Astrophysics of Galaxies
Constraints on the r-process Delay Time from Dwarf Spheroidal Galaxies
Lauren E. Henderson, Evan N. Kirby, Mithi A. C. de los Reyes et al. (+1 more)
The ancient stellar populations and simple structure of the local dwarf spheroidal
galaxies (dSphs) make them excellent laboratories for studying the chemical
evolution of the early universe. In this paper, we fit one-zone galactic chemical
evolution models to C, Mg, Si, Ca, Fe, Sr, Y, Ba, and Eu abundances in the dSphs Sculptor and Draco. By including the s- and r-processes in our model, we are able to place constraints on the timescale of r-process enrichment in these dSphs. We find that
neutron star mergers cannot be the only source of the r-process in Sculptor and Draco, and that a
prompt r-process source is required to explain the observed stellar abundances. When
neutron star mergers are the only source of the r-process in our models, their minimum delay time must be just 14-16 Myr. The
neutron-capture abundances in Sculptor and Draco can also be fit by models with a longer
neutron star merger minimum delay time combined with a
prompt r-process source that operates on the same timescale as massive
star evolution, such as magneto-rotational
supernovae. Additionally, the Sr and Y abundances in the dSphs set limits on the Sr and Y yields per r-process event. We find that theoretical r-process yields overestimate Sr and Y production by a factor of up to 100.
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All authors Lauren E. Henderson, Evan N. Kirby, Mithi A. C. de los Reyes, Rebecca Surman
Solar and Stellar Astrophysics
An asteroseismic age estimate for the Pleiades using a neural-network emulator of rotating $\delta$ Scuti pulsation models
Anuj Gautam and Simon J. Murphy
Asteroseismology of $\delta$ Sct
stars has strong potential for determining the ages of young
stars through individual mode fitting. We present a neural-network emulator trained on approximately 46 million rotating pulsation models. From stellar mass,
metallicity, age, and equatorial rotation velocity, it predicts 12 classical observables, two asteroseismic scalars, and the p mode, f mode and low-order g mode frequencies for degrees $\ell=0$-3, including the individual $m$ components of rotationally split multiplets. We couple the emulator to nested sampling through a multivariate likelihood that propagates correlated emulator residuals, making full
Bayesian posterior exploration practical. Applied to five $\delta$ Sct
stars in the Pleiades observed by TESS, the framework gives mutually consistent individual asteroseismic ages of 107-117 Myr. Combining their age posteriors gives a cluster age of $113.3\pm4.5$ Myr (statistical), consistent with the $112 \pm 5$ Myr lithium-depletion-boundary age and the 110-160 Myr range from rotating-isochrone fitting. Together with spectroscopic $v\sin i$, the inferred equatorial velocities also provide post-fit inclination estimates. Separate perturbed-grid tests using 100 matched synthetic pairs per input-physics variation give median absolute age shifts of $2.1$, $2.3$, and $5.2$ Myr for $|\Delta f_{\rm ov}|=0.005$, $|\Delta\alpha_{\rm MLT}|=0.1$, and $|\Delta Y|=0.02$, respectively; the corresponding 90th percentile shifts are $6.5$, $7.6$, and $16.2$ Myr. These tests describe conditional population sensitivities, not a systematic uncertainty on the Pleiades age. Together, the cluster-age agreement and the scale of these input-physics sensitivities support $\delta$ Sct asteroseismology as a complementary age estimation method for young
stars.
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Instrumentation and Methods for Astrophysics
The Simons Observatory: Frequency-resolved beam calibration for the SO SATs with POLOCALC
Nadia Dachlythra, Gabriele Coppi, Ludovico Bizzarri et al. (+30 more)
We present a far-field beam calibration of the Simons Observatory (SO) Small Aperture
Telescopes (SATs) using scanned single-frequency measurements of a drone-mounted source emitting in the 90 GHz band, where the SATs have an angular resolution of $\sim$30$'$. We then compare the results from two campaigns in April and December 2025 to the band-averaged beams from
planet observations by the SATs. Measuring the
telescope beam response at different frequencies across the observing bands enables modeling the system's frequency-dependent behavior. This helps track optical non-idealities. The comparison with
planet beams informs the frequency resolution necessary to accurately reconstruct the band-averaged beams in this way; it uses only the average drone and
planet products, as it is intended to demonstrate the feasibility of the frequency-resolved calibration scheme rather than to set the precise beam covariance and instrument requirements. We find that the beams of the two SATs near 90 GHz follow the frequency scaling expected for diffraction-limited optics, with only modest deviations observed in the nearest lobes of one
telescope. We establish consistency between the real band-averaged
planet beams and the synthesized drone band-averaged beams for the center wafers of both
telescopes, with an average deviation smaller than 4% for multipoles $\ell < 500$.
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All authors Nadia Dachlythra, Gabriele Coppi, Ludovico Bizzarri, Federico Nati, Alessandro Novelli, Elle C. Shaw, Samuel Day-Weiss, Federico Astori, Susanna Azzoni, Dillon J. Bass, Artem Basyrov, Federico Cacciotti, Rolando Dünner Planella, Nicholas Galitzki, Remington Gerras, John C. Groh, Jon E. Gudmundsson, Saianeesh K. Haridas, Kathleen Harrington, Carlos Hervías-Caimapo, Bradley R. Johnson, Brian Keating, Adrian T. Lee, Anto I. Lonappan, Noemi Mezzanzanica, Lyman Page, Giulia Rancati Cattaneo, Sara M. Simon, Thierry Souverin, Yoshinori Sueno, Edward J. Wollack, Kyohei Yamada, Mario Zannoni
Astrophysics of Galaxies
The DAWN JWST Archive: A spectroscopically-informed population study of the physical properties of galaxies at z>2
Rashmi Gottumukkala, Gabriel Brammer, Sune Toft et al. (+30 more)
Charting the
evolution of
star-formation, stellar mass and dust build-up over
cosmic time relies on the accurate characterisation of the stellar population properties of high
redshift galaxies. We present a catalogue of spectroscopically derived physical properties for ~12,000
galaxies at z>2, with archival JWST/NIRSpec PRISM spectroscopy and JWST/NIRCam imaging from the DAWN JWST Archive. We present a custom version of the SED fitting code BAGPIPES, used to perform joint spectrophotometric modelling of PRISM spectra and broadband NIRCam photometry. In doing so, we publicly release a science-ready catalogue of the physical properties of
galaxies beyond
cosmic noon. We report key physical properties, such as stellar masses,
star-formation rates (SFR) and timescales, and V-band dust attenuation (Av). We further probe the recent
star-formation histories (SFH) of
galaxies via their SFRs on 3 Myr, 10 Myr, and 100 Myr timescales, capturing both rising and falling recent SFHs. Through dust-corrected ugi colour-colour diagrams of massive
galaxies, we show how quiescent and dusty
galaxies populate this colour space at z>2, with
galaxies experiencing a recent downturn in
star-formation occupying distinct parameter space. We also study the dustiest
galaxies in our sample, showing that they are preferentially more massive and strongly
star-forming relative to the parent sample, residing on the high-mass end of the
star-forming main-sequence. The slope of the attenuation curve has a strong dependence on Av, varying from steep to shallow as the dust attenuation increases and the specific
star-formation rate decreases. Our findings show that the unparalleled number statistics of this catalogue of spectroscopically derived stellar population properties uniquely enables the study
star-formation, quenching and dust properties of
galaxies from
cosmic noon to
cosmic dawn.
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All authors Rashmi Gottumukkala, Gabriel Brammer, Sune Toft, Mengyuan Xiao, Anna de Graaff, Pascal A. Oesch, Francesco Valentino, Katherine E. Whitaker, William M. Baker, Laia Barrufet, Rachel Bezanson, Leindert A. Boogaard, Alex J. Cameron, Olivia R. Cooper, Emma Giovinazzo, Kasper E. Heintz, Michaela Hirschmann, Kei Ito, Ivo Labbe, Minju M. Lee, Zach J. Lewis, Jorryt Matthee, Ian McConachie, Desika Narayanan, Clara L. Pollock, Sedona H. Price, David J. Setton, Marko Shuntov, Pieter van Dokkum, Bingjie Wang, Joris Witstok, Yunchong Zhang, Pengpei Zhu
Solar and Stellar Astrophysics
Assessing the impact of background subtraction on a dust-free corona
Erika Palmerio, Cooper Downs, Phillip Hess et al. (+4 more)
Context. White-light observations of the solar corona contain contributions from both the electron-scattered K-corona and the dust-scattered F-corona. Because the diffuse F-corona dominates the measured intensity at altitudes of approximately 4 $R_{\odot}$ and above, background subtraction techniques are routinely employed to isolate the electron corona in coronagraph observations. Aims. Since no direct observational "ground truth" for the K-corona exists, the amount of coronal signal that is inadvertently removed by background subtraction methods remains unknown. We aim to quantify, for the first time, the impact of background subtraction on the inferred large-scale structure and brightness of the solar corona. Methods. We use a 32-day simulation based on a novel near-real-time, data-assimilative, time-evolving magnetohydrodynamic model to generate synthetic white-light observables. Because these synthetic observations are free from dust and instrumental stray-light contributions, they provide direct access to the "true" K-corona and enable a quantitative assessment of the effects of background subtraction. Results. We find that background subtraction generally preserves the large-scale morphology of the electron corona, including the locations and shapes of major coronal structures. However, the procedure systematically modifies the relative brightness of different features and removes a non-negligible fraction of the K-coronal signal. Conclusions. Although standard background subtraction techniques successfully recover the overall appearance of the electron corona, they can alter its quantitative photometric properties. These findings should be considered when interpreting coronal brightness measurements and deriving physical properties from processed white-light observations.
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All authors Erika Palmerio, Cooper Downs, Phillip Hess, Benjamin J. Lynch, Ryder Davidson, Ronald M. Caplan, Jon A. Linker
Earth and Planetary Astrophysics
Scaled three-dimensional simulations of giant-planet accretion and disk clearing
Ignacio Mosqueira
We develop accelerated three-dimensional simulations of growing
planet pairs that draw on a finite gas reservoir. An annulus compression (Scaling A) shortens the predicted clearing time and shrinks the computational domain at equal grid resolution while preserving key physical parameters. Planetary seeds start with Hill radii equal to the disk scale height, retaining three-dimensional
accretion. We demonstrate the method in scaled PDS 70 and Solar-System configurations, assuming perfect Hill capture by growing
planets on circular orbits. We compare Scaling A at radius-compression factor \(\Gamma=1.75\) with the unscaled PDS system at matched resolution, through a 1% reduction of the interplanetary gas inventory. The scaled run is nearly an order of magnitude faster, with similar accreted mass and a comparable partition of gas between the
planets. For the Solar-System configuration at \(\Gamma=3\), the scaling forecasts a speedup of nearly two orders of magnitude at equal local resolution. The scaling is complementary to orbital advection. On eight CPU cores of a desktop computer, the scaled PDS 70 and Solar-System runs reduce the gas inventory between the orbiting
planets by roughly half in less than a day.
Accretion-driven orbital convergence narrows the shared feeding zone and, together with gas clearing, limits the planetary growth budget. In our scaled PDS 70 and Solar-System runs, the angular momentum carried by meridional inflow directly constrains delivery theory. These results establish a practical route to testing
accretion theory against simulations at matched scaled parameters, before applying it to unscaled planetary systems.
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Instrumentation and Methods for Astrophysics
The Long-Term Radial Velocity Stability of the COS G130M/1291 Mode
John Debes, David M. French, Leonardo A. Dos Santos et al. (+3 more)
We investigate the long-term radial velocity (RV) stability of one of the Far-UV (FUV) modes on the
Cosmic Origins Spectrograph (COS). We do so by using a standard white dwarf, WD~0308-565, that has been observed over a large fraction of COS's operational lifetime of 17 years. We demonstrate that for modest signal-to-noise COS can return an RV stability of $<$3 km s$^{-1}$ over a baseline of 15 years. For higher SNR and a smaller number of epochs, we obtain $\sigma_{\mathrm V}=600$ m s$^{-1}$. We also show that the absolute radial velocity accuracy for this target is consistent with results from ground-based optical spectroscopy. We discuss some observational strategies and astrophysical objects that may be well suited to pushing to the very RV limit of the instrument. Utilizing COS for precision RV work opens a new scientific avenue for space-based UV astronomy as COS approaches 20 years of operations and hints at what may be possible with the stability of a high-resolution UV spectrograph on future missions such as the Habitable Worlds Observatory.
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All authors John Debes, David M. French, Leonardo A. Dos Santos, Travis Fischer, Svea Hernandez, Ravi Sankrit
Instrumentation and Methods for Astrophysics
Occultation polarimetry as a probe of unresolved polarization
A. G. Tevzadze
Context: Low polarization in an unresolved source may reflect weak local polarization or spatial cancellation between strongly polarized regions. An occultation can break this spatial degeneracy by differentially sampling the source as the occulting boundary moves. Aims: We develop a general theoretical framework for occultation polarimetry and determine what information can be inferred directly from unresolved full Stokes light curves, without reconstructing a polarization image or prescribing a source model. Methods: For a stationary, spatially incoherent source undergoing monotonic occultation, we relate Stokes variations to the polarization sampled by an arbitrarily curved occulting boundary and derive an exact variance decomposition of the normalized Stokes vector. Results: The polarization deficit decomposes exactly into three non-negative contributions: local polarization deficit, mixing within limb samples, and mixing between their mean polarization states. The last is directly measurable and provides a sharp, model-independent lower bound on total spatial mixing. The associated covariance tensor further characterizes the direction and correlations of the resolved polarization variations, including those between linear and circular polarization. Finite sampling preserves the bound, which can be strengthened through complementary occultation trajectories. Conclusions: Occultation polarimetry provides a powerful observational technique for extracting quantitative, model independent constraints on spatial polarization mixing directly from unresolved Stokes light curves. It offers a means to reveal both the extent and the form of polarization structure otherwise inaccessible at the available angular resolution.
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High Energy Astrophysical Phenomena
Rotating Vector Model predictions in millisecond pulsar magnetospheres with dipole and quadrupole field components
Anna V. Bilous
The rotating vector model (RVM) is widely used to interpret
pulsar radio polarization under the assumption of a dipolar
magnetic field. Motivated by tentative evidence for non-dipolar
magnetic structure in millisecond
pulsars provided by recent modeling of surface thermal X-ray pulsations, we examine how a global quadrupole component modifies position-angle (PA) behavior within the classical RVM framework. We numerically integrate
magnetic field lines in static
vacuum magnetospheres composed of a centered dipole component that is inclined with respect to the
spin axis, and a centered quadrupole component aligned with it. We then compute the open field line regions (OFLRs), emission skymaps, and PA curves for a range of dipole inclinations, relative quadrupole strengths, and light cylinder radii corresponding to two trial
spin periods of 1\,ms and 5\,ms. We find that quadrupole-modified magnetospheres produce a wide variety of PA behaviors and substantially alter the morphology and total area of OFLRs, with the OFLR area varying non-monotonically with quadrupole strength and, in some cases, exceeding that of the corresponding pure dipole. Depending sensitively on the field configuration and viewing geometry, three broad PA regimes can be distinguished: a) nearly dipolar PA swings that are largely insensitive to emission altitude; b) moderately distorted, altitude-dependent PA tracks that can bias dipolar RVM fits; and c) strongly dispersed PA behavior associated with emission from different OFLRs, which can remain incompatible with a single dipolar PA track even within narrow emission altitude ranges. These results demonstrate that dipole-like PA curves do not uniquely imply a purely dipolar
magnetic field, while global quadrupole components alone are insufficient to reproduce the full complexity of observed millisecond
pulsar PA profiles.
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Solar and Stellar Astrophysics
Radial increase of the compensated interplanetary magnetic field magnitude as a result of the growth of spherically polarized Alfvén waves
Stuart D. Bale, Timothy S. Horbury and Lorenzo Matteini
Measurements from the NASA Parker Solar Probe (PSP) mission demonstrate that inside $\sim20$ solar radii ($\Rs$) the magnitude of the interplanetary
magnetic field does not fall off simply as $1/R^2$, with $\avg{|B|}\,R^2$ 15–20% below its value at $\sim60\,\Rs$. Here we use PSP
magnetic field measurements over $10.6$–$56.8\,\Rs$ to show that the outward rise of $\avg{|B|}\,R^2$ is not due to the global structure of the heliospheric
magnetic field or proximity to the heliospheric current sheet but is the direct result of the growth of large-amplitude, spherically polarized Alfvén waves (so-called `switchbacks'). Over the same distance range, $\avg{B_R}\,R^2$ stays constant, so that the sector-signed radial flux is conserved. The wave amplitude $\epsilon = B_{\perp,{\rm rms}}/\avg{B_\parallel}$ grows from $0.26$ to $0.57$ as $R^{1/2}\cos\alpha$, and $\avg{|B|}/\avg{B_R}$ rises by $20\%$. A simple model parametrized by the broadening of the distribution of deflection angles reproduces the effect to high accuracy. These results demonstrate that as the relative wave amplitudes grow with increasing solar distance, a dynamo-like process operates to enhance the field magnitude by up to $20\%$. By enhancing
magnetic pressure this has implications for the large scale solar wind structure in the low-beta inner heliosphere, as well as partially resolving the long-standing discrepancy between remote measurements of the solar
magnetic field and those made in situ by earlier missions farther from the Sun.
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Earth and Planetary Astrophysics
Photometric and Spectroscopic Observations of Comet 2P/Encke's Nucleus in the Mid-Infrared Wavelength Region
Takafumi Ootsubo, Hideyo Kawakita, Jun-ichi Watanabe et al. (+2 more)
We observed comet 2P/Encke with the Cooled Mid-Infrared Camera and Spectrometer (COMICS) on the Subaru
telescope on UT 2003 November 12.3, when the comet was at heliocentric and geocentric distances of 1.09 and 0.27 au, respectively. Imaging observations of the comet with narrow-band filters centered at 8.8, 10.5, 11.7, 12.4, 18.8, and 24.5 $\mu$m and low-resolution spectroscopic observations in the N-band (8-13 $\mu$m, $R\sim250$) of the comet were performed. The observed spatial profiles of the comet were consistent with those of a standard
star (FWHM $\sim$ 0.3” at 10.5 $\mu$m, close to the diffraction-limited image size), indicating that the observed spectrum was dominated by thermal emission from the cometary
nucleus. The semi-axial ratio ($a$/$b$) of the
nucleus of 2P/Encke is estimated as 2.26$^{+0.33}_{-0.21}$ based on the isothermal, prolate ellipsoid model. The photometric data with the correction for rotational phases, can be explained by a blackbody temperature of $328\pm7$ K, consistent with the
nucleus surface temperature empirically estimated at 1.09 au from the Sun (327 K). This blackbody approximation for the
nucleus leads to $a = 3.6^{+0.5}_{-0.3}$ km and $b = 1.6^{+0.2}_{-0.2}$ km by assuming an emissivity of unity. The observed low-resolution N-band spectrum showed an overall smooth continuum with no prominent excess emission feature at $\sim$10 $\mu$m due to fine silicate grains in the cometary coma. The relative emissivity spectrum of the
nucleus showed a negative feature at $\sim$9.5 $\mu$m, as seen in the mid-infrared
nucleus spectrum of 460P/PanSTARRS [T. Ootsubo, et al. (2021), Icarus, 363, 114425].
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All authors Takafumi Ootsubo, Hideyo Kawakita, Jun-ichi Watanabe, Hitomi Kobayashi, Yoshiharu Shinnaka
High Energy Astrophysical Phenomena
Bayesian exploration of weakly interacting models of dark matter admixed neutron stars based on multi-density constraints
Payaswinee Arvikar, Prashant Thakur and Sarmistha Banik
We present a unified
Bayesian analysis of
Higgs-portal,
neutron-decay, and
axion-like-particle (ALP)-mediated dark matter in
neutron stars within the single-fluid approximation. Using a common relativistic mean-field description of hadronic matter, we combine finite-
nucleus and heavy-ion collision data, chiral effective field theory, NICER measurements of four
pulsars, and GW170817. The individual dark-sector parameters remain weakly determined, while model-dependent shifts in nuclear skewness reveal the sensitivity of the inferred hadronic equation of state to the assumed dark-matter mechanism. The three scenarios yield substantially overlapping mass-radius and tidal-deformability predictions, with median maximum masses near $2.1\,M_\odot$. For $1.4\,M_\odot$
stars, the
Higgs-portal model predicts higher $f$-mode frequencies and shorter damping times than the
neutron-decay and ALP models, although their credible regions overlap. Comparison with three consistently reanalysed two-fluid models gives the largest
Bayesian evidence to
neutron decay: under the adopted priors, its Bayes factors relative to the
Higgs-portal and two-fluid alternatives are approximately $24$-$37$, but only $2.2$ relative to ALP. This ranking concerns complete dark-matter models and does not establish a general preference for either fluid description or evidence for a dark component itself. Improved nuclear constraints and future gravitational-wave asteroseismology could provide complementary information to disentangle the hadronic and dark-sector contributions.
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High Energy Astrophysical Phenomena
Revisiting the Multiwavelength Data of GRB 240825A: Implications for a Two-Stage Central Engine and a Dusty Environment
Ren-Jie Xiong, Zi-Qi Wang, Xiao-Li Huang et al. (+1 more)
Reanalyzing the multi-wavelength data of GRB 240825A, we identify two distinct
prompt-emission episodes, i.e. an early, spectrally soft plateau and a subsequent bright, spectrally hard gamma-ray pulse. We show that this signature is consistent with a two-stage central engine model, in which the early soft plateau is powered by the dipolar
spin-down radiation of a transient proto-magnetar, while the later hard pulse arises from a relativistic jet launched by fallback
accretion onto the nascent black hole via the Blandford-Znajek mechanism. Adopting simulation-motivated initial black hole (BH) masses ($M_{\rm BH,0}$) and
spins ($a_0$), our fits to the second episode yield total masses supplied to the post-collapse disk of $M_{\rm fb}=0.45$–$0.96 M_\odot$, fallback radii of $r_{\rm fb}=16.9$–$17.6 r_g$, and characteristic fallback timescales of $t_{\rm fb}=0.13$–$0.25$ s. The corresponding maximum inner
accretion rates range from $0.18$ to $0.70 M_\odot \mathrm{s}^{-1}$, which is sensitive to $a_0$. Joint spectral fits with optical-X-ray afterglow data reveal a coupled temporal
evolution of dust extinction and equivalent hydrogen column density. Incorporating this extinction
evolution, an external forward-reverse shock model in a wind-like medium can account for the
radio-to-GeV band afterglow data. Although ambient dust and the bright host
galaxy may obscure any associated
supernova, late-time optical reddening remains compatible with a
supernova contribution. Applying the empirical relation between the
prompt spectral peak energy and the SN peak bolometric magnitude gives an illustrative estimate of $M_{\rm bol,peak}=-19.46\pm0.35$ mag for a putative associated SN. These results support a two-stage
evolution of the central engine and variable dusty environment of GRB 240825A, which provides insights into the nature of its progenitor.
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All authors Ren-Jie Xiong, Zi-Qi Wang, Xiao-Li Huang, En-Wei Liang
Instrumentation and Methods for Astrophysics · Cross-listed from physics.ins-det
Broadband 600- and 1200-GHz Subharmonically Pumped Schottky Diode Mixers
Peter Sobis, Vladimir Drakinskiy, Karl Jacob et al. (+3 more)
A subharmonic mixer
topology is introduced that uses quarter-wave stubs to create virtual RF/LO grounds and provide impedance matching in close proximity to the antiparallel Schottky barrier diode pair, thereby reducing the electrical length and enabling broadband operation. The RF/LO matching
topology is demonstrated at 600 GHz and 1200 GHz, with good agreement between measured and simulated performance. The 600-GHz mixer demonstrates approximately 20% RF bandwidth with a DSB receiver noise temperature below 1300 K across most of the measured band, while the 1200-GHz implementation achieves DSB receiver noise temperatures below 3000 K over a broad frequency range. Both mixers are characterized at room temperature with approximately 2 mW of LO power. The 600-GHz mixer is used in the Submillimeter Wave Instrument (SWI) onboard ESA's Jupiter Icy Moons Explorer. Overall, these results demonstrate state-of-the-art room-temperature performance for broadband receiver front ends targeting atmospheric research and remote-sensing applications.
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All authors Peter Sobis, Vladimir Drakinskiy, Karl Jacob, Axel Murk, Anders Emrich, Jan Stake
High Energy Astrophysical Phenomena
Mapping the Contracting Corona in GS 1354-64 with Insight-HXMT and XRISM: Evolving X-ray Lags and Quenched Reflection across a Complete State Transition
Kaushik Chatterjee, Min Wei, Jie Liao et al. (+13 more)
We present a comprehensive broadband spectro-temporal analysis of the dynamically confirmed Galactic black hole transient GS 1354-64 during its 2025-26 outburst, using near-simultaneous observations from Insight-HXMT and XRISM. The high spectral resolution of the XRISM-Resolve microcalorimeter, coupled with the high-cadence broadband coverage of Insight-HXMT, reveals a dramatic
evolution in the inner
accretion geometry. During the early hard-intermediate state, the spectrum was dominated by a hot Comptonizing corona accompanied by relativistically broadened reflection features. As the outburst progressed, the corona cooled efficiently, the
photon index steepened (Gamma >~ 2.5), and the reflection signatures, including the broad Fe K-alpha emission, were quenched, yielding a featureless, disk-dominated continuum. Concurrently, Type-C quasi-periodic oscillations (QPOs) evolved from 0.25 Hz to 6.52 Hz. Cross-spectral timing analysis revealed that the broadband X-ray time lags changed from pronounced positive (hard) delays (~160 ms) at low frequencies to near zero as the source softened. However, a statistical analysis incorporating the measurement uncertainties shows that the broadband lags lack a significant monotonic correlation with the QPO frequency,
photon index, or fractional rms. Instead, the scattered lag behavior suggests a competition between positive Comptonization delays and negative thermal reverberation. While the spectral softening and QPO acceleration provide strong evidence for a
geometric contraction of the corona (whether interpreted via Lense-Thirring precession or the Two-Component Advective Flow (TCAF) paradigm), the broadband timing properties underscore the turbulent and inhomogeneous nature of the inner flow as the advancing Keplerian disk drives the source into the soft state.
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All authors Kaushik Chatterjee, Min Wei, Jie Liao, Biswaraj Palit, Santanu Mondal, Honghui Liu, Chandra B. Singh, Sandeep K. Rout, Ashutosh Tripathi, Mayukh Pahari, Guobao Zhang, Zejun Jiang, Brajesh Kumar, Wei Wang, Hsiang-Kuang Chang, Xiaowei Liu
Cosmology and Nongalactic Astrophysics
Joint Constraints on the Hubble Constant and Cosmic Baryon Density from Localized Fast Radio Bursts and DESI DR2 Baryon Acoustic Oscillations
Ji-Guo Zhang, Tian-Nuo Li, Guo-Hong Du et al. (+3 more)
Fast
radio bursts (FRBs) probe free-electron columns along cosmological sightlines through their dispersion measures (DMs), whereas baryon acoustic oscillations (BAO) constrain
cosmic expansion geometry through acoustic distance ratios. In this work, we leverage their distinct physical sensitivities to simultaneously determine the Hubble constant ($H_0$) and
cosmic baryon density ($\Omega_{\rm b}$) without external
cosmic microwave background (CMB) or Big Bang nucleosynthesis (BBN) priors. Combining 120 localized FRBs and DESI DR2 BAO, we obtain $H_0=71.4^{+2.2}_{-2.5}\ {\rm km\ s^{-1}\ Mpc^{-1}}$ and $\Omega_{\rm b}=0.0503^{+0.0025}_{-0.0021}$ in $\Lambda$CDM, corresponding to precisions of $3.3\%$ and $4.6\%$, respectively. The inferred $H_0$ is statistically consistent with both SH0ES and CMB, and $\Omega_{\rm b}$ agrees with the joint constraint from BBN and CMB. Adopting IllustrisTNG-based DM distributions and fixing the diffuse-gas baryon fraction tightens the constraint to $H_0=68.8\pm1.0\ {\rm km\ s^{-1}\ Mpc^{-1}}$, but lowers the central value toward the CMB-inferred value, identifying extragalactic DM modeling as the dominant systematic uncertainty. These results establish FRB-BAO complementarity as a new avenue for simultaneously constraining $H_0$ and $\Omega_{\rm b}$.
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All authors Ji-Guo Zhang, Tian-Nuo Li, Guo-Hong Du, Wan-Peng Sun, Jing-Fei Zhang, Xin Zhang
Astrophysics of Galaxies
The Tilt of the Velocity Ellipsoid in the Milky Way Disk with GALAH-Gaia Data
Zhenzhen He, Ruilan Yang, Hui Li et al. (+1 more)
We investigate the
metallicity dependence of the tilt of the velocity ellipsoid using more than 572,000
stars selected from GALAH and Gaia. We find that the tilt angles of disk
stars can be well described by the relation $\alpha = \alpha_{0}\,\mathrm{arctan}(Z/R)$, and the $\alpha_{0}$ differ significantly among different disk populations, with $\alpha_{0}$ are 0.78 $\pm$ 0.05, 0.86 $\pm$ 0.07, and 0.77 $\pm$ 0.07 for the whole sample, the Low-[$\alpha$/Fe] and the High-[$\alpha$/Fe] populations, respectively. These results indicate that Galactic disk populations are globally tilted toward cylindrical
alignment, implying that the gravitational potential of the Galactic baryonic disk plays a dominant role in shaping the kinematics of dynamically relaxed
stars. Our detailed analysis further reveals a
metallicity dependence of $\alpha_{0}$ for various populations, with the Low-[$\alpha$/Fe] and the High-[$\alpha$/Fe] populations are respectively $\alpha_{0}$ = 0.12 $\mathrm{sin}$(3.72 [Fe/H] + 1.09) + 0.75 and $\alpha_{0}$ = 0.20 $\mathrm{sin}$(2.99 [Fe/H] + 1.90) + 0.71. These results indicate that the
metallicity dependence observed in the Low-[$\alpha$/Fe] population may be primarily associated with resonances induced by the Galactic bar, while the behavior of the High-[$\alpha$/Fe] population may also have been affected by additional dynamical and evolutionary processes, such as violent heating associated with mergers,
accretion, and/or the formation of these
stars in an environment shaped by mergers of gas-rich systems and/or a turbulent ISM.
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All authors Zhenzhen He, Ruilan Yang, Hui Li, Weixiang Sun
Astrophysics of Galaxies
Modelling the broken age-[Fe/H] relation and metallicity distribution function of mono-age populations
Qinhao Shao and Jianhui Lian
This study investigates the chemical
evolution history and radial migration in the Milky Way utilizing high-precision age measurements based on large-scale stellar spectroscopic surveys. Recent observational data have revealed a distinct break in the age-
metallicity relation of
stars in the solar neighborhood, suggesting that stellar populations of the Milky Way can be divided into two evolutionary sequences. Based on galactic chemical
evolution models, we confirm that this break in the age-
metallicity relation can be explained by a recent major gas
accretion event, which diluted the
metallicity in the disk and triggered a starburst, leading to the formation of an independent age-
metallicity sequence. To assess the impact of stellar radial migration, we incorporate a simplified treatment of this process into our multi-zone chemical
evolution model. Radial migration is modeled as a probabilistic
diffusion process, characterized by a Gaussian distribution. By fitting the model-predicted
metallicity distribution functions (MDFs) of mono-age stellar populations to observations, we infer a migration strength of $\sigma = 2.15^{+0.100}_{-0.103}\,{\rm kpc}$ for
stars with ages between 2 and 6 Gyr located at 9.5-11.5 kpc, corresponding to an average radial displacement of 1.92 kpc over 10 Gyr. This result is lower than previous estimates of stellar radial migration, suggesting that the role of radial migration in shaping the chemical structure of the Milky Way is less important than previously estimated.
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Astrophysics of Galaxies
Anisotropic Radiation in Super-Eddington Active Galactic Nuclei: The Responsivity of Broad-Line Regions to Continuum Variability
Feng-Na Fang, Pu Du and Jian-Min Wang
Anisotropic ionizing radiation is a natural theoretical expectation for super-Eddington
accretion in active galactic
nuclei (AGNs), implying that the ionizing flux incident on the broad-line region (BLR) clouds differs from that measured along the observer's line of sight. Reverberation mapping studies have revealed systematically shortened time lags of the broad H$\beta$ emission line relative to continuum variations in super-Eddington AGNs, a phenomenon that can be naturally interpreted as a consequence of anisotropic ionizing continuum radiation. To further investigate this anisotropy, we perform a systematic analysis of the H$\beta$ line responsivity, defined as the ratio of the variability amplitude of H$\beta$ to that of the driving continuum, for both sub- and super-Eddington AGNs. By combining the effective responsivities measured relative to the driving continuum, after correcting for the continuum–emission-line delay, with photoionization calculations, we infer the ionizing radiation field received by their BLRs. We find that, in super-Eddington AGNs, the ionizing flux inferred from the H$\beta$ responsivity differs significantly from that observed along the line of sight, whereas the two are in closer agreement in sub-Eddington AGNs. These results provide compelling evidence for strong anisotropy of the incident ionizing radiation in super-Eddington AGNs. We conclude by discussing the broader implications of this anisotropy, including its potential relevance to the "little red dots" recently discovered by the James Webb Space
Telescope.
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