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Research Trends

Latest preprints in space engineering and astrophysics.

physics.ed-phastro-ph.IMphysics.soc-phphysics.space-ph

A First Africa Wide Amateur Radio Contact Experiment with the International Space Station

Domingos Barbosa, Miracle Chibuzor Marcel, Declan Kirrane, Miguel Avillez, Amare Abebe Gidelew, Carla Sharpe Mitchell, Vidvuds Beldavs, Claudio Ariotti et al.

The Amateur Radio on the International Space Station (ARISS) program is recognized by its great Science, Technology, Engineering, and Mathematics (STEM) impact: it brings space science to education and outreach initiatives by enabling direct contact with astronauts in orbit and other space savvy professionals. Strategic partnerships between ARISS and digital platforms for citizen science act as a powerful real-world STEM motivator and can overcome logistical barriers, demonstrating a scalable mo…

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astro-ph.GAastro-ph.SR

Fragmentation of massive clumps: constant mass fraction and growing mass inequality of cores

Zu-Jia Lu, Qi-Tian Chen

The fragmentation of massive molecular clumps into dense cores sets the initial conditions for stellar clusters, yet how core mass distributions evolve remains unclear. Using the ALMAGAL survey (1,013 clumps and 6,348 cores), we analyze the Gini coefficient of core mass distributions for the 514 clumps containing at least four cores ($N_{\rm frag} \ge 4$), which host 5,728 cores in total. We find that the most massive core consistently accounts for $\sim 38\%$ of the total core mass ($f_{\rm cor…

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astro-ph.EP

The Polana-Eulalia Complex with JWST NIRSpec: Connections to Bennu, Ryugu, and Outer Solar System Bodies

Lucas McClure, Joshua Emery, Driss Takir, Julia de Leon, Mario de Pra, Brittany Harvison, Bryan Holler, Javier Licandro et al.

Carbon rich [C complex] asteroids provide insight into the early Solar System, and families of C complex asteroids serve as robust samples for learning about the internal structure of planetesimals and the materials of the protoplanetary disk. This work investigates the compositions of asteroids within the Polana Eulalia Complex [PEC] through analyses of JWST NIRSpec. Obtained as part of the Spectral Analysis of Main Belt Asteroids in the 3 um Region [SAMBA3] project. NIRSpec observations were c…

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astro-ph.COastro-ph.GA

Origin of the Sloshing Spiral in the Abell 2107 Galaxy Cluster

Muhammed Kıyami Erdim

We present a detailed thermodynamic analysis of a sloshing spiral discovered in the intracluster medium (ICM) of the galaxy cluster Abell 2107, based on deep Chandra X-ray Observatory observations. Spectral analysis reveals that the spiral arm is significantly cooler and exhibits lower entropy and higher metallicity compared to the surrounding ICM, consistent with an origin in the cool, dense cluster core. We detect three cold fronts at the edges of the spiral, roughly aligned along an east-west…

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physics.space-phastro-ph.EPphysics.plasm-ph

Electron Temperature Gradients Regulate the Duration of Two-Stage Plasmasphere Refilling

Jaden Fitzpatrick, Kausik Chatterjee, Naomi Maruyama, Xiangning Chu, Jacob Bortnik, Jerry Goldstein, Lauren Blum, Tyler Bishop et al.

After geomagnetic storms erode the plasmasphere, cold ionospheric plasma flows along magnetic field lines to refill the depleted flux tubes. Previous studies have suggested that refilling undergoes two stages characterized by their distinct refilling rates; however, not all observations or models exhibit this feature, and a recent analysis indicates that only a subset of refilling events display two clear stages. In this study, we show that the magnitude of the field-aligned electron temperature…

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astro-ph.HEastro-ph.CO

Gas Motions in Hydra-A: XRISM Constraints on ICM Kinematics Across Jet-Inflated Cavities

Anwesh Majumder, B. R. McNamara, P. E. J. Nulsen, H. Russell, T. Rose, T. Heckman, A. Simionescu, A. Fabian et al.

We report on two deep XRISM observations of the central and northern regions of Hydra-A's X-ray atmosphere covering the bubbles inflated by jets from the central galaxy's active galactic nucleus (AGN). We use spatial-spectral mixing that combines Chandra's high spatial resolution with XRISM's high spectral resolution to investigate atmospheric kinematics. The atmospheric velocity dispersion in the northern region, $σ_v = 140^{+30}_{-20}$ km s$^{-1}$, is comparable to that in the central region (…

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astro-ph.GAastro-ph.CO

The size of the HI disk across different environments: isolated, compact groups, clusters, and pairs

R. Ianjamasimanana, L. Verdes-Montenegro, K. M. Hess, P. Kamphuis, M. G. Jones, J. Garrido, S. H. A. Rajohnson, A. Sorgho et al.

The 21 cm line of atomic hydrogen (HI) is a sensitive tracer of the outer disk of galaxies, where environmental signatures are most apparent. The relative extent of HI disks compared to optical disks ($D_{\rm HI}$ vs $D_{25}$) is thought to provide a quantitative measure of such imprint, yet systematic comparisons between extreme environments remain scarce. We quantify the relative extent of HI disks in Hickson Compact Groups (HCGs) and in the Analysis of the interstellar Medium in Isolated GAla…

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gr-qcastro-ph.HE

Biases in Tests of General Relativity from Microlensed Gravitational-Wave Signals

Anirban Kopty, Apratim Ganguly, N. V. Krishnendu, Anuj Mishra

Gravitational-wave (GW) observations of compact binary mergers enable precision tests of general relativity (GR) in the strong-field regime, but their reliability depends on accurate waveform modeling. Unmodeled physical effects can induce systematic biases that mimic deviations from GR. Here we study the impact of GW microlensing on standard LIGO-Virgo-KAGRA tests of GR using GW150914-like simulated signals lensed by isolated point-mass objects with masses in the range $10-10^{5}M_\odot$. We pe…

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astro-ph.GA

VAR-PZnn: A machine-learning framework for AGN photometric redshifts using color and variability-based features

S. Satheesh-Sheeba, P. Sánchez-Sáez, R. J. Assef, T. Anguita, R. Shirley, M. Salvato, P. Arévalo, T T. Ananna et al.

Photometric redshift estimation for active galactic nuclei (AGNs) remains a fundamental challenge for current and upcoming large-scale photometric surveys. Traditional spectral energy distribution (SED) fitting suffers from color-redshift degeneracies, particularly for AGNs whose power-law continua hide the strong spectral features required to anchor redshift estimates. While AGN variability provides additional constraining power, existing frameworks require multi-band light curves that are not…

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astro-ph.HEastro-ph.GA

Simultaneous radio, optical and X-ray monitoring of hard X-ray selected AGN: a variability study

L. Hernández-García, F. Panessa, D. Williams-Baldwin, P. Arévalo, A. M. Muñoz Arancibia

AGN emission is intrinsically variable across the electromagnetic spectrum. Mapping the coupling between the accretion disk, the X-ray corona, and ejection flows is key to understanding the energy flow within the central engine. We characterize the multi-wavelength variability of 14 hard X-ray selected AGN from the INTEGRAL/IBIS catalog in the radio, optical, and X-ray bands, to determine the coupling between these frequencies and how variability relates to the physical properties of the central…

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astro-ph.SRastro-ph.EPastro-ph.GA

Dynamical friction in stratified stellar envelopes

Damien Gagnier

Dynamical friction prescriptions used for common-envelope and planetary engulfment inspirals often assume a homogeneous medium and/or rectilinear perturber motion. A gravitating object embedded in a giant-star envelope instead excites an orbit-scale wake while moving on a curved orbit through a finite, radially stratified medium. We formulate the linear barotropic acoustic response of a weak point perturber on a circular orbit in a hydrostatic, spherically stratified gaseous medium. We apply the…

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astro-ph.HE

Detectability of Gravitational-wave counterparts of EP-FXTs observed during the O4b LIGO-Virgo-KAGRA Observing Run

Ansh Chopra, Samuele Ronchini, Biswajit Banerjee, Marica Branchesi, Stefano Ascenzi, Maria Edvige Ravasio, Peter Jonker, Andrew Levan et al.

Fast X-ray transients (FXTs) detected by the Einstein Probe mission have emerged as a rapidly growing class of extragalactic transients, whose physical origin remains uncertain. Compact binary coalescence (CBC) systems have been proposed as one possible progenitor for at least a subset of these events, making FXTs promising targets for multi-messenger studies with gravitational-wave (GW) observations. This work presents the first systematic investigation of GW counterparts to FXTs observed by Ei…

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astro-ph.GAastro-ph.CO

LoVoCCS. III. Third Generation Pipeline & The Hercules Supercluster

Anthony M. Englert, Shenming Fu, Ian Dell'Antonio, Mohamed H. Abdullah, Shrouk Abdulshafy, Eddie Aljamal, William K. Black, Nicole Chidester et al.

The Local Volume Complete Cluster Survey (LoVoCCS) is a volume-complete survey of over one-hundred nearby ($0.03 10^{44} \text{ erg s}^{-1}$) galaxy clusters in the southern sky. Observations for the survey concluded in December 2025, reaching Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) Year 1-2 depth in each field and providing observations with $\lesssim 1"$ seeing for weak lensing science. In this paper, we present the latest pipeline for reducing observations using the…

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astro-ph.EP

Case Study of a Super-eccentric Warm Jupiter Migrating via Equilibrium and Dynamical Tides

Donald Liveoak, Sarah Millholland, Michelle Vick

A leading theory for hot Jupiter formation is high-eccentricity migration, in which planets are born at large separations and excited to near-unity eccentricities, creating extreme tidal dissipation that shrinks and circularizes their orbits. The most direct evidence for this scenario is the detection of highly eccentric planets caught in the act of migrating. Although such planets are rare, the recent discovery of TIC 241249530 b - a super-eccentric ($e = 0.94$) and retrograde hot Jupiter proge…

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astro-ph.GA

Cosmological simulations of the high-redshift galaxy population adopting a variable stellar initial mass function

Anna Durrant, Robert A. Crain, Cedric G. Lacey, Joop Schaye, Renske Smit, Andrea Gebek, Matthieu Schaller, Shengdong Lu et al.

JWST surveys reveal a greater space density of high-redshift UV-bright galaxies than predicted by conventional galaxy formation models. We present results from a $L=100$ cMpc cosmological simulation evolved to $z=5$ with a variation of the COLIBRE galaxy formation model that adopts a density-dependent stellar initial mass function (IMF), such that stellar populations formed from dense gas are born with a top-heavy IMF. Crucially, heavy element and dust yields, and supernova feedback energetics,…

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astro-ph.EP

Planet-moon ejections in close stellar encounters

Yannick Badoux, Simon Portegies Zwart

Free-floating planet-moon pairs (FFPMs) may form when planetary systems experience close stellar encounters. We quantify moon-retention probabilities and ejection cross sections for planets and planet-moon systems subject to close stellar encounters, and to dentify the orbital conditions most favorable for forming FFPMs. We conducted extensive numerical scattering experiments to compute ejection cross-sections on a grid in the orbital separation of the planet ($a_p$) and the moon ($a_m$), margin…

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astro-ph.HEastro-ph.SR

Superorbital variability in the quiescent black hole X-ray transient A0620-00

Enzo A. Saavedra, Roi Alonso, Teo Muñoz-Darias, Jorge Casares, Manuel A. P. Torres, Montserrat Armas Padilla, James F. Steiner, David M. Russell et al.

Quiescent black hole low-mass X-ray binaries provide a key setting for probing accretion physics at low luminosities. A0620-00, the archetypal system in this class, has remained in X-ray quiescence for decades and exhibits complex optical variability, yet the long-term behaviour of its accretion flow remains poorly understood. Here, we report an analysis of long-term optical monitoring of A0620-00 from ZTF, LCO, and ATLAS. The full dataset spans nearly two decades, with the ZTF light curve provi…

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astro-ph.GA

Morphologies of SAGAbg low-mass galaxies in Legacy Survey multi-band imaging: dependence on stellar masses, star-formation rates and low-redshift evolution

Joy Bhattacharyya, Guinevere Herron, Yasmeen Asali, Abby Mintz, Mithi A. C. de los Reyes, Yao-Yuan Mao, Annika H. G. Peter

The optical morphologies of low-mass galaxies can be used to directly trace their assembly and constrain models of galaxy evolution. We select a sample of 6211 low-mass ($7\lesssim {\rm log}(M_{\ast}/M_{\odot})\lesssim 10$) star-forming galaxies from the SAGAbg catalog that has high-completeness at low-redshifts ($z<0.1$). We obtain their galaxy maps in the $griz$ - bands of the Legacy Surveys and apply STATMORPH to calculate non-parametric morphological measures including the Gini index, $M_{20…

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astro-ph.GA

Euclid: Calibrating distances from surface brightness fluctuations with Early Release Observations of the Fornax cluster

R. Habas, M. Cantiello, G. Riccio, G. Raimondo, N. Hazra, S. Mei, A. Lançon, G. D'Ago et al.

Surface brightness fluctuations (SBF), the pixel-to-pixel variations in flux that arise from the statistical distribution of stars in galaxy images, provide a powerful tool to measure redshift-independent distances from photometric data alone. This method is particularly important in the era of large imaging surveys, such as those carried out during the Euclid mission. Here we present the first application of SBF to Euclid data, using the FAST-SBF code to measure stellar fluctuation amplitudes i…

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astro-ph.SR

SEP-PRISM Data: A multi-source dataset for solar energetic particle forecasting

Yian Yu, Yang Chen, Lulu Zhao, Kathryn Whitman, Ward Manchester, Tamas Gombosi

Solar energetic particle (SEP) event forecasting often involves integrating heterogeneous observations that differ in cadence, temporal coverage, format, and historical availability, posing challenges for reproducible analysis of data-driven approaches. This paper presents SEP-PRISM Data, a curated multi-source dataset designed for 24-hour ahead forecasting of operational SEP events, defined by proton flux exceeding 10 pfu in the GOES > 10 MeV channel. SEP-PRISM Data integrates flare records, ac…

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astro-ph.HE

X-ray polarization of Z-type neutron star low-mass X-ray binaries -- II. Spectropolarimetric analysis

Andrea Gnarini, Francesco Ursini, Giorgio Matt, Stefano Bianchi, Fiamma Capitanio, Massimo Cocchi, Sergio Fabiani, Ruben Farinelli et al.

IXPE has provided for the first time detailed energy- and time-resolved X-ray polarimetry of Z-type neutron star low-mass X-ray binaries (NS-LMXBs) as they move along their color-color diagrams (CCDs). These sources can reach the highest polarization observed for NS-LXMBs in the 2-8 keV range when they move along the horizontal branch. In a previous paper, we characterized the spectral state of a sample of Z-sources using the CCD and estimated the polarization with model-independent analysis. He…

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astro-ph.HE

Eccentricity as a Magnifying Glass: Precision Population Inference Enabled by Eccentric Neutron Star-Black Hole Mergers

Alberto Salvarese, Hsin-Yu Chen, Aaron Zimmerman, Snehal Tibrewal

The formation history of compact binary systems remains one of the key open questions in astrophysics. Theoretical studies generally favor isolated binary evolution for neutron star-black hole (NSBH) systems, which tends to produce nearly circular orbits. However, recent analyses of the gravitational-wave event GW200105 indicate that its source has measurable eccentricity, suggesting that alternative formation channels may also contribute. It has been shown that the intrinsic parameters of eccen…

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astro-ph.HE

Impact of eccentricity and higher-modes on neutron star-black hole parameter estimation

Snehal Tibrewal, Aasim Jan, Aaron Zimmerman, Hsin-Yu Chen

Detections of gravitational waves from neutron star-black hole systems provide avenues for studying extreme matter, constraining binary formation channels, and testing the nature of compact objects in strong gravity. Eccentric signatures in the signal further enhance this potential by improving parameter estimation and offering clues about binary formation. Because eccentricity is primarily imprinted during the inspiral phase, it is often weakly constrained or missed entirely in binary black hol…

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astro-ph.HE

Discovery of $γ$-Ray Pulsations from the Extreme-Spin-Down Millisecond Pulsar PSR J0435+3233

Mengqing Zhang, Shengbin Pei, Pengfei Zhang

Motivated by the recent discovery of PSR~J0435+3233, a millisecond pulsar with an exceptionally large period derivative of $\dot{P}=4.9\times10^{-17}\ {\rm s\,s^{-1}}$ and a high spin-down luminosity of $\dot{E}=5.89\times10^{37}\ {\rm erg\,s^{-1}}$, we analyze $\sim$17~yr of observations obtained with the \textit{Fermi} Large Area Telescope for the pulsar. We identify the cataloged source 4FGL~J0435.5+3232, located only $0.01^{\circ}$ from the radio timing position, as the $γ$-ray counterpart o…

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astro-ph.IM

Commissioning and on-sky performance of FiberPol: a fiber-fed spectropolarimetric system for the SAAO 1.9 m telescope

Siddharth Maharana, K. C. J. Dennison-Farrar, Sabyasachi Chattopadhyay, Nikita Rawat, Nidhi Mehandiratta, J. C. Viljoen, Matthew Bershady, David Buckley et al.

At the South African Astronomical Observatory (SAAO), we have developed FiberPol$-$ a spectropolarimetric front-end for the SpUpNIC spectrograph on the 1.9 m telescope fed by fibers. In conjunction with SpUpNIC, it combines two niche techniques: fiber-spectroscopy and polarimetry to enable a wide range of science cases, particularly for studies of the interstellar medium, and serves as a technology pathfinder for implementing polarimetry larger facilities such as the 10 m Southern African Large…

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astro-ph.GA

Dynamics and geometry of the inner sub-parsec-scale jet in 3C 279 observed with the Event Horizon Telescope

Hendrik Mueller, Sebastiano D. von Fellenberg, Ai-Ling Zeng, Paul Tiede, Thomas P. Krichbaum, Roman Gold, Tuomas Savolainen, Jae-Young Kim et al.

The 2021 Event Horizon Telescope observations resolve the innermost jet region of the blazar 3C279 with unprecedented detail. The reconstructed images consistently reveal a compact core elongated nearly orthogonal to the large-scale jet axis. This rarely observed morphology recurs across multiple epochs and from 22-230 GHz and is therefore intrinsic rather than an imaging artifact. Geometric model fitting identifies several components with apparent speeds up to 10c, requiring bulk Lorentz factor…

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physics.flu-dynastro-ph.GAastro-ph.SR

From Triadic Interactions to Kolmogorov Scaling: A Deterministic, Scale-Resolved Formulation of Energy Flux

Erik Bertram

We develop a deterministic, scale-resolved formulation of energy transfer in the three-dimensional incompressible Navier-Stokes equations based on an explicit triadic decomposition of the nonlinear term in Fourier space. Using a systematic dyadic localization of the velocity field, we derive an exact representation of the nonlinear energy flux across scales and organize it in terms of interactions between well-defined scale components. Under suitable smoothness assumptions, we obtain an absolute…

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astro-ph.IMastro-ph.CO

OpenCosmo: Community Portal and Analysis Framework for Flagship Cosmological Simulations

Patrick R. Wells, Michael Buelhmann, Patricia Larsen, William M. Hicks, Manpreet Dhillon, Idunnuoluwa A. Adeniji, Katrin Heitmann, Salman Habib et al.

Cosmology is a precision observational science, and large simulations are necessary components of many analyses. These simulations are computationally expensive and produce massive, complex datasets; sharing them widely -- to enable further explorations, comparison with observations, and communication with general audiences -- is crucial to realizing their scientific value. In this paper, we introduce the OpenCosmo project, which provides flexible access to, and analysis of, flagship cosmologica…

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astro-ph.GA

Infrared spectroscopy of gas-phase hydrogenated and methylated pyrenes: from laboratory spectra to the simulated 3.4 $μ$m emission band

Karine Demyk, Christine Joblin, Louan de Bentzmann, Dominique Toublanc, Giacomo Mulas

Observations of the aromatic infrared emission band at 3.3 $μ$m often reveal satellite emission features in the 3.4 - 3.6 $μ$m range. While the 3.3 $μ$m band is attributed to the CH stretching vibration of polycylic aromatic hydrocarbons (PAHs), the satellite bands - particularly its prominent 3.4 $μ$m component - is assigned to aliphatic CH stretching vibrations in hydrogenated and methylated PAH-like species. Our aim is to derive state-of-the-art infrared emission spectra for aliphatic-contain…

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astro-ph.IM

Coherence differential imaging using gradient-boosted decision trees for the direct detection of exoplanets

Johan Mazoyer, María J. Mellado-Tenorio, Axel Potier, Christian Wilkinson, Lukas Delaye, Raphaël Galicher, Iva Laginja

Coronagraphic imaging of exoplanets is limited by residual speckles that mimic planets. Advanced post-processing is essential for current and future instruments on the ground or in space. Current techniques are time-intensive and limited. ADI requires long sequences and is limited at small separations. RDI is also time-consuming and sensitive to speckle evolution, leading to imperfect subtraction. Coherence Differential Imaging (CDI), which we successfully demonstrated on SPHERE, offers a faster…

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