Solar and Stellar Astrophysics
Small-scale bright point characteristics at high-resolution with the Daniel K. Inouye Solar Telescope
Peter H. Keys, Ryan J. Campbell, Dylan K. J. Magill et al. (+9 more)
Bright points (BPs) are small-scale, dynamic features that are ubiquitous across the
solar disc and are often associated with the underlying
magnetic field. Using broadband photospheric images obtained with the Visible Broadband Imager at the National Science Foundation's Daniel K. Inouye
Solar Telescope (DKIST), the properties of BPs have been analyzed with DKIST for the first time at the highest spatial resolutions achievable. BPs were observed to have an average lifetime of 95$\pm$29 s and a mean transverse velocity of 1.60$\pm$0.41 km/s. The BPs had a log-normal area distribution with a peak at 2300 km$^2$. Transverse velocity and lifetimes across the DKIST images were comparable and consistent with previous studies. The area distribution of the DKIST data peaked in areas significantly lower than those from the literature. This was explored further and was observed to be due to an overestimation of BP areas due to the merging of close features when the spatial resolution is reduced, in tandem with possible over-splitting of features in the DKIST images. Furthermore, the effect of variable seeing within the data was determined. This showed that the average spatial resolution of the data was around 0.”034$\pm$0.”007 in comparison to the theoretical diffraction-limit of 0.”022. Accounting for the influence of seeing, the peak of the area distribution of BPs in the DKIST data was estimated as 4800 km$^2$, which is still significantly lower than previously observed.
Read the full abstract ▾
All authors Peter H. Keys, Ryan J. Campbell, Dylan K. J. Magill, Mateus A. Keating, Mihalis Mathioudakis, David B. Jess, Damian J. Christian, Arthur Berberyan, Samuel D. T. Grant, Shahin Jafarzadeh, Marco Stangalini, Robertus Erdélyi
High Energy Astrophysical Phenomena · Cross-listed from hep-ph
On the existence of bound states in SIMP dark sectors
Xiaoyong Chu, Josef Pradler and Daris Samart
In strongly interacting massive particle (SIMP) scenarios, dark matter is comprised of stable dark pions whose $3\to 2$ or $4\to 2$ reactions set the dark matter relic abundance. Recent work has shown that shallow two-pion bound states significantly affect the freeze-out, but did not establish whether such states actually form. In this work we demonstrate that a scalar isosinglet bound state does exist in a well-defined region of parameter space by solving an on-shell Lippmann–Schwinger equation in a
chiral-
unitary framework and analyzing the $S$-wave $\pi\pi$ amplitude in the complex energy plane. We determine the range of $m_\pi/f_\pi$ for which a pole appears below the two-pion threshold, extract the corresponding residue, and, in the non-relativistic limit, obtain the bound-state wave function at the origin, $|\Psi(0)|$, which controls bound-state-assisted annihilation and decay rates relevant for catalyzed freeze-out. Comparing this T-
matrix based result with variational estimates using simple finite-range potentials, we find agreement within order-one factors for shallow binding. For binding energies of order the freeze-out temperature, $E_B \sim m_\pi/20$, we obtain $|\Psi(0)|\sim \mathcal{O}(0.1)\,m_\pi^{3/2}$, thereby supporting the parametric assumptions used in previous phenomenological analyses.
Read the full abstract ▾
High Energy Astrophysical Phenomena
Radiation pressure instability: from heart-beat states in black hole binary systems to Quasars and Changing-Look AGN
Agnieszka Janiuk, Bozena Czerny, Pulkit Ojha et al. (+2 more)
Radiation-pressure instability was identified soon after the seminal classical
accretion disk models of Shakura-Sunyaev and Novikov-Thorne, yet its full implications remain an active area of investigation. These models form the backbone of our understanding of
accretion onto compact objects and successfully describe the phenomenology of black hole and
neutron star X-ray binaries, as well as luminous active
galactic nuclei (AGN), in the regime of high mass
accretion rates. At luminosities approaching a significant fraction of the Eddington limit (L/LEdd > 0.1), standard thin disks are predicted to become thermally unstable due to the dominance of radiation pressure. This prediction has found empirical support in several
Galactic stellar-mass black hole systems, where the instability manifests as quasi-periodic, large-amplitude luminosity oscillations, so-called "heartbeat states", and has been proposed as a driver of observed signatures of deterministic chaos in
accretion-driven light curves. The scope of radiation-pressure-induced variability extends beyond
stellar-mass black holes: both black holes across mass scales and accreting
neutron stars can exhibit related behavior, though the presence of a boundary layer in
neutron stars adds complexity and offers a unique laboratory for testing the interplay between
accretion dynamics and the central object. On extragalactic scales, the instability has been invoked to explain the duty cycles and apparent short lifetimes of
radio-loud AGN, as well as the dramatic spectral-state transitions seen in Changing-Look AGN. (...)
Read the full abstract ▾
All authors Agnieszka Janiuk, Bozena Czerny, Pulkit Ojha, Yuri Cavecchi, Federico Vincentelli
High Energy Astrophysical Phenomena · Cross-listed from gr-qc
Sub-threshold post-merger gravitational waves can constrain the hot nuclear equation of state
Fiona H. Panther and Paul D. Lasky
We show how to coherently combine information from a population of sub-threshold, gravitational-wave binary
neutron star post-merger remnants. Although no individual event in our synthetic population can be claimed as a confident detection, we show how to statistically determine the fraction of merger events that promptly collapse to form a black hole, compared to those for which a
neutron star survives the merger for at least tens of milliseconds. This fraction, when combined with information about the
neutron star mass distribution gleaned from the inspiral portion of the signals, provides an indirect measure of the
neutron star maximum mass. Using conservative measures of the post-merger waveforms, we show that 50-70 events with binary
neutron star inspiral measurements can be combined to give an $11-20\%$ fractional uncertainty on the maximum mass of rapidly rotating, hot
neutron stars, which can potentially be turned into a $12-21\%$ fractional constraint on the Tolman-Oppenheimer-Volkoff mass. We discuss how this measure of the hot
nuclear equation of state can be combined with information of cold
neutron stars to see the effect of temperature on physics in the densest regions of the Universe by providing indirect evidence for first-order phase transitions in
neutron star interiors.
Read the full abstract ▾
Earth and Planetary Astrophysics
Supervised Classification of LEO Debris Families Using Multi-Set Proper Elements
Michael Ling and Yang Yang
Machine learning techniques using proper elements to reconnect families of satellite fragmentation debris have recently advanced, becoming key to space sustainability and domain awareness. However, an evolving circumterrestrial environment may limit their applicability, particularly when models are trained on outdated debris representations. In this work, we devise a computational pipeline using synthetic fragmentation data from explosive breakup events, generated via a Standard Breakup Model and propagated under a high-fidelity dynamical model. Proper elements are extracted using adapted
algorithms for modified equinoctial (MEE), Poincar'e (PNC), and quaternion (QTN) sets. Extending beyond previous approaches limited to MEE space, we include PNC and QTN sets to broaden the dynamical fingerprints available to the classifier. Neural networks trained on various element combinations are used to determine if fragment pairs share a parent. Crucially, we identify a fundamental limitation when applying standard quaternion sets to neural networks: the loss of orbital size information during feature normalization. We introduce an augmented representation (QTN$_p$) that explicitly restores the semi-latus rectum, improving accuracy from 0.31 to 0.60 compared to the standard set. In synthetic Starlink-like LEO experiments, expanding proper-element sets generally improves discrimination. The best model, using a joint feature set (MEE + PNC + QTN), achieves an ROC-AUC of 0.858 compared to 0.789 for the MEE-only baseline, alongside higher accuracy and F1 scores.
Read the full abstract ▾
Astrophysics of Galaxies
Investigating ionising sources and the complex interstellar medium of GHZ2 at $z=12.3$
M. Castellano, L. Napolitano, B. Moreschini et al. (+27 more)
An accurate characterisation of the physical properties of
galaxies at
cosmic dawn is key to understanding the origin of the high abundance of UV-bright
galaxies at z$\gtrsim$10. We exploit deep NIRSpec PRISM observations of GHZ2 to constrain the sources of ionising radiation and the properties of the ISM in this bright, compact, and highly ionising
galaxy at z=12.3. We measure with high significance the prominent N IV, C IV, He II, O III, C III, O II, and Ne III emission features previously detected in shallower observations, and confirm the detection of the N III] $\lambda 1750$ multiplet, yielding tight constraints on the N/O ratio, which is found to be $\simeq$2 times the
solar value. We also detect the Mg II $\lambda 2800$, [Fe IV] $\lambda 2833$ and Si II $\lambda 1812$ doublets, the H8+HeI $\lambda\lambda 3889$ blend, and the Si IV+O IV] $\lambda\lambda 1400$ absorption complex. The O III $\lambda 3133$ fluorescence line is only detected in the first observing epoch, implying variability on a rest-frame time span of 19 days, strongly suggesting the presence of an active
nucleus. Combining the NIRSpec
dataset with available optical and far-infrared constraints from MIRI and ALMA, we show that the emission spectrum of GHZ2 cannot be reproduced by single-density spectro-photometric models. Multi-zone photoionisation modelling performed with the HOMERUN code demonstrates that
star formation must be occurring in a strongly stratified ISM, where both low-/intermediate-density gas and high-density regions (log($n_e$/cm$^{-3}) \gtrsim 4$) coexist. The GHZ2 emission landscape is consistent with either a composite
star-formation plus AGN scenario, or with
star formation occurring in a combination of radiation- and matter-bounded regions. Purely radiation-bounded
stellar models fail to reproduce the observed He II emission, making an additional hard ionising component unavoidable.
Read the full abstract ▾
All authors M. Castellano, L. Napolitano, B. Moreschini, A. Calabrò, L. Christensen, M. Llerena, T. J. L. C. Bakx, F. Belfiore, D. Bevacqua, M. Dickinson, A. Fontana, G. Gandolfi, T. Gasparetto, A. Marconi, S. Mascia, E. Merlin, T. Morishita, T. Nanayakkara, D. Paris, L. Pentericci, B. Pérez-Díaz, G. Roberts-Borsani, S. Rojas Ruiz, P. Santini, T. Treu, E. Vanzella, B. Vulcani, X. Wang, I. Yoon, J. Zavala
High Energy Astrophysical Phenomena
Relativistic MHD simulations of merging and collapsing stars and effects on GRB transient
Agnieszka Janiuk, Gerardo Urrutia, Joseph Saji et al. (+1 more)
Compact binary mergers and the collapse of massive
stars can produce intense transients observable across high-energy wavelengths. Events such as gamma-ray bursts and kilonova emissions are often accompanied by gravitational wave detections, making them crucial sources for multimessenger astrophysics. To explore these phenomena theoretically, state-of-the-art approaches of General Relativistic magnetohydrodynamic simulations are used. We present recent findings from our simulations, and discuss observational consequences of the
stellar/post-merger environment on the gamma ray burst
prompt emission properties.
Read the full abstract ▾
All authors Agnieszka Janiuk, Gerardo Urrutia, Joseph Saji, Piotr Plonka
Astrophysics of Galaxies
J-PAS: First Identification, Physical Properties and Ionization Efficiency of Extreme Emission Line Galaxies
A. Giménez-Alcázar, R. Amorín, J. M. Vílchez et al. (+32 more)
Extreme emission line
galaxies (EELGs) are key tracers of intense
star formation and potential analogues of the sources that reionized the early Universe. Their low-
redshift counterparts offer a unique opportunity to study the physical conditions that enable high ionizing-
photon escape fractions. We present a robust method to photometrically identify EELGs in the J-PAS survey, which provides 56 optical bands over 8500 deg^2. Using data from a fully observed 30 deg^2 region, we combine narrow-band equivalent widths with machine-learning techniques to select
galaxies with emission lines above 300 Å. The method achieves 95% purity and 96% completeness for $i_\mathrm{SDSS}<22.5$ mag. We identify 917 EELGs up to $z=0.8$; spectroscopic cross-matching with DESI/DR1 confirms the reliability of our
redshifts and emission-line measurements. The selected
galaxies show strong correlations between $\xi_\mathrm{ion}$ and EW([OIII]), consistent with previous low- and high-z studies. Most sources exceed the ionizing efficiency threshold required for reionization, reinforcing their role as local analogues of early-Universe
galaxies.
Read the full abstract ▾
All authors A. Giménez-Alcázar, R. Amorín, J. M. Vílchez, A. Hernán-Caballero, M. González-Otero, A. Arroyo-Polonio, J. Iglesias-Páramo, A. Lumbreras-Calle, J. A. Fernández-Ontiveros, L. Bonatto, R. M. González Delgado, C. Kehrig, A. Torralba, P. T. Rahna, Y.Jiménez-Teja, I. Márquez, I. Breda, A. Álvarez-Candal, R. Abramo, J. Alcaniz, N. Benitez, S. Bonoli, S. Carneiro, J. Cenarro, D. Cristóbal-Hornillos, R. Dupke, A. Ederoclite, C. Hernández-Monteagudo, A. Marín-Franch, C. Mendes de Oliveira, M. Moles, L. Sodré Jr., K. Taylor, J. Varela, H. Vázquez Ramió
Astrophysics of Galaxies
Globular Cluster Systems in Dwarf Galaxies: Catalogs and Comparisons
Veronika Dornan and William E. Harris
The connection between a
galaxy's total globular cluster system (GCS) mass and its
halo mass has been studied for decades and it has been found that
galaxies at nearly all observed masses adhere to a linear scaling relation between these properties. However, while we have ample, homogeneous data for
galaxies with
halo masses $M_h \gtrsim 10^{10} M_{\odot}$ the data available for low-mass
galaxies is more sparse, and both GCS mass and
halo mass estimates are determined using varying methodologies. This work compiles all available literature data for
dwarf galaxies with confident
stellar mass and GC count estimates, and converts these estimates to GCS masses and peak
halo masses using a standard conversion. This allows for a consistent comparison of these masses to be made and a complete study of the behaviour of the $M_{GCS}-M_h$ relation to be conducted. We compare the positions of classical
dwarfs on the scaling relation to that of ultra diffuse
galaxies and extremely low-surface brightness
galaxies and find that these non-classical
dwarfs have, on average, systematically higher GC specific frequencies. This also makes them, on average, systematically positively offset from the $M_{GCS}-M_h$ relation, driving much of the high-$M_{GCS}$ scatter observed.
Read the full abstract ▾
High Energy Astrophysical Phenomena
Delving into the depths of NGC 3783 with XRISM III. Birth of an ultrafast outflow during a soft flare
Liyi Gu, Keigo Fukumura, Jelle Kaastra et al. (+18 more)
The 2024 X-ray/UV observation campaign of NGC 3783, led by XRISM, revealed the launch of an ultrafast
outflow (UFO) with a radial velocity of 0.19c (57000 km/s). This event is synchronized with the sharp decay, within less than half a day, of a prominent soft X-ray/UV
flare. Accounting for the look-elsewhere effect, the XRISM Resolve data alone indicate a low probability of 2e-5 that this UFO detection is due to random chance. The UFO features narrow H-like and He-like Fe lines with a velocity dispersion of 1000 km/s, suggesting that it originates from a dense clump. Beyond this primary detection, there are hints of weaker
outflow signatures throughout the rise and fall phases of the soft
flare. Their velocities increase from 0.05c to 0.3c over approximately three days, and they may be associated with a larger stream in which the clump is embedded. The radiation pressure is insuffcient to drive the acceleration of this rapidly evolving
outflow. The observed
evolution of the
outflow kinematics instead closely resembles that of
solar coronal mass ejections, implying
magnetic driving and, conceivably, reconnection near the
accretion disk as the likely mechanisms behind both the UFO launch and the associated soft
flare.
Read the full abstract ▾
All authors Liyi Gu, Keigo Fukumura, Jelle Kaastra, Megan Eckart, Ralf Ballhausen, Ehud Behar, Camille Diez, Matteo Guainazzi, Timothy Kallman, Erin Kara, Chen Li, Missagh Mehdipour, Misaki Mizumoto, Shoji Ogawa, Christos Panagiotou, Matilde Signorini, Atsushi Tanimoto, Keqin Zhao, Hirofumi Noda, Jon Miller, Satoshi Yamada
High Energy Astrophysical Phenomena
Photon Dynamics and Collision Risks in Relativistic Spaceflight: A Comparative Study of Methods and Implications
Li Kai Wen and Joao Rodrigues
This dissertation explores the dynamics of relativistic spaceflight, focusing on the risks associated with collisions and
photon interactions as a spacecraft approaches velocities near the speed of light. The study emphasizes two primary collision types: (1) collisions with interstellar
dust and particles, and (2) interactions with
cosmic molecules, specifically hydrogen. Using principles of energy conservation and relativistic mechanics, the energy transfer from these collisions is calculated, showing that even small particles can impart massive energy at relativistic speeds. The dissertation also examines the impact of the
cosmic microwave background (CMB) radiation, particularly its blue-shifting effect at high velocities, which influences
photon interactions with the spacecraft. Additionally, the Schwinger limit, which sets an upper bound on the electromagnetic field strength for sustained relativistic travel, is discussed in the context of
photon-induced pair production. Lastly, advanced
photon interactions, such as Compton scattering, are analyzed for their role in thermal management and spacecraft design. The findings highlight the importance of shielding, thermal regulation, and collision avoidance strategies in the design of spacecraft for interstellar travel, offering insights into the potential challenges and solutions for achieving relativistic spaceflight.
Read the full abstract ▾
High Energy Astrophysical Phenomena
Self-lensing flares from black hole binaries V: systematic searches in LSST
Kevin Park, Zoltan Haiman, Chengcheng Xin et al. (+3 more)
The Vera C. Rubin Observatory has now seen first light, and over a 10 year duration, LSST is projected to catalogue tens of millions of
quasars, many of which are expected to be associated with sub-parsec supermassive black hole binaries (SMBHBs). Out of these SMBHBs, up to thousands of relatively massive binary-
quasars are expected to exhibit gravitational self-
lensing flares (SLFs) that last for at least 20-30 days. We assess the effectiveness of the Lomb-Scargle (LS) periodogram and matched filters (MFs) as methods for systematic searches for these binaries, using toy-models of hydrodynamical, Doppler, and self-
lensing variability from equal-mass, eccentric SMBHBs. We inject SLFs into random realizations of damped random walk (DRW) lightcurves, representing
stochastic quasar variability, and compute the LS periodogram with and without the SLF. We find that periodograms of SLF+DRW light-curves do not have maximum peak heights that could not arise from DRW-only periodograms. On the other hand, the matched filter signal-to-noise ratio (SNR) can distinguish SLFs from noise even with LSST-like cadences and DRW noise. Furthermore, we develop a three-step procedure with matched filters, which can also recover injected binary parameters from these light-curves. We expect this method to be computationally efficient enough to be applicable to millions of
quasar light-curves in LSST.
Read the full abstract ▾
All authors Kevin Park, Zoltan Haiman, Chengcheng Xin, Tzuken Shen, Ashley Villar, Jordy Davelaar
Astrophysics of Galaxies
Collisional rate coefficients for OH-H$_2$ at high temperatures
Zeno van den Heuvel, Benoît Tabone, Ewine F. van Dishoeck et al. (+2 more)
OH is a cornerstone molecule in the chemistry of interstellar and circumstellar media and is ubiquitously detected in warm gas thanks to its infrared rotational lines. However, the excitation processes of OH remain poorly characterized. We provide a new set of collisional rate coefficients for OH with H$_2$, expanding the existing data to $j$ levels up to $j=15/2$ and temperatures up to 750 K. These rate coefficients are obtained from state-to-state collision cross sections calculated by means of well-converged close-coupling
quantum scattering calculations for collisions of OH with para- and ortho-H$_2$ with energies up to 1700 cm$^{-1}$ ($\simeq 2450$ K). We reproduce the rate coefficients computed by Klos et al. (2017) and extend their results to higher temperatures and higher rotational levels of OH. The de-excitation rate coefficients are lower in collisions with para-H$_2$ ($j_{\rm H_2} = 0$) due to the absence of a quadrupole moment, but this difference decreases at higher temperatures. We find that the rate coefficients follow scaling relations with the energy gap between the upper and lower levels of a given transition, which allows extrapolation to higher OH rotational states $j_{\rm OH}$. As a first application, we show that under astrophysical conditions typical of warm and dense gas around nascent
stars, the populations of low-$j_{\rm OH}$ states are dominated by collisions, even when chemical pumping is included. The full set of rate coefficients is made available in the LAMDA database.
Read the full abstract ▾
All authors Zeno van den Heuvel, Benoît Tabone, Ewine F. van Dishoeck, Gerrit C. Groenenboom, Ad van der Avoird
Astrophysics of Galaxies
Photochemistry of interstellar ice forming Complex Organic Molecules
Guillermo M. Muñoz Caro, Héctor Carrascosa de Lucas and Rafael Martín-Doménech
Astrochemistry is a well-established multidisciplinary field devoted to study molecules in space. While most astrochemists are oriented to observe molecules in the gas phase and reproduce their abundances by modeling the physical conditions of the medium, the microscopic
dust particles wandering in the interstellar medium deserve the
attention of a smaller community. Radiation and thermally-driven processes taking place in the bare
dust, and particularly in
dust particles covered by ice mantles, are mimicked in the laboratory. In addition to water, interstellar ice contains other simple species. In this Review we present our current knowledge on ice photochemistry and thermal processing that ultimately leads to formation of complex organic molecules (COMs). Numerous COMs are of astrobiological interest and match those present in comets and asteroids. Upon impact of these minor bodies, water and COMs were delivered to the earth and might have intervened in the first prebiotic reactions.
Read the full abstract ▾
Astrophysics of Galaxies
Chemical analysis of the Milky Way's Nuclear Star Cluster: Evidence for a metallicity gradient
M. Schultheis, L. Serrano, B. Thorsbro et al. (+5 more)
The Milky Way
nuclear star cluster (MWNSC) is located together with its surrounding
nuclear stellar disc (MWNSD) in the
Galactic centre and they dominate the gravitational potential within the inner 300\,pc. However, the formation and
evolution of both systems and their possible connections are still under debate. We reanalyse the low-resolution KMOS spectra in the MWNSC with the aim to improve the
stellar parameters ($\rm T_{eff}$, $\rm \log\,g$, and $\rm [M/H])$ for the MWNSC. We use an improved line-list, especially dedicated for cool M
giants allowing to improve the
stellar parameters and to obtain in addition global $\rm \alpha$-elements. A comparison with high-resolution IR spectra (IGRINS) gives very satisfactory results pinning down the uncertainties to $\rm T_{eff} \simeq 150\,K$, $\rm log\,g \simeq 0.4\,dex$, and $\rm [M/H] \simeq 0.2\,dex$. Our $\rm \alpha$-elements agree within 0.1\,dex compared to the IGRINS spectra. We obtain a high-quality sample of 1140 M
giant stars where we see an important contribution of a metal-poor population ($\rm \sim 20\,\%$) centered at $\rm [M/H] \simeq -0.7\,dex$ while the most dominant part comes from the metal-rich population with $\rm [M/H] \simeq 0.26\,dex$. We construct a
metallicity map and find a
metallicity gradient of $\rm \sim -0.1 \pm 0.02 \,dex/pc$ favouring the inside-out formation scenario for the MWNSC.
Read the full abstract ▾
All authors M. Schultheis, L. Serrano, B. Thorsbro, F. Nogueras-Lara, A. Feldmeier-Krause, G. Nandakumar, K. Fiteni, M.C. Sormani
High Energy Astrophysical Phenomena
Kick & spin: new probes for multi-messenger black-hole mergers in AGNs
Samson H. W. Leong and Juan Calderón Bustillo
Recoiling remnants of black-hole mergers in dense environments can produce bright electromagnetic (EM) counterparts to the gravitational-wave (GW) emission. Significance assessments of such GW-EM candidates are restricted to time and sky-localisation consistency, omitting the physics governing the EM emission process. Different emission mechanisms, however, impose different observability constraints on the remnant black-hole
recoil and
spin, which are gravitational-wave observables. We present a statistical framework that includes such parameters. We assess the consistency of the GW190521-ZTF19abanrhr pair with two types of emission processes: a Blandford-Znajek jet closely aligned with the final
spin axis and a diffusive isotropic
flare. Assuming the sky-location of ZTF19abanrhr, we find these mechanisms to be respectively strongly and moderately disfavoured with log-evidences $\log_{10}{\cal I}_{\rm jet} = -1.65$ and $\log_{10}{\cal I}_{\rm diff} = -0.075$. Combining these with odds for a common sky-location $\Omega$ we obtain respective combined odds $\log_{10} {\cal O}_{\Omega,{\rm jet}}= -1.17$ and $\log_{10} {\cal O}_{\Omega,{\rm diff}}= +0.39$ for a true GW-EM coincidence as opposed to a random one. Our method leverages a previously unexplored evidence axis to assess GW-EM associations and constrain both the physics powering
flare mechanisms and the properties of AGNs.
Read the full abstract ▾
Cosmology and Nongalactic Astrophysics · Cross-listed from gr-qc
Probing Cosmic Strings via Black Hole Quasinormal Modes in Gravitational Wave Astronomy
Ishan Swamy and Deobrat Singh
Black holes, the simplest solution to Einstein's field equations, do not emit light, making their observations a major challenge for researchers. However, discovery of binary black holes (BBHs) in 2015 by LIGO has transformed the study of compact objects, with over 300 BBHs recorded, providing a new avenue for probing new physics. GWs remain a prominent and precise method of observing not only BBHs, but also dark matter and
cosmic strings.
Cosmic strings – hypothetical one dimensional topological defects formed in the early universe, are yet to be observed, with multiple detection methods such as particle radiation, gravitational waves and
lensing being proposed. Here we present a novel framework to search for
cosmic strings by modeling them as perturbations within non-rotating black hole spacetime, focusing on their imprint on the spectrum of quasinormal modes (QNMs). Our numerical simulations identify a lower limit on perturbation strength, $\lambda \sim 10^{-10}$ for uncharged string and $\lambda \sim 10^{-7}$ for charged string, below which
cosmic string effects become unobservable in QNM signals. By analyzing
eigenvalue splitting and centers, we show that
cosmic string properties impart distinct and detectable features to GW signals. Our results establish QNM analysis as a powerful, alternative observational strategy for constraining or detecting
cosmic strings, and offer an inverse approach to estimate string energy or charge if a signal is detected. With upgrades in LIGO technologies and advanced multimessenger astronomy under development, these findings highlight new potential for detecting
cosmic strings.
Read the full abstract ▾
Solar and Stellar Astrophysics
Extremely energetic EUV late phase of a pair of C-class flares caused by a non-eruptive sigmoid
Ya Wang, Sargam M. Mulay and Lyndsay Fletcher
The EUV late phase is the second increase of the irradiance of the warm coronal lines during
solar flares, and has a crucial impact on the Earth's ionosphere. In this paper, we report on the extremely energetic EUV late phase of a pair of C-class
flares (SOL2012-06-17T17:26:11) observed on 2012 June 17 in NOAA active region 11504 by the Atmospheric Imaging Assembly (AIA) instrument on board the
Solar Dynamics Observatory (SDO). The light curves integrated over the flaring region show that a factor of 4.2 more energy is released in the “warm” (2$-$3$\times 10^6$~K) temperature passbands (e.g. AIA 335 Å) during the late phase than during the main peaks. The origin of the emission in this extremely energetic EUV late phase is a non-eruptive sigmoid situated in a multi-polar
magnetic field configuration, which is rapidly energised by C-class
flares. The sigmoid
plasma appears to reach temperatures in excess of $10^7$~K, before cooling to produce the EUV late-phase emission. This is seen in high-temperature passbands (e.g. AIA 131 Å) and by using differential emission measure analysis.
Magnetic extrapolations indicate that the sigmoid is consistent with formation by
magnetic reconnection between previously existing J-shaped loops. The sigmoid experienced a fast and a slow cooling stages, both of which were dominated by conductive cooling. The estimated total cooling time of the sigmoid is shorter than the observed value. So, we proposed that the non-eruptive sigmoid, heated by the continuous
magnetic reconnection, leads to the extremely energetic EUV late phase.
Read the full abstract ▾
Instrumentation and Methods for Astrophysics
PolySwyft: sequential simulation-based nested sampling
Kilian H. Scheutwinkel, Will Handley, Christoph Weniger et al. (+1 more)
We present PolySwyft, a novel, non-amortised simulation-based inference framework that unites the strengths of nested sampling (NS) and neural ratio estimation (NRE) to tackle challenging posterior distributions when the likelihood is intractable but a forward simulator is available. By nesting rounds of NRE within the exploration of NS, and employing a principled KL-divergence criterion to adaptively terminate sampling, PolySwyft achieves faster convergence on complex,
multimodal targets while rigorously preserving
Bayesian validity. On a suite of toy problems with analytically known posteriors of a dim(theta,D)=(5,100) multivariate Gaussian and multivariate correlated Gaussian mixture model, we demonstrate that PolySwyft recovers all modes and credible regions with fewer simulator calls than swyft's TNRE. As a real-world application, we infer cosmological parameters dim(theta,D)=(6,111) from CMB power spectra using CosmoPower. PolySwyft is released as open-source software, offering a flexible toolkit for efficient, accurate inference across the astrophysical sciences and beyond.
Read the full abstract ▾
All authors Kilian H. Scheutwinkel, Will Handley, Christoph Weniger, Eloy de Lera Acedo
High Energy Astrophysical Phenomena
Machine learning classification of baseband data of CHIME FRBs
Mohanraj Madheshwaran, Tetsuya Hashimoto, Tomotsugu Goto et al. (+5 more)
Fast
Radio Bursts (FRBs) are bright millisecond
radio pulses. Their origin is still unknown in the field of astronomy. A notable distinction among FRBs is that some sources repeat, while others appear to be non-repeating events. Interestingly, repeating FRBs tend to exhibit broader temporal widths and narrower spectral bandwidths compared to non-repeat events, suggesting they may arise from different physical mechanisms. However, current
radio telescopes have limited coverage and sensitivity, which hinders a complete survey with continuous long-term monitoring. This issue makes it difficult to confirm repeat activity and potentially leads to misclassification of repeaters as non-repeaters; these are referred to as repeater candidates. To address this, machine learning techniques have emerged as a useful tool for classifying distinct FRB types in previous studies. In this study, we utilize the CHIME/FRB baseband catalog with three orders of magnitude better time resolution than the intensity catalog. Measured fluences are available in the baseband catalog, while only upper limits are reported in the intensity catalog. We apply machine learning to the baseband catalog to evaluate classification outcomes. We identify 15 repeater candidates among 122 non-repeating FRBs in the baseband catalog. Additionally, our classification identifies 31 sources previously categorized as repeater candidates as non-repeaters, highlighting a significant difference from the prior work. Of these repeater candidates, 14 overlap with previous findings, while 1 is newly identified in this work. Notably, one of our candidates was confirmed as a repeater by CHIME/FRB. Follow-up observations for the 14 candidates are highly encouraged.
Read the full abstract ▾
All authors Mohanraj Madheshwaran, Tetsuya Hashimoto, Tomotsugu Goto, William J. Pearson, Murthadza Aznam, Simon C.-C. Ho, Vignesh V.V. Rao, Sridhar Gajendran
Solar and Stellar Astrophysics
Magnetic activity of ultracool dwarfs in the LAMOST DR11
Yue Xiang, Shenghong Gu and Dongtao Cao
Ultracool
dwarfs consist of lowest-mass
stars and brown
dwarfs. Their interior is fully convective, different from that of the partly-convective Sun-like
stars.
Magnetic field generation process beneath the surface of ultracool
dwarfs is still poorly understood and controversial. To increase samples of active ultracool
dwarfs significantly, we have identified 962 ultracool
dwarfs in the latest LAMOST data release, DR11. We also simulate the Chinese Space Station Survey
Telescope (CSST) low-resolution slitless spectra by degrading the LAMOST spectra. A semi-supervised machine learning approach with an autoencoder model is built to identify ultracool
dwarfs with the simulated CSST spectra, which demonstrates the capability of the CSST all-sky slitless spectroscopic survey on the detection of ultracool
dwarfs.
Magnetic activity of the ultracool
dwarfs is investigated by using the H$\alpha$ line emission as a proxy. The rotational periods of 82 ultracool
dwarfs are derived based on the Kepler/K2 light curves. We also derive the activity-rotation relation of the ultracool
dwarfs, which is saturated around a Rossby number of 0.12.
Read the full abstract ▾
Cosmology and Nongalactic Astrophysics
Isocurvature Induced Gravitational Waves at Pulsar Timing Arrays
Yi-Fu Cai, Peizhi Du and Jiahang Zhong
Gravitational waves (GWs) are powerful probes of new physics in the early Universe. In particular, GWs induced by
primordial isocurvature perturbations encode information of novel dynamics beyond the standard $\Lambda$CDM model. Existing studies of isocurvature induced GWs focus on a particular type: cold dark matter (CDM) isocurvature. In this work, we present a more comprehensive study of four kinds of isocurvature involving CDM,
baryons,
neutrinos and free-streaming dark radiation (DR). We first reformulate initial conditions of isocurvature with coupled
neutrinos because modes relevant for observations at
Pulsar Timing Arrays enter the horizon before
neutrino decoupling. With these new initial conditions,
neutrino isocurvature is phenomenologically similar to CDM isocurvature up to an overall coefficient, which leads to an interesting conversion of isocurvature between radiation and matter sectors. We then find that the spectrum of isocurvature induced GWs from free-streaming DR is qualitatively different than that from CDM due to the presence of anisotropic stress. Unlike GWs induced by CDM isocurvature that are suppressed at high frequencies due to matter density being suppressed at early times, DR isocurvature induced GWs is proportional to the constant ratio between DR density and total radiation. Finally, we utilize two general parametrizations of the isocurvature power spectrum: a delta function and a broken power law, and derive novel constraints with recent NANOGrav data. Our results set stringent constraints on isocurvature around $10^{6}\,\textrm{Mpc}^{-1}$, which are complementary to cosmological observations at large scales.
Read the full abstract ▾
Astrophysics of Galaxies
The Milky Way Imaging Scroll Painting Survey: Data Release 1
Ji Yang, Qing-Zeng Yan, Yang Su et al. (+32 more)
We present the first data release (DR1) of the Milky Way Imaging Scroll Painting (MWISP) survey, a mapping in the J=(1-0) transition lines of 12CO, 13CO, and C18O toward the northern
Galactic plane during 2011-2022. The MWISP survey was conducted using the PMO 13.7 m
telescope at a spatial resolution of approximately 50" and a velocity resolution of 0.16 km/s at 115 GHz. DR1 fully covered 2310 square degrees within the
Galactic longitude (l) and latitude (b) range of 9.75 deg =< l =< 229.75 deg and |b| =< 5.25 deg. The surveyed area was divided into
cell units of 30'x30' for practical purposes and On-The-Fly (OTF) mapping was performed toward each target
cell unit. The data were regridded into a regular 3D datacube in l-b-V_LSR with a pixel size of 30" in l-b axes and 0.16 km/s in theV_LSR axis. The median rms noise is 0.47 K, 0.25 K, and 0.25 K for 12CO, 13CO, and C18O, respectively. The equivalent 3 sigma sensitivity in 12CO luminosity is approximately 0.23 K km/s, making MWISP the most sensitive survey of its kind. In this paper, we describe the survey data, including the calibration, data cleaning, data mosaic processes, and the data products. The final mosaicked data cubes contain about 3.33x10^7 spectra (pixels) for each CO isotopologue line. Color composite images, made from the intensities of the isotopologue lines, and some concise descriptions are provided. We constructed a molecular cloud catalog based on the mosaicked 12CO data cube using the clustering
algorithm DBSCAN, detecting 103,517 molecular clouds, 10,790 of which exhibit 13CO emission and 304 of which show C18O emission. Based on the histogram of voxel brightness temperature, we estimated a total 12CO flux of 7.69+/-0.38x10^7 K km/s arcmin^2, 82% of which is captured by the DBSCAN
algorithm. The data, together with the cloud sample, provide unique information on molecular gas in the northern Milky Way.
Read the full abstract ▾
All authors Ji Yang, Qing-Zeng Yan, Yang Su, Shaobo Zhang, Xin Zhou, Yan Sun, Yiping Ao, Xuepeng Chen, Zhiwei Chen, Fujun Du, Min Fang, Yan Gong, Zhibo Jiang, Shengyu Jin, Binggang Ju, Chong Li, Yingjie Li, Yi Liu, Dengrong Lu, Chunsheng Luo, Yuehui Ma, Ruiqing Mao, Jixian Sun, Chen Wang, Hongchi Wang, Min Wang, Min Wang, Xindong Wang, Wenting Xu, Ye Xu, Kun Yan, Ping Yan, Lixia Yuan, Miaomiao Zhang, Yongxing Zhang
Earth and Planetary Astrophysics
The Impact of Irradiation on the Radius and Thermal Evolution of Transiting Brown Dwarfs
Sagnick Mukherjee, Jonathan J. Fortney, Theron W. Carmichael et al. (+2 more)
Masses and radii of transiting brown
dwarfs can be measured directly in contrast to isolated field brown
dwarfs, whose mass and radius inferences are model dependent. Therefore, transiting brown
dwarfs are a testbed for the interior and evolutionary models of brown
dwarfs and
giant exoplanets. We have developed atmospheric and evolutionary models for this emerging population. We show that intense
stellar irradiation can cause a large enhancement in the radius of transiting brown
dwarfs at all masses, especially if the incident flux exceeds $log_{10}(F/cgs)\ge$9 ($T_{\rm eq}\ge 1450$ K).
Stellar irradiation can significantly alter rates of
nuclear burning in irradiated brown
dwarfs, making the Deuterium-burning and Hydrogen-burning minimum masses strong functions of incident
stellar flux. We show that the D-burning and H-burning minimum masses can decrease by 16% and 13%, respectively, between isolated and strongly irradiated brown
dwarfs ( $log_{10}(F/cgs)\ge$10 ($T_{\rm eq}\ge 2570$ K)). This shows that
stellar irradiation has a larger impact on the
planet-brown
dwarf-
star mass boundaries than
metallicity or clouds. We show that metal cores or migration affect their
evolution to a much lesser extent, whereas low mass highly irradiated old sources can help us test the physics of hot Jupiter radius anomaly. We fit the observed radii of 46 transiting brown
dwarfs and show that our irradiated evolutionary models fit their radii better than models that ignore the host
star, especially for highly irradiated objects. However, the measured radii of 10 objects are still inconsistent at $>3\sigma$ level, indicating residual gaps in our irradiated evolutionary model.
Read the full abstract ▾
All authors Sagnick Mukherjee, Jonathan J. Fortney, Theron W. Carmichael, C. Evan Davis, Daniel P. Thorngren
High Energy Astrophysical Phenomena
The Head-on Collision of a Neutron Star with a White Dwarf
Zong-kai Peng, He Gao and Xian-Fei Zhang
We have computed the physical processes involved in a head-on collision between a
neutron star (NS) and a white
dwarf (WD). The outcomes of such collisions vary depending on the mass and type of the WD. We have separately examined the dynamical processes for collisions between NSs and helium WDs (He-WDs), carbon-oxygen WDs (CO-WDs), and oxygen-neon WDs (ONe-WDs). We aim to investigate whether the collision can trigger a thermonuclear explosion of the WD, and if not, whether the NS can remain bound within the WD to form a Thorne-Zytkow-like object (TZlO). For a thermonuclear explosion to occur, at least two conditions must be satisfied: (i) the collision-induced temperature must reach the ignition threshold of the relevant
nuclear reactions, and (ii) the burning material must remain in a degenerate state. For different types of WDs, there exist parameter ranges where both conditions are fulfilled, implying that NS-WD collisions can indeed induce thermonuclear explosions, leading to sub-Chandrasekhar Type Ia
supernovae or other exotic optical transients powered by thermonuclear explosion. On the other hand, the formation of a TZlO requires that the WD material exerts sufficient drag on the NS to prevent its escape, while the interaction must not trigger a thermonuclear explosion of the WD. Our results indicate that such conditions can be realized in the case of low-mass CO-WDs and low-mass ONe-WDs, provided that the viscous coefficient is sufficiently large.
Read the full abstract ▾
Solar and Stellar Astrophysics
The Birth of Be Star Disks II. A High-Resolution Spectroscopic Campaign and TESS Observations of an Outburst of the Classical Be star {\lambda} Pavonis
Sola S. Nova, Noel D. Richardson, Jonathan Labadie-Bartz et al. (+1 more)
Be
stars are rapidly-rotating B
stars that have shown emission lines originating in a circumstellar disk. The mechanisms that lead to disk formation and dissipation are not known although progress has been made with some systems. We present a study of a disk outburst of the Be
star lambda Pavonis. Our
dataset comprises 698 high-resolution spectra contemporaneous with TESS photometry in 2023. Near the end of TESS monitoring, the
star began disk building from a pristine diskless state. We find the disk built within 5 days in optical H I and He I lines, while the disk circularized in about 12 days. The disk began to decay in higher excitation He I first, then lower excitation transitions, with the decay ending last for H-alpha. We examine non-radial pulsations both through TESS photometry and the line profile variations (LPVs) in the spectroscopy. Our analysis indicates that two periodicities seen in TESS photometry (at 1.644 and 1.485 cycles/d) are not seen in the spectral lines before, during, or after the outburst. The strongest photometric signal is a periodicity at 0.163 cycles/d, which appears as a difference between the two weaker signals and is visible in the spectra without any apparent changes in amplitude or phase. We additionally find evidence for fast non-photometric pulsational variations over the course of spectroscopy obtained before, during, and after the outburst. These fast LPVs are strong, and interfere with the two weaker signals, hampering our ability to detect them in spectroscopy.
Read the full abstract ▾
All authors Sola S. Nova, Noel D. Richardson, Jonathan Labadie-Bartz, Samantha Garcia Flores
High Energy Astrophysical Phenomena
Multi-wavelength Signatures of Supernova Shock Breakout from Red Supergiants in Two Dimensions
Wun-Yi Chen, Ke-Jung Chen, Keiichi Maeda et al. (+3 more)
We present new two-dimensional radiation hydrodynamic simulations of
supernova shock breakout from red supergiants using the $\texttt{CASTRO}$ code. Our progenitors are 20 and 25 M$_{\odot}$
solar-
metallicity stars evolved from the zero-age main sequence with $\texttt{MESA}$ and exploded in one dimension using $\texttt{FLASH}$. We consider a range of circumstellar media (CSM) produced by
stellar winds to investigate how pre-explosion mass-loss affects shock breakout. The multigroup flux-limited
diffusion scheme in $\texttt{CASTRO}$ captures the interaction between the explosion shock, its radiation precursor, and the surrounding CSM. We find that strong radiation precursors, generated by radiation leakage behind the shock, can drive fluid instabilities and move the effective photosphere outward before the shock reaches the
stellar surface. The resulting breakout emissions reach peak luminosities of ${\sim}10^{44}$ erg s$^{-1}$ with full-width half-maximum durations of 1-3 hr, , fainter and longer than previous 1D models. The light-curve colors gradually evolve from blue to red after the peak. The 25 M$_{\odot}$ model with explosion energy $E \sim 1.69\times10^{51}$ erg produces ${\sim}$10-30% higher maximum luminosity than the 20 M$_{\odot}$ model with $E \sim 1.09\times10^{51}$ erg. The dense CSM further extends the breakout rise time by increasing the
photon diffusion. These results provide new constraints on red supergiant atmospheres and mass-loss histories prior to core collapse.
Read the full abstract ▾
All authors Wun-Yi Chen, Ke-Jung Chen, Keiichi Maeda, Masaomi Ono, Po-Sheng Ou, F. K. Roepke
High Energy Astrophysical Phenomena
First detection of X-ray polarization from the long-period X-ray pulsar 4U 1954+319
Alexander Salganik, Lingda Kong, Sofia V. Forsblom et al. (+6 more)
We report the first detection of X-ray polarization with the Imaging X-ray Polarimetry Explorer from the X-ray
pulsar (XRP) 4U 1954$+$319. The source belongs to an extremely rare class of systems in which a slowly rotating
neutron star accretes from the dense wind of a red supergiant companion. We detect coherent pulsations at $P_{\rm spin}=5.49\pm0.05$ h, which is one of the longest
spin periods known among XRPs. While the phase-averaged analysis shows no significant polarization, with a 99% confidence minimum detectable polarization (MDP$_{99}$) of 4.9% in the 2-8 keV band, the phase-resolved analysis shows a single interval at pulse maximum in which the polarization degree (PD) exceeds the MDP$_{99}$, yielding ${\rm PD}=10.2_{-3.0}^{+3.1}$%. The polarization angle (PA) exhibits a smooth $\approx150^{\circ}$ rotation over the pulse, and a joint evaluation of all phase bins yields an overall detection significance of $3.3\sigma$. Using the rotating vector model, we identify a
geometric solution that reproduces the observed PA variation. From this model, we infer a phase-independent ${\rm PD}$ of $6.1\pm1.1$% in the 2-8 keV band.
Read the full abstract ▾
All authors Alexander Salganik, Lingda Kong, Sofia V. Forsblom, Menglei Zhou, Honghui Liu, QingChang Zhao, Sergey S. Tsygankov, Andrea Santangelo, Juri Poutanen
Astrophysics of Galaxies
Supermassive Black Holes with High Accretion Rates in Active Galactic Nuclei. XV. Reverberation Mapping of Mg II Emission Lines
Hua-Rui Bai, Pu Du, Chen Hu et al. (+25 more)
As the 15th paper in a series reporting on a large reverberation mapping (RM) campaign of super-Eddington accreting massive black holes (SEAMBHs) in active
galactic nuclei (AGNs), we present the results of measurements of the Mg II lines in 18 SEAMBHs monitored spectroscopically from 2017 to 2024. Among these, the time lags of Mg II have been successfully determined for 8 of the 18 objects, thereby expanding the current Mg II RM sample, particularly at higher
accretion rates. By incorporating measurements of the line widths, we determine the masses of their central supermassive black holes. Based on these new measurements, we update the relation between the Mg II radius and the monochromatic luminosity at 3000 $\mathring{\mathrm{A}}$ ($R_{\rm MgII}-L_{3000}$ relation), yielding a slope of $0.24 \pm 0.03$, which is slightly shallower than, yet still consistent with, previously reported values. Similar to the H$\beta$ lines, the Mg II time lags in SEAMBHs are shorter than those of AGNs with normal
accretion rates at comparable luminosities. The deviation of AGNs from the best-fit $R_{\rm MgII}-L_{3000}$ relation shows a strong correlation with the
accretion rate, while no significant correlation is found between the deviation and the flux ratio of UV iron to Mg II.
Read the full abstract ▾
All authors Hua-Rui Bai, Pu Du, Chen Hu, Yong-Jie Chen, Zhu-Heng Yao, Yan-Rong Li, Yi-Xin Fu, Yi-Lin Wang, Yu Zhao, Hao Zhang, Jun-Rong Liu, Sen Yang, Yue-Chang Peng, Feng-Na Fang, Yu-Yang Songsheng, Ming Xiao, Shuo Zhai, Sha-Sha Li, Kai-Xing Lu, Zhi-Xiang Zhang, Dong-Wei Bao, Wei-Jian Guo, Jia-Qi Feng, Yi-Peng Zhao, Jesús Aceituno, Jin-Ming Bai, Luis C. Ho, Jian-Min Wang
Solar and Stellar Astrophysics
Follow-up Observations of Candidate White Dwarf Planets with MIRI
Fergal Mullally, Susan E. Mullally, Misty Cracraft et al. (+6 more)
We report on second-epoch imaging of two candidate
planet-hosting white
dwarfs stars, WD2105-82 and WD1202-232. Both
stars showed evidence of resolved,
planet-mass candidate companions in observations using the MIRI mid-infrared imager on JWST. WD2105-82 also showed evidence of an infrared excess consistent with an unresolved 1.4 Jupiter mass companion with an orbital separation of <4 au. Our second epoch observations confirm that the source of the excess shares common proper motion with the
star. The excess is almost certainly due to a companion
planet or debris disk. However, neither of the two resolved sources with projected separations of >1" in the first epoch of JWST observations show measurable proper motion and are thus likely faint, unresolved background
galaxies. We also search for common proper motion companions out to hundreds of au, but find no evidence of widely separated companions.
Read the full abstract ▾
All authors Fergal Mullally, Susan E. Mullally, Misty Cracraft, Samantha N. Bianco, Loic Albert, John Debes, J. J. Hermes, Mukremin Kilic, William T. Reach