Cosmology and Nongalactic Astrophysics
Inferring Cosmology and Astrophysics from the High-redshift 21cm Signal with SKA-Low
Anshuman Acharya, Satadru Bag, Sabrina Berger et al. (+29 more)
The Square Kilometre Array's low frequency
telescope (SKA-Low) will enable inference of astrophysical and cosmological parameters from the redshifted 21 cm signal, probing the
Cosmic Dawn and Epoch of Reionisation. While the power spectrum is the primary target for initial detection, the inherently non-Gaussian nature of the 21 cm signal, driven by the patchy
evolution of ionised regions and
spin temperature fluctuations, encodes rich information accessible through higher-order statistics and morphological measurements. Extracting these constraints requires diverse inference tools, encompassing both sophisticated modelling frameworks (analytical, semi-numerical, numerical, and emulators) used to predict the 21 cm signal, and advanced inference techniques (
Bayesian, simulation-based, field-level) to connect statistics to the underlying physics. This chapter reviews these tools and explores the constraining power of different statistical probes accessible with SKA-Low, including the power spectrum, statistics beyond order two, moments of the signal distribution, and morphological measures. Combining these complementary statistics is crucial for breaking parameter degeneracies and unveiling the properties of the early Universe. We specifically assess the potential of the initial SKA-Low configuration (AA*) to measure
galaxy and IGM properties, demonstrating its capability for early science results. This chapter forms part of a comprehensive set detailing the Epoch of Reionisation and
Cosmic Dawn science case for the SKA-Low
telescope.
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All authors Anshuman Acharya, Satadru Bag, Sabrina Berger, Michele Bianco, Daniela Breitman, Lilian Crascall-Kennedy, Saswata Dasgupta, Abhirup Datta, Marian Douspis, Ivelin Georgiev, Sambit K. Giri, Adélie Gorce, Caroline Heneka, Julien Hiegel, Ian Hothi, Akanksha Kapahtia, Nicholas Kern, Yashrajsinh Mahida, Barun Maity, Suman Majumdar, Romain Mériot, Rajesh Mondal, Steven G. Murray, Leon Noble, Samit Kumar Pal, Aurel Schneider, Benoit Semelin, Abinash Kumar Shaw, Hayato Shimabukuro, Emilie Thélie, Anshuman Tripathi, Cathryn M. Trott
Astrophysics of Galaxies
MSA-3D: Rotation Curves and Dark Matter Fractions at z~0.5-1.7 with JWST/NIRSpec
Juan M. Espejo Salcedo, Danail Obreschkow, Karl Glazebrook et al. (+17 more)
We present rotation curves and inner mass distributions for 30
star-forming
galaxies at $0.5<z<1.7$, observed with JWST/NIRSpec as part of the MSA-3D Cycle 1 survey. Combining spatially resolved ionised-gas kinematics with JWST/NIRCam imaging, we constrain baryonic and dark matter contributions through forward dynamical modelling for
galaxies extending down to
stellar masses of $\sim10^{9}M_\odot$. For the 23
galaxies in our primary statistical sample, we find predominantly rotationally supported disks with intrinsic dispersions $\sigma_0\sim31$-65 km s$^{-1}$ and a wide range of dark matter fractions, $f_{DM}(R_e)\sim0.1$-0.9, with a median of 0.63 and substantial
galaxy-to-
galaxy scatter of $\sim0.2$ dex. These results are supported by a complementary consistency check using
stellar mass maps and SFR-derived gas profiles. Among the 19
galaxies reaching $\gtrsim2R_e$, we identify six rising, six flat, and seven falling rotation curves. These classes define an observed ordering from rotationally dominated, dark-matter-rich disks ($V_{rot}/\sigma_0\approx4$, $f_{DM}\gtrsim0.7$) to more dispersion-supported systems with centrally concentrated baryonic mass distributions ($V_{rot}/\sigma_0\approx2$, $f_{DM}\lesssim0.55$). The
stellar Tully-Fisher relation lies close to the local relation evolved under the adopted self-similar $\Lambda$CDM scaling. A simplified seeing-degradation test shifts the inferred normalisation by ~0.2 dex at fixed $V_c$, suggesting that spatial resolution contributes to, but does not fully explain, differences among high-
redshift Tully-Fisher measurements. Overall, MSA-3D provides a high-resolution extension of previous surveys toward lower
stellar masses, spanning $9.0 < \log(M_\star/M_\odot) < 11.2$, and reinforces that
star-forming disks near $z\sim1$ span a broad range of dynamical states and inner mass distributions.
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All authors Juan M. Espejo Salcedo, Danail Obreschkow, Karl Glazebrook, Tucker Jones, Ivana Barišić, Natascha M. Förster Schreiber, Takafumi Tsukui, Xin Wang, Mengting Ju, Qianqiao Zhou, Amit Nestor-Schachar, Ryan L. Sanders, Stavros Pastras, Namrata Roy, Alaina Henry, Kyle Westfall, Themiya Nanayakkara, Matthew Malkan, Fahmi M. Al Farisy, Isaac Kanowski
High Energy Astrophysical Phenomena
Mass-Ratio Reversal as an Alternative to Hierarchical Mergers for GW241011
Rui-Chong Hu, Ying Qin and Bing Zhang
Recent gravitational-wave (GW) observations have revealed binary black hole (BBH) mergers with both extreme mass ratios and large effective
spin parameters ($\chi_{\rm{eff}}$). GW241011 is a notable example that shows these properties. Although hierarchical mergers (second-generation + first-generation BHs) can naturally produce high
spins and become more prevalent than first-generation + first-generation mergers at mass ratios $q \lesssim 0.6$, they are negligible at the extreme mass ratio $\sim 0.3$ and are further limited by gravitational
recoil kicks that can eject the second-generation BH from the host environment. Moreover, recent studies have argued against a dynamical origin for GW241011. Here, we investigate the formation of GW241011-like systems through the mass-ratio reversal (MRR) channel in isolated binary
evolution. By quantifying the probability of producing such systems across a range of binary-
evolution models, we identify the key dependencies on
stellar-
evolution and binary-interaction physics. Our results demonstrate the conditions under which the MRR channel can provide a viable alternative to hierarchical mergers for GW241011-like events, although its predicted merger rate density remains relatively low.
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High Energy Astrophysical Phenomena
Polarimetry of Ultraluminous X-ray sources
Haruka Sakemi
Ultraluminous X-ray sources (ULXs) are non-
nuclear X-ray emitters exceeding the Eddington luminosity, offering key insights into extreme
accretion physics. Their origin is attributed to either sub-Eddington
accretion onto intermediate-mass black holes (IMBHs) or supercritical
accretion onto
stellar-mass compact objects in binary systems. A subset of ULXs shows
radio jets and surrounding bubbles, indicative of strong mechanical feedback, but no polarization detection has been reported to date because of limited sensitivity and angular resolution at multi-megaparsec distances. Next-generation facilities such as the Square Kilometre Array (SKA) will enable polarimetric studies of ULX
outflows and bubbles, providing vital information on their
magnetic field structure and jet-ISM interactions. Using Holmberg II X-1 (3.39 Mpc) as a representative system, we evaluated the detectability of its polarized jet and bubble with the SKA-Mid AA4 configuration. Assuming a fractional polarization of 20% and Band 2 observations centered at 1310 MHz, the expected polarized intensities are 260 $\mu$Jy beam$^{-1}$ for the jet and 20 $\mu$Jy beam$^{-1}$ for the bubble. A Holmberg II X-1-like jet is detectable within 10 hours even at $\sim$ 10 Mpc, while bubble polarization requires $\sim$ 100 hours. Although resolving fine structures is feasible only for nearby ULXs, future SKA-VLBI capabilities will help overcome this limitation and enable detailed mapping of
magnetic field morphology. These results indicate that the SKA will enable the first detection of polarized emission from ULXs, advancing our understanding of
magnetic field geometry, jet formation, and feedback in super- and sub-Eddington accretors.
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Astrophysics of Galaxies
An ACA map of a molecular cloud interacting with supernova remnant W28
Tian-Yu Tu, Wenjin Yang, Siyi Feng et al. (+4 more)
Supernova remnants (SNRs) strongly influence the physical and chemical properties of the molecular clouds (MCs) with which they interact. We carried out a high-resolution observation toward W28F, a chemically rich MC interacting with SNR W28, with the Atacama Compact Array (ACA) in Band 7. Significant emission (> 10 sigma) of CO, CH3OH, p-H2CO, SiO and SO is detected. We reveal the clumpy structures of the shocked MC, with different spatial distributions between CH3OH and SiO. We select six molecular clumps to conduct spectral decomposition and non-local-thermodynamic-
equilibrium analysis with the CH3OH and p-H2CO lines. The best-fit results show a H2 density of nH2 ~ (1-3) * 10^5 cm^-3 and a gas temperature of Tgas ~ 50-170 K in most of the fitted components. The H2 density and gas temperature show a clear anti-correlation across different regions, with the thermal pressure consistent with that of the adjacent X-ray-emitting hot
plasma. This is consistent with the picture that the SNR shocks propagate into multi-phase gas, with a pressure balance existing between different phases. We propose that the high abundance ratio between E-CH3OHand A-CH3OH (> 0.9) suggests extra gas-phase processes to enhance this ratio, such as
proton exchange with H3+ and HCO+. The chemical segregation between CH3OH and SiO, in both the spatial and spectral regime, can be explained by the fact that CH3OH traces slow shocks while SiO traces fast shocks.
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All authors Tian-Yu Tu, Wenjin Yang, Siyi Feng, Valentine Wakelam, Yang Chen, Ping Zhou, Qian-Qian Zhang
High Energy Astrophysical Phenomena
Shortterm optical variability of 4C 29.45
Aykut Özdönmez
We observed the flat-spectrum
radio quasar 4C 29.45 in the BVRI optical bands for 39 nights from February 2022 to July 2022 with the T60
telescope at TÜBİTAK National Observatory (TUG) in Turkey. In this study, we aimed to study flux, color, and spectral variability on short timescales. The object was in an active (bright) phase with an average optical R-band brightness of 14.7 mag and was variable in the BVRI bands throughout the monitoring period. We analyzed the flux variability during our observation period, and the variability amplitudes in V, R, and I bands were determined to be 220%, 208%, and 209%, respectively. Optical spectral energy distributions of 4C 29.45 were derived from the observational data of 33 nights, indicating spectral indices ranging from 1.032 to 1.573. We found modest correlations between optical light curves, and between R-band light curve and spectral indices, suggesting that the time lag ranges from several hours to days. Investigation on relation between spectral and color indices versus R-band magnitude revealed achromatic trend during the bright phase of 4C 29.45 in the first half of 2022. Our periodicity search suggested that the periodicity would be larger than 100 days, and no significant signal for periodicity was found for short timescales.
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Astrophysics of Galaxies
Unraveling the Imprints of Fluctuation-dynamo on the Intracluster Medium with the SKA
Aritra Basu, Sharanya Sur, Nadia Biava et al. (+1 more)
Studying the morphology and coherence scale of the
magnetic fields in synchrotron emitting
halos of
galaxy clusters through detection of polarized synchrotron emission is important in order to understand how they distribute relativistic
plasma, their contribution to pressure balance, and how they may affect gas content in
galaxies and set up initial conditions during non-linear collapse to eventually form
galaxies in the intracluster medium (ICM). Using synthetic maps over broad-bandwidths, generated from high resolution magnetohydrodynamic simulations of fluctuation dynamo, we study the efficacy of SKA-Low and Mid in Array Assembly AA4 in our quest for detecting polarized synchrotron emission from the intracluster medium (ICM). Fluctuation dynamo action in the ICM are expected to generate ubiquitous filamentary and sheet-like
magnetic field structures. The associated synchrotron emission projected in the plane of the sky appear highly filamentary that can span hundreds of kiloparsecs. Such filaments can be robustly identified and quantified through high angular resolution ($\lesssim 1^{\prime\prime}$), sensitive observations (about $\rm 0.25\textrm{--}1\,\mu Jy\,beam^{-1}$) above about 3\,GHz, a niche for the SKA-Mid in Band\,5a. Statistical properties of polarized emission and morphological measures, such as, Minkowski functionals, can then be used to infer the
turbulence driving scales in the ICM with deep observations of
galaxy clusters using SKA-Mid. Availability of a Band\,4 receiver covering 2–4\,GHz would be a major boost in studying the polarization properties of the ICM.
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All authors Aritra Basu, Sharanya Sur, Nadia Biava, Marisa Brienza
High Energy Astrophysical Phenomena
A pulsar escaping an ancient open cluster via tidal stripping
Lei Zhang, Xiaoting Fu, Di Li et al. (+21 more)
Open clusters are the primary birthplaces of
stars in the Milky Way disk, yet their
neutron star progeny are rarely found within them, presumably due to
supernova-induced kicks that eject them at birth. Here we report the arcsec-level localization of the
pulsar PSR J1921+3745 to the
tidal tail of NGC 6791, one of the oldest and most massive open clusters. Our N-body simulation shows that more than 95% of
neutron stars formed in such clusters have been ejected. This
pulsar's location in the
tidal tail indicates it was retained for billions of years before being stripped by
Galactic tides. This long-term retention requires low natal kicks, consistent with formation via electron-capture
supernova. Our findings capture a rare snapshot of a
neutron star transitioning into the
Galactic field, identifying
tidal stripping of ancient clusters as a verified source of the
Galactic neutron star population.
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All authors Lei Zhang, Xiaoting Fu, Di Li, Emma Carli, Long Wang, Jiaqi Zhao, Craig O. Heinke, Emanuele Dalessandro, Yang Chen, Angela Bragaglia, Duncan R. Lorimer, Ewan D. Barr, Sarah Buchner, Shi Dai, Zhiyu Zhang, Erbil Gügercinoğlu, Alessandro Ridolfi, Jie Zhang, Meng Guo, Mengmeng Ni, Jiale Hu, Yi Feng, Pei Wang, Qijun Zhi
High Energy Astrophysical Phenomena
Fe K{\alpha} equivalent-width mapping with 3D radiative transfer calculation: A general model and application to the RS Canum Venaticorum-type stars with XRISM/Resolve
Shun Inoue, Masahiro Tsujimoto, Takayuki Hayashi et al. (+4 more)
The Fe K $\alpha$ fluorescence line at 6.4 keV has long been used to probe the relative geometry between photoionizing X-ray sources and surrounding cold material in a wide range of astrophysical systems. With the advent of the X-ray microcalorimeter XRISM/Resolve, Fe K $\alpha$ lines with equivalent widths down to $\sim 5$ eV-previously inaccessible-are now detectable, and even non-detections can place upper limits of a few eV, making non-detections themselves valuable for constraining the geometry. Considering that Fe K $\alpha$-based
geometric diagnostics are entering a new stage in the microcalorimeter era, we present Fe K $\alpha$ equivalent-width maps computed with the three-dimensional Monte Carlo radiative-transfer code SKIRT for a generalized configuration consisting of a spherical reflector of radius $R_{*}$ and a point source located at a height $h$ above the surface. The equivalent-width maps exhibit two characteristic features: (1) an increase toward the center of the projected surface of the sphere; and (2) an overall decrease with increasing $h/R_{*}$. The key point is that we confirm these features for equivalent widths of $< 40$ eV, a regime that has become accessible for the first time thanks to the improved detection threshold from $\sim 50$ eV with Chandra/HETG to $\sim 5$ eV with XRISM/Resolve. As an illustrative application, we compare the maps with XRISM/Resolve spectra of three RS Canum Venaticorum-type
stars (GT Muscae, $\sigma$ Geminorum, and HR 1099) and constrain the locations of the
flare loop and coronal bright points in these systems. Because the maps are constructed for a highly generalized point-source–spherical-reflector geometry, they are readily applicable to many other objects, including X-ray binaries and cataclysmic variables.
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All authors Shun Inoue, Masahiro Tsujimoto, Takayuki Hayashi, Teruaki Enoto, Yuta Notsu, Hiroyuki Uchida, Miki Kurihara
Cosmology and Nongalactic Astrophysics · Cross-listed from hep-ph
HydroGrav: Precise hydrodynamics and gravitational waves for cosmological phase transitions
Flynn Linton, William Searle, Xiao Wang et al. (+1 more)
We present HydroGrav, a C++ code used to construct self-similar fluid profiles, using the exact equation of state determined directly from the effective potential, for any particle physics model capable of producing a first-order electroweak phase transition. HydroGrav also supports the bag and $\mu\nu$ (or improved bag) equations of state and includes an implementation of the sound shell model for computing the corresponding gravitational wave spectra. Using this framework, we compare the fluid profiles and gravitational wave spectra for the simplified (bag and $\mu\nu$) and exact equations of state for a $\mathbb{Z}_2$-symmetric extension of the Standard Model. Furthermore, we perform a scan across the parameter space of this model to identify regions where the simplified and exact equations of state differ in peak amplitude and spectral shape. Finally, we estimate the effect of using the exact equation of state on the signal-to-noise ratio across the parameter space, as measured by LISA after a 4-year mission.
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All authors Flynn Linton, William Searle, Xiao Wang, Csaba Balázs
Earth and Planetary Astrophysics
KMT-2025-BLG-2093: Free-Floating Planet Candidate Near the Shore of the Einstein Desert
Yoon-Hyun Ryu, Andrew Gould, Kyu-Ha Hwang et al. (+16 more)
We analyze KMT-2025-BLG-2093, with angular Einstein radius $\theta_{\rm E}=13.1\pm 2.8\,\mu{\rm as}$, which makes it the second isolated microlens that lies in the “Einstein Desert” ($9\,\mu{\rm as}<\theta_{\rm E}<25\,\mu{\rm as}$) between free-floating
planets (FFPs) on one side and brown
dwarfs and
stars on the other. We discuss how its characteristics may give clues to future exploration of FFPs, especially in the era of satellite missions that have a major FFP focus, including Earth 2.0 and Roman.
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All authors Yoon-Hyun Ryu, Andrew Gould, Kyu-Ha Hwang, Qiyue Qian, Michael D. Albrow, Sun-Ju Chung, Cheongho Han, Youn Kil Jung, Zhixing Li, Shude Mao, In-Gu Shin, Yossi Shvartzvald, Hongjing Yang, Jennifer C. Yee, Weicheng Zang, Dong-Jin Kim, Chung-Uk Lee, Byeong-Gon Park, Richard W. Pogge
Cosmology and Nongalactic Astrophysics
Fast Radio Bursts as Cosmological Probes
Manisha Caleb, Jéferson A. S. Fortunato, Steffen Hagstotz et al. (+14 more)
Fast
radio bursts (FRBs) are brief, coherent
radio pulses of extragalactic origin. They typically last from microseconds to milliseconds and have energies large enough to be visible over cosmological distances. Since FRBs interact with free electrons along their paths, the original burst is dispersed (Dispersion Measure, DM) and broadened (scattering). Furthermore, the burst's polarization is altered by Faraday rotation. Consequently, FRBs are excellent probes of the cosmological distribution of
baryons, the expansion of the Universe,
magnetic fields, and minuscule effects of fundamental physics that accumulate over vast distances. This chapter is the second of a trilogy of FRB chapters and discusses FRBs as a standalone probe. We first introduce the foundation of FRB observables related to those questions. Next, we lay the groundwork for
forecasting SKA's potential by describing the method to simulate the expected FRB population observable with the SKA. These synthetic FRB catalogues are then used to investigate the SKA's potential to probe the Universe's expansion rate and fundamental physics, such as the equivalence principle and the existence of massive
photons. Furthermore, we investigate the possibility of tracing
cosmic magnetic fields and investigating different dark matter candidates.
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All authors Manisha Caleb, Jéferson A. S. Fortunato, Steffen Hagstotz, Clancy W. James, Joscha N. Jahns-Schindler, Dylan Jow, Evan Keane, Koustav Konar, Yin-Zhe Ma, Daniele Michilli, Robert Reischke, Amit Seta, Priyanka Singh, Laura G. Spitler, Yidan Wang, Amanda Weltman, The SKA Transients SWG
Solar and Stellar Astrophysics
Laura N. Driessen, Alex Andersson, Joseph R. Callingham et al. (+6 more)
Stellar radio emission is highly variable with
stellar flares lasting from milliseconds to hours. For some
stars, their
flares or bursts can repeat once every couple of hours, while other
stars may
flare only once in hundreds of hours of observing. Some
stars and
stellar systems vary slowly over months to years. In this chapter we present the current methods for identifying
radio stars and the important role that variability plays in these detection methods. We highlight that
radio stars are the second most common
radio variable object in image-plane searches for
radio variable sources. We also present our predictions for the number of
stars both the SKA-mid and SKA-low AA$^{*}$ arrays could detect based on searches using SKA pathfinders and precursors.
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All authors Laura N. Driessen, Alex Andersson, Joseph R. Callingham, Barnali Das, Jakob van den Eijnden, Tara Murphy, Kovi Rose, Joshua Pritchard, Miguel Pérez-Torres
Astrophysics of Galaxies
Mapping the Milky Way with Masers
Ye Xu, Kazi Rygl, Huib Jan van Langevelde et al. (+10 more)
SKA-VLBI is poised to revolutionize our understanding of the
Galactic structure through its unprecedented astrometric precision and sensitivity. As a next-generation facility, it will answer long-standing questions about the
Galactic structure by mapping its entire spiral structure in detail, spanning from the
solar neighborhood, through the
Galactic Center, to the far side of the Milky Way. Its access to the Southern sky will allow us to obtain more precise 3D parameters of the
Galactic bar, reveal the nature of the 3-kpc Arm, and clarify the dynamical coupling between the bar and the spiral arms. By leveraging high-precision astrometry of numerous celestial objects with SKA-VLBI, the
Galactic fundamental parameters such as the
Solar motion and the
Galactic rotation curve can be constrained more precisely. These advancements will not only elucidate the structure of our Milky Way, but also provide
benchmarks for understanding barred spiral
galaxies in general. Furthermore, they are important for advancing our knowledge of cosmological structure formation. The capabilities of SKA-VLBI will open a new era of high precision
Galactic astrometry.
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All authors Ye Xu, Kazi Rygl, Huib Jan van Langevelde, Dejian Liu, Jingjing Li, Yingjie Li, Simon P. Ellingsen, María J. Rioja, Richard Dodson, Zehao Lin, Chaojie Hao, Yiwei Dong, Jun Yang
High Energy Astrophysical Phenomena
A Model for Magnetic Reconnection as the Origin of TeV Outbursts from NGC 1275
Zhen-Jie Wang, Hong-Bin Tan and Ruo-Yu Liu
NGC 1275 showed two TeV $\gamma$-ray outbursts between November 2022 and January 2023, as detected by the Large High Altitude Air Shower Observatory (LHAASO). The source was also active in the X-ray and GeV bands during the TeV outburst period. Very-long-baseline
radio observations reported a sudden acceleration and deflection of a jet
knot in late 2022, before the main TeV activity. Motivated by this sequence, we examine whether
magnetic reconnection triggered by the interaction between the jet and the ambient medium can explain the TeV
flares. In this picture, reconnection produces many plasmoids, and a large “monster” plasmoid becomes the main
flare region. We model the low-state emission with a multi-zone
stochastic-dissipation component and add a compact reconnection-powered region for the flaring state. We then compare leptonic and hadronic interpretations. The leptonic model explains the enhanced X-ray emission as electron synchrotron radiation and the TeV emission mainly as inverse-Compton radiation. A pure
proton–
proton model can also produce TeV
photons if dense target gas is present, but it requires a compact cloud with a density above the values directly inferred from free–free absorption and a large
proton power. These requirements are demanding, but they do not by themselves exclude the hadronic interpretation, because the gas may be compressed by the jet or may contain denser cloud cores. Our results show that
magnetic reconnection in the parsec-scale jet is a viable origin of the 2022–2023 TeV activity of NGC 1275, while better constraints on the gas density and jet power are needed to distinguish between leptonic and hadronic radiation channels.
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Astrophysics of Galaxies
OzSSy1: The Australian Southern Seyfert-1 Spectroscopic Atlas and Catalogue at z < 0.1
Neelesh Amrutha, Christian Wolf, Christopher A. Onken et al. (+3 more)
We present a spectroscopic atlas of 887 broad-line active
galactic nuclei (AGNs) in the Southern sky, spanning
redshifts $z < 0.1$, declinations $\delta < 0$ deg and
Galactic latitudes $|b| > 10$ deg. The sample aims at being a largely complete census of nearby broad-line AGN. The atlas is constructed from observations with $R\sim3000$ using the integral-field Wide Field Spectrograph at the Australian National University 2.3 m
telescope. Spectra are extracted in a 6.7 arcsec aperture and have a median signal-to-noise ratio of 13 and 23 per Angstrom in the blue and red arms, respectively. Each spectrum is accompanied by a spectral decomposition that models the AGN continuum and host
galaxy, along with fits to the emission lines H$\gamma$, H$\beta$, H$\alpha$, He II, He I, [O III], [O I], [N II] and [S II], including broad Balmer and Helium components. The data products are publicly available and designed to support studies of population demographics and AGN variability in conjunction with future time-domain surveys.
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All authors Neelesh Amrutha, Christian Wolf, Christopher A. Onken, Wei Jeat Hon, Samuel Lai, Rachel Webster
Instrumentation and Methods for Astrophysics
A Dual-Burst Geometrical Prescription for Concurrent Signaling
Naoki Seto
We propose a dual-burst implementation of concurrent signaling for technosignature searches. Concurrent signaling is a Schelling-point prescription for implicit coordination between transmitters and receivers without prior communication, using salient astronomical phenomena as coordination anchors. It allows possible transmitters at different line-of-sight distances to be searched collectively through a time-dependent locus on the sky. In the dual-burst implementation, the coordination anchors are two cosmological transients. At a chosen observing time after the later burst, the leading geometrical prescription specifies a precisely defined sky ring from the two burst directions and their observed arrival times at the receiver. No distance to either burst, to a candidate transmitter, or to a
Galactic spatial anchor is required to construct this angular search locus. The finite width of the ring is therefore controlled primarily by burst localization rather than by an astrophysical distance scale, thereby reducing the set of sky directions to be searched.
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High Energy Astrophysical Phenomena
Extreme Mass Ratio Inspirals in Light of Quasi-periodic Eruptions: Milli-Hertz Gravitational Wave Background
Brennen Black, Xian Chen and Zhen Pan
Quasi-periodic eruptions (QPEs) are repeated X-ray bursts originating in
galactic nuclei. Of the many proposed models, the favored model is the disk-collision model in which a
stellar mass orbiter collides with a disk formed from a
tidal disruption event, generating
flares twice per orbit. In this model QPEs are tracers of circular extreme mass ratio inspirals (EMRIs) and can be used to infer the EMRI formation rate and estimate their contribution to the
stochastic gravitational wave background (SGWB) in the
Laser Interferometer Space
Antenna (LISA) band. Whether the secondary is a
stellar-mass black hole or a main sequence
star is still debated and leads to different results for the EMRI rate and SGWB. We obtain fiducial rates – subject to systematic uncertainties – of $R_{\rm SE} = 2.88\times10^{-6}$ per
galaxy per year for
stellar EMRIs and $R_{\rm BHE} = 6.07\times10^{-6}$ per
galaxy per year for black hole EMRIs, then estimate their contribution to the SGWB. We find that only black hole EMRIs contribute to the 1 - 10 milliHertz band resolvable by LISA, and depending on the secondary mass and formation radius can contribute from just below the LISA sensitivity curve to roughly two orders of magnitude above it.
Stellar EMRIs, being tidally disrupted before reaching the 1 - 10 milliHertz band, only contribute to sub-milliHertz frequencies and remain below the LISA sensitivity curve.
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Instrumentation and Methods for Astrophysics · Cross-listed from gr-qc
First Demonstration of Optical Feedback Control to Parametric Instability at Advanced LIGO
Juntao Pan, Carl Blair, Vladimir Bossilkov et al. (+5 more)
Increasing the circulating power in gravitational-wave detectors to the megawatt level is essential for future sensitivity improvement, but this is critically limited by optomechanical parametric instabilities. Current mitigation strategies are projected to be inadequate against instabilities when circulating power reaches a megawatt. Optical feedback offers a novel independent paradigm to mitigate parametric instability. In this Letter, we report the first demonstration of optical feedback control in a full-scale gravitational wave detector. We successfully suppressed an unstable mode at 10.428 kHz, reducing the parametric gain from R = 2 to R < 0.02. This work validates optical feedback control as an effective mitigation scheme for kilometre-scale interferometric gravitational-wave detectors, providing an effective strategy to allow detectors to reach the megawatt level.
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All authors Juntao Pan, Carl Blair, Vladimir Bossilkov, Jian Liu, Alex Adam, Chunnong Zhao, Li Ju, Anamaria Effler
Solar and Stellar Astrophysics
Unprecedent fast winking of solar flares triggered by bursty magnetic reconnection
Ting Li, Xuchun Duan, Yijun Hou et al. (+13 more)
Flare ribbons form as a result of energy deposition associated with particles accelerated in low layers of the
solar atmosphere. The fine-scale structures of
flare ribbons, also called ribbon kernels, offer a potentially powerful diagnostic of the
flare reconnection process, however to date the dynamic
evolution of ribbon kernels has not been fully characterized in statistical studies. Here, we checked the state-of-the-art observations (cadence $\leq$ 2.5 seconds) of
solar flares in the ultraviolet from space by Interface Region Imaging Spectrograph (IRIS) over the past 12 years. Our results showed the first statistical study of multiple spatially-resolved
flare kernel quasi-periodic pulsation events for 31
flares, with the period of 6-24 seconds. The ribbon kernels have a spatial scale of 480$-$1200 km and some kernels exhibit unprecedent fast “winking" process, i.e., quasi-periodic pulsation-like flashing of individual kernels. The shortest heating time reaches about 2$-$3 s, implying that the energy is deposited only in a small localized region within
flare ribbons, persisting for only a few seconds. Meanwhile, some ribbon kernels were observed to slip along the ribbon at speeds of 20-1800 km s$^{-1}$. These observations strongly imply a joint picture for the dynamics and the bursty nature of ribbon kernels as being due to coupled effects of plasmoid formation and three-dimensional (3D)
magnetic reconnection in the overlaying coronal current sheet. We suggest that the observed
flare behaviors provide strong observational evidences of 3D bursty reconnection.
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All authors Ting Li, Xuchun Duan, Yijun Hou, Guillaume Aulanier, Ivan Zimovets, Jun Zhang, Juraj Lorincik, Larisa Kashapova, Zhentong Li, Yining Zhang, Yulei Wang, Leping Li, Suli Ma, Jing Huang, Shuhong Yang, Guiping Zhou
Solar and Stellar Astrophysics
EWOCS-VI: Probing the hidden intermediate-mass population of Westerlund 1
C. Ordenes-Huanca, A. Bayo, M. Guarcello et al. (+11 more)
Context: Westerlund 1 (Wd1), the most massive young
star cluster in the Milky Way, is an excellent laboratory for studying
star formation and early
stellar evolution in a starburst-like environment. However, high extinction restricts studies of its
stellar content, and focus on high-mass
stars limits our knowledge of the full spatial extent of the cluster. Aims: We characterize the near-infrared (NIR) variability of the
stellar population of Wd1, filling the mass gap between massive
stars traced by
Gaia and very low-mass
stars from previous Extended Westerlund 1 and 2 Open Clusters Survey (EWOCS) studies, to provide a more complete view of cluster membership across
solar and super-
solar masses.} Methods: We exploited data from the VISTA Variables of the Vía Láctea survey and its extension (VVVX), using NIR point spread function (PSF) photometry and astrometric solutions from its latest data release, namely the VIRAC2 catalogs, mainly in the Ks band. Their large spatial coverage enables study of both the central regions and outskirts of the cluster. We applied HDBSCAN clustering
algorithm in a 6D parameter space to differentiate cluster members from field contaminants, assessing robustness through Monte Carlo simulations. Variable sources along the line of sight were also identified and characterized. Results: We identify 1286 high-probability candidate members (12 < J < 18 mag) spanning $\sim 1.5$–$20\,M_{\odot}$, adopting both PARSEC 5 and 6 Myr isochrones ($A_{K_{\rm{s}}}=0.6\,\rm{mag}$, $d=4.23\,\rm{kpc}$). A considerable fraction (34%) shows statistically significant flux variations. We present, for the first time, a parametric analysis of variability modes of Wd1 candidate members in the Ks band, providing a membership catalog suitable for future kinematic studies.
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All authors C. Ordenes-Huanca, A. Bayo, M. Guarcello, M. Zoccali, A. Rojas-Arriagada, V. Almendros-Abad, M. Andersen, R. Bonito, V. Guzmán, E. Moraux, K. Muzic, L. Prisinzano, S. Sciortino, N.J. Wright