Peer Revenue Returns subject to peer review

Papers

Fresh from arXiv, typeset properly. Highlighted words trade on the market.

Physics Astrophysics

astro-ph Watch Astrophysics

Tuesday 28 July

Astrophysics of Galaxies

ATLAS. II. Extremely High Incidence of Balmer Line Absorption with Predominant Blueshifts in LRDs: Statistical Insights through Comparison with Type 1 AGNs

Hiroto Yanagisawa, Masami Ouchi, Tomokazu Kiyota et al. (+6 more)

We present the statistical properties of H$\alpha$ and H$\beta$ line absorption in little red dots (LRDs) at $z\simeq2.5$–7.2 using archival JWST/NIRSpec spectra from the DAWN JWST Archive and complementary NIRSpec/IFU observations. Among 40 LRDs with broad H$\alpha$ and [O~iii] obtained with medium- or high-resolution gratings, 14 objects exhibit H$\alpha$ absorption. We find that the incidence of Balmer line absorption is $\sim35$% ($=14/40$), significantly higher than that in SDSS low-$z$ type 1 AGNs ($\sim0.04$%), demonstrating that Balmer line absorption occurs approximately 850 times more frequently in LRDs than in type 1 AGNs. We combine our 14 detections with 32 additional LRD Balmer absorbers from the literature, yielding a census of 46 absorbers. Their velocities span $\Delta v_\mathrm{abs}(\mathrm{H\alpha})\sim-430$ to $+140\ {\rm km\,s^{-1}}$, markedly narrower than the $-800$ to $+1600\ {\rm km\,s^{-1}}$ range of Balmer absorption in SDSS type~1 AGNs, for which our simulations confirm that the velocity difference is too large to be explained by detection incompleteness. The lower absolute absorber velocities in LRDs may partly reflect the shallower gravitational potential at their characteristic BLR radii. We also find that 38 of the 46 absorbers (83%) are blueshifted, with only eight redshifted, indicating that most of Balmer absorbers are moving outward. An analytic model with radiation pressure suggests that most absorbers with $N_{\rm H}\gtrsim10^{24}\ {\rm cm^{-2}}$ remains gravitationally bound. The smaller number of redshifted (i.e., infalling) absorbers may indicate that outbound absorbers lose density: some return to the BLR, whereas others undergo stronger radiative acceleration and escape.
Read the full abstract

All authors Hiroto Yanagisawa, Masami Ouchi, Tomokazu Kiyota, Makoto Ando, Yuichi Harikane, Yuta Kageura, Minami Nakane, Yoshiaki Ono, Yui Takeda

Solar and Stellar Astrophysics

Asteroseismic study of KUV03442+0719 with parallax constraints

Agnès Bischoff-Kim

Hydrogen atmosphere white dwarf KUV03442+0719 was first reported as a pulsator by Gianninas et al. in 2006. Follow up campaigns by Su et al. (2014) revealed more periods. Some spectroscopic results suggest that KUV03442+0719 has a slightly below average mass and an effective temperature of 11000 K. But Gaia data (parallax and magnitude) suggest that it may be a low mass white dwarf. Such an object would have a helium core. We perform the asteroseismic fitting of KUV03442+0719, modeling it both as a carbon/oxygen normal mass white dwarf, and a helium core, low mass white dwarf. To perform the study, we perfom a grid search with WDEC models, refined by simplex minimization of the best fits. Both analyses result in best fit models that are comparable in terms of quality of fit. More pulsation data would be required to allow us to distinguish between the two scenarios. We present and constrast our results with expectations from stellar evolution. We also provide analytic formulae for a temperature dependent mass-radius relationship for helium core white dwarfs.
Read the full abstract

Astrophysics of Galaxies

Tracing the Cosmic web across Cosmic time through SKA observations of radio galaxies

Pratik Dabhade, Gianluca Castignani, Mousumi Mahato et al. (+4 more)

The Square Kilometre Array will transform studies of the cosmic web by tracing radio galaxies (RGs) and star-forming systems across cosmic time with unprecedented sensitivity, angular resolution, frequency coverage, and survey speed. Powered by accreting supermassive black holes, RGs are not only signposts of AGN feedback but also incisive probes of their environments, from dense clusters to the low-density intergalactic medium. Their lobes, magnetic fields, and energy outflows encode the thermal and non-thermal histories of the surrounding gas, offering diagnostics of IGM pressure, particle ageing, and magnetisation over megaparsec scales. With its broad frequency coverage (50 MHz-15 GHz), microJy to sub-microJy continuum sensitivity, and wide field of view, the SKA will detect vast radio-source populations across broad ranges of redshift and environment. Measurements of source size, morphology, spectral ageing, radio power, polarisation, and Faraday rotation will reveal how the environment regulates jet propagation and lobe evolution, how radio plasma heats and magnetises the intracluster and intergalactic media, and how early AGN activity influences galaxy growth and star formation in protoclusters. Combined with host identifications, spectroscopic redshifts, and optical, infrared, X-ray, Sunyaev–Zel'dovich, and cosmic-web catalogues, SKA observations will place RGs within their three-dimensional large-scale environments. This chapter presents a framework for using RGs to trace and probe the cosmic web, from nearby filaments and clusters to high-redshift protoclusters, and to test how environment, magnetic fields, feedback, and gas dynamics shape radio-galaxy evolution, protocluster assembly, and star formation across cosmic time.
Read the full abstract

All authors Pratik Dabhade, Gianluca Castignani, Mousumi Mahato, Shishir Sankhyayan, D.J. Saikia, Viviana Casasola, Francoise Combes

Instrumentation and Methods for Astrophysics

ForMoSA: Forward Modeling tool for Spectral Analysis

ForMoSA Collaboration, Simon Petrus, Paulina Palma-Bifani et al. (+9 more)

ForMoSA (FORward MOdeling tool for Spectral Analysis) is an open-source Python package to fit spectroscopic and photometric observations using a Bayesian framework. It can utilize different self-consistent atmospheric models to perform robust parameter space exploration. It has been mainly designed for fitting directly imaged young planetary-mass brown dwarfs and exoplanets. The developments within ForMoSA are supported by an international collaboration of several laboratories in France (IPAG, LIRA, LAM, and Lagrange), Germany (MPIA), USA (NASA Goddard), and Chile (FCLA, Universidad Diego Portales, and Universidad de Chile). The evolution of the code and the growing interest from the scientific community has led to the need for this dedicated publication alongside the release of ForMoSA v2.0, which has been refactored into a class architecture with user-friendly features and extended functionalities.
Read the full abstract

All authors ForMoSA Collaboration, Simon Petrus, Paulina Palma-Bifani, Matthieu Ravet, Allan Denis, Bhavesh Rajpoot, Mickaël Bonnefoy, Gaël Chauvin, Arthur Vigan, Alice Radcliffe, Pablo Requeijo, Kevin Hoy

Astrophysics of Galaxies

Binary disruptions driven by massive disks around massive black holes

Mark Dodici

Accretion disks around massive black holes (MBHs) in galactic nuclei can contain significant mass, in which case their non-spherical potentials exert significant torques on single and binary stars orbiting the MBHs. These torques can drive orbits to very large eccentricities. Previous works have shown that this driving can cause disruptions of single stars by the tidal gravity of the MBH. Here, we characterize the ability of these torques to drive binary stars to the point of disruption via the Hills mechanism. We derive semi-analytical estimates, validated with numerical simulations, of the number of binary disruptions driven by a generic disk in a generic nucleus. Using these results, we estimate that the formation of the ~5-Myr-old disk of stars in the Galactic Center drove a burst of ~10^2 binary disruptions. These disruptions produced an excess of S-cluster stars and hypervelocity stars — possibly including S5-HVS1, the fastest-known hypervelocity star. In other galaxies, analogues of S-cluster stars produced by this process may evolve into tidal disruption events following a disk phase. Hypervelocity star observations may help clarify the importance of disk-driven disruptions, which eject stars nearly isotropically and in temporal bursts — a unique combination among processes driving binary disruptions.
Read the full abstract

Cosmology and Nongalactic Astrophysics

Cosmology beyond standard sirens: cross-correlation of gravitational waves and neutral hydrogen intensity mapping

Matteo Schulz, Ulyana Dupletsa, Andrea Cozzumbo et al. (+8 more)

We explore the potential of cross-correlation between gravitational wave (GW) events and neutral hydrogen (HI) intensity mapping surveys to serve as an independent cosmological probe. Focusing on the ET and the SKAO, and assuming that binary black hole mergers and HI emission are biased tracers of the underlying dark matter distribution, we use their angular auto- and cross-correlation spectra to constrain cosmological parameters. We test three different GW detector networks: ET alone, both in its $\Delta$ and 2L configuration, and ET-2L together with Cosmic Explorer. We show that the cross-correlation method, by naturally mitigating tracer-specific systematics, yields robust cosmological bounds, allowing for a sub-percent ($\sim 0.5\%$) precision on the Hubble constant $H_\mathrm{0}$. Furthermore, this approach robustly constrains the cosmic expansion history throughout the post-reionization era of the Universe and, unlike conventional standard sirens, simultaneously probes the large scale distribution of matter perturbations, achieving relative uncertainties of approximately 1.3% on the total matter density $\Omega_\mathrm{m}$ and 1.6% on the late-time clustering amplitude $\sigma_8$.
Read the full abstract

All authors Matteo Schulz, Ulyana Dupletsa, Andrea Cozzumbo, Giona Sala, Tommaso Ronconi, Marta Spinelli, Riccardo Murgia, Simone Mastrogiovanni, Jan Harms, Erik de la Haye, Felicitas Keil

Solar and Stellar Astrophysics

HCO$^+$ and the Effect of Mixing in SN 1987A

H. M. Davies, M. Matsuura, H. L. Gomez et al. (+8 more)

We present high angular resolution observations of the HCO$^+$ emission in the central ejecta of the supernova remnant SN 1987A using the Atacama Large Millimeter Array (ALMA). We use this to infer the degree and type of mixing required within the ejecta in order to form HCO$^+$. The distribution of the $J=3-2$ HCO$^+$ emission is co-spatial with that of the $J=2-1$ CO emission, with an overlap between their brightest peaks. The correlation between the two molecules is strong and suggests that HCO$^+$ could form from reactions involving CO. We obtain additional observations of the $J=4-3$ HCO$^+$ emission to calculate the mass of HCO$^+$. The estimated HCO$^+$ mass is $3\text{--}9 \times 10^{-6}\,M_{\odot}$. The relatively large fractional abundance of HCO$^+$ with respect to CO ($M_{\mathrm{HCO}^+}/M_{\mathrm{CO}} = 3 \times 10^{-6}\text{--}3 \times 10^{-4}$) suggests that a moderate amount of hydrogen was mixed into the carbon- and oxygen-rich nuclear zones of the ejecta prior to and during the supernova explosion, in addition to large-scale macroscopic mixing.
Read the full abstract

All authors H. M. Davies, M. Matsuura, H. L. Gomez, A. M. S. Richards, P. Cigan, R. Indebetouw, F. D. Priestley, R. Wesson, M. J. Barlow, J. Larsson, C. Fransson

Solar and Stellar Astrophysics

A tale of two isotopes: Spatial variation in HCN fractionation toward young cores

Sigurd S. Jensen, Silvia Spezzano, Olli Sipilä et al. (+3 more)

Context. Isotopic fractionation can serve as a powerful tracer of the chemical evolution during star and planet formation. To accurately interpret observations, it is crucial to identify the dominant pathways of nitrogen and carbon fractionation at different evolutionary stages. Aims. We aim to study nitrogen and carbon fractionation in a sample of young cores at the onset of star formation. Methods. We map H$^{13}$CN and HC$^{15}$N around one starless and three pre-stellar cores. We compute the $N$(H$^{13}$CN)/$N$(HC$^{15}$N) column density ratio across the cores and compare the distribution with $N$(H$_2$) maps from $\textit{Herschel}$/SPIRE. In addition, we calculate $^{14}$N/$^{15}$N maps using the double isotope method for comparison with earlier studies. The results are compared with astrochemical modeling of carbon and nitrogen fractionation for a one-dimensional pre-stellar core model. Results. The computed $N$(H$^{13}$CN)/$N$(HC$^{15}$N) ratio exhibit clear spatial variation across the maps. This variation is correlated with $N$(H$_2$) in three out of four cores. Conclusions. Our analysis reveals a correlation between the H$^{13}$CN/HC$^{15}$N ratios and the $N$(H$_2$) maps. According to the astrochemical model, the correlation is mainly due to variations in the $^{12}$C/$^{13}$C ratio. Consequently, the results caution against applying the double-isotope method to derive $^{14}$N/$^{15}$N ratios without independently assessing possible spatial variations in the $^{12}$C/$^{13}$C ratio. Furthermore, the leading cause of the isotopic variation in the model is not isotope-selective photodissociation, but rather more efficient fractionation through exchange reactions at lower temperatures in the denser regions of the cores.
Read the full abstract

All authors Sigurd S. Jensen, Silvia Spezzano, Olli Sipilä, Paola Caselli, Laura Colzi, Elena Redaelli

Astrophysics of Galaxies

A Supermassive Black Hole Mass Measurement in NGC 5102 with Schwarzschild Orbit-superposition Modeling

Thomas K. Waters, Kayhan Gultekin, Karl Gebhardt et al. (+2 more)

We present a stellar-dynamical mass measurement of the central black hole in the lenticular galaxy NGC~5102 (SA0$^-$). Our analysis combines high-quality integral-field spectroscopy from the VLT Multi Unit Spectroscopic Explorer with high-spatial- and high-spectral-resolution Hubble Space Telescope Imaging Spectrograph observations, using the Ca II triplet as a stellar kinematic tracer. We constrain the black hole mass with axisymmetric, three-integral Schwarzschild orbit-superposition models, incorporating surface brightness measurements from HST F547M WFPC2 imaging. Assuming a distance of $3.66\,\mathrm{Mpc}$, we find a black hole mass of $(1.30^{+0.19}_{-0.18})\times10^6\,\mathrm{M_{\scriptscriptstyle\odot}}$, which is within $1.7\sigma$ of a previous CO band-head-based Jeans Anisotropic Modeling result ($M_{\bullet}=(9.1^{+1.8}_{-1.5})\times10^5\,\mathrm{M_{\scriptscriptstyle\odot}}$). Our measurement is also consistent with literature extrapolations of the $M_{\bullet}$-$\sigma_e$ relation into the currently under-sampled low-mass regime. The close agreement between these independent dynamical approaches provides external validation of the Jeans Anisotropic Modeling framework and supports the robustness of our Schwarzschild orbit-superposition result, bolstering confidence in future black hole mass measurements with this framework.
Read the full abstract

All authors Thomas K. Waters, Kayhan Gultekin, Karl Gebhardt, Soch Foskic, Ahmad Kadri

Earth and Planetary Astrophysics

The JWST weather report: Unravelling the atmospheric variability of isolated worlds using principal component analysis

Merle A. Schrader, Johanna M. Vos, Evert Nasedkin et al. (+17 more)

Brown dwarf variability directly probes atmospheric dynamics beyond the Solar System, and recent JWST time-resolved spectroscopy has opened a new window into these processes. Principal component analysis (PCA) offers a data-driven framework to identify the dominant, independent patterns of spectral variability of variable targets without relying on prior atmospheric assumptions. SIMP 0136 is a young, T2.5, brown dwarf at the planetary-mass boundary, making it an ideal analogue for directly imaged exoplanets. We analysed one rotation of JWST/NIRSpec PRISM time-series spectroscopy to investigate the drivers of its variability using PCA. Two principal components are sufficient to reduce the residual spectra to the propagated noise floor, indicating that they capture the detectable coherent spectroscopic variability. The leading principal component captures broadband variability consistent with temperature changes, while the second traces chromatic variability linked to vertical cloud structure. The dominance of two components implies that the spectra can be described as mixtures of three distinct atmospheric states, whose relative contributions we mapped as a function of rotational phase. The observed spectra are described as evolving linear combinations of these states, indicating that the variability arises from the changing visibility of spatially distinct atmospheric regions. By projecting Sonora Diamondback forward models into the same principal component space, we found that the principal components capture a large fraction of the model variance, demonstrating that the same physical processes that govern SIMP-0136's observed variability also capture much of the model grid's variation. Our results establish PCA as a computationally efficient, physically interpretable framework for analysing JWST time-resolved spectroscopy of substellar atmospheres.
Read the full abstract

All authors Merle A. Schrader, Johanna M. Vos, Evert Nasedkin, Jennifer Kestell, Nicolas B. Cowan, Roman Akhmetshyn, Samuel Beiler, Beth A. Biller, Ben Burningham, Jacqueline Faherty, Eileen C. Gonzales, Allison M. McCarthy, Caroline V. Morley, Barry O'Donovan, Cian O'Toole, Genaro Suarez, Xianyu Tan, Channon Visscher, Niall Whiteford, Yifan Zhou

Cosmology and Nongalactic Astrophysics

Radio Recombination Line Contamination in Post-Reionization 21 cm Intensity Mapping

Pip Petersen, Yakov Faerman and Matthew McQuinn

We explore radio recombination line (RRL) contamination in post-reionization 21 cm intensity mapping observations. We develop a formalism to estimate the contamination of the 21 cm auto-power spectrum from the myriad of RRL lines that redshift into a 21 cm map and predict contamination of the 21 cm power spectrum at all redshifts. At $z\lesssim 2$, extrapolation of the conservative upper-bound model of Petrovic & Oh (2011) predicts high contamination to the 21 cm power spectrum, whereas our empirically-calibrated models suggest contamination several orders of magnitude smaller. We also estimate the contribution from carbon RRLs and find it to be subdominant. We find the RRL contamination is highly oscillatory in wavenumber, owing to the dominant contamination from RRLs emitted close in physical space to the 21 cm emission. These oscillations could in principle bias distance measurements derived from Baryon Acoustic Oscillations (BAO), a key science driver of post-reionization 21 cm intensity mapping. We find the shift in the BAO extrema is at least two orders of magnitude smaller than relevant for percent-precision cosmology from BAO.
Read the full abstract

Astrophysics of Galaxies

How to raise a supermassive black hole: interpreting early JWST AGN with the AESOPICA simulations

Sophie Koudmani, Jan Scholtz, Anthony J. Taylor et al. (+11 more)

The active black holes uncovered by JWST in the early Universe are highly abundant and seemingly overmassive with respect to local scaling relations, challenging standard models of black hole formation and growth. Yet it remains unclear whether they trace an efficient early growth channel, the observable tail of a broader population, or suffer from systematic uncertainties in mass estimates. We introduce the AESOPICA project, a suite of twelve mid-volume ($L = 60\,\mathrm{Mpc}$) cosmological simulations based on the FABLE galaxy formation model, varying the black hole seed mass across the theoretical formation channels ($M_\mathrm{seed} = 10^{2}$-$10^{5} \, \mathrm{M_{\odot}}$), the accretion efficiency, including super-Eddington bursts, and the supernova feedback strength. We forward-model observational selection with BALMERSOPICA, a mock JWST broad-line survey pipeline that assesses the detectability of each simulated AGN for a given grating and exposure time. We find that the bulk of the JWST AGN population can be assembled from any seed mass provided the accretion efficiency is high, although light seeds require the most favourable accretion conditions explored. Applying broad-line selection naturally recovers the apparently overmassive population, with the detected AGN lying furthest above the intrinsic $M_\mathrm{BH}$-$M_\mathrm{stellar}$ relation for inefficient accretion models. Notably, the selected AGN lie on the local, weakly evolving $M_\mathrm{BH}$-$\sigma_\mathrm{stellar}$ relation, supporting a scenario where black holes assemble before the stellar component is fully established. Since efficient accretion rapidly erases the imprint of the initial seed mass, the low-mass end of the black hole mass function and host gas-phase metallicities offer the most promising discriminants between seeding channels.
Read the full abstract

All authors Sophie Koudmani, Jan Scholtz, Anthony J. Taylor, Ignas Juodžbalis, Debora Sijacki, Rachel S. Somerville, Roberto Maiolino, Emma Curtis-Lake, Steven L. Finkelstein, Martin A. Bourne, Francesco D'Eugenio, Sophia Geris, Lucy R. Ivey, Hannah Übler

High Energy Astrophysical Phenomena

Spectroscopic Analysis of Fermi-detected Blazars using SDSS-V

Mohammed Iddrisu Nlowie, James Aird, Eli Kasai et al. (+17 more)

The automated spectroscopic pipeline of the Sloan Digital Sky Survey (SDSS) systematically assigns Galactic star, galaxy, or typical quasar classifications to jet-dominated blazars, owing to the absence of a non-thermal jet continuum component in its template library. In this study, we present a new, physically motivated, multi-component spectral fitting pipeline that we apply to 746 optical counterparts of Fermi/4FGL-DR4 $\gamma$-ray sources in the SDSS-V Data Release 20 spectroscopic database, yielding 707 well-fitted blazar candidates dominated by Power-law+Galaxy (59.4%), Power-law+Lines (22.6%), and Power-law+QSO (15.0%) model families. Independent WISE infrared (IR) photometry confirms that 96.6% of the 88 sources originally misclassified as Galactic stars by SDSS fall within the canonical blazar region, with 90.9% reclassified as BL Lacertae object (BL Lac) candidates, demonstrating the success of our new pipeline. The new classification scheme naturally recovers the known cosmological separation between BL Lac and Flat Spectrum Radio Quasar (FSRQ) candidates and a separation of approximately one order of magnitude in median $\gamma$-ray luminosity. We compare our redshift estimates to a validation sample of 111 sources in the Third Fermi-LAT Catalogue of High-Energy Sources (3FHL), finding a 10.4% reduction in catastrophic failures ($\eta = 0.387$ vs 0.432) over the SDSS pipeline. The equivalent width analysis validates the traditional |EW| = 5 Ang classification boundary at the population level (BL Lac: 4.47 $\pm$ 0.15 Ang; FSRQ: 22.86 $\pm$ 0.86 Ang), although 49.5% of individual BL Lac candidates exceed this threshold and 51.4% show simultaneous emission and absorption features. This hybrid population challenges the traditional binary blazar classification and points towards a more physically continuous description of blazar properties.
Read the full abstract

All authors Mohammed Iddrisu Nlowie, James Aird, Eli Kasai, Amy L. Rankine, Paloma Guetzoyan, Scott Anderson, Catarina Aydar, William N. Brandt, Joel R. Brownstein, Xinyu Dai, Lorena Hernández-García, Paola Rodríguez Hidalgo, Pranavi Hiremath, Anton Koekemoer, Andrea Merloni, Sean Morrison, Mara Salvato, Donald P. Schneider, Axel Schwope, Benny Trakhtenbrot

Cosmology and Nongalactic Astrophysics

A Periodically Interacting Dark Sector: Signatures and Constraints from CMB and Cosmic Expansion Data

Marco Antonio Cardoso Alvarez, Micol Benetti, Leila Graef et al. (+1 more)

We introduce a novel cosmological model that provides an effective description of the back-reaction of super-Hubble fluctuations on the cosmological background, a generic effect expected to arise in any cosmological scenario without requiring additional ingredients. At the phenomenological level, it can be interpreted as an interacting dark sector scenario in which the sign of the energy transfer changes periodically over time. We constrain the model using CMB, BAO, and Type Ia supernova data. We find that a significant amplitude of the oscillatory interaction is allowed by the data, although there is no statistically significant preference for this model over $\Lambda$CDM.
Read the full abstract

All authors Marco Antonio Cardoso Alvarez, Micol Benetti, Leila Graef, Robert Brandenberger

Solar and Stellar Astrophysics

Multi-Wavelength Diagnostics of Pre-Flare Evolution with Aditya-L1: From the Solar Chromosphere to the Corona

Adithya H.N., Sreejith Padinhatteeri, Soumya Roy et al. (+13 more)

The pre-flare phase of solar flares provides important insight into the processes that drive active regions toward instability. We investigate chromospheric pre-flare activity using observations from the Solar Ultraviolet Imaging Telescope (SUIT) onboard Aditya-L1, complemented with X-ray measurements from High Energy L1 Orbiting X-ray Spectrometer (HEL1OS) and Solar Low Energy X-ray Spectrometer (SoLEXS). We analyse seven M- and X-class flares, focusing on spatially resolved Mg II h (2803~Å) observations from SUIT. We identify 102 pre-flare transients within regions of interest prior to flare onset. These transients are detected in the Mg II h channel, with no counterparts in continuum filters, confirming their chromospheric origin. In most cases, the transients are co-spatial with polarity inversion lines (PILs) and the eventual flaring region. Approximately 28~% of transients have X-ray counterparts in HEL1OS (10-30~keV); The Spectrometer Telescope for Imaging X-rays (STIX) spectral analysis reveals non-thermal emission in a subset, indicating that some transients are small-scale flare-like events. A hot X-ray onset is identified in four cases. For the remaining three cases, the signal-to-noise ratio above the background is insufficient to determine whether a hot-onset phase is present. The peak-flux distribution of the transients follows a broken power law with indices $\alpha_1 = 1.64^{+0.59}_{-0.57}$ and $\alpha_2 = 3.12^{+0.64}_{-0.61}$, with the higher-energy slope consistent with the Ly-$\alpha$ flare distribution. These results suggest that chromospheric pre-flare transients represent small-scale magnetic energy-release events that contribute to the progressive destabilisation of active regions prior to major flare onset.
Read the full abstract

All authors Adithya H.N., Sreejith Padinhatteeri, Soumya Roy, K. Sankarasubramanian, Durgesh Tripathi, Abhilash R Sarwade, Srikar Paavan Tadepalli, Harshavardhan G Hegde, Nived V. N, Janmejoy Sarkar, Rahul Gopalakrishnan, Rushikesh Deogaonkar, A. N. Ramaprakash, Sami K. Solanki, Dibyendu Nandy, Dipankar Banerjee

Instrumentation and Methods for Astrophysics

Tricouplers for nulling interferometry with photonic integrated circuits

Anusha Pai Asnodkar, Nemanja Jovanovic, Harry-Dean Kenchington Goldsmith et al. (+7 more)

Solar System analog gas giants and habitable-zone terrestrial planets are observationally elusive to conventional exoplanet detection and characterization techniques, i.e. transits, radial velocities, and direct imaging. Long baseline nulling interferometry across multiple apertures suppresses starlight and enables detection of faint planetary signals at higher spatial resolution than traditional coronagraphs on single-aperture telescopes. Leveraging technological advancements from the telecommunications industry, photonic integrated circuits (PICs) offer a promising platform for performing the optical operations necessary for astronomical applications, including phasing and beam combination for nulling interferometry in both long-baseline and cross-aperture configurations. PICs provide compact, scalable architectures with reduced sensitivity to alignment as well as thermal and mechanical perturbations compared to bulk optics. However, their design and manufacturing precision remain insufficient for the stringent requirements of exoplanet instrumentation. Here, we investigate the nulling capabilities of photonic tricouplers, devices composed of three equal-width waveguides that are geometrically predisposed to produce achromatic nulls upon beam combination through their symmetric construction. In the laboratory, we characterize null depths in monochromatic light at 1.55 $\mathrm{\mu}$m with devices on a planar silica-on-silicon platform. In broadband $H$-band light, we explore chromatic effects from components such as thermo-optic phase modulators used for fine-phasing. Our ongoing efforts towards maturation of PICs for direct detection and atmospheric characterization of exoplanets will support scalable testing and deployment of high-contrast technologies for future space-based observatories, such as the Habitable Worlds Observatory.
Read the full abstract

All authors Anusha Pai Asnodkar, Nemanja Jovanovic, Harry-Dean Kenchington Goldsmith, Ahmed Sanny, Yoo Jung Kim, Hani Nejadriahi, Isabelle Rivera, Michael P. Fitzgerald, Dimitri Mawet, Pradip Gatkine

Instrumentation and Methods for Astrophysics

High-statistics simulations of NewAthena WFI background using Geant4

Matthew K. Heine, Catherine E. Grant, Marshall W. Bautz et al. (+14 more)

The observation of hot gas structures is one science goal of the Wide Field Imager (WFI) on ESA's NewAthena X-ray observatory. Because the measurement of these faint diffuse sources is limited by background from cosmic ray particle interactions within the instrument, understanding and reducing this background is critical. To this end, we employ a two-pronged approach, performing high-fidelity Geant4 simulations on both detailed, realistic geometry models as well as complementary simple geometry models. The former can reveal subtle sensitivities of background to details of the instrument design. The latter allows for fast iteration, useful in guiding and understanding the larger simulations. We show how we leverage High Performance Computing (HPC) resources to achieve simultaneously high throughput and fast time to result. We discuss our recent results, which are applicable not only to WFI, but also other X-ray missions.
Read the full abstract

All authors Matthew K. Heine, Catherine E. Grant, Marshall W. Bautz, Beverly J. LaMarr, Eric D. Miller, Michael W. J. Hubbard, David Hall, Joan Requena, Emanuele Perinati, Steven W. Allen, Artem Poliszczuk, Dan Wilkins, Fabio Gastaldello, Silvano Molendi, Ralph P. Kraft, Gerrit Schellenberger, Arnab Sarkar

Astrophysics of Galaxies

The extended globular cluster system of the archetypal "failed galaxy" Dragonfly-44 from deep white-light Hubble Space Telescope imaging

Maria Luisa Buzzo, Pieter van Dokkum, Roberto Abraham et al. (+2 more)

For nearly a decade, Dragonfly-44 (DF44, $M_{\star} = 3\times10^8\,{\rm M}_\odot$) has been considered an archetypal “failed galaxy”, a system so rich in globular clusters (GCs) and dark matter that it challenges standard dwarf galaxy formation scenarios. Yet a key measurement underpinning this classification has remained controversial, with published GC counts differing by a factor of four. Here we present new ultra-deep Hubble Space Telescope WFC3/UVIS imaging of DF44 in the F350LP filter, reaching more than one magnitude below the canonical turnover of the GC luminosity function. We find that DF44 hosts $N_{\rm GC}=73.1\pm8.6$ GCs in a spatially extended system with a half-number radius of $R_{\rm gc}=1.48^{+0.39}_{-0.51}R_{\rm e}$, at the high end of previously published values. The GC system comprises ${\sim}3.9\%$ of the total stellar mass and, if DF44 follows the empirical GC number–halo mass relation, implies $\log(M_{\rm vir}/M_\odot)=11.5\pm0.3$, consistent within the uncertainties with the cored halo mass inferred from stellar kinematics by van Dokkum et al. 2019. Together with a specific frequency of $S_N=42.1\pm4.9$, the rich GC population strongly supports the interpretation of DF44 as a failed-galaxy candidate that assembled a massive halo and rich GC population early, but never formed the field stellar mass expected for its halo. Current formation models reproduce several individual properties of DF44, but its combination of GC richness, early quenching, and high inferred halo mass remains an important constraint on models of dwarf-galaxy formation.
Read the full abstract

All authors Maria Luisa Buzzo, Pieter van Dokkum, Roberto Abraham, Shany Danieli, Aaron J. Romanowsky

Astrophysics of Galaxies

The Twentieth Data Release of the Sloan Digital Sky Survey: First All-Sky BOSS Spectra, eROSITA-SDSS-V Mapper Coordinated Observations, and a Preview of the Local Volume Mapper

SDSS Collaboration, Mojgan Aghakhanloo, David Aguilar et al. (+272 more)

This paper presents the twentieth data release (DR20) from the Sloan Digital Sky Survey, the third data release of its fifth generation (SDSS-V). SDSS-V is a panoptic spectroscopy survey that is mapping the stars, gas, and galaxies through three scientific programs: the Milky Way Mapper (MWM), the Local Volume Mapper (LVM), and the Black Hole Mapper (BHM). DR20 presents the first optical (BOSS) SDSS-V spectra from southern hemisphere for the MWM and BHM surveys; new optical MWM and BHM data from the northern hemisphere are also available, for a total over 3 million spectra of 1.5 million stars and half a million galaxies and quasars, with galactic and extragalactic x-ray targets coordinate with eROSITA DR2. DR20 includes integral field spectroscopy maps from LVM of six targets and 169 tiles, spanning Galactic HII regions, planetary nebulae, and nearby galaxies. Additionally, eighteen value added catalogs are also released with DR20, based on SDSS-V MWM and BHM data, and we present a new LVM visualization tool including an RGB HiPS map as a value added product.
Read the full abstract

All authors SDSS Collaboration, Mojgan Aghakhanloo, David Aguilar, James Aird, Andrés Almeida, Bella Abigail Sanabria Alonso, Hillary Diane Andales, Scott F. Anderson, Stefan Arseneau, Consuelo González Ávila, Shir Aviram, Catarina Aydar, Carles Badenes, Carolina Andonie, Jorge K. Barrera-Ballesteros, Franz E. Bauer, Chad Bender, Michelle A. Berg, F. Besser, Binod Bhattarai, Christian Moni Bidin, Jonathan C. Bird, Dmitry Bizyaev, Guillermo A. Blanc, Alexandra Bonkoski, Jo Bovy, Andrea Bracamonte, W. N. Brandt, Jaco Brink, Joel R. Brownstein, Esra Bulbul, Joseph N. Burchett, Robert E. Butler, Leticia Carigi, Joleen K. Carlberg, Andrew R. Casey, Lesly Castañeda-Carlos, Fernanda Milla Castro, Priyanka Chakraborty, Julio Chanamé, Vedant Chandra, Brian Cherinka, Igor Chilingarian, Arlin Cortes, Maren Cosens, Irene Cruz-Gonzalez, Elena D'Onghia, Collin Dabbieri, Xinyu Dai, Jeremy Darling, James W. Davidson Jr., Megan C. Davis, Nathan De Lee, Niall Deacon, José Eduardo Méndez Delgado, Sebastian Demasi, Mariia Demianenko, Delvin Demke, Francesco Di Mille, Bruno Dias, Ariana Didiano, John Donor, Ethan Driscoll, Niv Drory, Liam Dubay, Moníca A Villa Durango, Tom Dwelly, Oleg Egorov, Evgeniya Egorova, Kareem El-Badry, Michael Eracleous, Xiaohui Fan, Liliana Flores, Peter Frinchaboy, Nicola Pietro Gentile Fusillo, Luis Daniel Serrano Félix, Boris T. Gänsicke, Emma Galligan, Dante Garcia, Pablo García, Junqiang Ge, Joseph Gelfand, Simon C. O. Glover, Juan Daniel Gonzalez Ruiz, Katie Grabowski, Eva K. Grebel, Paul J. Green, Catherine Grier, Emily J. Griffith, Paloma Guetzoyan, Pramod Gupta, Patrick B. Hall, Audrey Hauck, Keith Hawkins, Saskia Hekker, T. M. Herbst, J. J. Hermes, J. Hernández, Lorena Hernández-García, Thomas Hilder, Pranavi Hiremath, David W Hogg, Jon Holtzman, Keith Horne, Danny Horta, Yang Huang, Maximilian Häberle, Hector Javier Ibarra-Medel, Julie Imig, Alex Ji, Ó. Jiménez-Arranz, Paula Jofre, James W. Johnson, Jennifer Johnson, Evelyn J. Johnston, Patricio Jones, Amy M. Jones, Mary Kaldor, Amir Kalechman, Ivan Katkov, Sergey Khoperskov, Dong-Woo Kim, Jinyoung Serena Kim, Ralf Klessen, Matthias Kluge, Anton M. Koekemoer, Juna A. Kollmeier, Marina Kounkel, Kathryn Kreckel, Dhanesh Krishnarao, Mirko Krumpe, Nimisha Kumari, Thomas Kupfer, Ivan Lacerna, Sean D. Lam, Sorya Lambert, Chervin Laporte, Sebastien Lepine, Jiadong Li, Bowen Li, Jianhui Lian, Guilherme Limberg, Xin Liu, Sarah Loebman, Dan Long, Knox Long, Yuxi Lu, Madeline Lucey, Alejandra Z. Lugo-Aranda, Steven Raymond Majewski, Dan Maoz, M. L. Martínez-Aldama, Rachel Lee McClure, Madeleine McKenzie, Kevin McKinnon, Timothy McQuaid, Ilija Medan, Alfredo J. Mejía-Narváez, Andrea Merloni, Szabolcs Mészáros, Dante Minniti, Takamitsu Miyaji, Stephanie Monty, Leslie M. Morales, Sean Morrison, Adam Moss, Johanna Müller-Horn, Natalie R. Myers, C. Alenka Negrete, Shannon Neilson, Melissa Ness, David L. Nidever, Christian Nitschelm, Mohammed Iddrisu Nlowie, Daniel Oravetz, Audrey Oravetz, Jonah M. Otto, Gautham Adamane Pallathadka, Kaike Pan, Facundo Pérez Paolino, Ziming Peng, Leah Peterson, Marc Pinsonneault, Anastasiia Plotnikova, Moire K. M. Prescott, Adrian M. Price-Whelan, Nadiia Pulatova, M. Jordan Raddick, Amy L. Rankine, Paola Rodríguez Hidalgo, M. Katy Rodriguez Wimberly, A. Roman-Lopes, Carlos G. Román-Zúñiga, Daniela Fernández Rosso, William Roster, Serat Mahmud Saad, Mara Salvato, Sebastián F. Sánchez, Andreas A. C. Sander, Rodrigo Sandoval-Orozco, Ravi Sankrit, Saroon Sasi, Natascha Sattler, Andrew K. Saydjari, Maryum Sayeed, Conor Sayres, Fabian Scheuermann, Kevin C. Schlaufman, Donald P. Schneider, Axel Schwope, Conner Scoresby, Lucas M. Seaton, Javier Serna, Kayvon Sharifi, Allyson Sheffield, Paula Silva, Amrita Singh, Amaya Sinha, Tawny Sit, Peter J. Smith, Ying-Yi Song, Diogo Souto, Keivan Stassun, Matthias Steinmetz, Zachary Stone, Alexander Stone-Martinez, Guy S. Stringfellow, Amelia Stutz, José Sánchez-Gallego, Manuchehr Taghizadeh-Popp, Jonathan C. Tan, Emma Tasso, Jamie Tayar, Aniruddha R. Thakar, Pierre Thibodeaux, Yuan-Sen Ting, Andrew Tkachenko, Gagik Tovmasian, Benny Trakhtenbrot, José G. Fernández-Trincado, Nicholas Troup, Jonathan R. Trump, Sarah Tuttle, Natalie Ulloa, Ana Sofía Uzsoy, Ricardo López Valdivia, Greique A. Valk, Roeland P. van der Marel, Luciano Vargas-Herrera, Pablo Vera, Valentina Bonilla Villalobos, Sandro Villanova, Jaime I. Villaseñor, Zach Way, Anne-Marie Weijmans, John C. Wilson, Aida Wofford, Tony Wong, Qiaoya Wu, Dominika Wylezalek, Xiang-Xiang Xue, Renbin Yan, Qian Yang, Nadia Zakamska, Abner Zapata, Eleonora Zari, Gail Zasowski, Grisha Zeltyn, Guangquan Zeng, Jichen Zhang, Jingkun Zhao, Zezhou Zhu, Igor Zinchenko, Catherine Zucker, Rodolfo de J. Zermeño

Solar and Stellar Astrophysics

The Stellar Winds Atlas II: Black Hole Formation at Solar Metallicity

Amedeo Romagnolo, Floor S. Broekgaarden, Alex C. Gormaz-Matamala et al. (+7 more)

Stellar winds are a primary source of uncertainty in predicting the masses of black holes (BHs) from massive stars. At solar metallicity, theoretical models lead to widely divergent results due to differing wind prescriptions. A key obstacle remains the lack of systematic investigations across a common parameter space. To address this, we construct a “Wind Atlas” using detailed 1D MESA stellar evolution models and population synthesis techniques to estimate the Galactic population of solar metallicity BH progenitors. We systematically investigate 14 distinct wind models, ranging from the most traditional and widespread prescriptions to the most recent. By evaluating stellar evolution across this extensive grid, we show that the final BH mass is dictated by a fundamental bifurcation: whether a star collapses as a cool supergiant or is first stripped of its envelope to become a Wolf-Rayet (WR) star. If a star enters the WR stage, its strong thick winds dominate, making the final mass sensitive to the WR wind prescription while largely erasing the memory of its prior mass-loss history. Conversely, stars that face core collapse as supergiants form significantly more massive BHs, producing a mass peak around an initial mass of 40 $M_\odot$. Rather than simply reproducing these divergent outcomes, our comprehensive evaluation demonstrates that this bifurcation is universally controlled by the highly uncertain mass loss during the cool supergiant phase. This framework strongly constrains the problem of BH mass prediction by identifying two key bottlenecks for future studies: envelope stripping efficiency and WR mass-loss rates. Our atlas provides a clear baseline for interpreting current theoretical discrepancies and testing wind models against observational constraints, such as the Galactic WR/OB population ratio.
Read the full abstract

All authors Amedeo Romagnolo, Floor S. Broekgaarden, Alex C. Gormaz-Matamala, Lucas M. de Sá, Daniel Pauli, Avishai Gilkis, Lumen Boco, Michela Mapelli, Konstantinos Antoniadis, Laya Binu

High Energy Astrophysical Phenomena

Unchanged X-Ray Polarization During Accretion Dips in the Low Hard State of Cygnus X-1

Yu-shan Ling, Fei Xie, Alessandro Di Marco et al. (+2 more)

Cygnus X-1 serves as a foundational benchmark for studying accretion mechanisms in stellar-mass black hole X-ray binaries. While traditional X-ray timing and spectroscopy have mapped its bimodal state transitions, constraining the exact geometric configuration of its accreting plasma requires additional tools. In this letter, we present a joint spectro-polarimetric analysis of Cygnus X-1 during flux-decrease events, or “dips”, observed in its low hard state using simultaneous data from IXPE, NICER, and NuSTAR. The broadband spectral model reveals that the energy-dependent flux reduction during these dips is best described by a partial-covering absorption model, heavily impacting the softer energy bands. This absorption is consistent with obscuration by dense, cold clumps originating from the companion's stellar wind or the outer accretion disk during superior conjunction. Notably, our polarimetric analysis demonstrates that despite significant flux drops, the polarization degree and polarization angle in the 2-8 keV band remain largely consistent between dip and off-dip intervals. The stability of the polarization signature during these highly absorbed periods indicates that the obscured thermal disk emission does not significantly contribute to the total polarization. Ultimately, these results strongly support a scenario where the X-ray polarization originates from an extended, likely oblate, accretion-disk corona whose large scale renders its overall geometry unaffected by localized clumping.
Read the full abstract

All authors Yu-shan Ling, Fei Xie, Alessandro Di Marco, Fabio La Monaca, Ming-Yu Ge

Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph

A multi-axion model of inflation and dark matter

Marcos A.G. Garcia, Hansel Gordillo-Ruiz, Raul Henriquez-Ortiz et al. (+1 more)

Models with extra dimensions include a tower of massive states that unavoidably contribute to cosmological dynamics. In particular, after compactification, a higher-dimensional axion gives rise to a set of states whose dynamics at early times exhibit the properties of inflation and, at late times, those of dynamical dark matter. Interestingly, natural choices of parameters imply that the inflationary trajectory in field space is approximately geodesic, meaning that inflation is effectively driven by a single inflaton corresponding to the heaviest state. In this scenario, all inflationary observables, including the emerging spectral distortions, are consistent with current observational constraints, and exact numerical solutions of the equations of motion show that reheating can consistently proceed down to temperatures of a few MeV. Furthermore, all states lighter than the inflaton only come to dominate the energy density of the Universe during the matter-dominated era, thus behaving as dark matter at late times. These states undergo a cascade of decays into radiation, while maintaining a sufficient dark-matter abundance to account for the observed relic density. The lightest dark-matter candidate remains stable on timescales far exceeding the age of the Universe, thereby satisfying even the most conservative observational constraints.
Read the full abstract

All authors Marcos A.G. Garcia, Hansel Gordillo-Ruiz, Raul Henriquez-Ortiz, Saul Ramos-Sanchez

High Energy Astrophysical Phenomena

X-ray and optical decline of the intermediate mass black hole HLX-1

Roberto Soria, Maya Garbaccio Gili, Francesco Massaro et al. (+2 more)

HLX-1 is a prominent intermediate-mass black hole (IMBH) candidate, historically exhibiting recurrent X-ray outbursts with spectral state transitions analogous to those observed in stellar-mass black holes. Here, we present new Hubble Space Telescope, Chandra, and Swift observations from 2018-2022 to characterise the late-time flux decline. HLX-1 has persisted in a low X-ray luminosity state (L_X ~ a few x 10^{39} erg/s) since the end of its last outburst in 2017. We observe a significant decoupling between the X-ray and optical/UV emission: while the X-rays have faded by at least two orders of magnitude from peak outburst luminosity (in 2010) to the current low state, the optical/UV flux has declined much more slowly over the same time. This results in an X-ray/optical luminosity ratio inconsistent with X-ray reprocessing in a standard accretion disk, as this would require an unphysical reprocessing fraction >100% at late times. Instead, we find that the optical/UV evolution is well-fitted by a cooling, expanding photosphere (T ~ 30,000 K), similar to the late-stage evolution seen in tidal disruption events (TDEs). The redder component of the optical emission is instead consistent with the old stellar population of a massive star cluster (IMBH host). The pre-2017 X-ray bursting phase is consistent with simulations of disk instabilities in TDE evolution: this strengthens the scenario of HLX-1 as an IMBH TDE. Furthermore, our observations resolve the morphology and flux of the mysterious far-UV emitter, seen in projection next to HLX-1, into a ring-like star-forming structure. We re-assess the possibility that HLX-1 and its host star cluster are physically associated with this starburst dwarf, perhaps via a high-speed collision.
Read the full abstract

All authors Roberto Soria, Maya Garbaccio Gili, Francesco Massaro, Alister W. Graham, Luca Zampieri

Astrophysics of Galaxies

Identifying backsplash galaxies using machine learning

Roan Haggar, Elizaveta Sazonova, Cameron R. Morgan et al. (+5 more)

The galaxy population in the outskirts of a cluster contains members that have been pre-processed in groups and filaments, as well as backsplash galaxies – those that have recently passed through the cluster's center. However, disentangling these two pathways is challenging observationally. In this work, we present a machine-learning-powered model, trained on simulations of galaxy clusters from The Three Hundred suite of simulations, which can identify individual backsplash galaxies in astronomical observations. This model can build samples of backsplash galaxies with a purity and completeness of up to ~70%, and galaxies on their first infall with a purity and completeness of over 80%. It can be tuned to optimise either of these two metrics, and can be used with any combination of a set of observable quantities. We have also applied this model to galaxies with asymmetric HI distributions in the Virgo Cluster, and have demonstrated that these galaxies are all likely approaching the cluster for the first time. This supports the idea that cold gas is removed from these galaxies soon after entering a cluster, and demonstrates how this classifier can provide a better understanding of which properties of galaxies are caused by a previous passage through a cluster. We have made this model publicly available in the form of a web app, with a link in the Conclusions of this paper.
Read the full abstract

All authors Roan Haggar, Elizaveta Sazonova, Cameron R. Morgan, Alexander Knebe, Rhys Jordan, Weiguang Cui, Frazer R. Pearce, James E. Taylor

Cosmology and Nongalactic Astrophysics

The FRB–Galaxy Overdensity Cross-Correlation Statistic in Dispersion Space

Ryan Raikman, Haochen Wang, Kiyoshi Masui et al. (+1 more)

Cross-correlating the dispersion of fast radio bursts (FRBs) with galaxies provides a means to study the distribution of the baryons in the Universe, even in the absence of FRB redshifts. To this end, two variants of angular cross-power spectrum statistics have been proposed: one between DM and galaxy density binned by redshift $C^{Dg}_l(z_g)$ (abbreviated $D \times g$), and one between FRB counts binned by dispersion measure (DM) and galaxy density binned by redshift $C^{fg}_l(\textrm{DM}, z_g)$ (abbreviated $f \times g$). Here we show the $D \times g$ statistic can be recovered as a DM-moment of $f \times g$, implying the latter is strictly more informative. By slicing in both DM space and galaxy redshift space, the $f\times g$ statistic separates contributions from the clustering of free electrons and from the clustering of FRB sources. We perform Fisher forecasts for FRB samples consistent with CHIME (1,600 FRBs) and the upcoming CHORD (20,000 FRBs) survey cross-correlated against the DESI Legacy Survey BGS sample and Euclid galaxy surveys, respectively. We show that, compared to the $D \times g$ statistic, the $f \times g$ statistic results in $S/N\approx 12$ for CHIME$\times$DESI(LS) and SNR $\approx 54$ for CHORD$\times$Euclid. The $f \times g$ statistics is more sensitive to the redshift distribution of FRBs with forecasted errors on a simple parameterization of order $10 \%$. It measures the logarithmic cutoff scale for clustering of baryons due to feedback $k_{cut}$ to 26% precision with CHIME and 14% precision with CHORD. Since most FRBs currently lack host identifications, and scaling optical followup to large samples will remain challenging even with precise localizations, reliable redshifts will be unavailable for most FRBs for the foreseeable future. The $f \times g$ statistic provides a means to extract maximum cosmological information in their absence.
Read the full abstract

All authors Ryan Raikman, Haochen Wang, Kiyoshi Masui, Shion Andrew

Astrophysics of Galaxies

Stellar rotation of S301 as a macroscopic gyroscope to test general relativity

Pau Amaro Seoane, Xian Chen, Alejandro Torres-Orjuela et al. (+16 more)

Stellar trajectories around the Galactic Center provide a testing environment for general relativity. The intrinsic rotation of these stars evolves under covariant transport in curved spacetime and classical Newtonian quadrupole torques. We analyze the recently observed S301 S-star to quantify the relativistic precession of its rotational axis. Its 8.7-year period and eccentricity of $e = 0.982$ localize geodetic precession and Newtonian quadrupole torques to a step function at periapsis. We incorporate first-order post-Newtonian corrections into the orbital kinematics to calculate the spatial trajectory. Sampling an isotropic distribution of initial orientations and viewing geometries over a 40-year period across a grid of equatorial velocities and rotational ellipticities, we calculate the statistical likelihood of an absolute shift in the projected rotational line broadening, $|\Delta v \sin i|$. The relativistic geodetic shift scales linearly with $v_{\rm rot}$ and the classical quadrupole shift is independent of rotation speed, scaling with $q$. The absolute maximum velocity shift saturates at $46.1\,\kms$ for oblate stars. The absolute median shifts, driven by geodetic precession, range from $3\,\kms$ to $6.3\,\kms$. We calculate the time-domain observable $|\Delta v \sin i|$ to provide a target for infrared spectrographs testing the Schwarzschild metric around Sgr~A$^\ast$. The spin of S301 acts as a flying gyroscope whose drift, if measured, can test Einstein's theory in a regime that has not previously been accessible.
Read the full abstract

All authors Pau Amaro Seoane, Xian Chen, Alejandro Torres-Orjuela, Reinhard Genzel, Frank Eisenhauer, Thomas Ott, Stefan Gillessen, Guillaume Bourdarot, Diogo C. Ribeiro, Matteo Sadun Bordoni, Simran Joharle, Felix Mang, Andreas Burkert, Jorge Cuadra, Diego Calderón, Hagai B. Perets, Tsvi Piran, Thorsten Naab, Re'em Sari

High Energy Astrophysical Phenomena

Gamma-ray burst progenitors revisited

Andrew J. Levan, Jillian C. Rastinejad, Helena-Margaret S. Grabham et al. (+11 more)

Recently, several long-duration gamma-ray bursts (GRBs) associated with kilonovae have cast doubt on the traditional, dichotomous mapping between gamma-ray duration and progenitor system. Here, we investigate the rates and properties of bursts which appear to cross this dichotomy using a sample of GRBs for which progenitor constraints are possible. We first build a sample of known Swift-detected GRBs at z<0.3, finding 8 short- and 21 long-duration GRBs. Of these long GRBs, we find 9 bursts with deep limits on supernova emission, evidence for kilonova emission, or association with a quiescent galaxy (31% $\pm$ 9% of all GRBs at z<0.3), implying that a significant fraction of nearby long GRBs likely do not come from massive stars. At z<0.3, no short GRB has an observed supernova counterpart. We find comparable numbers when expanding to z<0.5 and other gamma-ray telescopes, though we obtain a decreased fraction of bursts with robust constraints on a progenitor. We further find that the long GRBs with no associated supernovae possess on-average fainter afterglows and lie in less star-forming host galaxies than those with supernovae, supporting that these events may originate in compact object mergers. We estimate approximate volumetric rates, finding similar (on-axis) rates for short GRBs and supernova-less long GRBs of $\sim 0.5-2.5$ Gpc$^{-3}$ yr$^{-1}$, although a search for possible low-redshift hosts of the complete Swift catalog suggests that our sample may be $\sim$50% complete. If supernova-less long GRBs arise from compact object mergers, this implies that $\sim$ 30-70% of all z<0.3 Swift long GRBs may arise from mergers and that the $z<0.3$ rates of mergers from long and short GRBs are comparable. These findings hold substantial implications for gravitational-wave coincidence and heavy element enrichment.
Read the full abstract

All authors Andrew J. Levan, Jillian C. Rastinejad, Helena-Margaret S. Grabham, Daniele B. Malesani, Nial R. Tanvir, Eric Burns, Benjamin P. Gompertz, Gavin P. Lamb, Ashley A. Chrimes, Peter G. Jonker, Om Salafia, Nikhil Sarin, Ilya Mandel, Antonio Martin-Carrillo

High Energy Astrophysical Phenomena

The ultra-fast afterglow of GRB 260226A

Biswajit Banerjee, Alessio Mei, Annarita Ierardi et al. (+13 more)

Long-duration gamma-ray bursts are typically powered by relativistic jets launched after the core collapse of some rapidly rotating massive stars. Internal dissipation releases part of the jet energy as highly variable MeV prompt emission, while the remaining kinetic energy drives an external shock into the surrounding medium and produces the so-called afterglow. During the first minutes of the afterglow, the unsteady jet transfers energy to the external shock. The early afterglow emission in MeV-GeV energies is rarely observed because the emergence of afterglow can be overshined by the prompt emission. Here we report exceptional observations of GRB 260226A with the Fermi Large Area Telescope, which recorded the largest number of photons above 100 MeV from a gamma-ray burst. These data allow us to reconstruct the evolution of the bolometric flux of the afterglow from its emergence during the prompt emission phase with unprecedented detail. The afterglow component peaks near 50 MeV and fades rapidly, first as t$^{-1.5}$ and then transiting to an ultra-fast t$^{-2.8}$ decay after about one minute. This behavior cannot be explained by standard synchrotron emission from a blast wave propagating into a cold medium. We interpret it as external inverse Compton radiation from freshly heated electrons cooling on prompt photons in a dense, pair-loaded stellar wind. GRB 260226A therefore shows that MeV-GeV observations can directly reveal the formation of the external shock and the massive-star environment is significantly reshaped by the prompt emission.
Read the full abstract

All authors Biswajit Banerjee, Alessio Mei, Annarita Ierardi, Samanta Macera, Gor Oganesyan, Shraddha Mohnani, Elias Kammoun, Pawan Tiwari, Stefano Ascenzi, Samuele Ronchini, Ansh Chopra, Alessio Ludovico De Santis, Stefano Covino, Paolo D'Avanzo, Andrea Melandri, Silvia Piranomonte

High Energy Astrophysical Phenomena · Cross-listed from hep-ph

Probing Neutrino Flavor Composition with the Glashow Resonance at Tau Air-Shower Neutrino Telescopes

Tianyi Ding and Qinrui Liu

The flavor composition of high-energy astrophysical neutrinos encodes information about their production and propagation. The Glashow resonance, $\bar{\nu}_e + e^-\to W^-$, provides a unique way to distinguish antineutrinos from neutrinos and thereby extends the reach of flavor composition studies. Proposed tau air-shower neutrino telescopes target Earth-skimming and mountain-skimming $\nu_\tau$ above a PeV, but through the decay $W^-\to \bar{\nu}_\tau+\tau^-$ they are also sensitive to $\bar{\nu}_e$. These experiments can therefore measure the ratio of $\bar{\nu}_e$ to $\nu_\tau+\bar{\nu}_\tau$ fluxes. We evaluate this prospect with explicit simulations and project sensitivities for TAMBO and TRINITY, assuming 10 years of operation. We find that mountain-skimming geometries yield substantially higher $\bar{\nu}_e$ acceptance than Earth-skimming ones due to the shorter path length in rock. For standard astrophysical source scenarios, our projections show that differentiating $pp$ and $p\gamma$ production, including their muon-damped scenarios, is challenging with a standalone measurement by tau air-shower experiments in their currently designed configurations, though optimistically the flux ratio can be constrained to $\lesssim$2 at 1$\sigma$. A $\bar{\nu}_e$-rich flux, as expected from neutron-decay sources or from certain new physics models, would stand out from the standard pion-production scenarios and can otherwise be constrained.
Read the full abstract

Astrophysics of Galaxies

From S2 to LISA: Astrometric Bounds on Extreme-Mass-Ratio Inspirals and Bursts

Andrea Caputo and Valerie Domcke

Stellar orbits around the massive black hole at the center of our galaxy provide a unique local probe of the compact-object population in the Galactic Centre and, consequently, of the sources of millihertz gravitational waves: periapse passages lead to extreme-mass-ratio bursts (EMRBs) while successful captures lead to extreme-mass ration inspirals (EMRIs). In this paper we use recent astrometric limits from the GRAVITY observatory on perturbations of the orbit of the star S2 to place upper limits on the normalisation of a stellar-mass black-hole cusp within ${\sim} \,0.02\,\mathrm{pc}$. For a benchmark $10\,M_\odot$ Bahcall–Wolf population anchored to this data, we obtain upper limits of ${\sim} \,2.4\times10^{2}\,\mathrm{Gyr}^{-1}$ on the EMRI rate and ${\sim} \, 0.2\,\mathrm{yr}^{-1}$ on the detectable EMRB rate in the Milky Way, which fall within the broad range of previous theoretical estimates. Assuming a self-similar scaling of the cusp normalisation with central black-hole mass, we extend this calibration to cosmological populations. The resulting EMRI background is detectable by LISA across all scenarios considered, whereas the flatter EMRB background can reach LISA sensitivity when mass segregation is efficient in low-mass galactic nuclei. Our results highlight the complementarity of precision stellar astrometry and millihertz gravitational-wave observations.
Read the full abstract