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Research Trends

Latest preprints in space engineering and astrophysics.

astro-ph.GA

Anisotropic Radiation in Super-Eddington Active Galactic Nuclei: The Responsivity of Broad-Line Regions to Continuum Variability

Feng-Na Fang, Pu Du, 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$β$ emission line relative to continuum variations in super-Eddington AGNs, a phenomenon that can be naturally interpreted as a conse…

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physics.space-phastro-ph.SR

Validation of Space Weather Forecasting at Leonid Space

Scott Shambaugh

We validate Leonid Space's space weather forecasts through comprehensive cross-validation of retroforecasts scored against the entire F10.7 and Ap historical record. We built a unified forecast model that jointly forecasts F10.7 and Ap on all timescales from 3 hours up to multi-decade chains of future solar cycles. This was used to generate an archive of historical 15-year retroforecasts, after performing a leave-one-out fit of the model on held-out data and conditioning only on historical data…

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astro-ph.GA

The NIVARIA-Local Group simulations: Unveiling the origin of rotation curve diversity in dwarf galaxies and its connection to galaxy morphology

A. Contreras-Santos, A. Di Cintio, A. Negri, J. Sarrato-Alós, S. Cardona-Barrero, G. García-Bethencourt, C. Brook, N. I. Libeskind et al.

Dwarf galaxies exhibit a large diversity in rotation curve shapes, challenging galaxy formation models within the $Λ$CDM paradigm. We present NIVARIA-LG, a new suite of cosmological simulations studying dwarf galaxy evolution in realistic Local Group environments. This intermediate-resolution pilot lays the groundwork for the full-scale NIVARIA project. The simulations combine constrained Local Group initial conditions from HESTIA with the NIHAO galaxy formation model. The simulated galaxies rep…

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astro-ph.GA

Photometric Identification and Dynamical Purification of Blue Horizontal Branch Stars in DESI MWS DR1

Shuai Zhang, Xiaolong Wang, Kai Xiao, Guozhen Hu, Wenyuan Cui, Ce Cai, Shuai Feng, Jie Ju et al.

Blue horizontal-branch (BHB) stars are ideal tracers for mapping the structure of the Galactic stellar halo. However, traditional spectroscopic identification is limited by data quality and sample size, while broad-band photometric methods often achieve only moderate completeness and purity. Building upon the color-space BHB identification method of \citet{2025ApJS..278...62H}, we synthesize SkyMapper $(u,v,g,z)$ photometry from DESI MWS DR1 spectroscopy and identify 9,237 BHB candidates in the…

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astro-ph.GA

The Galactic disk structure revealed by Gaia XP spectra

Zhenkang Tang, Jianhui Lian, Jialong Zhou, Jiadong Li

The spatial structures of chemical populations constrain Galactic disk evolution and its underlying physical processes. Gaia XP spectra provide one of the largest spectroscopic samples available. We use Gaia XP spectra to study Galactic disk mono-abundance populations (MAPs), measuring their scale heights as a function of radius and radial surface-mass-density profiles. We construct a red giant branch (RGB) sample and divide it into MAPs according to $[α/{\rm M}]$ and $[{\rm M/H}]$. The sample c…

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astro-ph.SRastro-ph.GA

The $R$-Process Alliance: On J0010$-$1735, an Accreted, Chemically Unusual, Metal-poor Star with $R$-process Enhancement

Zoe Hackshaw, Rana Ezzeddine, Shivani P. Shah, Terese T. Hansen, Ruijie Shi, Yangyang Li, Timothy C. Beers, Anna Frebel et al.

We present a detailed chemo-dynamical analysis of the chemically peculiar very metal-poor ([Fe/H]$=-2.22\pm 0.11$) Milky Way (MW) halo star, 2MASS J00101758$-$1735387 (hereafter J0010-1735), discovered by the $R$-Process Alliance. We derive abundances for 45 elements, including 28 neutron-capture elements, and confirm that \thestar\ is highly $r$-process-enhanced, with [Eu/Fe]=$+1.30$. The light, $α$, and Fe-peak element abundances ratios relative to Fe are all sub-solar, aside from C, Si, and m…

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astro-ph.HE

A GeV Gamma-Ray Spectral Excess in the Fermi Blazar 4FGL J0136.5+3906

Shi-Ju Kang, Yue Yin, Yong-Gang Zheng, Qingwen Wu, Junhui Fan

We report the detection of a $\sim${19} GeV gamma-ray spectral excess (peak energy in observer frame) at $\sim$5.7$σ$ significance (3 degrees of freedom, without correction for trials and the look-elsewhere effect) in the Fermi-LAT data of the blazar 4FGL J0136.5$+$3906, based on $\sim${17} years of observations. The excess manifests as a distinct bump-like feature in the 100 MeV$-$1 TeV spectrum, with a flux of $\sim$3.6$\rm \times10^{-10}~ph~cm^{-2}~s^{-1}$. No similar feature is detected in n…

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astro-ph.IM

From Sky to Science: Time Domain Astronomy with the ILMT Survey

Kuntal Misra, Bhavya Ailawadhi, Talat Akhunov, Monalisa Dubey, Naveen Dukiya, Sara Filali, Paul Hickson, Priyanshi Kumari et al.

The PyLMT transient detection pipeline has been operational since November 2023 and has detected $\sim$10,000 transients and variable objects in ILMT images in near real time. The survey has enabled the discovery and characterisation of a range of bright and faint optical transients. The detected population spans a broad diversity of astrophysical phenomena, including supernovae, variable stars, active galactic nuclei (AGN) variability, and Solar System objects such as asteroids and comets. We p…

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astro-ph.IM

Modelling the Point Spread Function of ILMT images

Naveen Dukiya, Bhavya Ailawadhi, Talat Akhunov, Monalisa Dubey, Sara Filali, Paul Hickson, Priyanshi Kumari, Gokul Singh Mehra et al.

We have devised an approach to model the empirical Point Spread Function (PSF) of the images taken with the 4-meter International Liquid Mirror Telescope (ILMT). The characteristics of the ILMT PSF are influenced by the nature of the Liquid Mirror, as well as by instrument specific and atmospheric factors. As the telescope uses Time Delay Integration (TDI) mode for tracking the passing objects, the PSF varies along the declination axis due to differential motion and star-trail curvature. The 5-e…

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astro-ph.IMastro-ph.EP

Mid-IR Water-Vapor Seeing: Implications for ELT/METIS High-Contrast Imaging from VLTI Data

Abhirami S Raghu, Prashant Pathak, Olivier Absil, Benjamin Courtney-Barrer, Gilles Orban de Xivry, Julien Woillez, Alexis Matter, Philippe Bério et al.

Direct imaging and characterization of rocky exoplanets remains one of the central challenges in exoplanetary science. The mid-infrared (mid-IR) offers a favorable high-contrast imaging (HCI) regime, as the planet-star contrast is more moderate than at shorter wavelengths. However, mid-IR observations with extremely large ground-based telescopes (ELTs) are strongly affected by spatio-temporal fluctuations in atmospheric water vapor (WV), which introduce chromatic wavefront errors that are largel…

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astro-ph.EPastro-ph.IM

Milani and Juventas Optical Navigation Images in Support of the Hera Radio Science Experiment

Edoardo Gramigna, Ozgur Karatekin, Birgit Ritter, Iosto Fodde, Fabio Ferrari, Felice Piccolo, Paolo Tortora, Riccardo Lasagni Manghi et al.

The European Space Agency's Hera mission aims to advance planetary defense by investigating the Didymos binary asteroid system following NASA's DART impact on Dimorphos. Incorporating simulated CubeSat images into Hera's orbit determination framework significantly improves positional accuracy, reducing uncertainties by up to three orders of magnitude for Milani and one for Juventas. This data enable more precise estimation of key parameters such as asteroid masses, rotational states, and moments…

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astro-ph.EPastro-ph.IM

Hera Orbit Determination Covariance Analysis of Didymos Binary Asteroid with the Full Two-Body Problem

Edoardo Gramigna, Riccardo Lasagni Manghi, Marco Zannoni, Paolo Tortora, Michalis Gaitanas, Ioannis Gkolias, Kleomenis Tsiganis, Ryan S. Park et al.

Standard planetary radio science analyses may be inadequate for accurately interpreting data from the Hera mission at the Didymos system due to the anticipated challenge posed by the coupling between the translational and rotational motions of the asteroids. A more precise dynamical model, the full two-body problem model, which includes a mutual gravitational potential, may be required to fit the Hera data properly. This work presents a covariance analysis of the Hera radio science experiment us…

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astro-ph.GA

Multiphase Analysis of (U)LIRG Nuclear Activity (MAUNA). I. Spatially Resolved Optical Emission-Line Diagnostics

Justin A. Kader, Vivian U, Marina Bianchin, Yiqing Song, George C. Privon, Sabrina Stierwalt, Tanio Diaz-Santos, Lee Armus et al.

We present resolved optical integral-field spectroscopy of the 32 luminous and ultraluminous infrared galaxy systems of the Multiphase Analysis of (U)LIRG Nuclear Activity (MAUNA) sample, drawn from the GOALS survey and selected to have JWST/MIRI medium-resolution spectrometer (MRS) observations. The data set combines new Keck/KCWI observations of 10 systems with archival VLT/MUSE cubes for 22 systems, covering H$β$ to [S II] at ~1 arcsecond spatial resolution (~0.9 kpc at the sample median dist…

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astro-ph.GAstat.AP

Beyond the Damped Random Walk: Multiband AGN Variability from SDSS to Rubin LSST

Izak Schmidlkofer, Zhirui Hu, Weixiang Yu, Hyungsuk Tak

The flux variability of Active Galactic Nuclei (AGNs) is commonly modeled using the damped random walk (DRW), but increasingly rich multiband time-domain surveys motivate more flexible stochastic models that characterize variability beyond a single timescale and exploit dependence across bands. Multivariate continuous-time autoregressive moving average (MCARMA) processes extend the multivariate DRW to higher-order stochastic dynamics and provide a matrix-valued power spectral density for charact…

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astro-ph.IMastro-ph.HE

ELISA: A Bayesian X/$γ$-ray Spectral Analysis Toolkit

Wang-Chen Xue, Sheng-Lun Xie, Chao Zheng, Shao-Lin Xiong, Xiao-Bo Li, Yong Chen, Peng Zhang, Yan-Qiu Zhang et al.

Forward-folded X/$γ$-ray spectral fitting increasingly benefits from Bayesian workflows to better capture counting statistics, background uncertainties, and complex parameter degeneracies, while fully reproducible end-to-end implementations are still not always straightforward to deploy in routine analyses. We present ELISA (Efficient Library for Spectral Analysis), an open-source Python toolkit that streamlines the full spectral analysis loop for X/$γ$-ray astronomy: data loading, model constru…

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astro-ph.HE

Magnetar X-ray flares as elementary reconnection events in a self-organized critical magnetosphere

Sheng-Lun Xie, Yi Zhao, Wen-Long Zhang, Chen-Wei Wang, Yun-Wei Yu, Shao-Lin Xiong

Magnetar bursts are commonly attributed to magnetic energy release, yet the physically relevant dissipation unit has remained uncertain. Here we argue that this unit is not the burst as conventionally defined, but the short substructures within bursts, namely magnetar X-ray flares (MXFs). Using 789 MXFs from SGR~J1935+2154, we show that their waiting times separate into two components, interpreted as reflecting clustered intra-episode events and longer inter-episode intervals, that their proxy e…

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astro-ph.HE

Impact of Decay-Chain Feeding by Long-Lived Heavy Nuclei on Nuclear Cosmochronology

Qiu-Hong Chen, Meng-Hua Chen, Xianlin Yang, En-Wei Liang

Nuclear cosmochronology provides an independent method for determining the ages of astrophysical objects without relying on Galactic chemical evolution models. Long-lived radioactive actinides synthesized via the rapid neutron-capture process ($r$-process) particularly thorium and uranium serve as ideal chronometric nuclei. However, predicting the initial abundances of these nuclei and their subsequent long-term evolution remains a major source of uncertainty in nuclear cosmochronology. In this…

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astro-ph.HEastro-ph.SR

Reawakening of GS 1843+00: A Multiwavelength Study of its 2026 Giant X-ray Outburst

Gaurava K. Jaisawal, Georgios Vasilopoulos, Francesco Carotenuto, Hannah C. I. Wichern

GS 1843+00 (Ginga 1843+009) is a poorly studied Be/X-ray binary system that underwent a major X-ray outburst in 2026 February-May after nearly sixteen years of quiescence. We present an X-ray, optical, and radio study of GS 1843+00 during this outburst, focusing on the evolution of the neutron star emission geometry, Be-disk connection, and possible outflow activity. We analyse three NuSTAR observations obtained at different stages of the outburst, complemented by archival RXTE and Chandra data,…

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astro-ph.SRastro-ph.EP

TESS Pulsation Timing Reveals the JWST Calibration Star HD 158485 as a Double-pulsator Binary

Chenglong Lv, Ali Esamdin, Shuguo Ma, Shahidin Yaqup, Haozhi Wang, Ayzada Jmahali, Jianwei Yao, Kedieryemu Kamili et al.

HD~158485 is an A-type $δ$~Scuti star in the CALSPEC network and the JWST absolute-flux calibration program. Gaia DR3 assigns it a binary classification probability close to unity but provides no orbital solution. Using TESS observations from Sectors 14--26, 40--41, 47--60, and 73--86, we measure the pulsation phases of six $δ$~Scuti modes. The frequencies form two groups with opposite light-travel-time delays, revealing two pulsating components. A direct light-curve forward model yields an orbi…

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astro-ph.HEastro-ph.SR

The effect of triples on the Chemically Homogeneous Evolution Channel for producing Gravitational Wave Sources

Silvia A. Popa, Selma E. de Mink, Stephen Justham, Jakob Stegmann, Alejandro Vigna-Gomez, Lieke A. C. van Son

Despite the growing number of gravitational-wave (GW) detections, the formation of merging binary black holes (BBHs) is still debated. One of the proposed formation channels is Chemically Homogeneous Evolution (CHE), which makes distinct predictions for the properties of the resulting black holes (BHs): high masses ($\gtrsim35\, M_\odot$) and large, orbitally-aligned spins. These predictions are based on studies that consider this channel only in isolated binaries. However, most massive stars re…

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astro-ph.SR

Mapping Wolf-Rayet winds with spectro-interferometry I. Detection of multiple co-rotating interaction regions in WR 6

K. Deshmukh, A. -N. Chené, A. J. Frost, T. De Prins, L. Fabiani, H. Sana, R. R. Lefever, A. Mérand et al.

WR 6 is the prototype for periodic variability due to large-scale wind structures in Wolf-Rayet (WR) stars, showing a consistent periodicity of 3.76 d in photometry, spectroscopy, and polarimetry. However, the origin of this variability is debated, attributed either to corotating interaction regions (CIRs) or a low-mass companion. We use time-resolved interferometry to investigate the origin of periodic variability in WR 6. We aim to detect and characterize structures in the stellar winds of WR…

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astro-ph.IM

Harmonic and intermodulation emission from direct-to-device satellites - Harmonics of the Starlink 2.6 GHz downlink and the products around them

Balthasar Indermuehle, Benjamin Winkel, Federico Di Vruno, Gyula Jozsa, Liroy Lourenco

Direct-to-device (DTD) satellites carry mobile base stations transmitting in terrestrial mobile bands. Their non-linear emission products can fall into radio astronomy bands, including passive bands. We measure the harmonics of the Starlink DTD downlink at 2620-2630 MHz and the intermodulation products around them, search for products next to the carriers, and compare them with the ITU-R unwanted-emission limits and radio astronomy protection criteria. We use autocorrelations of single Australia…

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astro-ph.SRastro-ph.IM

What does self-supervision add to engineered features for stellar light curves?

Zijun Liu, Yue Ma, Christopher A. Theissen

TESS light curves encode a star's pulsation, rotation, binarity and oscillations, among other physical properties, but the survey produces far more light curves than can be labelled by hand. Astronomers have engineered a few dozen physically motivated features from them, which together remain a strong baseline. Previous work has trained encoders on light curves and judged them by their own downstream scores, but has not asked what they add to the engineered features. We pre-train a convolutional…

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hep-phastro-ph.HEhep-th

A Comprehensive Interpretation of the LZ High-Energy Recoil Event: A Minimal $U(1)_B$ Dark Sector and Its Experimental Tests

Mattia Di Mauro

The $248$ keV nuclear-recoil candidate reported by LUX-ZEPLIN (LZ) motivates an inelastic dark matter (DM) interpretation, in which scattering converts the DM particle into a slightly heavier state. We provide a comprehensive study of this interpretation in an anomaly-free model of gauged baryon number, where a new vector boson, $Z_B$, mediates interactions between DM and quarks. Breaking the baryonic gauge symmetry generates the new particle masses and a small splitting between two DM states, w…

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astro-ph.HEastro-ph.IMphysics.data-an

A Pipeline for the AI-Assisted Analysis of Imaging X-ray Polarimetry Explorer Observations of Black Hole X-ray Binaries and Limits on Their Polarization Variability

B. Domine, B. Liu, H. Krawczynski, M. Kundu, Shravan Vengalil Menon, Fang Zhou

The Imaging X-ray Polarimetry Explorer (IXPE) has opened a new window into the high-energy Universe, with the capability to measure the arrival time, arrival direction, energy, and, for the first time with the required sensitivity, the polarization of X-rays from black holes, neutron stars, and other cosmic sources of X-rays. In this paper, we discuss the use of Artificial Intelligence (AI) agents for the analysis of IXPE data. The pipeline combines an immutable code base with evolving knowledge…

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astro-ph.GA

Globular cluster Observations for Luminosity-dispersion Distances (GOLD): Project description and velocity catalogue

K. Fahrion, M. A. Beasley, A. Gvozdenko, I. Ortega-Casas, A. Ferre-Mateu, F. I. Aros, D. Dold, T. Jerabkova et al.

We introduce and describe the Globular cluster Observations for Luminosity-Dispersion distances (GOLD) project, which has the principal aim of determining independent distances based on the globular cluster (GC) absolute magnitude-velocity dispersion ($M_V - σ$) relation calibrated with Milky Way GCs with Gaia distances. The project comprises observations of GCs in 19 early- and late-type galaxies taken with FLAMES/GIRAFFE on ESO's Very Large Telescope. So far, 17 galaxies have been observed. Th…

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astro-ph.GAastro-ph.IMastro-ph.SR

Stellar discs and intermediate-mass black holes in galactic nuclei II. Fragmenting the disc and forming the S-stars in a live nuclear star cluster

Taras Panamarev, Bence Kocsis

We present direct $N$-body simulations of a stellar disc around the supermassive black hole Sgr~A*, perturbed by an intermediate-mass black hole (IMBH) and embedded in a live nuclear star cluster. A retrograde IMBH with $m_\bullet=2000\,M_\odot$, relative inclination $θ_\bullet=150^\circ$, and initial semi-major axis $a_\bullet=0.15$~pc breaks the disc into three disc-like components and an angular momentum filament. The stochastic torques of the cluster, together with the IMBH's inward migratio…

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astro-ph.GAastro-ph.HE

A first view of interstellar Fe-bearing dust grains with XRISM

I. Psaradaki, L. Corrales, E. Costantini, M. Mehdipour, D. Rogantini, H. Takahasi, R. Ballhausen, P. Chakraborty et al.

Understanding the reservoirs of iron (Fe) in our Galaxy is crucial for probing the mechanisms that drive dust grain growth in the interstellar medium (ISM). High-resolution X-ray absorption spectroscopy offers a powerful tool to investigate the chemistry of dust grains, particularly those containing Fe, through spectroscopic features near photoabsorption edges known as X-ray Absorption Fine Structures (XAFS). With the Resolve spectrometer aboard XRISM, we can now examine the Fe K-edge (7.1 keV)…

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astro-ph.GA

Searching for Nearby Supermassive Black Hole Binaries with GRAVITY

GRAVITY Collaboration, K. Abd El Dayem, N. Aimar, A. Berdeu, J. -P. Berger, G. Bourdarot, W. Brandner, Y. Cao et al.

We present a systematic interferometric search for close supermassive black hole (SMBH) binaries in 20 nearby type 1 active galactic nuclei (AGN) observed with VLTI/\grav. We investigate parsec-scale asymmetric emission by modeling the squared visibilities and closure phases with a single circular Gaussian component plus a background point source for the central AGN, and searching for additional compact companions through grid-based binary models. The robustness of the search is validated using…

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astro-ph.GA

Cluster Ages to Reconstruct the Milky Way Assembly (CARMA). VI. The age-metallicity relation of in-situ clusters and the age of the Universe

Chiara Zerbinati, Davide Massari, Fernando Aguado-Agelet, Cristiano Fanelli, Massimiliano Matteuzzi, Santi Cassisi, Matteo Monelli, Cristiana Spingola et al.

Within the homogeneous framework for the derivation of GC ages defined by the CARMA collaboration, we focus on the clusters born in-situ in the MW. As they are the oldest among the old GCs, their absolute age provides constraints about the age of the Universe. Moreover, the shape of their AMR is expected to show the imprints of past merger events, in case these were able to trigger GC formation in the Galaxy. We derive new homogeneous ages for 18 GCs dynamically and/or chemically classified as i…

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