Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
Gravitational waves from the sound shell model: direct and inverse phase transitions in the early Universe
Giulio Barni, Simone Blasi, Eric Madge et al. (+1 more)
Cosmological phase transitions are a frequent phenomenon in particle physics models beyond the Standard Model, and the corresponding gravitational wave signal offers a key probe of new physics in the early Universe. Depending on the underlying microphysics, the transition can exhibit either direct or inverse hydrodynamics, leading to a different phenomenology. Most studies to date have focused on direct transitions, where the
cosmic fluid is pushed or dragged by the expanding
vacuum bubbles. In contrast, inverse phase transitions are characterized by fluid profiles where the
plasma is sucked in by the expanding bubbles. Using the sound shell model, we derive and compare the gravitational wave spectra from sound waves for direct and inverse phase transitions, providing new insights into the potential observable features and the possibility of discriminating among the various fluid solutions in gravitational wave experiments.
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All authors Giulio Barni, Simone Blasi, Eric Madge, Miguel Vanvlasselaer
Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc
Optimizing searches for gravitational wave bursts using coherent WaveBurst 2G
Alessandro Martini, Andrea Miani, Marco Drago et al. (+11 more)
The most general searches for gravitational wave transients (GWTs) rely on data analysis methods that do not assume prior knowledge of the signal waveform, direction, or arrival time on Earth. These searches provide data-driven signal reconstructions that are crucial both for testing available emission models and for discovering yet-to-be-uncovered sources. Here, we discuss progress in the detection performance of the coherent WaveBurst second-generation pipeline (cWB-2G), which is highly adaptable to both minimally modeled and model-informed searches for GWTs. Several search configurations for GWTs are examined using approximately 14.8 days of observation time from the third observing run by LIGO-Virgo-KAGRA (LVK). Recent enhancements include a ranking statistic fully based on multivariate classification with eXtreme Gradient Boosting, a thorough validation of the statistical significance accuracy of GWT candidates, and a measurement of the correlations of false alarms and simulated detections between different concurrent searches. For the first time, we provide a comprehensive comparison of cWB-2G performance on data from networks made of two and three detectors, and we demonstrate the advantage of combining concurrent searches for GWTs of generic morphology in a global observatory. This work offers essential insights for assessing our data analysis strategies in ongoing and future LVK searches for generic GWTs.
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All authors Alessandro Martini, Andrea Miani, Marco Drago, Claudia Lazzaro, Francesco Salemi, Sophie Bini, Osvaldo Freitas, Edoardo Milotti, Giacomo Principe, Shubhanshu Tiwari, Agata Trovato, Gabriele Vedovato, Yumeng Xu, Giovanni Andrea Prodi
Astrophysics of Galaxies
AGN STORM 2. XI. Spectroscopic reverberation mapping of the hot dust in Mrk 817
Hermine Landt, Benjamin D. Boizelle, Michael S. Brotherton et al. (+41 more)
The AGN Space
Telescope and Optical Reverberation Mapping 2 (STORM 2) campaign targeted Mrk 817 with intensive multi-wavelength monitoring and found its soft X-ray emission to be strongly absorbed. We present results from 157 near-IR spectra with an average cadence of a few days. Whereas the hot
dust reverberation signal as tracked by the continuum flux does not have a clear response, we recover a
dust reverberation radius of $\sim 90$ light-days from the blackbody
dust temperature light-curve. This radius is consistent with previous photometric reverberation mapping results when Mrk 817 was in an unobscured state. The heating/cooling process we observe indicates that the inner limit of the dusty
torus is set by a process other than sublimation, rendering it a luminosity-invariant `dusty wall' of a carbonaceous composition. Assuming thermal
equilibrium for
dust optically thick to the incident radiation, we derive a luminosity of $\sim 6 \times 10^{44}$ erg s$^{-1}$ for the source heating it. This luminosity is similar to that of the obscured spectral energy distribution, assuming a disk with an Eddington
accretion rate of $\dot{m} \sim 0.2$. Alternatively, the
dust is illuminated by an unobscured lower luminosity disk with $\dot{m} \sim 0.1$, which permits the UV/optical continuum lags in the high-obscuration state to be dominated by diffuse emission from the broad-line region. Finally, we find hot
dust extended on scales $> 140-350$ pc, associated with the rotating disk of ionised gas we observe in spatially-resolved [SIII] $\lambda 9531$ images. Its likely origin is in the compact bulge of the barred spiral host
galaxy, where it is heated by a
nuclear starburst.
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All authors Hermine Landt, Benjamin D. Boizelle, Michael S. Brotherton, Laura Ferrarese, Travis Fischer, Varoujan Gorjian, Michael D. Joner, Daniel Kynoch, Jacob N. McLane, Jake A. J. Mitchell, John W. Montano, Rogemar A. Riffel, David Sanmartim, Thaisa Storchi-Bergmann, Martin J. Ward, Aaron J. Barth, Edward M. Cackett, Gisella De Rosa, Rick Edelson, Jonathan Gelbord, Yasaman Homayouni, Keith Horne, Erin A. Kara, Gerard A. Kriss, Nahum Arav, Elena Dalla Bontà, Maryam Dehghanian, Gary J. Ferland, Carina Fian, Diego H. González Buitrago, Dragana Ilić, Shai Kaspi, Christopher S. Kochanek, Andjelka B. Kovačević, Collin Lewin, Yan-Rong Li, Missagh Mehdipour, Hagai Netzer, Rachel Plesha, Luka Č. Popović, Daniel Proga, Jian-Min Wang, Fatima Zaidouni, Ying Zu
Solar and Stellar Astrophysics
Gaia and massive stars in 2025
J. Maíz Apellániz
I present some of the highlights of the
Gaia mission on massive
stars and discuss what the fourth data release (DR4) will bring in late 2026. In the first part of the contribution I describe the different types of
Gaia products available now and for DR4 and their caveats. In the second part I present the most significant results on massive
stars regarding parameter determination, binaries, photometric variability,
stellar groups, and the sample and spatial distribution.
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Cosmology and Nongalactic Astrophysics
Luminosity-Dependent Assembly Bias of Central Galaxies from Weak Lensing and Clustering
Zhenjie Liu, Hironao Miyatake, Joop Schaye et al. (+3 more)
Assembly bias, which is the variation in
halo clustering at fixed mass driven by formation history, has long been predicted by numerical simulations but remains difficult to confirm observationally. Previous studies have reported evidence for
halo assembly bias by dividing samples according to
galaxy stellar mass using various methods. In this work, we present observational measurements of
halo assembly bias based on the luminosity of spectroscopically confirmed brightest cluster
galaxies (BCGs). Using cluster catalogs and shear measurements from the DESI Legacy Imaging Surveys, we employ a mass-dependent
halo-bias model to disentangle
halo bias from its underlying mass dependence in
galaxy-
galaxy lensing and clustering measurements. We confirm that brighter BCGs are less strongly clustered on large scales, with a relative bias ratio deviating from unity at the $\sim3\sigma$ level, suggesting the presence of assembly bias. Similar qualitative trends are also found in the FLAMINGO and MillenniumTNG hydrodynamical simulations, strengthening the connection between
galaxy luminosity and
halo formation history.
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All authors Zhenjie Liu, Hironao Miyatake, Joop Schaye, Matthieu Schaller, Keitaro Ishikawa, Tomomi Sunayama
High Energy Astrophysical Phenomena
A simple toy model for the electromagnetic variability of lump-dominated circumbinary disks around binary black holes
R. Mignon-Risse, P. Varniere and F. Casse
The electromagnetic detection of circumbinary disks around pre-merger binary black holes (BBHs) relies on theoretical predictions. These are generally obtained through expensive numerical simulations, but simple or fast toy models are lacking to unleash the potential of these theoretical advances for observational purposes. We aim to present a simple toy model to compute the electromagnetic variability of circumbinary disks around circular-orbit BBHs at relativistic separations, focusing on the impact of disk non-axisymmetries. We assume that the disk is threaded by spiral arms and hosts a hotspot linked to an overdense structure (the {\lq}lump{\rq}) preferably reported in binaries close to equal mass. We build a simple temperature distribution, and estimate its thermal emission, perceived by a distant observer, via a ray-tracing code in a BBH approximate metric. We propose a toy model reproducing the main lightcurve features and show it is consistent with 2D general-hydrodynamical simulations under the assumption of compressional heating and expansional cooling except for purely dynamical effects such as the binary-lump beat. The lightcurve exhibits a main modulation at the lump's period (i.e. a few times the orbital period), due to relativistic Doppler effect, and a shorter one at the orbital-like period, due to spiral arms or the beat. These are more prominent in the optical/UV band for a total binary mass $M\, {=} \, 10^{4-10}\mathrm{M_\odot}$, where the disk energy spectrum peaks. For $M=10^{9}\mathrm{M_\odot}$, a $4\%$-amplitude lump modulation is detectable with the Vera Rubin Observatory after six months of observation, up to $z\, {=}\, 0.5$. We proposed a new, simple toy model that can be used, for instance, to test the compatibility of the periodicity of BBH candidate sources with a circumbinary disk origin.
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Earth and Planetary Astrophysics · Cross-listed from physics.ao-ph
Space waste: An update of the anthropogenic matter injection into Earth atmosphere
Leonard Schulz, Karl-Heinz Glassmeier, Moritz Herberhold et al. (+4 more)
Large satellite constellations are one of the main reasons for an increasing amount of mass being brought into low Earth orbit in recent years. After end of life, the satellites, as well as rocket stages, reenter Earth's atmosphere. This space waste burns up and thus injects a substantial amount of its matter into the mesosphere and lower thermosphere. A first comprehensive analysis of the anthropogenic injection and a comparison to the natural injection by meteoroids was presented by Schulz & Glassmeier (2021). They found significant and even the dominant injection of several metal elements regularly used in spacecraft compared to the natural injection. The first observations of space waste remnants in stratospheric aerosol particles (Murphy et al., 2023) confirmed several of these estimates, but also revealed differences and new insights. The current study presents an update to the space waste injection estimates of Schulz & Glassmeier (2021), assessing the years from 2015 to 2025 but also considering future mass influx scenarios. 43 elements are considered and thus a much more detailed comparison to the meteoric injection is possible. Comparison of estimated elemental fluxes to stratospheric aerosol data shows excellent agreement. From 2020 onward, a strong rise in space waste mass influx to the atmosphere can be seen. Future scenarios discussed by Schulz & Glassmeier (2021) may already be reached by the end of 2025. In 2024, 24 elements were dominating the meteoric injection compared to 18 in 2015. Several of them are transition metals, which are known for their catalytic activity. This indicates a substantial risk of long-term adverse effects on the atmosphere such as ozone depletion, radiative effects and changes in cloud formation, if no action is taken. Research is urgently needed into the atmospheric accumulation, chemistry, and general atmospheric effects of specific elements.
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All authors Leonard Schulz, Karl-Heinz Glassmeier, Moritz Herberhold, Adam Mitchell, Daniel M. Murphy, John M. C. Plane, Ferdinand Plaschke
High Energy Astrophysical Phenomena
The relation between the optical variability timescale, magnetic field of jets and black hole spin in active galactic nuclei
Yongyun Chen, Qiusheng Gu, Junhui Fan et al. (+5 more)
We investigate the relationship among the jet
magnetic field, black hole
spin, black hole mass, Eddington ratio, and optical variability timescales in jetted active
galactic nuclei (AGNs). By fitting a damped random walk (DRW) model to the g-band light curves, we obtain the characteristic variability timescale ($\tau_{\rm DRW}$) for 41 jetted AGNs with precise supermassive black hole (SMBH) mass measurements. Our main results are as follows: (i) Our analysis reveals a significant correlation between the jet
magnetic field ($B_{\rm 1pc}$), black hole
spin ($j$) and the characteristic variability timescale within our sample. These findings suggest that the optical variability of jetted AGNs is influenced by the jet
magnetic field and black hole
spin. Furthermore, the characteristic variability timescale aligns with the electron escape timescale, as evidenced by the relationship between the characteristic variability timescale and jet
magnetic field ($\tau_{\rm DRW}\propto B_{\rm 1pc}^{0.76\pm0.22}$). (ii) We confirm a significant correlation between the characteristic variability timescale and SMBH mass, expressed as: $\log \rm \tau_{\rm DRW} = 0.52(\pm0.21)\log M _{\rm BH}/M_{\rm \odot}-3.12(\pm1.90)$, with an intrinsic scatter of 0.08 dex. The slope of this relationship is consistent with that between the thermal timescale and black hole mass. Our results support the hypothesis that magnetorotational instability (MRI) fluctuations drive the intrinsic variability observed in the light curves emitted by the AGNs
accretion disk.
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All authors Yongyun Chen, Qiusheng Gu, Junhui Fan, Dingrong Xiong, Xiaoling Yu, Xiaotong Guo, Nan Ding, Ting-Feng Yi
Cosmology and Nongalactic Astrophysics
Forecasts of constraining isotropic cosmic birefringence on AliCPT-1
Jiazheng Dou and Wen Zhao
Cosmic birefringence (CB) is a promising probe of parity-violating physics beyond the Standard Model, characterized by the rotation of the linear polarization plane of
cosmic microwave background (CMB)
photons. This effect, quantified by the birefringence angle $\beta$, generates non-zero $EB$ and $TB$ correlations that are otherwise absent in standard cosmology. However, instrumental miscalibration angles $\alpha$ can mimic this signal, necessitating a joint estimation approach. In this work, we forecast the sensitivity of the AliCPT experiment, combined with Planck HFI data, on constraining the isotropic CB angle using a semi-analytical maximum-likelihood method. We simulate observations under various foreground complexities, rotation angles, and scanning strategies, and demonstrate that AliCPT can achieve an uncertainty of $\sigma(\beta)=0.09^\circ$ with one-year data, which will improve to $0.026^\circ$ after four years' observations. We also find that neglecting or mismodeling the foreground $EB$ correlation will introduce significant biases, which can be alleviated under a clean but small sky patch.
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Astrophysics of Galaxies
Modelling the scattering by porous aggregate dust grains in the Far-Ultraviolet halos of Spica and Achernar
Nilanjana Dey Choudhury, P. Shalima, Keerthana U. et al. (+1 more)
Far-Ultraviolet (FUV)
halos have been detected around six bright
stars by Murthy and Henry (2011) using GALEX observations. These
halos are thought to be caused by forward scattering of the starlight by
dust grains present in thin foreground clouds. The optical constants of grains producing such
halos have been constrained earlier by using a single scattering model, that considered the Henyey-Greenstein empirical phase function instead of theoretical phase functions for the scattering grains. In this work, we have modelled the FUV
halos for two
stars, Spica and Achernar, by considering the realistic porous aggregates of different sizes and compositions. As the Henyey-Greenstein phase function is known to deviate from theoretical predictions, we have utilized theoretical scattering phase functions for modelling. The
dust is placed in a double-layered plane-parallel sheet with its distance and optical depth varied to get the best fit. We find that the
halo intensities are dominated by scattering due to 0.05 {\mu}m sized porous
dust aggregates made of amorphous silicate and carbonaceous aggregates for Spica and Achernar, respectively. We find that the medium in front of Achernar has a lower optical depth ({\tau}) of 0.032 compared to Spica which has a value of {\tau} = 0.1. This low value is close to the optical depth of the local ISM (0.01) within 40 pc of the Sun. This study demonstrates an effective method to constrain the
dust grain properties in the local interstellar medium.
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All authors Nilanjana Dey Choudhury, P. Shalima, Keerthana U., J. Murthy
High Energy Astrophysical Phenomena
Detection of Quasi-periodic Oscillations in the $\gamma$-Ray Light Curve of 4FGL J0309.9-6058
Jingyu Wu, Zhihao Ouyang, Hubing Xiao et al. (+7 more)
In this work, we report, for the first time, a quasi-periodic oscillation (QPO) in the $\gamma$-ray band of 4FGL J0309.9-6058, also known as PKS 0308-611. We employed three analytical methods (the Lomb-Scargle periodogram, REDFIT, and the weighted wavelet Z-transform) to analyze the QPO signal using
Fermi $\gamma$-ray light curve data. The analysis reveals a potential QPO during MJD 57983$-$60503, with a period of approximately 550 days and a maximum local significance of 3.72$\sigma$ and global significance of 2.72$\sigma$ derived from the WWZ analysis. To validate this result, we applied Gaussian Process (GP) to the same light curve, which independently confirms the presence of QPO signal consistent with our
Fourier-based results. We further extended the analysis to the full duration of the
Fermi observations, and the results consistently support and strengthen the presence of this QPO signal. Additionally, a time lag between the optical and $\gamma$-ray bands indicates separate emission regions for these two bands. Given the year-like timescale of the QPO signal and the fact that a QPO signal with local significance over 3$\sigma$ for full
Fermi-LAT observed time, we suggest that the QPO is most likely caused by a precessing jet.
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All authors Jingyu Wu, Zhihao Ouyang, Hubing Xiao, Elisa Prandini, Shangchun Xie, Sheng Yang, Jianzhen Chen, Shaohua Zhang, Haoyang Zhang, Junhui Fan
Astrophysics of Galaxies
Supernovae Driven Winds Impede Lyman Continuum Escape from Dwarf Galaxies in First 10 Myr
Cody Carr, Renyue Cen, Stephan McCandliss et al. (+25 more)
Observations suggest that UV-bright, compact
star-forming
galaxies produce enough ionizing (Lyman continuum; LyC)
photons to reionize the Universe. Yet, the efficiency of LyC escape and the roles of radiation,
stellar winds, and
supernovae remain uncertain. Using medium-resolution spectra of six nearly identical local
star-forming
galaxies, we directly trace, for the first time, the
evolution of a multiphase wind through individual spectral lines alongside measurements of the LyC escape fraction. We find that LyC escape peaks early, during a period dominated by intense radiation and
stellar winds but lacking a fast
galactic wind. As the starbursts age,
supernovae drive and accelerate the wind, progressively suppressing LyC escape. These results highlight the need for cosmological simulations to incorporate early feedback as a key driver of reionization.
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All authors Cody Carr, Renyue Cen, Stephan McCandliss, Jack Ford, Alberto Saldana-Lopez, Claudia Scarlata, Mason Huberty, Anne Jaskot, Sophia Flury, M. S. Oey, Ricardo O. Amorín, Sanchayeeta Borthakur, Matthew Hayes, Timothy Heckman, Zhiyuan Ji, Lena Komarova, Alexandra Le Reste, Floriane Leclercq, Rui Marques-Chaves, Leo Michel-Dansac, Göran Östlin, Swara Ravindranath, Michael J. Rutkowski, Daniel Schaerer, Trinh Thuan, Eros Vanzella, Bingjie Wang, Xinfeng Xu
High Energy Astrophysical Phenomena
Dissipation and particle acceleration at intermittent structures with velocity and magnetic shear: Interaction of Kelvin-Helmholtz and Drift-Kink instabilities
Tsun Hin Navin Tsung, Gregory R. Werner, Dmitri A. Uzdensky et al. (+1 more)
We present two-dimensional (2D) particle-in-
cell simulations of a magnetized, collisionless, relativistic pair
plasma subjected to combined velocity and
magnetic-field shear, a scenario typical at intermittent structures in
plasma turbulence. We create conditions where only the Kelvin-Helmholtz (KH) and Drift-Kink (DK) instabilities can develop, while tearing modes are forbidden. The interaction of DKI and KHI generates qualitatively new structures, marked by a thickened shear layer with very weak electromagnetic field, modulated by KH
vortices. Over a range of moderately strong velocity shears explored, the interaction of DKI and KHI results in a significant enhancement of dissipation over cases with only velocity shear or only
magnetic shear. Moreover, we observe a new and efficient way of particle acceleration where particles are stochastically accelerated by the motional electric field exterior to the shear layer as they meander in an S-shaped pattern in and out of it. This process takes advantage of the bent geometry of the shear layer caused by the DK-KHI interaction and is responsible for most of the highest-energy particles produced in our simulations. These results further our understanding of dissipation and particle acceleration at intermittent structures, which are present in
plasma turbulence across a wide range of astrophysical contexts such as in AGN jet sheaths, potentially relevant to limb-brightened emission, etc., and highlight the sensitivity of dissipation to multiple interacting instabilities, thus providing a strong motivation for further studies of their nonlinear interaction at the kinetic level.
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All authors Tsun Hin Navin Tsung, Gregory R. Werner, Dmitri A. Uzdensky, Mitchell C. Begelman
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
WimPyC: an extension module of WimPyDD for the calculation of WIMP capture in celestial bodies
Sunghyun Kang, Stefano Scopel and Gaurav Tomar
We introduce WimPyC, a Python code for the calculation of the capture rate of Weakly Interacting Massive Particles (WIMPs) by celestial bodies through
nuclear scattering in the optically thin regime. WimPyC is an extension of the WimPyDD code, that calculates WIMP-
nucleus scattering signals in direct detection (DD) experiments, and allows to combine DD and capture in celestial bodies in virtually any scenario within the framework of Galilean-invariant non-relativistic effective theory (NREFT), including inelastic scattering, an arbitrary WIMP
spin and a generic WIMP velocity distribution in the
Galactic halo. WimPyDD and WimPyC are suitable for both top-down approaches, where the interaction operators of a high-energy physics model are matched to those of the NREFT, and to bottom-up studies, where the Wilson coefficients of the NREFT are explored in a model-independent way and/or where the velocity distribution is written in terms of a superposition of streams taken as free parameters. As in the case of WimPyDD WimPyC exploits the factorization of the three main components that enter in the calculation of the capture rate: i) the Wilson coefficients that encode the dependence of the signals on the ultraviolet completion of the effective theory; ii) a response function that depends on the
nuclear physics; iii) the
halo function that depends on the WIMP velocity distribution. In WimPyC these three components are calculated and stored separately for later interpolation and combined together only as the last step of the signal evaluation procedure. This makes the phenomenological study of the capture rate with WimPyC transparent and improves computational speed.
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High Energy Astrophysical Phenomena
Observation of In-ice Askaryan Radiation from High-Energy Cosmic Rays
ARA Collaboration: N. Alden, S. Ali, P. Allison et al. (+73 more)
We present the first experimental evidence for in-ice Askaryan radiation – coherent charge-excess
radio emission – from high-energy particle cascades developing in the Antarctic ice sheet. In 208 days of data recorded with the phased-array instrument of the Askaryan
Radio Array, a previous analysis has incidentally identified 13 events with impulsive radiofrequency signals originating from below the ice surface. We here present a detailed reanalysis of these events. The observed event rate, radiation arrival directions, signal shape, spectral content, and electric field polarization are consistent with in-ice Askaryan radiation from
cosmic ray air shower cores impacting the ice sheet. For the brightest events, the angular radiation pattern favors an extended cascade-like emitter over a pointlike source. An origin from the geomagnetic separation of charges in
cosmic ray air showers is disfavored by the arrival directions and polarization. Considering the arrival angles, timing properties, and the impulsive nature of the passing events, the event rate is inconsistent with the estimation of the combined background from thermal noise events and on-surface events at the level of $5.1\,\sigma$.
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All authors ARA Collaboration: N. Alden, S. Ali, P. Allison, S. Archambault, J.J. Beatty, D.Z. Besson, A. Bishop, P. Chen, Y.C. Chen, Y.-C. Chen, S. Chiche, B.A. Clark, A. Connolly, K. Couberly, L. Cremonesi, A. Cummings, P. Dasgupta, R. Debolt, S. de Kockere, K.D. de Vries, C. Deaconu, M.A. DuVernois, J. Flaherty, E. Friedman, R. Gaior, P. Giri, J. Hanson, N. Harty, K.D. Hoffman, M.-H. Huang, K. Hughes, A. Ishihara, A. Karle, J.L. Kelley, K.-C. Kim, M.-C. Kim, I. Kravchenko, R. Krebs, C.Y. Kuo, K. Kurusu, U.A. Latif, C.H. Liu, T.C. Liu, W. Luszczak, A. Machtay, K. Mase, M.S. Muzio, J. Nam, R.J. Nichol, A. Novikov, A. Nozdrina, E. Oberla, C.W. Pai, Y. Pan, C. Pfendner, N. Punsuebsay, J. Roth, A. Salcedo-Gomez, D. Seckel, M.F.H. Seikh, Y.-S. Shiao, J. Stethem, S.C. Su, S. Toscano, J. Torres, J. Touart, N. van Eijndhoven, A. Vieregg, M. Vilarino Fostier, M.-Z. Wang, S.-H. Wang, P. Windischhofer, S.A. Wissel, C. Xie, S. Yoshida, R. Young
High Energy Astrophysical Phenomena
Detecting Population III Gamma-Ray Bursts with Einstein Probe and Space-Based Multi-band Astronomical Variable Objects Monitor
Jun-Jie Wei, Qing-Bo Ma and Xue-Feng Wu
High-
redshift gamma-ray bursts (GRBs), putative counterparts of massive, low-
metallicity Population III (Pop III)
stars, are a promising probe of the first
stars. We assess the detectability of these Pop III GRBs using a
metallicity-based progenitor criterion and cosmological $N$-body/hydrodynamical simulations with three distinct Pop III initial mass functions (IMFs), focusing on the capabilities of the Wide-field X-ray
Telescope (WXT) aboard the Einstein Probe (EP) and the coded-mask gamma-ray imager (ECLAIRs) aboard the Space-based multi-band astronomical Variable Objects Monitor (SVOM). Our population synthesis model, calibrated to Swift data, predicts the following Population II/I (Pop II/I) GRB detection rates at $z>6$: $\sim2.4\,\mathrm{events\,yr^{-1}}$ for EP/WXT and $\sim0.9\,\mathrm{events\,yr^{-1}}$ for SVOM/ECLAIRs. For the IMF with very massive first
stars ($\mathrm{100\textrm{--}500\,M_\odot}$), we derive upper limits on the Pop III GRB rate at $z>6$ of $<0.06\,\mathrm{events\,yr^{-1}}$ (EP/WXT) and $<0.13\,\mathrm{events\,yr^{-1}}$ (SVOM/ECLAIRs), based on the absence of confirmed Pop III progenitors in Swift bursts at $z>5.5$. Our results indicate that while Pop III GRBs are subdominant to Pop II/I GRBs at $z<10$, their fractional contribution rises significantly with
redshift, reaching $\sim8\%$ ($\sim34\%$) at $z>10$ and $\sim28\%$ ($\sim68\%$) at $z>16$ for EP/WXT (SVOM/ECLAIRs). This trend is systematically enhanced in the other two IMF models, which adopt a lower
stellar mass range of $\mathrm{[0.1,\,100]\,M_\odot}$. We conclude that detecting Pop III GRBs at high
redshifts is a realistic prospect, and any GRB detected at $z>16$ is most likely of Pop III origin.
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Solar and Stellar Astrophysics
Backmapping of the High- and Low-latitude Solar Wind under Multiple Heliospheric and Coronal Magnetic Field Configurations
Xinyi Ma, Liping Yang, Xueshang Feng et al. (+7 more)
Solar wind backmapping is a critical technique for analyzing the origin of the
solar wind and space weather events by correlating in situ measurements with
solar remote-sensing observations. This technique typically traces
magnetic field lines using a heliospheric
magnetic field (HMF) model coupled with a coronal
magnetic field (CMF). However, the impact of different HMF and CMF configurations on backmapping uncentainty-particularly regarding high-latitude
solar wind-remains inadequately quantified. This study comprehensively evaluates
solar wind backmapping by combining two HMF models (Parker spiral, Fisk-type) with three CMF models (Potential Field Source Surface (PFSS), Potential Field Current Sheet (PFCS), Current Sheet Source Surface (CSSS)). Our analysis primarily uses in situ measurements from Ulysses and remote-sensing data from STEREO-A. Key findings are that: (1) while both Fisk and Parker HMF models show comparable consistency with measured
magnetic field strength and polarity, they produce certain longitudinal displacements in their back-mapped footpoints on the source surface (2.5$R_{\odot}$); (2) For CMF models (PFSS, PFCS, CSSS), predicted photospheric footpoints exhibit minor variations for high/mid-latitude
solar wind but some divergences for ecliptic/low-latitude wind; (3) All three CMF models link high/mid-latitude wind to active regions or coronal holes, yet associate a fraction of ecliptic/low-latitude wind with quiet-Sun regions; (4) Ecliptic/low-latitude sources show significantly stronger dependence on the PFSS source surface height compared to high-latitude wind. These results demonstrate that simpler models (PFSS + Parker) appear reasonably adequate for polar coronal hole wind studies, while low-latitude/ecliptic
solar wind exhibits the heightened sensitivity to model choices.
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All authors Xinyi Ma, Liping Yang, Xueshang Feng, Hui Tian, Honghong Wu, Fang Shen, Wangning Zhang, Mengxuan Ma, Xiao Zhang, Ziwei Wang
Solar and Stellar Astrophysics
Photospheric Chemical Depletion in Post-AGB/Post-RGB Binaries with Second-Generation Protoplanetary Discs
Maksym Mohorian
The origin and
evolution of chemical elements in the Universe are governed not only by nucleosynthesis processes in
stars, but also by mechanisms that alter observed photospheric compositions. Among these, chemical depletion (underabundance of refractory elements in
stellar photospheres) presents a key puzzle in understanding the full chemical lifecycle. This PhD thesis explores the role of disc-binary interaction in shaping chemical abundances in evolved low- and intermediate-mass binary
stars, focusing on systems that have undergone the red
giant branch (RGB) or asymptotic
giant branch (AGB) phase. In this thesis, we investigate binary systems containing post-asymptotic
giant branch (post-AGB, $L_{\rm post-AGB}\,\gtrsim\,2\,500\,L_\odot$) and post-red
giant branch (post-RGB, $L_{\rm post-RGB}\,\lesssim\,2\,500\,L_\odot$) binaries as key tracers of AGB/RGB nucleosynthesis. Although the effects of these interactions remain poorly understood, they are known to drive photospheric chemical depletion. This depletion closely resembles that observed in young
planet-hosting
stars with protoplanetary discs. Combined with other structural and dynamical similarities in disc properties, this suggests a potential link to second-generation
planet formation in post-AGB/RGB binaries with circumbinary discs. Although direct imaging of such
planets is not feasible, studying signatures such as photospheric depletion provides an indirect means of exploring their possible presence within these systems.
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Solar and Stellar Astrophysics · Cross-listed from cs.LG
Scalable Machine Learning Analysis of Parker Solar Probe Solar Wind Data
Daniela Martin, Connor O'Brien, Valmir P Moraes Filho et al. (+4 more)
We present a scalable machine learning framework for analyzing Parker
Solar Probe (PSP)
solar wind data using distributed processing and the
quantum-inspired Kernel Density
Matrices (KDM) method. The PSP
dataset (2018–2024) exceeds 150 GB, challenging conventional analysis approaches. Our framework leverages Dask for large-scale statistical computations and KDM to estimate univariate and bivariate distributions of key
solar wind parameters, including
solar wind speed,
proton density, and
proton thermal speed, as well as anomaly thresholds for each parameter. We reveal characteristic trends in the inner heliosphere, including increasing
solar wind speed with distance from the Sun, decreasing
proton density, and the inverse relationship between speed and density.
Solar wind structures play a critical role in enhancing and mediating extreme space weather phenomena and can trigger geomagnetic storms; our analyses provide quantitative insights into these processes. This approach offers a tractable, interpretable, and distributed methodology for exploring complex physical
datasets and facilitates reproducible analysis of large-scale in situ measurements. Processed data products and analysis tools are made publicly available to advance future studies of
solar wind dynamics and space weather
forecasting. The code and configuration files used in this study are publicly available to support reproducibility.
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All authors Daniela Martin, Connor O'Brien, Valmir P Moraes Filho, Jinsu Hong, Jasmine R. Kobayashi, Evangelia Samara, Joseph Gallego