
star orbited by a Neptune-sized
exoplanet in a polar eccentric orbit.
Stellar activity indicators show enhancements at a period corresponding to the
exoplanet orbit, modulated by
stellar rotation, and the
star's 8-year
magnetic cycle. We interpret this as a signal of
star-
planet magnetic interaction. Using a
geometric model, we reproduce these periods if GJ 436 b has a
magnetic field strength of 6 to 110 Gauss.
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All authors D. Revilla, P.J. Amado, R. Luque, P. Schöfer, A.F. Lanza, A. Binnenfeld, J.A. Caballero, A.P. Hatzes, G.W. Henry, S.V. Jeffers, S. Kaur, E. Pallé, L. Peña-Moñino, M. Pérez-Torres, A. Quirrenbach, A. Reiners, I. Ribas, D. Viganò, M.R. Zapatero Osorio, S. Zucker
Astrophysics of Galaxies · Cross-listed from physics.flu-dyn
Solitary wave structure of transitional flow in the wake of a sphere
Lin Niu, Hua-Shu Dou, Changquan Zhou et al. (+1 more)
The
soliton-like coherent structure (SCS), which has been verified to exist in both transitional and turbulent boundary layers1-4, still poses a challenge in the understanding of its formation and behavior. In our previous study (Niu et al.5), the SCS was also found to exist in the transitional wake flow behind a sphere. In present study, the formation and
evolution of the SCS is further investigated at four Reynolds numbers by numerical simulation. The results show that at the early stage of the
turbulence transition, the SCS appears as a form of wave packet during the Tollmien-Schlichting (T-S) wave stage. With the increase of the Reynolds number, the SCS reaches its maximum amplitude downstream where the velocity discontinuity occurs. This position is located after the breakdown of the T-S wave and the three-dimensional structure is formed. Then, the SCS conserves its shape and amplitude over a long distance downstream. The relationships among the SCS, the spikes, the
vortex structures, and the high-shear layers are further analyzed. It is found that the SCS in the wake flow has similarities to the phenomena observed in boundary layer flows during the turbulent transition. The
vortex structures and high-shear layers mostly wrap around the border of the SCS. The
vortex structure is considered to be as a consequence of the development of the SCS rather than its cause.
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All authors Lin Niu, Hua-Shu Dou, Changquan Zhou, Wenqian Xu
Cosmology and Nongalactic Astrophysics
Cosmological Dynamics of Exponential Quintessence Constrained by BAO, Cosmic Chronometers, and DES-SN5YR/Pantheon+ Data
Sanjeeda Sultana and Surajit Chattopadhyay
We perform a comprehensive observational test of a canonical quintessence model driven by an exponential potential, motivated by its emergence in higher-dimensional theories, string-inspired scenarios, and modified
gravity. Using a Markov Chain Monte Carlo framework, we constrain the model with the latest high-precision observational
datasets including
Cosmic Chronometers,
Baryon Acoustic Oscillation, Pantheon+, and DES-SN5YR Type Ia
Supernovae. The combined data significantly tighten the parameter bounds on (H0, Omega_m0, eta0, gamma) and yield predictions for the Hubble parameter H(z), the distance modulus mu(z), and the scaled comoving angular diameter distance that remain in excellent agreement with observations and closely follow the LCDM baseline. An information-theoretic model comparison using the Akaike Information Criterion shows that the exponential quintessence model remains statistically comparable with LCDM despite having additional parameters. The model successfully reproduces the transition from matter domination to late-time acceleration, maintains w_tot > -1, and provides an age of the universe consistent with Planck 2018. Statefinder diagnostics indicate trajectories approaching the LCDM fixed point with small deviations, and energy condition analysis confirms physical viability, with only the Strong Energy Condition violated at late times as required for acceleration.
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High Energy Astrophysical Phenomena
Probing the accretion geometry of the transient accreting millisecond pulsar SAX J1808.4-3658: transitions to the propeller regime
Mahasweta Bhattacharya, Aditya S. Mondal and Gulab C. Dewangan
We analyze three NuSTAR observations and two NICER observations of the transient accreting millisecond
pulsar SAX J1808.4-3658 in the hard spectral state during its most recent outbursts in 2022 and 2025. The spectral analysis of the persistent emission shows that the continuum is well described by an absorbed thermal Comptonization model with a high
plasma temperature of ~25-90 keV. A prominent iron emission line around 5-8 keV and a Compton hump around 15-30 keV have been detected from all NuSTAR observations, indicating the reflection of the hard X-ray
photon from the
accretion disk. We employ the relativistic reflection model relxillCP to describe the reflection phenomena. The spectral fit of three NuSTAR observations shows that the inner disk radius moves outward, the Comptonized thermal emission decreases in flux, the mass
accretion rate decreases, and the disk becomes less ionized as we proceed from the 2022 to the 2025 observations. Reflection studies also reveal a moderate inclination of the source within ~30-50 degrees. During the 2025 September observation, the inner radius of the disk is significantly truncated (~23R_g), and the corresponding magnetospheric radius is comprehensively larger than the disk's co-rotation radius, suggesting a hint of the transition to the propeller regime. Although the disk is truncated at the larger radius, accreted material is still reaching the surface of the
neutron star, which is confirmed through the detection of a Type-I X-ray burst during this NuSTAR observation. The spectral analysis of the burst suggests helium burning at a low ignition depth.
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High Energy Astrophysical Phenomena
The broadband spectral energy distribution of candidate neutrino blazars
Athira M Bharathan, C. S. Stalin, Markus Böttcher et al. (+3 more)
Blazars, the jet dominated class of AGN comprising flat spectrum
radio quasars (FSRQs) and BL Lac objects (BL Lacs) are now increasingly identified as potential sources of high energy
neutrinos. Such
neutrino blazars are ideal targets to investigate the high energy emission processes and to understand their role as
neutrino sources. We report results on four candidate
neutrino blazars, PKS 0446+112, TXS 0506+056, PKS 1424$-$418 and PKS 1502+106. We carried out $\gamma$-ray spectral and timing analysis on three time periods that comprise a quiescent epoch, an epoch that corresponds to
neutrino detection and a flaring epoch. We also carried out modeling of the broadband pectral energy distribution (SED) on those three epochs. We found that the $\gamma$-ray spectra of the BL Lac TXS 0506+056 can be adequately described by a power-law, while the spectra of the other three FSRQs require a log-parabola model. On shorter timescales, we observed flux variability with doubling/halving timescales of 4.70 hrs, 9.24 hrs, 30.76 hrs and 15.42 hrs for PKS 0446+112, TXS 0506+056, PKS 1424$-$418 and PKS 1502+106, respectively. The SEDs of most of the epochs for the sources are well explained by a leptonic scenario. However, the quiescent epoch of PKS 1502+106 and the
neutrino-emission epoch of PKS 0446+112 required an additional hadronic component to reproduce the observed SEDs. Our analysis reveals a complex interplay of leptonic and hadronic processes. While certain
neutrino-associated epochs align with a leptonic model, others necessitate a hadronic component to explain the emission features.
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All authors Athira M Bharathan, C. S. Stalin, Markus Böttcher, S. Sahayanathan, Blesson Mathew, Subir Bhattacharyya
Astrophysics of Galaxies
Galactic Rotation Curves from Full-Disk Newtonian Modeling: The Lost and Found Framework
Adolfo Santa Fe Dueñas
The approximately flat outer parts of spiral
galaxy rotation curves are commonly interpreted as evidence for a discrepancy between the observed baryonic mass and the dynamical mass inferred from the measured orbital velocities. In many analyses, simplified mass estimates are often expressed through the relation $v^2(R)=GM(<R)/R$, which is exact only under spherical
symmetry. Spiral
galaxies, however, are flattened disk systems, for which mass exterior to the galactocentric radius under consideration can contribute non-negligibly to the gravitational field. We introduce the Lost and Found (LF) model, a geometrically consistent Newtonian framework based on direct full-disk gravitational integration and a parametrized representation of the disk surface density. This approach is closely related to previous thin-disk treatments that compute the gravitational field from the full mass distribution, while providing a simplified parametrization suitable for systematic fitting across heterogeneous
galaxy samples. We apply the LF model to a heterogeneous sample of disk
galaxies spanning a broad range of masses and radial extents. The model reproduces the main observed features of the rotation curves, including the inner rise and the approximately flat outer behavior, while yielding systematically lower inferred masses compared to conventional dynamical mass estimates. Across the sample, the LF-inferred mass scales nearly linearly with the conventional dynamical mass, with a characteristic scaling factor $\eta_{\rm LF}\sim0.67$. These results suggest that part of the inferred mass discrepancy in disk
galaxies may be associated with
geometric assumptions in standard mass estimates, and highlight the importance of full-disk treatments when interpreting
galactic rotation curves.
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Solar and Stellar Astrophysics
Magnetic-Field-Induced Inspiral of Binaries with Circumbinary Disk: Black Hole and Protostellar Systems
Tomoaki Matsumoto, Kenta Hotokezaka and Kohei Inayoshi
The orbital decay of binary systems is a critical process for understanding the
evolution of massive binary black holes (MBBHs) and binary
star formation. Performing high-resolution three-dimensional magnetohydrodynamic (MHD) simulations, we investigate a binary system that accretes gas from an infalling envelope analogous to the collapse of molecular cloud cores in the context of binary
star formation. Our simulations reveal the presence of
outflows/jets launched from both the circumstellar (mini) disks and the circumbinary disk (CBD). The magneto-rotational instability is also excited within the CBD. These
magnetic processes efficiently transport angular momentum in the gas surrounding the binary and thereby drive orbital decay, while a purely hydrodynamical model exhibits orbital expansion. The decay rate reaches $\sim 0.3-0.7\%$ per orbital period, depending on the initial
magnetic field strength. By appropriately scaling these numerical results, we propose a new mechanism for MBBHs mergers within a Hubble time, overcoming the bottlenecks encountered at separations near the final parsec scales. Additionally, we present a formation scenario for close twin binary
star systems, emphasizing the significant role of
magnetic processes in driving orbital
evolution across various astrophysical systems.
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Cosmology and Nongalactic Astrophysics
Low-redshift-agnostic BAO Constraints on Binned Dark-energy Density Evolution from DESI DR1 and DR2
Qian-Mo Liu and Gong-Bo Zhao
We present a low-
redshift-agnostic compression of anisotropic
baryon acoustic oscillation (BAO) distances to constrain the normalized dark-energy density
evolution, $X(z)\equiv \rho_{\rm DE}(z)/\rho_{\rm DE}(0)$, above the lowest BAO
redshift node $z_1$. Standard BAO summaries include the transverse comoving distance $D_{\rm M}/r_{\rm d}$, which depends on the integral of $H^{-1}(z)$ from $z=0$ to $z$ and therefore mixes the expansion history at $z<z_1$ with the higher-
redshift signal. We instead replace the set $D_{\rm M}(z_i)/r_{\rm d}$ by adjacent increments $\Delta D_{\rm M}(z_i,z_{i+1})/r_{\rm d}$ while retaining the radial distances $D_{\rm H}(z_i)/r_{\rm d}$. The mapping is linear, so the covariance propagates exactly. This compression intentionally removes one absolute transverse-distance mode, namely the additive contribution to $D_{\rm M}/r_{\rm d}$ below the first BAO node, and preserves the remaining information relevant to reconstructing the expansion history above $z_1$. Applied to DESI DR1 and DR2 anisotropic BAO measurements, the method yields almost uncorrelated constraints on piecewise-constant interval parameters $X_j$. In this sense, the compressed likelihood provides a conservative band-power-like estimate of dark-energy
evolution: each interval is constrained mainly by BAO information from its own
redshift range, while one nonlocal transverse mode and stronger global assumptions are deliberately projected out or marginalized over. Because our baseline analysis also marginalizes over bin-local matter-density and distance-scale parameters with broad external priors, the resulting $X_j$ constraints should be interpreted as a low-
redshift-agnostic BAO baseline rather than as a fully prior-free reconstruction. All bins are consistent with $X=1$ within current uncertainties.
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Astrophysics of Galaxies
Phase spirals induced by the gas warp
Shuyu Wang, Anthony G. A. Brown, Victor P. Debattista et al. (+1 more)
The discovery of the phase space spirals in the
Solar neighborhood in
Gaia Data Release 2 has prompted various attempts to understand their origin. A source of bending waves, which has been neglected as a cause of the phase spiral, is irregular gas inflow along the warp. We aim to study whether perturbations by the gas warp could induce phase spirals. Accounting for this additional formation scenario for phase spirals could improve our current understanding of the perturbation history of the Milky Way disc. We use two N-body + SPH (Smooth Particle Hydrodynamics) simulations of an isolated
galaxy to search for, and study, warp-induced phase spirals. We study the emergence and propagation of the detected phase spirals using
Fourier decomposition. We detect strong one-armed phase spirals in the warped simulation. These phase spirals are prevalent and persist over ~10 Gyr. The morphology of these phase spirals varies with location and evolves with time. In particular, the emergence rate of the phase spiral evolves with the gas inflow at the outer disc and the bending wave amplitude, indicating that these phase spirals are a record of warp-induced bending waves. We find that these phase spirals can reach amplitudes comparable to those in the
Gaia DR3. We only detect weak and stochastically distributed phase spirals in an unwarped control simulation. We conclude that phase spirals can be induced by the irregular gas
accretion along the warp. These phase spirals occur globally and are long-lived.
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All authors Shuyu Wang, Anthony G. A. Brown, Victor P. Debattista, Tigran Khachaturyants
Solar and Stellar Astrophysics
Effects of Geomagnetic Cutoff Rigidity Variations during Forbush Decreases
Pengwei Zhao and Jie Feng
Forbush decreases (FDs) are short-term reductions in
galactic cosmic ray flux caused by interplanetary disturbances. During some interplanetary coronal mass ejection (ICME) events,
neutron monitor (NM) data also contain variations produced by geomagnetic storms. Earlier studies emphasized apparent effects near 10~GV, but storm-time changes in geomagnetic cutoff
rigidity can either increase or decrease the ground-level count rate. Using a recently published hourly
proton flux reconstructed from NM data for May 2011 through October 2019, the interval covered by the published AMS daily
proton fluxes, we show that these localized anomalies can extend to lower
rigidities and reach 1~GV in some events. Such effects can bias the
rigidity dependence inferred from NM-based hourly
proton spectra during disturbed intervals. Because AMS measures
proton rigidity directly in space, its daily
proton spectrum is not affected by cutoff variations at ground stations and provides a stable reference. We therefore use AMS to constrain corrections for selected events. The correction removes localized anomalies while preserving the broader FD
evolution, and for a representative ICME event it brings the corrected daily averages closer to the AMS measurements. Our results show that short-timescale
cosmic ray variability during FDs reflects both heliospheric modulation and storm-time changes in geomagnetic shielding.
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High Energy Astrophysical Phenomena
A 4.5-s Quasiperiodic Spectral Oscillation in GRB 230307A: Evidence for Free Precession of a Post-Merger Magnetar?
Run-Chao Chen, Jun Yang, Bin-Bin Zhang et al. (+4 more)
Millisecond magnetars, rapidly rotating
neutron stars with ultra-strong
magnetic fields, have long been proposed as central engines of gamma-ray bursts (GRBs). For GRBs produced by
neutron star mergers, the survival of a long-lived magnetar remnant remains uncertain, as the merger remnant may rapidly collapse into a black hole. In GRB 230307A, multiwavelength observations together with a previously reported 909-Hz periodic signal consistent with millisecond
spin in its
prompt emission provide strong evidence that such a post-merger magnetar may power the burst. Here we report the discovery of a quasiperiodic modulation with a characteristic period of 4.5 s in the spectral
evolution of GRB 230307A, detected consistently across multiple gamma-ray instruments. The modulation is manifested as a coherent, energy-dependent variation of the spectral shape, with the strongest signature in the
evolution of the peak energy. Within the magnetar-engine framework, such a low-frequency modulation can be interpreted as a manifestation of large-scale periodic variations associated with the central engine. If interpreted in terms of free precession, the observed timescale implies a
stellar ellipticity of $\epsilon \gtrsim 2.4 \times 10^{-4}$, corresponding to an internal
magnetic field strength of $B_t \gtrsim 1.6 \times 10^{16}$ G, alongside a dipole field of $B_p \approx 5.6 \times 10^{15}$ G inferred from the early X-ray emission. These results suggest that such systems may provide potential sources of post-merger gravitational waves (GWs), motivating targeted searches following GRB triggers.
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All authors Run-Chao Chen, Jun Yang, Bin-Bin Zhang, Chen-Wei Wang, Wen-Jun Tan, Shao-Lin Xiong, Bing Zhang
Solar and Stellar Astrophysics
Magnetic geometry of M dwarfs in the southern PLATO field
M. Diez, P. I. Cristofari, J. Morin et al. (+9 more)
M
dwarfs are the most abundant
stars in the
Galaxy and exhibit diverse
magnetic behaviours. Understanding their large-scale
magnetic fields is essential to study
stellar dynamos and assess the impact of
magnetic activity on planetary environments, yet their
magnetic properties and long-term variability remain poorly characterised. We aim to characterise the large-scale
magnetic fields of 6 M
dwarfs in the southern PLATO field, with rotation periods from ~1 to 17 days and masses between 0.26 and 0.64 Msun. Five
stars are partially convective, one fully convective, extending the mass-rotation diagram to previously unsampled regions. We analysed TESS light curves to determine accurate rotation periods and optimise phase coverage for spectropolarimetric observations. SPIRou data were reduced to obtain LSD profiles and longitudinal field measurements, while synthetic spectra fitting yielded small-scale field strengths. ZDI was applied to reconstruct large-scale
magnetic topologies. We report a wide diversity of
magnetic topologies among the 6 M
dwarfs, with 3 main results: (1) Rapidly-rotating (Prot < 2 d) early M
dwarfs can generate dipole-dominated fields of moderate intensity, similar to less massive mid-M
dwarfs; (2) rapidly-rotating mid-M
dwarfs can generate non-axisymmetric large-scale fields with a significant toroidal component; (3) a moderately-rotating (Prot ~ 17 d) early M
dwarf shows a surprisingly weak large-scale field. Our findings highlight the diversity of
magnetic configurations, including in previously unexplored regions. Long-term monitoring is crucial to distinguish persistent features from variability-driven excursions and to characterise the
evolution of surface
magnetic fields. Complementary PLATO photometry, including
flare and spot-induced variability analyses, will be essential to link surface activity with
magnetic properties.
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All authors M. Diez, P. I. Cristofari, J. Morin, P. Petit, S. Bellotti, A. Vidotto, A. Carmona, X. M. Delfosse, C. P. Folsom, G. A. J. Hussain, A. F. Lanza, S. Messina
Earth and Planetary Astrophysics
Chemical Abundances Shape History (CASH). I. A Link between Giant Planets Orbital Periods and Host Stellar C/O Ratios
Ruisheng Zhang, Ji-Wei Xie, Mengrui Pan et al. (+5 more)
The chemical abundance of host
stars plays a pivotal role in shaping the formation history of planetary systems, yet the influence of elements beyond iron remains poorly understood. Here, we investigate the relationship between the carbon-to-oxygen (C/O) ratio of host
stars and the orbital periods of
giant planets. By analyzing high-resolution spectroscopic data from 598
planet-hosting
stars (hosting 929
planets) across SDSS, Keck, and HARPS surveys, we identify a correlation:
stars with higher C/O ratios are more likely to host longer-period
giant planets. Theoretical models of pebble-driven
planet formation and migration further support this observation, demonstrating that elevated C/O ratios enhance solid material availability at outer disk regions, promoting
giant planet formation at larger distances and subsequent moderate inward migration. Our findings establish
stellar C/O as a critical factor in shaping the orbital architecture of
giant planets, bridging disk chemistry to planetary system
evolution.
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All authors Ruisheng Zhang, Ji-Wei Xie, Mengrui Pan, Beibei Liu, Ji-Lin Zhou, Ji Wang, Haiyang S. Wang, Yapeng Zhang
Instrumentation and Methods for Astrophysics
A TESS Test of the Hybrid Ring Strategy for Technosignature Searches Using GRB 221009A
Naoki Seto
We present the first observational test of the hybrid ring strategy, a general coordinated signaling scheme proposed by Seto (2025), which provides a practical Schelling-point realization for interstellar signaling. We use the exceptionally bright GRB 221009A as the anchoring flash for the scheme, together with the accurately measured distance to the
Galactic center. This combination provides a high-precision relation linking sky position to a tightly constrained arrival-time window. TESS observed the region around the GRB nearly continuously for ~50 days in 2024, providing survey light curves that enable a direct test of this scheme with sharply predicted arrival-time windows of $\sim$3.4 days. Among 58 carefully selected
stars, we identify two that show noticeable single-time-bin brightenings inside their predicted windows (where each time bin corresponds to a 200 s integrated TESS exposure). In both cases the brightenings coincide with excursions in at least one nearby
star and are therefore most consistent with instrumental origins. This test demonstrates that the hybrid ring strategy is practical with existing survey data and could serve as a promising basis for future technosignature searches.
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Astrophysics of Galaxies
RadioAstron reveals a change in the jet collimation profile of 3C 84
P. Benke, T. Savolainen, G. Giovannini et al. (+5 more)
Due to its brightness and proximity, the
radio galaxy 3C 84 (optical counterpart NGC 1275 in the Perseus cluster) has been the target of extensive studies investigating the central parsec region of its active
galactic nucleus. In 2003, its most recent active phase resulted in a
plasma ejection visible in the southern jet, which presented a unique opportunity to study jet formation and
evolution at high angular resolution with very long baseline interferometry (VLBI). We aim to study the morphology,
evolution, and spectral properties of the restarted jet three years after the first ultra-high angular resolution observations with the RadioAstron space-VLBI satellite in September 2013. To study 3C 84, we used space-VLBI observations carried out in September 2016 at 22 GHz with a global VLBI network and the 10 m Spektr-R
radio telescope in orbit as well as quasi-simultaneous multifrequency observations at 4.8, 8, 15, and 43 GHz from the Very Long Baseline Array, including the Effelsberg 100 m
telescope. We present the 22 GHz RadioAstron image of 3C 84 from 2016, which reveals the source's central region at a 58 microarcsecond effective resolution. During the three years that elapsed between the first and second space-VLBI observations, the source underwent significant morphological changes. We confirm the existence of the limb-brightened jet and counter-jet reported earlier as well as a flip in the position of the hotspot discovered recently via VLBI monitoring at 43 GHz. Based on measuring the collimation profile, we find that it has evolved from being quasi-cylindrical to
parabolic. This is most likely the result of the decreased pressure of the mini-cocoon, which was inflated by the jet and contains hot gas that cannot confine the jet efficiently as it propagates further away from the core. Finally, we also constrained the
magnetic field strength in the core region and the hotspot.
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All authors P. Benke, T. Savolainen, G. Giovannini, Y. Y. Kovalev, G. Bruni, M. M. Lisakov, M. Giroletti, E. Ros
Earth and Planetary Astrophysics
Habitability Study of Terrestrial Planets: Application to Venus-like Worlds
Swathi Raviprakash, Madhu Kashyap Jagadeesh, Margarita Safonova et al. (+1 more)
The study of planetary habitability beyond Earth remains central and a challenging project in planetary science. Analysis of large volumes of planetary data from space missions such as CoRoT, Kepler, and JWST is directed ultimately at finding a
planet similar to Earth, the Earth's twin, and answering the question of potential exo-habitability. The Earth Similarity Index (ESI) is a first step in this quest, ranging from 1 (Earth) to 0 (totally dissimilar to Earth). To identify
planets that may be habitable to the extreme forms of life, we introduce the Mars Similarity Index (MSI). However, extreme forms of life have also been hypothesized under specific conditions in the upper atmosphere of Venus, motivating comparative habitability studies beyond Earth and Mars. The Venus Similarity Index (VSI), introduced here, is defined as the
geometric mean of radius, density, escape velocity, and surface temperature, normalized in Venus units (VU). VSI values range from 0 (complete dissimilarity) to 1 (maximum similarity). The VSI provides a comparative framework for identifying Venus-like planetary environments within
exoplanet populations. To explore habitability
evolution, we further introduce the Ancient Venus Similarity Index (AVSI) and the Future Earth Similarity Index (FESI) to examine early Venusian conditions relative to ancient Earth and to assess potential future evolutionary pathways for Earth-like
planets.
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All authors Swathi Raviprakash, Madhu Kashyap Jagadeesh, Margarita Safonova, Oleg Kotsyurbenko
Solar and Stellar Astrophysics
A Major Geomagnetic Storm in 2024 October Linked to Sympathetic CME–Prominence Eruptions
Rui Wang, Huidong Hu, Xiaowei Zhao et al. (+11 more)
Improving predictions of the geomagnetic impact of coronal mass ejections (CMEs) requires understanding how
solar source properties relate to in-situ measurements at Earth. However, major geomagnetic storms frequently arise from interacting CMEs, complicating the link back to their
solar origins. We analyze a CME interaction event that caused a major geomagnetic storm in 2024 October 10-11 (D$_{st}$ $\sim$-333 nT). Multiviewpoint observations reveal that the storm was related to a sympathetic eruption involving a quiescent filament and an active-region CME. The coronagraph on board the Advanced Space-based
Solar Observatory clearly shows that this sympathetic eruption resulted in two distinct CMEs. Due to the overlap of the CMEs in the coronagraph field of view (FOV), a spheroid shock model was used to fit the observed shock. Kinematic analysis indicates that the interacting CMEs had completed their impulsive acceleration phase before entering the coronagraph FOV, with a slow deceleration continuing beyond 100 R$_\odot$. In-situ measurements indicate that the enhanced southward
magnetic fields, arising from compression during CME interactions, were the primary driver of the storm. Compared to photospheric fields, the in-situ
magnetic fields suggest that the trailing CME maintained flux-rope-like signatures consistent with the source region. In contrast, the compressed leading CME displayed varying
magnetic configurations between Wind and STEREO-A, featuring distorted flux-rope signatures and inconsistent inferred axis orientations. Our study bridges
solar source dynamics to in-situ multipoint measurements, providing key insights for space weather prediction. Nevertheless, the direct linkage between source-region
magnetic field configurations and these measurements remains tentative and requires further investigation.
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All authors Rui Wang, Huidong Hu, Xiaowei Zhao, Chong Chen, Suli Ma, Zhongwei Yang, Lei Lu, Li Feng, Wenshuai Cheng, Chong Huang, Quan Wang, Xiaoshuai Zhu, Bei Zhu, Yiming Jiao
High Energy Astrophysical Phenomena
Neutron Star Merger Rates from Multi-messenger Observations: Clues to the Physical Origin of the Short and Long-short Gamma-ray Bursts
Zhi-Ping Jin, Yuan-Zhu Wang, Yin-Jie Li et al. (+4 more)
Short and long-short gamma-ray bursts (GRBs) are widely believed to be powered by
neutron star mergers. In this work, we calculate local rate of such GRBs and find a relatively high value of $\sim 786-2468~{\rm Gpc^{-3}~yr^{-1}}$ when including the very narrow collimation event GRB 061201. Considering that its
redshift is not very reliable, after excluding this event, the rate is $\sim 195-666~{\rm Gpc^{-3}~yr^{-1}}$. We also calculate the electromagnetically (EM) bright
neutron star merger rate inferred from the LIGO/Virgo/KAGRA observations up to the end of the first epoch of the O4 run, and derive a rate of $\sim 66-347~{\rm Gpc^{-3}~yr^{-1}}$. This rate is somewhat lower than the value obtained from the GRBs, even after excluding GRB 061201. The non-detection of any viable EM bright merger in the O4b and O4c observing runs favors an even lower rate, which starts to challenge the
neutron star merger origin of the short and long-short GRBs and may suggest additional contribution from the mergers of other compact object (like the
neutron star-white
dwarf) binaries, as speculated initially by King et al. (2007) in interpreting the long-short event GRB 060614.
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All authors Zhi-Ping Jin, Yuan-Zhu Wang, Yin-Jie Li, Yun Wang, Hao Wang, Shao-Peng Tang, Da-Ming Wei