UchUchU

Research Trends

Latest preprints in space engineering and astrophysics.

astro-ph.SRphysics.flu-dyn

Grand minima and intermittency in near-critical convection-driven dynamos

P. J. Käpylä

Context: Solar magnetism exhibits long-term variations on timescales of decades to centuries. Aims: The main aim is to study how the supercriticality of the dynamo affects the variability of magnetic fields on timescales relevant to the Sun. Methods: Three-dimensional rotating magnetohydrodynamic simulations in a spherical wedge geometry are used to produce self-consistent convection-driven dynamos. The supercriticality of the dynamo is controlled by varying the magnetic diffusivity. Results: Th…

Read →
astro-ph.HE

Direct Observational Constraint on Upstream Magnetic Field Amplification Reveals the Particle Acceleration Limit in a Supernova Remnant

Yuya Kawabata, Takaaki Tanaka, Hiromasa Suzuki, Tsuyoshi Inoue

The origin of Galactic cosmic rays up to the knee energy (PeV) remains a long-standing open question in astrophysics. Supernova remnant shocks are leading candidates for accelerating particles to PeV energies, yet this requires strong magnetic field amplification in the upstream region to confine the highest energy particles. Despite its importance, the upstream magnetic field strength has long lacked direct observational constraints. Here we report the observation of numerous synchrotron X-ray…

Read →
astro-ph.IMastro-ph.HEcs.LG

Deep learning methods for gamma event selection in TAIGA-IACT image analysis in stereo-mode

E. O. Gres, A. P. Kryukov, P. A. Volchigov, A. P. Demichev, J. J. Dubenskaya, D. P. Zhurov, S. P. Polyakov, E. B. Postnikov et al.

In astrophysical complex TAIGA there are four Imaging Atmospheric Cherenkov telescopes (IACTs), located at a distance of 300-500 m from each other, due to which extensive air showers (EAS) generated by cosmic and gamma radiation are recorded by a single telescope or by multiple telescopes simultaneously (stereo-mode). The analysis of EAS images from two or more Cherenkov telescopes together is of particular interest, since for this approach the reconstruction of physical parameters of the primar…

Read →
astro-ph.GA

Galaxy Clusters from the DESI Legacy Imaging Surveys. IV. Alignment of Member Galaxy Orientations at z < 0.5

Zhaobin Chen, Yizhou Gu, Shufei Liu, Hu Zou, Qirong Yuan

Using DESI photometric catalog data, we systematically analyze the spatial alignment of star-forming galaxies (SFGs) and quiescent galaxies (QGs) in clusters. The results reveal that, in both brightest central galaxy (BCG) alignment (BA) and satellite alignment (SA), the alignment signals of SFGs and QGs exhibit opposite trends in several aspects. For the BA signal, SFGs show stronger alignment in cluster outskirts, whereas QGs exhibit stronger alignment in inner regions. For the SA signal, both…

Read →
astro-ph.GA

Intrinsic Soft X-ray Emission from the Hot Circumgalactic Medium in IllustrisTNG

Minjae Kim, Junhan Kim

We study the intrinsic 0.5--2~keV emission of the hot circumgalactic medium (CGM) in the IllustrisTNG simulation TNG100-2 at redshifts 0, 0.1, and 0.2. We calculate the emission of gas cells with $T \geq 10^6$~K in the spherical shell between $0.15R_{500}$ and $R_{500}$ and compare samples selected by their star-formation activity. X-ray luminosity increases with halo mass, although the class-dependent fits cover different mass intervals. Among galaxies with positive luminosity and star formatio…

Read →
astro-ph.HEastro-ph.IMgr-qc

Equation of State Classification of Core-Collapse Supernovae with a Network of Gravitational-Wave Detectors

A. Akhmetali, Y. S. Abylkairov, J. A. Font, M. Zanolin, E. Abdikamalov

Gravitational waves from core-collapse supernovae may provide a unique probe of the equation of state (EOS) of dense nuclear matter. In previous work, we assessed the potential of machine-learning methods for EOS classification for rapidly rotating supernovae using individual gravitational-wave detectors. Here, we extend the framework to detector networks and investigate the impact of detector configuration, source distance, arrival time, and sky location on the classification. Using convolution…

Read →
astro-ph.EPphysics.ao-phphysics.flu-dyn

Interaction of eccentricity tide and convection

Jiachen Zheng, Xing Wei

Aim. We try to understand the interaction of eccentricity tide and convection in icy satellites. Method. We use the numerical calculation of rotating convection with eccentricity tide in a spherical shell. Results. We have the following results. (1) Energy scaling exponent about buoyancy force (or tidal force) decreases with increasing tidal force (or buoyancy force). (2) The combined tide-convection flow is not identical to superposition of two pure flows in respect of energy spectrum. (3) Tide…

Read →
astro-ph.HE

Radiation-Regulated Spherical Accretion with an Inner Accretion Disk

Cheng-Liang Jiao, Liying Zhu, Xiang-dong Shi, Er-gang Zhao

We develop a theoretical model for radiation-regulated spherical accretion with an inner accretion disk. In our model, the outer accretion flow remains quasi-spherical and optically thick, while the luminosity generated by the inner disk is self-consistently coupled to the accretion rate and irradiates the inflowing gas. By solving the global transonic structure with radiative transfer treated in the diffusion approximation, we investigate how radiation regulates the flow structure and the accre…

Read →
astro-ph.GA

WALLABY pilot survey: accurate and automated linewidth measurements from global HI profiles

Shinna Kim, Tobias Westmeier, Lister Staveley-Smith, Danail Obreschkow, Barbara Catinella, Nathan Deg, Karen Lee-Waddell, Jonghwan Rhee et al.

Current-generation 21-cm surveys of extragalactic neutral hydrogen (HI) with instruments such as FAST and ASKAP are providing detailed spectral and spatial information for over 10^5 galaxies. Future HI surveys with next-generation radio telescopes could provide sample sizes larger by orders of magnitude. There is therefore a need for accurate, automated, and reliable parameterisation of the HI emission from galaxies. We have developed an automated estimator for HI global profile widths to better…

Read →
gr-qcastro-ph.HE

Quasinormal modes of rotating black holes with ultralight scalar fields

Leif Lui, Adrian Ka-Wai Chung

We report the first accurate computation of the leading-order shifts in the quasinormal-mode frequencies of rapidly rotating black holes surrounded by massive scalar fields with nonminimal curvature coupling. For fields with reduced Compton wavelengths no shorter than the black-hole mass scale, the numerical errors in the frequency shifts are typically $10^{-8} - 10^{-5}$ for dimensionless spins between 0 and 0.9, and at most $\mathcal{O}(10^{-3})$ next to the scalar-mass threshold. Our results…

Read →
astro-ph.EP

Capture of Interstellar Planetesimals in Protoplanetary Discs in Binary Star Systems

Alia Pollard, Evgeni Grishin

Planet formation requires growth over 12 orders of magnitude in size, from micron-sized dust grains to fully formed planets. The formation of km sized planetesimals is the most challenging stage, where radial drift and fragmentation rapidly remove meter- sized solids from the protoplanetary disc. Overcoming this barrier requires favourable conditions for streaming instability to concentrate solids. These problems are exacerbated in binary star systems, where gravitational perturbations and disc…

Read →
astro-ph.GAastro-ph.IM

TractorJAX: GPU-Accelerated SPHEREx Forced Photometry and the Trade-offs of Regularization and External Priors

Hyeonguk Bahk, Ho Seong Hwang

We present TractorJAX, an open-source GPU reimplementation of the catalog-forced mode of The Tractor. We use it to test whether regularization or external flux priors enable reliable fitting of reference catalogs that extend below the depth directly constrained by undersampled SPHEREx images. For full-depth regularized fits, TractorJAX fits $100\times100$-pixel cutouts at 11.9 ms each on a single NVIDIA H100 GPU. In simulated images of the Abell 2537 galaxy-cluster field, extending the fitted ca…

Read →
astro-ph.SR

Integration of a CME Flux Rope Model with Magnetic Field Draping in Heliospheric Simulations

Ranadeep Sarkar, Jens Pomoell, Emilia Kilpua, Eleanna Asvestari

Accurate prediction of the magnetic structure of interplanetary coronal mass ejections (ICMEs) remains a key challenge in space weather forecasting. Despite several efforts using global MHD modeling, it remains difficult to deduce a flux-rope solution that can accurately and reliably reproduce the magnetic structure of a CME. We present FROST (Flux Rope embedded in the Solar Magnetic Field), a new flux-rope model implementation within the European Heliospheric Forecast Information Asset (EUHFORI…

Read →
astro-ph.GA

Constraints on the r-process Delay Time from Dwarf Spheroidal Galaxies

Lauren E. Henderson, Evan N. Kirby, Mithi A. C. de los Reyes, Rebecca Surman

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 neutr…

Read →
astro-ph.SRastro-ph.GA

An asteroseismic age estimate for the Pleiades using a neural-network emulator of rotating $δ$ Scuti pulsation models

Anuj Gautam, Simon J. Murphy

Asteroseismology of $δ$ 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…

Read →
astro-ph.IM

The Simons Observatory: Frequency-resolved beam calibration for the SO SATs with POLOCALC

Nadia Dachlythra, Gabriele Coppi, Ludovico Bizzarri, Federico Nati, Alessandro Novelli, Elle C. Shaw, Samuel Day-Weiss, Federico Astori et al.

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 mo…

Read →
astro-ph.GA

The DAWN JWST Archive: A spectroscopically-informed population study of the physical properties of galaxies at z>2

Rashmi Gottumukkala, Gabriel Brammer, Sune Toft, Mengyuan Xiao, Anna de Graaff, Pascal A. Oesch, Francesco Valentino, Katherine E. Whitaker et al.

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 mode…

Read →
astro-ph.SRastro-ph.IM

Assessing the impact of background subtraction on a dust-free corona

Erika Palmerio, Cooper Downs, Phillip Hess, Benjamin J. Lynch, Ryder Davidson, Ronald M. Caplan, Jon A. Linker

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 in…

Read →
astro-ph.EPastro-ph.SR

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 cap…

Read →
astro-ph.IM

The Long-Term Radial Velocity Stability of the COS G130M/1291 Mode

John Debes, David M. French, Leonardo A. Dos Santos, Travis Fischer, Svea Hernandez, Ravi Sankrit

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 $σ_{\mathrm V}=600$ m s$^{-1}$. We als…

Read →
astro-ph.IMphysics.optics

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…

Read →
astro-ph.HE

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…

Read →
astro-ph.SRphysics.plasm-ph

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, 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 shee…

Read →
astro-ph.EP

Photometric and Spectroscopic Observations of Comet 2P/Encke's Nucleus in the Mid-Infrared Wavelength Region

Takafumi Ootsubo, Hideyo Kawakita, Jun-ichi Watanabe, Hitomi Kobayashi, Yoshiharu Shinnaka

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 $μ$m and low-resolution spectroscopic observations in the N-band (8-13 $μ$m, $R\sim250$) of the comet were performed. The observed spatial profiles of the co…

Read →
astro-ph.HEhep-ph

Bayesian exploration of weakly interacting models of dark matter admixed neutron stars based on multi-density constraints

Payaswinee Arvikar, Prashant Thakur, 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 r…

Read →
astro-ph.HE

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, En-Wei Liang

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 bl…

Read →
physics.ins-detastro-ph.IM

Broadband 600- and 1200-GHz Subharmonically Pumped Schottky Diode Mixers

Peter Sobis, Vladimir Drakinskiy, Karl Jacob, Axel Murk, Anders Emrich, Jan Stake

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 tem…

Read →
astro-ph.HE

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, Biswaraj Palit, Santanu Mondal, Honghui Liu, Chandra B. Singh, Sandeep K. Rout et al.

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 ho…

Read →
astro-ph.GA

The Tilt of the Velocity Ellipsoid in the Milky Way Disk with GALAH-Gaia Data

Zhenzhen He, Ruilan Yang, Hui Li, Weixiang Sun

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 $α= α_{0}\,\mathrm{arctan}(Z/R)$, and the $α_{0}$ differ significantly among different disk populations, with $α_{0}$ are 0.78 $\pm$ 0.05, 0.86 $\pm$ 0.07, and 0.77 $\pm$ 0.07 for the whole sample, the Low-[$α$/Fe] and the High-[$α$/Fe] populations, respectively. These results i…

Read →
astro-ph.GA

Modelling the broken age-[Fe/H] relation and metallicity distribution function of mono-age populations

Qinhao Shao, 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-meta…

Read →