High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Compact binary system dynamics at the second post-Newtonian order: analytical formula of the coordinate time for eccentric and circular orbits
Vittorio De Falco and Marco Gallo
This work is based on the letter Phys. Lett. B, 865, 139484 (2025), where we developed the analytical expression of the coordinate time in terms of the eccentric anomaly at the second post-Newtonian order in General Relativity for a compact binary system moving on eccentric orbits. The aim of this paper is to provide more details about the performed calculations and to produce other new results. More specifically, we will focus on deriving the analytical expression of the coordinate time at the second Post-Newtonian order for circular orbits and then discuss two astrophysical applications involving binary
neutron star and black hole systems.
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Astrophysics of Galaxies
SPHEREx: Aromatics, Aliphatics and PAH Size across the Iris Nebula
Christiaan Boersma, Alexandros Maragkoudakis, Louis J. Allamandola et al. (+4 more)
Observations by the SpectroPhotometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx) are combined with Spitzer spectral map data to study the aromatic, aliphatic, and PAH size
evolution across the northwest photo-dissociation region (PDR) of the Iris Nebula (NGC7023). The 3.3-3.4 $\mu$m complex (I$_{3.3}$) and 11.2 $\mu$m (I$_{11.2}$) PAH band strength are determined through direct integration. In addition, the former is decomposed into a 3.3 (I'$_{3.3}$) and 3.4 $\mu$m (I'$_{3.4}$) sub-feature by fitting SPHEREx bandpass-integrated photometry using a modeled, highly sampled, multi-component spectrum. I$_{3.3}$, I$_{11.2}$, I'$_{3.3}$, and I'$_{3.4}$ all peak at the PDR. The NASA Ames PAH IR Spectroscopic Database is used to obtain the average number of carbon atoms ($\overline{\rm N_{C}}$) and small PAH fraction ($f_{\rm small}$) by fitting the isolated PAH component of the Spitzer segment; $70\lesssim\overline{N_{C}}\lesssim76$ and $0.24\lesssim\text{f}_{\rm small}\lesssim0.36$. I'$_{3.4}$/I'$_{3.4}$, I$_{11.2}$/I$_{3.3}$, $\overline{\rm N_{C}}$, and $f_{\rm small}$ all show a demarcation that matches the large-scale morphology of the region. For I'$_{3.3}$ and I'$_{3.4}$ this is reflected by two distinct trends when plotted against each other, one associated with the dense, the other with the diffuse medium; $[N_{\rm H,ali}/N_{\rm H,aro}]_{\rm dense}$ = 0.42$\pm$0.01 and $[N_{\rm H,ali}/N_{\rm H,aro}]_{\rm diffuse}$ = 0.10$\pm$0.01. $\overline{\rm N_{C}}$ and $f_{\rm small}$ are tentatively correlated with I$_{11.2}$/I$_{3.3}$ (R=0.54$\pm$0.05 and -0.45$\pm$0.05, respectively). A wider variety of large(r) extended interstellar medium objects is required to tighten the correlations, turn them into quantitative calibrators for PAH size, and pin down the discrepancy of correlations with I'$_{3.3}$ involved.
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All authors Christiaan Boersma, Alexandros Maragkoudakis, Louis J. Allamandola, Jesse D. Bregman, Pasquale Temi, Vincent J. Esposito, Ryan C. Fortenberry
High Energy Astrophysical Phenomena
Multiwavelength view of circumstellar interaction in supernovae
Poonam Chandra
The interaction of post-explosion
supernova ejecta with the surrounding circumstellar medium creates emission across the electromagnetic spectrum. Since the circumstellar medium is created by the mass lost from the progenitor
star, it carries tell-tale signatures of the progenitor. Consequently, observations and modeling of radiation produced by the interaction in various types of
supernovae have provided valuable insights into their progenitors. Detailed studies have shown that the interaction in
supernovae begins and sustains over various timescales and lengthscales, with differing mass-loss rates in distinct sub-classes. This reveals diverse progenitor histories for these
stellar explosions. This review paper summarizes various
supernova subtypes, linking them to
stellar death pathways, and presents an updated
supernova classification diagram. We then present a multi-wavelength study of circumstellar interaction in different
supernova classes. We also present unpublished Chandra X-ray as well as
radio observations of a type IIn
supernova, SN 2010jl, which allow us to extend its circumstellar interaction studies to about 7 years post-explosion. The new data indicates that the extreme mass-loss rate 0.1 Msun/yr in SN 2010jl, reported by Chandra et al. (2015), commenced within the last 300 years before the explosion. We summarize the current status of the field and argue that via detailed studies of the circumstellar interaction, a.k.a. Time Machine technique, one of the big mysteries of
stellar evolution, i.e., mapping
supernovae progenitors to their explosive outcomes can be solved.
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Astrophysics of Galaxies
Chemical modeling of aminoketene, ethanolamine, and glycine production in interstellar ices
Sydney A. Willis, Serge A. Krasnokutski, Nathaniel J. Morin et al. (+1 more)
Icy interstellar
dust grains are a source of complex organic molecule (COM) production, although their formation mechanisms are debated. Laboratory experiments show that atomic C deposited onto interstellar ice analogs can react with solid-phase NH3 to form a CHNH2 radical, a possible precursor to COMs, including aminoketene (NH2CHCO). We used astrochemical kinetics models to explore the role of the reaction of atomic C with NH3 and subsequent reaction with CO in the formation of NH2CHCO and other COMs. We applied the three-phase chemical model MAGICKAL to hot molecular core conditions from the cold-collapse through to the hot-core stage. The chemical network was extended to include NH2CHCO and a range of associated gas-phase, grain-surface, and bulk-ice products and reactions. We also approximated conditions in a shocked cloud, including sputtering of ice mantles. NH2CHCO is formed on grains at low temperatures (~10 K) with a peak solid-phase abundance of ~2x10^-10 nH. Its formation is driven by nondiffusive reactions, in particular the Eley-Rideal reaction of C with surface NH3, followed by immediate reaction with CO. Surface hydrogenation of NH2CHCO produces ethanolamine with a significant abundance of ~8x10^-8 nH. In the gas-phase, although ethanolamine reaches a modest abundance peak immediately following its desorption from grains under hot-core conditions, it is destroyed more rapidly due to its high
proton affinity. Molecular survival is much higher in the shocked regions, where these species seem most likely to be detected. NH2CHCO is produced efficiently on simulated interstellar grain surfaces, acting subsequently as an important precursor to more complex organics, including ethanolamine and glycine. Ion-molecule gas-phase destruction of NH3-bearing COMs is less efficient in shocked lower-density regions, in contrast to hot cores, enhancing their abundances and lifetimes.
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All authors Sydney A. Willis, Serge A. Krasnokutski, Nathaniel J. Morin, Robin T. Garrod
High Energy Astrophysical Phenomena
Auger@TA: In-situ Cross-Calibration of the World's Largest Cosmic Ray Observatories
Adriel G B Mocellin, J. Caraça-Valente, C. Covault et al. (+21 more)
The Pierre Auger Observatory (Auger) and the
Telescope Array (TA) are the world's two largest ultra-high-energy
cosmic ray (UHECR) observatories. They operate in the Southern and Northern hemispheres, respectively, at similar latitudes but with distinct surface detector (SD) designs. A significant challenge in studying UHECR physics across the full sky is the apparent discrepancy in flux measurements between the two experiments. This discrepancy could arise from astrophysical differences and/or systematic effects related to their detector designs and sensitivities to extensive air shower components. To address this, the Auger@TA working group aims to cross-calibrate the two observatories with a self-triggering micro-Auger array within the TA array. This micro-array consists of eight Auger Surface Detector (SD) stations equipped with Water Cherenkov Detectors (WCDs) and AugerPrime Surface Scintillator Detectors. Seven SD stations, configured with a centered-1-PMT design, are arranged in a hexagonal pattern with one station in the center, with 1.5 km spacing, mirroring the Auger layout. The eighth station, which features a standard 3-PMT Auger station, is located in conjunction with a TA detector at the center of the hexagon, forming a triplet for high-statistics and low-uncertainty cross-calibration. A custom communication system that uses readily available components enables seamless communication between stations and remote access to each station through a central computer. The micro-array is now fully deployed, and initial data-taking is about to start. This presentation will detail the instrumentation, communication systems, central data acquisition system, expected performance of the micro-array, and preliminary results as appropriate.
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All authors Adriel G B Mocellin, J. Caraça-Valente, C. Covault, E. Dalcan, T. Fujii, S. Im, R. James, J. Johnsen, K.H. Kampert, H. Kern, J.N. Matthews, E. Mayotte, S. Mayotte, X. Moskala, H. Que, J. Rautenberg, M. Roth, H. Sagawa, T. Sako, F. Sarazin, R. Sato, D. Schmidt, S.B. Thomas, G. Wörner
High Energy Astrophysical Phenomena
It's always the quiet ones: Single Degenerate Double Detonation Type Ia Supernova from Quiescent Helium Accretion
Amir Michaelis, Yael Hillman and Hagai B. Perets
We investigate a sub-Chandrasekhar mass double detonation pathway for Type Ia
supernovae arising from single degenerate helium accreting carbon-oxygen white
dwarfs. Building on our previous one dimensional study of recurrent helium novae (Hillman et al. 2025), we evolve a 0.7
solar mass white
dwarf through steady
accretion at 10^-8 Msun yr^-1 until it reaches 1.1
solar mass, yielding realistic, time evolved helium rich profiles. These profiles are mapped into FLASH simulations, incorporating
nuclear burning for helium and carbon-oxygen detonation, in multi-dimensional hydrodynamic runs. A localized, modest temperature perturbation near the base of the helium shell robustly triggers an outward helium-shell detonation. The ensuing inward propagating shock converges in the carbon-oxygen core, igniting a secondary detonation that unbinds the
star. We obtain a Ni56 yield of ~0.64
solar mass, an intermediate-mass element (Si-Ca) mass of ~0.41
solar mass, and maximum ejecta velocities approaching 22,000 km/s, values consistent with normal Type Ia
supernovae. Our results demonstrate that recurrent helium accretors, typically quiescent over long timescales, can evolve under subtle, "quiet" conditions to trigger robust double detonations, supporting their role as viable progenitors of sub-Chandrasekhar mass Type Ia
supernovae.
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Astrophysics of Galaxies
Magnetic clumping of charged dust in the dense interstellar medium
V. Vallucci-Goy, P. Hennebelle, U. Lebreuilly et al. (+1 more)
Context:
Dust grains undergo significant growth in
star-forming environments, especially in dense regions prone to gravitational collapse. Although
dust is generally assumed to represent $1 \%$ of the gas mass,
dust density variations are expected on small scales due to differential dynamics with the gas, leading to enhanced coagulation rates in regions of
dust enrichment. Aims: We aim to investigate the clumping of charged
dust in the turbulent magnetized dense regions of the interstellar medium. Methods: We develop a dusty model that goes beyond the standard non-ideal MHD and use the code {\ttfamily shark} to perform multifluid 1D simulations of a single size charged
dust species and neutral gas with large scale driven
turbulence and including ion-neutral friction. Results: We identify a mechanism similar to the parametric instability that efficiently forms
dust clumps even in presence of dissipative processes. Such strong clumping survives and is sustained when driving
turbulence, and thus high levels of
dust concentration are produced due to compressive
magnetic effects in regions of shocks.
Dust density enhancements are favored by a high transverse-to-longitudinal
magnetic ratio which is controlled by: transverse Mach number and
plasma parameter. We find that a substantial fraction of
dust experiences a density increase of more than a factor of 10 under reasonable conditions, thus promoting
dust growth. Conclusion: Our novel dusty non-ideal MHD model shows that
dust grains (main charge carriers) are subject to small-scale compressive
magnetic effects driven by a parametric instability - like mechanism in regions of shocks, and consequently experience high density enhancements in turbulent environments that go beyond those permitted by pure hydrodynamical processes, making in-situ formation of large grains (sub-mm) in protostellar envelopes a plausible scenario.
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All authors V. Vallucci-Goy, P. Hennebelle, U. Lebreuilly, G. Verrier
High Energy Astrophysical Phenomena
Illuminating gravitational wave sources with Sgr A* flares
Pau Amaro Seoane
Sagittarius A* exhibits daily energetic
flares characterized by non-thermal emission in the infrared and X-ray bands. While the underlying
accretion flow is a Radiatively Inefficient
Accretion Flow (RIAF) peaking at
radio frequencies, the mechanism powering these non-thermal transients remains debated.
Stellar dynamics predict a population of faint brown
dwarfs orbiting Sgr A*. We investigate whether the
tidal stripping of brown
dwarfs provides a viable fueling mechanism for the observed
flares. These objects are progenitors of Extremely Large Mass Ratio Inspirals (XMRIs), crucial sources of low-frequency gravitational waves for the future LISA mission. We present high-resolution hydrodynamic simulations of grazing
tidal interactions coupled with a parameterized non-thermal radiation model. We numerically model the stripping of the brown
dwarf envelope and the subsequent
accretion of this material. We demonstrate that the dynamics of the
tidal fallback and subsequent viscous
evolution naturally reproduce the fundamental temporal characteristics of observed
flares: the peak luminosity and the characteristic 1-hour duration. We show that this fueling mechanism is dynamically viable and energetically consistent, placing strong constraints on the required efficiency of the non-thermal emission process, suggesting extreme radiative inefficiency. These findings provide compelling evidence for a hidden population of brown
dwarfs in the
Galactic Center. Crucially, the observed high
flare frequency implies tight orbits characteristic of advanced inspirals. This establishes a direct link between electromagnetic transients and active gravitational wave sources, alerting the LISA consortium years in advance to the presence of specific XMRI systems promising exceptionally high signal-to-noise ratios for precision tests of general relativity.
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Astrophysics of Galaxies
Positive AGN Feedback Enhances Star Formation in Starburst Dwarf Galaxies
Tingfang Su, Suoqing Ji, Feng Yuan et al. (+2 more)
The role of active
galactic nuclei (AGN) feedback in
dwarf galaxies remains poorly understood, with conventional wisdom suggesting it primarily suppresses
star formation. Using high-resolution MACER3D simulations that directly resolve the Bondi radius, we demonstrate that AGN feedback can significantly enhance rather than suppress
star formation in starburst
dwarf galaxies. Our simulations reveal that AGN feedback increases global
star formation rates by approximately 25% when comparing our models with both AGN and
supernova feedback to those with only
supernova feedback. This enhancement occurs through AGN-driven
outflows creating compressed gas regions where efficient cooling preserves high-density gas while quickly radiating away thermal energy, creating ideal conditions for
star formation. This positive feedback mechanism operates in gas-rich starburst environments with efficient cooling and moderate AGN energy input ($\sim 10^{42}\,\mathrm{erg\,s^{-1}}$) that compresses gas without expelling it from the
galaxy. Critically, it requires both AGN and
supernova feedback working in concert: without SN feedback to regulate black hole activity, AGN
outflows become too powerful and expel gas rather than compress it. Our results align with observations of the starburst
dwarf galaxy Henize 2-10, where similar shock-compressed regions of enhanced
star formation have been observed. These findings challenge conventional understanding of AGN feedback and suggest that AGN may play a previously unrecognized role in accelerating
star formation during active phases of
dwarf galaxy evolution.
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All authors Tingfang Su, Suoqing Ji, Feng Yuan, Haojie Xia, Yuxuan Zou
Astrophysics of Galaxies
Direct Measurement of Galaxy Assembly Bias using DESI DR1 Data
Zhiwei Shao, Ying Zu, Andrés N. Salcedo et al. (+54 more)
We report the first direct measurement of
galaxy assembly bias, a critical systematic in cosmology, from the Dark Energy Spectroscopic Instrument (DESI) Bright
Galaxy Survey. We introduce a novel, cosmology-independent method to measure the
halo occupation distribution (HOD) by combining a state-of-the-art group catalog with weak gravitational
lensing. For groups binned by total luminosity, we determine the
galaxy occupation number $N_{\rm gal}$ from group-
galaxy cross-correlations, while weak
lensing constrains the average
halo mass $M_h$. Applying this to a volume-limited sample at $z{\in}[0.05,0.2]$, we measure the dependence of HOD, $N_{\rm gal}(M_h)$, on large-scale overdensity $\delta_{g}$. Focusing on the satellite
galaxies, we find an assembly bias parameter of $Q_{\rm sat}{=}0.05{\pm}0.14$, a result consistent with zero and in tension with many empirical
galaxy formation models. Our method provides a robust approach for characterizing
galaxy assembly bias to achieve precision cosmology with DESI and future Stage-V surveys.
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All authors Zhiwei Shao, Ying Zu, Andrés N. Salcedo, Jiaqi Wang, Xiaohu Yang, David H. Weinberg, Xiaoju Xu, Zhongxu Zhai, Zhuowen Zhang, J. Aguilar, S. Ahlen, D. Bianchi, D. Brooks, R. Canning, F. J. Castander, T. Claybaugh, S. Cole, A. Cuceu, A. de la Macorra, Arjun Dey, P. Doel, S. Ferraro, J. E. Forero-Romero, E. Gaztañaga, S. Gontcho A Gontcho, G. Gutierrez, K. Honscheid, C. Howlett, D. Huterer, M. Ishak, R. Joyce, T. Kisner, A. Kremin, O. Lahav, C. Lamman, M. Landriau, L. Le Guillou, M. E. Levi, M. Manera, A. Meisner, R. Miquel, J. Moustakas, S. Nadathur, N. Palanque-Delabrouille, W. J. Percival, F. Prada, I. Pérez-Ràfols, G. Rossi, L. Samushia, E. Sanchez, D. Schlegel, J. Silber, D. Sprayberry, G. Tarlé, B. A. Weaver, R. Zhou, H. Zou
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Ab uno disce omnes: Single-harmonic search for extreme mass-ratio inspirals
Lorenzo Speri, Rodrigo Tenorio, Christian Chapman-Bird et al. (+1 more)
Extreme mass-ratio inspirals (EMRIs) are one of the key sources of gravitational waves for space-based detectors such as LISA. However, their detection remains a major data analysis challenge due to the signals' complexity and length. We present a semi-coherent, time-frequency search strategy for detecting EMRI harmonics without relying on full waveform templates. We perform an injection and search campaign of single mildly-eccentric equatorial EMRIs in stationary Gaussian noise. The detection statistic is constructed solely from the EMRI frequency
evolution, which is modeled phenomenologically using a Singular Value Decomposition basis. The pipeline and the detection statistic are implemented in time-frequency, enabling efficient searches over one year of data in approximately one hour on a single GPU. The search pipeline achieves 94% detection probability at $\mathrm{SNR} = 30$ for a false-alarm probability of $10^{-2}$, recovering the frequency
evolution of the dominant harmonic to 1% relative error. By mapping the EMRI parameters consistent with the recovered frequency
evolution, we show that the semi-coherent detection statistic enables a sub-percent precision estimation of the EMRI intrinsic parameters. These results establish a computationally efficient framework for constructing EMRI proposals for the LISA global fit.
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All authors Lorenzo Speri, Rodrigo Tenorio, Christian Chapman-Bird, Davide Gerosa
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ex
SENSEI: A Search for Diurnal Modulation in sub-GeV Dark Matter Scattering
Itay M. Bloch, Ana M. Botti, Mariano Cababie et al. (+28 more)
Dark matter particles with sufficiently large interactions with ordinary matter can scatter in the Earth's atmosphere and crust before reaching an underground detector. This Earth-shielding effect can induce a directional dependence in the dark matter flux, leading to a sidereal daily modulation in the signal rate. We perform a search for such a modulation using data from the SENSEI experiment, targeting MeV-scale dark matter. We achieve an order-of-magnitude improvement in sensitivity over previous direct-detection bounds for dark-matter masses below 1 MeV, assuming the Standard
Halo Model with a Maxwell–Boltzmann velocity distribution, and constrain the amplitude of a general daily modulation signal to be below 6.8 electrons per gram per day.
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All authors Itay M. Bloch, Ana M. Botti, Mariano Cababie, Gustavo Cancelo, Brenda A. Cervantes-Vergara, Miguel Daal, Ansh Desai, Alex Drlica-Wagner, Rouven Essig, Juan Estrada, Erez Etzion, Guillermo Fernandez Moroni, Stephen E. Holland, Jonathan Kehat, Ian Lawson, Steffon Luoma, Aviv Orly, Santiago E. Perez, Dario Rodrigues, Nathan A. Saffold, Silvia Scorza, Miguel Sofo-Haro, Kelly Stifter, Javier Tiffenberg, Sho Uemura, Edgar Marrufo Villalpando, Tomer Volansky, Federico Winkel, Yikai Wu, Tien-Tien Yu, Xavier Bertou
Cosmology and Nongalactic Astrophysics
Swampland Conjectures through ACT Observations: Observational Signatures of Radiative-Corrected Inflation
Mohammad Ali S Afshar, Saeed Noori Gashti, Mohammad Reza Alipour et al. (+3 more)
We investigate the consistency of radiatively corrected inflationary models with both the latest observational data from the Atacama Cosmology
Telescope (ACT) combined with Planck 2018 and
Baryon Acoustic Oscillation (BAO) measurements, and the theoretical constraints imposed by the swampland program. We systematically test two distinct models against three key swampland
conjectures: the further refined de Sitter swampland
conjecture (FRDSSC), the scalar weak
gravity conjecture (SWGC), and the strong scalar weak
gravity conjecture (SSWGC). Model I, based on radiatively corrected
Higgs inflation, satisfies the FRDSSC and remains consistent with current observational constraints ($n_s = 0.9743 \pm 0.0034$, $r < 0.038$), but fails to meet the SWGC and SSWGC requirements, indicating limited theoretical compatibility with
quantum gravity principles. In contrast, Model II, incorporating radiative corrections with scalar sectors, demonstrates full consistency by satisfying all three swampland
conjectures simultaneously while maintaining observational viability. The compatibility of Model II is highly sensitive to the non-minimal coupling $\xi$ and renormalization scales $\mu_b$, with larger values extending the range of swampland-consistent solutions. Our results highlight the critical role of radiative corrections in achieving simultaneous theoretical and observational consistency, and identify Model II as a promising candidate for a fully viable inflationary scenario within the swampland framework. This work provides a methodology for classifying inflationary models based on their swampland compatibility, demonstrating that satisfaction of the FRDSSC alone is insufficient for full theoretical consistency.
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All authors Mohammad Ali S Afshar, Saeed Noori Gashti, Mohammad Reza Alipour, Behnam Pourhassan, Izzet Sakalli, Jafar Sadeghi
Instrumentation and Methods for Astrophysics
pyROX: Rapid Opacity X-sections
Sam de Regt, Siddharth Gandhi, Louis Siebenaler et al. (+1 more)
In recent years, significant advances have been made in
exoplanet and brown
dwarf observations. By using state-of-the-art models, astronomers can determine properties of their atmospheres, such as temperatures, the presence of clouds, or the chemical abundances of molecules and atoms. Accurate and up-to-date opacities are crucial to avoid inconclusive or biased results, but it can be challenging to compute opacity cross-sections from the line lists provided by various online databases. We introduce pyROX, an easy-to-use Python package to calculate molecular and atomic cross-sections. Since pyROX works on CPUs, it can compute a small line list on a regular workstation, but it is also easily parallelised on a cluster for larger line lists. In addition to line opacities, pyROX also supports calculations of collision-induced absorption. Tutorials are provided in the online documentation which explain the configuration parameters and different functionalities of pyROX.
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All authors Sam de Regt, Siddharth Gandhi, Louis Siebenaler, Darío González Picos
Solar and Stellar Astrophysics
Doubling the Number of Blue Large-Amplitude Pulsators: Final Results of Searches for BLAPs in the OGLE Inner Galactic Bulge Fields
J. Borowicz, P. Pietrukowicz, J. Skowron et al. (+13 more)
Blue Large-Amplitude Pulsators (BLAPs) are rare short-period ($\lesssim$80 min) pulsating variable
stars exhibiting large-amplitude brightness variations (typically between 0.1 and 0.4 mag). As a recently discovered class of radial-mode pulsators, the origin and nature of these variables remain the subject of ongoing investigations. Here, we present a comprehensive summary of all BLAPs identified in the data of the Optical Gravitational
Lensing Experiment (OGLE), including the discovery of 88 new BLAPs in the inner
Galactic bulge fields. We performed a systematic search for periodic signals in the $I$-band light curves of more than 400 million
stars with magnitudes down to $I = 21$. Our search effectively doubles the number of these variables to almost 200. The detected BLAPs exhibit pulsation periods between roughly 5 and 76 minutes. The analyzed
dataset covers a timespan from 2001 to 2024, with some
stars observed up to 20,000 times, providing the temporal coverage needed to study period and amplitude variations. We report on three objects that show enormous period changes, at a rate of $10^{-5}$ yr$^{-1}$, which could provide important clues to the evolutionary status of BLAPs. Full
dataset is incorporated into the publicly available OGLE Collection of Variable
Stars (OCVS), enabling future studies of these enigmatic objects.
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All authors J. Borowicz, P. Pietrukowicz, J. Skowron, M.J. Mróz, A. Udalski, M.K. Szymański, I. Soszyński, K. Ulaczyk, R. Poleski, S. Kozłowski, P. Mróz, D.M. Skowron, K. Rybicki, P. Iwanek, M. Wrona, M. Gromadzki
Cosmology and Nongalactic Astrophysics
Efficient analytic approximation for small-scale non-cold relic perturbations
Nanoom Lee, Yacine Ali-Haïmoud and Marc Kamionkowski
We develop a highly accurate analytic approximation for small-scale non-cold relic perturbations by solving the collisionless Boltzmann equation in the quasi-stationary regime. The approximation is implemented in CLASSIER (CLASS Integral Equation Revision), a modified version of the Boltzmann solver CLASS that replaces the traditional truncated Boltzmann hierarchy of non-cold relic multipoles with a small set of integral equations solved iteratively. Applying it to massive
neutrinos yields a factor-of-two reduction in total runtime relative to CLASSIER without the approximation. Compared to standard CLASS runs (with $\ell_{\rm max}^{\rm NCDM}=40$ and no late-time massive
neutrino fluid approximation) under the same precision setting, CLASSIER with this approximation is faster by a factor of 3-6. The approximation faithfully reproduces the late-time behavior of massive
neutrino perturbations and preserves sub-$0.1\%$ accuracy in the matter power spectrum today up to comoving wavenumber $k=100\,{\rm Mpc}^{-1}$. With this approximation, massive-
neutrino perturbations are no longer the computational bottleneck on small scales for linear-theory predictions. The approach can be readily extendable to non-standard dark-matter models, and offers prospects for further efficiency gains in high-precision cosmological analyses.
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High Energy Astrophysical Phenomena
Simulation-calibrated Bayesian inference for progenitor properties of the microquasar SS 433
Nathan Steinle, Matthew Mould, Sarah Al-Humaikani et al. (+3 more)
SS$\,$433 is one of the most extreme
Galactic X-ray binaries, launching semi-relativistic jets and showing clear signs of super-critical
accretion onto what is likely a black hole. Yet the properties of the binary system that produced it remain uncertain. To solve the inverse problem of inferring the progenitor properties of binaries that evolve into SS$\,$433-like systems, we use an iterative, simulation-based calibration framework that combines
Bayesian inference with the isolated binary-
evolution code
COSMIC. Using six measured properties of SS$\,$433 and the dynamic nested sampler $\texttt{dynesty}$, we explore a ten-dimensional space of possible progenitor masses, orbits, mass-transfer histories, and natal-kick velocities. This approach identifies the regions of parameter space most consistent with SS$\,$433 and allows us to iteratively refine the resulting progenitor distributions. We find 90% confidence intervals for the progenitor initial primary mass of (8, 11) M$_\odot$, secondary mass of (32, 40) M$_\odot$, orbital period of (136, 2259) days, eccentricity of (0.26, 0.6), common-envelope efficiency of (0.44, 0.76), accreted fraction during stable mass transfer of (0.22, 0.6), and black-hole natal-kick magnitude of (5, 68) km/s. These results show that direct probabilistic inference of X-ray binary progenitors can yield new constraints on the formation of extreme
accretion systems like SS$\,$433, which has important implications for theoretical expectations of the population of SS$\,$433-like systems in the
Galaxy and their connection with
cosmic ray observations.
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All authors Nathan Steinle, Matthew Mould, Sarah Al-Humaikani, Austin MacMaster, Brydyn Mac Intyre, Samar Safi-Harb
Astrophysics of Galaxies
Testing the AGN Paradigm, Part I: a generic SED for Seyfert 1 galaxies
Paulina Alejandra Roco-Avilez, Roger Coziol, Juan Pablo Torres-Papaqui et al. (+4 more)
This article presents the first part of a study aimed at testing the unification paradigm for AGN (UPAGN) using the SED reconstruction code X-CIGALE. Our method consists in obtaining a generic SED for a large sample of Seyfert 1 (Sy1; part 1), then applying this SED to Seyfert 2 (Sy2; Part~II), expecting that the only difference will be the line-of-sight (LOS) angle, $i$, relative to the polar axis of the
torus of gas and
dust obscuring the broad line regions (BLRs). Our sample is composed of 3,896 Type 1, Sy1 at low
redshifts, $ z<0.4$, separated into four spectral subgroups depending on the presence or absence in their spectra of narrow emission lines, Sy1N/Sy1B, and AGN wind, Sy1Bw and Sy1Nw. The generic SED produced by X-CIGALE applies to 90% of the Sy1 in our sample. It includes a clumpy
torus with an AGN engine seen face-on ($i \sim 10^\circ \pm 5^\circ$). Our analysis not only supports the existence of a
torus in Sy1, in good agreement with UPAGN, but also reveals new facts about the
accretion of matter and AGN wind: 1- a sudden
accretion of matter from the BLR to the
accretion disk triggered the wind, 2- matter from the wind replenishes the
torus, consistent with a gradual formation of this structure by recurrent AGN winds, and 3- Sy1Bw and Sy1Nw eventually evolve as AGN without wind, leaving behind a
torus as evidence of a higher AGN activity in their past.
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All authors Paulina Alejandra Roco-Avilez, Roger Coziol, Juan Pablo Torres-Papaqui, Karla Alejandra Cutiva-Alvarez, María Fernanda La Rotta-Wilches, César David Aguirre-Gutierrez, Angélica Gabriela Sandoval-Esparza
Cosmology and Nongalactic Astrophysics
Bayesian Inference of Primordial Magnetic Field Parameters from CMB with Spherical Graph Neural Networks
Juan Alejandro Pinto Castro, Héctor J. Hortúa, Jorge Enrique García-Farieta et al. (+1 more)
Deep learning has emerged as a transformative methodology in modern cosmology, providing powerful tools to extract meaningful physical information from complex astronomical
datasets. This paper implements a novel
Bayesian graph deep learning framework for estimating key cosmological parameters in a
primordial magnetic field (PMF) cosmology directly from simulated
Cosmic Microwave Background (CMB) maps. Our methodology utilizes DeepSphere, a spherical convolutional neural network architecture specifically designed to respect the spherical geometry of CMB data through HEALPix pixelization. To advance beyond deterministic point estimates and enable robust uncertainty quantification, we integrate
Bayesian Neural Networks (BNNs) into the framework, capturing aleatoric and epistemic uncertainties that reflect the model confidence in its predictions. The proposed approach demonstrates exceptional performance, achieving $R^{2}$ scores exceeding 0.89 for the
magnetic parameter estimation. We further obtain well-calibrated uncertainty estimates through post-hoc training techniques including Variance Scaling and GPNormal. This integrated DeepSphere-BNNs framework not only delivers accurate parameter estimation from CMB maps with PMF contributions but also provides reliable uncertainty quantification, providing the necessary tools for robust cosmological inference in the era of precision cosmology.
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All authors Juan Alejandro Pinto Castro, Héctor J. Hortúa, Jorge Enrique García-Farieta, Roger Anderson Hurtado
Cosmology and Nongalactic Astrophysics
Addressing Synchrotron Challenges for CMB Observations: ELFS-SA Collaboration for Robust Foreground Removal
E. de la Hoz, A. Mennella, K. Arnold et al. (+17 more)
Upcoming
cosmic microwave background (CMB) experiments aim to detect
primordial gravitational waves with unprecedented sensitivity. Effective foreground removal is essential to avoid biases in the measurement of the tensor-to-scalar ratio ($r$) in this high-precision regime. Recent analyses highlight the unexpected complexity of synchrotron emission at low frequencies, underscoring the need for more sensitive low-frequency data. To address this challenge, the European Low-Frequency Survey (ELFS) initiative and the Simons Array collaboration propose installing two European low-frequency receivers on one of the Simons Array
telescopes. These receivers will enable measurements in the Southern Hemisphere between $6$ and $20$,GHz, complementary to those of current and proposed experiments targeting the measurement of cosmological gravitational waves. In this work, we study the benefits of combining these low-frequency observations with a representative future CMB experiment operating from the Southern Hemisphere. We find that the extra information can improve the knowledge of the underlying synchrotron spectral energy distribution (SED), with positive impacts on the robustness of measurement of the tensor-to-scalar ratio, $r$, against the complexity of low-frequency foregrounds.
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All authors E. de la Hoz, A. Mennella, K. Arnold, C. Baccigalupi, A. J. Banday, R. B. Barreiro, D. Barron, M. Bersanelli, F. J. Casas, S. Casey, C. Franceschet, M. E. Jones, R. T. Genóva-Santos, R. Hoyland, A. T. Lee, E. Martinez-Gonzalez, F. Montonati, J.-A. Rubiño-Martín, A. C. Taylor, P. Vielva
High Energy Astrophysical Phenomena
A Microphysical Probe of Neutron Star Interiors: Constraining the Equation of State with Glitch Dynamics
Zhonghao Tu and Ang Li
Glitches in
neutron stars originate from the sudden transfer of angular momentum between superfluid components and the observable crust. By modeling this glitch dynamics–including
vortex motion, mutual friction, and angular momentum exchange–one may hope to probe the dense matter equation of state. In this work, we explore, within a highly idealized three-component framework, whether the glitch rise could in principle carry information about microphysical inputs such as entrainment and mutual friction. We compute the glitch rise in response to self-consistently calculated microphysical parameters (pinning and mutual friction) based on unified equations of state, and compare theoretical predictions of the overshoot patterns and timing residuals to the 2016 Vela glitch. Within this specific framework, the models favor crustal superfluid coupling on timescales of order $\sim100$ s, overshoot behavior in the core associated with relatively strong central mutual friction, and rise times consistent with the observed upper limit of 12.6 s. Using a Markov Chain Monte Carlo analysis of the timing residuals, we then map the regions of parameter space that are compatible with the data under our adopted assumptions. Our analysis favors comparatively weak entrainment in the inner crust and an overall core mutual friction that is weaker than that in the inner crust. These exploratory results demonstrate that, under such restrictive assumptions, glitch-rise morphology is sensitive to microphysical inputs and that future high-cadence timing observations, interpreted with more realistic dynamical models, could potentially help constrain the internal dynamics and composition of
neutron stars.
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Cosmology and Nongalactic Astrophysics
Debiasing cosmological parameters from large-scale foreground contamination in Cosmic Microwave Background data
Alessandro Carones
Current and future
Cosmic Microwave Background (CMB) experiments aim to achieve high-precision reconstruction of the CMB polarization signal, with the most ambitious objective being the detection of
primordial $B$ modes sourced by
cosmic inflation. Given the expected low amplitude of the signal, its estimate-parametrized by the tensor-to-scalar ratio $r$-is highly susceptible to contamination from
Galactic foreground residuals that remain after component separation. In this work, we introduce a model-independent procedure to construct a spectral template of residual foreground contamination in the observed angular power spectrum. Specifically, a cleaned multifrequency set of foreground-emission maps is blindly reconstructed from the observed data using the Generalized Needlet Internal Linear Combination (GNILC) technique. These maps are then combined with the weights adopted for CMB reconstruction, yielding an estimate of the spatial distribution of foreground residuals after component separation. The power spectrum of this estimated residual map is incorporated into the spectral model of the cosmological likelihood. We validate the proposed method using realistic simulations of a LiteBIRD-like experiment processed with two Internal Linear Combination (ILC) component-separation techniques, focusing on constraints on the tensor-to-scalar ratio. When the foreground contribution is not included in the model, the resulting $r$ posteriors are biased, irrespective of its input value, the assumed foreground model, or the adopted masking strategy. Conversely, when the residual template is included in the likelihood, the analysis yields unbiased estimates of $r$ for all considered cases, thereby demonstrating the robustness of the proposed procedure. The pipeline has been made publicly available as part of the BROOM Python package (https://github.com/alecarones/broom).
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Cosmology and Nongalactic Astrophysics
Lens Model Accuracy in the Expected LSST Lensed AGN Sample
Padmavathi Venkatraman, Sydney Erickson, Phil Marshall et al. (+13 more)
Strong gravitational
lensing of active
galactic nuclei (AGN) enables measurements of cosmological parameters through time-delay cosmography (TDC). With data from the upcoming LSST survey, we anticipate using a sample of O(1000) lensed AGN for TDC. To prepare for this
dataset and enable this measurement, we construct and analyze a realistic mock sample of 1300 systems drawn from the OM10 (Oguri & Marshall 2010) catalog of simulated lenses with AGN sources at $z<3.1$ in order to test a key aspect of the analysis pipeline, that of the lens modeling. We realize the lenses as power law elliptical mass distributions and simulate 5-year LSST i-band coadd images. From every image, we infer the lens mass model parameters using neural posterior estimation (NPE). Focusing on the key model parameters, $\theta_E$ (the Einstein Radius) and $\gamma_{lens}$ (the projected mass density profile slope), with consistent mass-light ellipticity correlations in test and training data, we recover $\theta_E$ with less than 1% bias per lens, 6.5% precision per lens and $\gamma_{lens}$ with less than 3% bias per lens, 8% precision per lens. We find that lens light subtraction prior to modeling is only useful when applied to data sampled from the training prior. If emulated deconvolution is applied to the data prior to modeling, precision improves across all parameters by a factor of 2. Finally, we combine the inferred lens mass models using
Bayesian Hierarchical Inference to recover the global properties of the lens sample with less than 1% bias.
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All authors Padmavathi Venkatraman, Sydney Erickson, Phil Marshall, Martin Millon, Philip Holloway, Simon Birrer, Steven Dillmann, Xiangyu Huang, Sreevani Jaragula, Ralf Kaehler, Narayan Khadka, Grzegorz Madejski, Ayan Mitra, Kevin Reil, Aaron Roodman, the LSST Dark Energy Science Collaboration
High Energy Astrophysical Phenomena
The Opacity Project: R-Matrix Calculations for Opacities of High-Energy-Density Astrophysical and Laboratory Plasmas
Anil K. Pradhan and Sultana N. Nahar
Accurate determination of opacity is critical for understanding radiation transport in both astrophysical and laboratory
plasmas. We employ atomic data from R-
Matrix calculations to investigate radiative properties in high-energy-density (HED)
plasma sources. Specifically, we analyze environments such as the base of the convective zone (BCZ) of the Sun 2 x 10^6$ K, N_e = 10^{23}/cc and the inertial confinement fusion (ICF) device at the Sandia Z facility 2.11 x 10^6 K, N_e = 3.16 x 10^{22}/cc. We calculate Rosseland Mean Opacities (RMO) within a range of temperatures and densities and analyze how they vary under different
plasma conditions. In this study, we specifically focus on electron collisional and Stark ion microfield broadening effects on autoionizing resonances in photoabsorption cross sections. Our results are relevant to astrophysical models, particularly in the context of the
solar opacity problem, and provide insights into discrepancies between theoretical calculations and experimental measurements. In addition, we investigate the equation-of-state (EOS) and its impact on opacities. In addition, we examine the equation-of-state (EOS) and its impact on opacities of the "chemical picture" Mihalas-Hummer-Dappen EOS with respect to level populations of excited levels included in the R-
matrix calculations. This study should contribute to improving opacity models of HED sources such as
stellar interiors adn laboratory fusion
plasma experiments.
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High Energy Astrophysical Phenomena
Multi-messenger constraints on LIGO/Virgo/KAGRA gravitational wave binary black holes merging in AGN disks
Tomás Cabrera, Antonella Palmese and Maya Fishbach
While the LIGO/Virgo/KAGRA (LVK) gravitational wave (GW) detectors have detected over 300 binary black hole (BBH) mergers to date, the first confirmation of an electromagnetic (EM) counterpart to such an event remains elusive. Previous works have performed searches for counterpart candidates in transient catalogs and have identified active
galactic nuclei (AGN)
flares coincident with GW events; existing theory predicts that such
flares may arise from the interaction of the merger remnant with the
embedding accretion disk environment. We apply a statistical formalism to measure the significance of coincidence for the catalog as a whole, measuring that less than 3% (90% credible interval) of LVK BBH mergers give rise to observable AGN
flares. This result still allows up to $\sim 40\%$ of BBH mergers to originate in AGN disks. We also examine the individual coincidences of each merger/
flare pairing, determining that in all cases the
flares are more likely to belong to a background population of
flares not associated with GW events. Our results are consistent with theoretical predictions accounting for the observability of EM counterparts in AGN disks, as well as based on the fact that the most massive/luminous AGNs (such as those included in the search) are not expected to harbor the majority of the BBHs. We emphasize that developing both the means to distinguish BBH counterpart
flares from background AGN
flares and an understanding of which BBHs are most likely to produce AGN
flares as counterparts is critical to optimize the use of follow-up resources.
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Astrophysics of Galaxies
Black Hole-Host Galaxy Correlations with Machine Learning: A Comparative Study of Illustris, TNG, and EAGLE
Jacob Reinheimer, Yuan Li, Trung Ha et al. (+3 more)
Supermassive black holes (SMBHs) are known to correlate with many properties of their host
galaxies, but we do not fully understand these correlations. The strengths (tightness) of these correlations have also been widely debated. In this work, we explore SMBH-host relations in three state-of-the-art cosmological simulations: Illustris, TNG, and EAGLE. Using a variety of machine learning regressors, we measure the scaling relations between black hole mass ($M_{\rm BH}$) and
galaxy properties including
stellar velocity dispersion ($\sigma$),
stellar mass ($M_{\star}$), dark matter
halo mass ($M_{\rm Halo}$), and the Sersic index. We find that machine learning regressors provide predictive capabilities superior to linear regression in many scaling relations in simulations, and Multi-layer Perceptron (MLP) regressor has the strongest performance. SMBH-host relations have different strengths in different simulations as a result of their sub-grid models. Similar to the observations, the $M_{\rm BH} $-$\sigma$ relation is a strong correlation in all simulations, but in TNG, the $M_{\rm BH} $-$M_{\star}$ relation is even tighter than $M_{\rm BH} $-$\sigma$. EAGLE produces the weakest SMBH-host correlations among all simulations. Low mass SMBHs tend to be poorly correlated with their host
galaxies, but including them can still help machines better grasp the correlations in Illustris and TNG. Combining
galaxy properties that strongly correlate with $M_{\rm BH} $ but poorly correlate with each other can improve MLP's performance. $M_{\rm BH} $ is most accurately predicted when all
galaxy properties are included in the training, suggesting that SMBH-host correlations are fundamentally multi-dimensional in these simulations.
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All authors Jacob Reinheimer, Yuan Li, Trung Ha, Melanie Habouzit, Brandon M. Matthews, George Blaney
Earth and Planetary Astrophysics
Early Evidence for Polar Orbits of Sub-Saturns Around Hot Stars
Emma Dugan, Xian-Yu Wang, Agustin Heron et al. (+4 more)
Sub-Saturns have been reported to preferentially occupy near-polar orbits, but this conclusion has so far been based primarily on systems with cool host
stars; obliquity measurements for sub-Saturns orbiting hot
stars remain scarce. Expanding the census into the hot-
star regime is essential to test whether the polar preference persists across the Kraft break and to diagnose the underlying excitation mechanisms. In this work, we present Rossiter-McLaughlin observations of TOI-1135 b, a sub-Saturn orbiting a hot
star with $T_{\rm eff}=6320\pm120$ K, using WIYN/NEID. We confirm its near-polar architecture, measuring a sky-projected obliquity of $\lambda=-68.1^{+7.5}_{-5.3}$ degrees and a true obliquity of $\psi=72.2^{+6.4}_{-6.6}$ degrees. Coupling our new measurement with
stellar-obliquity data from the literature, we find that sub-Saturns and hot Jupiters around cool
stars are unlikely to be drawn from the same parent distribution at the $5.2\sigma$ level, consistent with weaker
tidal realignment induced by lower-mass
planets. Of the two known misaligned sub-Saturns around hot
stars, both are near-polar, suggesting that the polar preference may extend above the Kraft break. Moreover, their obliquities lie near $\sim 65$ degrees, supporting predictions from secular resonance crossing for sub-Saturns around rapidly rotating hot
stars.
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All authors Emma Dugan, Xian-Yu Wang, Agustin Heron, Hareesh Gautham Bhaskar, Malena Rice, Cristobal Petrovich, Songhu Wang
Cosmology and Nongalactic Astrophysics
Iskay2: Signal Extraction of the Kinematic Sunyaev-Zel'dovich Effect Through The Pairwise Estimator. Pipeline and Validation
Patricio A. Gallardo, Yulin Gong, Boryana Hadzhiyska et al. (+1 more)
The peculiar motions of massive
halos probe the distribution of matter in the universe, the gravitational potential, and the history of
cosmic structure growth. The kinematic Sunyaev-Zeldovich (kSZ) effect offers a robust observational window into these properties. The pairwise kSZ
estimator probes the pairwise momentum of groups of
galaxies by cross-correlating
cosmic microwave background (CMB) maps with spectroscopic
galaxy catalogs, using
galaxies to trace the positions of dark matter
halos. This note introduces iskay2, an efficient pipeline designed to apply the pairwise kSZ
estimator to maps of the CMB and large
galaxy catalogs. Pairwise kSZ measurements obtained using this pipeline are compared to previously published results and are shown to be consistent within statistical expectations. This pipeline will enable high-precision measurements of the pairwise kSZ utilizing
galaxy catalogs like DESI combined with past, current and next-generation high-resolution CMB experiments such as ACT, SPT and the Simons Observatory.
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All authors Patricio A. Gallardo, Yulin Gong, Boryana Hadzhiyska, Yun-Hsin Hsu
Cosmology and Nongalactic Astrophysics
Measuring cosmic dipole with the GRB luminosity-time relation
Jessica Santiago, Kerkyra Asvesta, Maria Giovanna Dainotti et al. (+1 more)
We present a new analysis of
cosmic dipole anisotropy using gamma-ray bursts (GRBs) as high-
redshift standardizable candles. GRBs are ideal probes for testing the cosmological principle thanks to their high luminosity, wide
redshift range, and nearly isotropic sky coverage. For the first time, we employ the luminosity-time (L-T) relation, known in the literature as the bidimensional X-ray Dainotti relation, corrected for
redshift evolution, to standardize a sample of 176 long GRBs detected by Swift. We test for dipolar modulations in the GRB Hubble diagram using both the Dipole Fit Method and a new approach introduced here, the Anisotropic Residual Analysis Method. Both methods yield consistent results: a dipole amplitude of $A_d \simeq 0.6 \pm 0.2$ pointing towards (RA, DEC) $\approx (134^\circ \pm 30^{\circ}, -36^\circ \pm 21^{\circ})$ (equatorial coordinates). As shown in the Appendix, this corresponds to a boost velocity of the observer with respect to the GRB rest-frame in the antipodal direction from the dipole direction. Extensive isotropy tests and 20,000 Monte Carlo simulations confirm that the detected signal cannot be explained by chance
alignments or by the angular distribution of the GRB sample. We also show how, by incorporating a dipole term, residual correlations are eliminated, showing that the dipole model provides a better fit than standard isotropic $\Lambda$CDM.
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All authors Jessica Santiago, Kerkyra Asvesta, Maria Giovanna Dainotti, Pisin Chen
Astrophysics of Galaxies
Observationally derived change in the star formation rate as mergers progress
W. J. Pearson, L. Wang, V. Rodriguez-Gomez et al. (+2 more)
Galaxy mergers can change the rate at which
stars are formed. We can trace when these changes occur in simulations of
galaxy mergers. However, for observed
galaxies we do not know how the
star formation rate (SFR) evolves along the merger sequence as it is difficult to probe the time before or after coalescence. We aim to derive how SFR changes in observed mergers throughout the merger sequence, from a statistical perspective. Merger times were estimated for observed
galaxy mergers in the Kilo Degree Survey (KiDS) using a convolutional neural network (CNN). The CNN was trained on mock KiDS images created using IllustrisTNG data. The SFRs were derived from spectral energy density fitting to KiDS and VIKINGs data. To determine the change in SFR for the merging
galaxies, each merging
galaxy was matched and compared to ten comparable non-merging
galaxies; matching each
galaxy in
redshift,
stellar mass, and local density. Mergers see an increase in the SFR for
galaxies from 300~Myr before the merger until coalescence, continuing until at least 200~Myr after the merger event. After this, there is a possibility that SFR activity in the mergers begins to decrease, but we need more data to better constrain our merger times and SFRs to confirm this. We find that more
galaxies with higher
stellar mass (M$_{\star}$) have greater SFR enhancement as they merge compared to lower-M$_{\star}$
galaxies. There is no clear trend of changing SFR enhancement as local density changes, but the least dense environments have the least SFR enhancement. The increasing SFR enhancement is likely due to the closer proximity of
galaxies and the presence of more close passes as the time before the merger approaches 0~Myr, with the SFR slowing 200~Myr after the merger event.
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All authors W. J. Pearson, L. Wang, V. Rodriguez-Gomez, B. Margalef-Bentabol, L. E. Suelves