Sazuna/UAT_keywords huggingface dataset:
Did Binary Neutron Star Merger GW170817 Leave Behind a Long-lived Neutron Star?. We consider the observational implications of the binary neutron star merger GW170817, which may have left behind a rapidly rotating massive neutron star that launches a relativistic, equatorial outflow as well as a jet. We show that if the equatorial outflow (ring) is highly beamed in the equatorial plane, its luminosity can be "hidden" from view until late times, even if carrying a significant fraction of the spin-down energy of the merger remnant. This hidden ring reveals itself as a rebrightening in the light curve once it slows down enough for the Earth to be within the ring's relativistic beaming solid angle. We compute semianalytic light curves using this model and find they are in agreement with the observations thus far, and we provide predictions for the ensuing afterglow.

Keywords: Neutron stars, Light curves, Gamma-ray bursts, Relativistic fluid dynamics
Discovery of a Hypervelocity L Subdwarf at the Star/Brown Dwarf Mass Limit. We report the discovery of a high-velocity, very low-mass star or brown dwarf whose kinematics suggest it is unbound to the Milky Way. CWISE J124909.08+362116.0 was identified by citizen scientists in the Backyard Worlds: Planet 9 program as a high-proper-motion (μ = 0.″9 yr‑1) faint red source. Moderate-resolution spectroscopy with Keck/NIRES reveals it to be a metal-poor early L subdwarf with a large radial velocity (‑103 ± 10 km s‑1), and its estimated distance of 125 ± 8 pc yields a speed of 456 ± 27 km s‑1 in the Galactic rest frame, near the local escape velocity for the Milky Way. We explore several potential scenarios for the origin of this source, including ejection from the Galactic center ≳3 Gyr in the past, survival as the mass donor companion to an exploded white dwarf, acceleration through a three-body interaction with a black hole binary in a globular cluster, and accretion from a Milky Way satellite system. CWISE J1249+3621 is the first hypervelocity very low-mass star or brown dwarf to be found and the nearest of all such systems. It may represent a broader population of very high-velocity, low-mass objects that have undergone extreme accelerations.

Keywords: Globular star clusters, Galactic archaeology, Hypervelocity stars, L subdwarfs, Type Ia supernovae, Low mass stars, Metallicity
The Unluckiest Star: A Spectroscopically Confirmed Repeated Partial Tidal Disruption Event AT 2022dbl. The unluckiest star orbits a supermassive black hole elliptically. Every time it reaches the pericenter, it shallowly enters the tidal radius and gets partially tidally disrupted, producing a series of flares. Confirmation of a repeated partial tidal disruption event (pTDE) requires not only evidence to rule out other types of transients but also proof that only one star is involved, as TDEs from multiple stars can also produce similar flares. In this Letter, we report the discovery of a repeated pTDE, AT 2022dbl. In a quiescent galaxy at z = 0.0284, two separate optical/UV flares have been observed in 2022 and 2024 with no bright X-ray, radio, or mid-infrared counterparts. Compared to the first flare, the second flare has a similar blackbody temperature of ∼26,000 K, slightly lower peak luminosity, and slower rise and fall phases. Compared to the Zwicky Transient Facility TDEs, their blackbody parameters and light-curve shapes are all similar. The spectra taken during the second flare show a steeper continuum than the late-time spectra of the previous flare, consistent with a newly risen flare. More importantly, the possibility of two independent TDEs can be largely ruled out because the optical spectra taken around the peak of the two flares exhibit highly similar broad Balmer, N III, and possible He II emission lines, especially the extreme ∼4100 Å emission lines. This represents the first robust spectroscopic evidence for a repeated pTDE, which can soon be verified by observing the third flare, given its short orbital period.

Keywords: Time domain astronomy, Supermassive black holes, Tidal disruption, Black holes
TOI-1408: Discovery and Photodynamical Modeling of a Small Inner Companion to a Hot Jupiter Revealed by Transit Timing Variations. We report the discovery and characterization of a small planet, TOI-1408 c, on a 2.2 day orbit located interior to a previously known hot Jupiter, TOI-1408 b (P = 4.42 days, M = 1.86 ± 0.02 M Jup, R = 2.4 ± 0.5 R Jup) that exhibits grazing transits. The two planets are near 2:1 period commensurability, resulting in significant transit timing variations (TTVs) for both planets and transit duration variations for the inner planet. The TTV amplitude for TOI-1408 c is 15% of the planet's orbital period, marking the largest TTV amplitude relative to the orbital period measured to date. Photodynamical modeling of ground-based radial velocity (RV) observations and transit light curves obtained with the Transiting Exoplanet Survey Satellite and ground-based facilities leads to an inner planet radius of 2.22 ± 0.06 R ⊕ and mass of 7.6 ± 0.2 M ⊕ that locates the planet into the sub-Neptune regime. The proximity to the 2:1 period commensurability leads to the libration of the resonant argument of the inner planet. The RV measurements support the existence of a third body with an orbital period of several thousand days. This discovery places the system among the rare systems featuring a hot Jupiter accompanied by an inner low-mass planet.

Keywords: Exoplanet dynamics, Hot Jupiters, Hot Neptunes, Transit timing variation method, Radial velocity, Transit photometry
Big Galaxies and Big Black Holes: The Massive Ends of the Local Stellar and Black Hole Mass Functions and the Implications for Nanohertz Gravitational Waves. We construct the z = 0 galaxy stellar mass function (GSMF) by combining the GSMF at stellar masses M * ≲ 1011.3 M ⊙ from the census study of Leja et al. and the GSMF of massive galaxies at M * ≳ 1011.5 M ⊙ from the volume-limited MASSIVE galaxy survey. To obtain a robust estimate of M * for local massive galaxies, we use MASSIVE galaxies with M * measured from detailed dynamical modeling or stellar population synthesis modeling (incorporating a bottom-heavy initial mass function) with high-quality spatially resolved spectroscopy. These two independent sets of M * agree to within ∼7%. Our new z = 0 GSMF has a higher amplitude at M * ≳ 1011.5 M ⊙ than previous studies, alleviating prior concerns of a lack of mass growth in massive galaxies between z ∼ 1 and 0. We derive a local black hole mass function (BHMF) from this GSMF and the scaling relation of supermassive black holes (SMBHs) and galaxy masses. The inferred abundance of local SMBHs above ∼1010 M ⊙ is consistent with the number of currently known systems. The predicted amplitude of the nanohertz stochastic gravitational-wave background is also consistent with the levels reported by Pulsar Timing Array teams. Our z = 0 GSMF therefore leads to concordant results in the high-mass regime of the local galaxy and SMBH populations and the gravitational-wave amplitude from merging SMBHs. An exception is that our BHMF yields a z = 0 SMBH mass density that is notably higher than the value estimated from quasars at higher redshifts.

Keywords: Stellar mass functions, Supermassive black holes, Gravitational wave sources, Stellar masses
GRB 211211A: The Case for an Engine-powered over r-process-powered Blue Kilonova. The recent gamma-ray burst (GRB) GRB 211211A provides the earliest (∼5 hr) data of a kilonova (KN) event, displaying bright (∼1042 erg s‑1) and blue early emission. Previously, this KN was explained using simplistic multicomponent fitting methods. Here, in order to understand the physical origin of the KN emission in GRB 211211A, we employ an analytic multizone model for r-process-powered KNe. We find that r-process-powered KN models alone cannot explain the fast temporal evolution and the spectral energy distribution (SED) of the observed emission. Specifically, (i) r-process models require high ejecta mass to match early luminosity, which overpredicts late-time emission, while (ii) red KN models that reproduce late emission underpredict early luminosity. We propose an alternative scenario involving early contributions from the GRB central engine via a late low-power jet, consistent with plateau emission in short GRBs and GeV emission detected by Fermi-LAT at ∼104 s after GRB 211211A. Such late central engine activity, with an energy budget of ∼a few percent of that of the prompt jet, combined with a single red KN ejecta component, can naturally explain the light curve and SED of the observed emission, with the late-jet–ejecta interaction reproducing the early blue emission and r-process heating reproducing the late red emission. This supports claims that late low-power engine activity after prompt emission may be common. We encourage early follow-up observations of future nearby GRBs and compact binary merger events to reveal more about the central engine of GRBs and r-process events.

Keywords: Neutron stars, Gamma-ray bursts, Hydrodynamics, R-process, Relativistic jets, Gravitational waves
A Potential Second Shutoff from AT2018fyk: An Updated Orbital Ephemeris of the Surviving Star under the Repeating Partial Tidal Disruption Event Paradigm. The tidal disruption event (TDE) AT2018fyk showed a rapid dimming event 500 days after discovery, followed by a rebrightening roughly 700 days later. It has been hypothesized that this behavior results from a repeating partial TDE (rpTDE), such that prompt dimmings/shutoffs are coincident with the return of the star to pericenter and rebrightenings generated by the renewed supply of tidally stripped debris. This model predicted that the emission should shut off again around August of 2023. We report AT2018fyk's continued X-ray and UV monitoring, which shows an X-ray (UV) drop-in flux by a factor of 10 (5) over a span of two months, starting 2023 August 14. This sudden change can be interpreted as the second emission shutoff, which (1) strengthens the rpTDE scenario for AT2018fyk, (2) allows us to constrain the orbital period to a more precise value of 1306 ± 47 days, and (3) establishes that X-ray and UV/optical emission track the fallback rate onto this supermassive black hole—an often-made assumption that otherwise lacks observational verification—and therefore, the UV/optical lightcurve is powered predominantly by processes tied to X-rays. The second cutoff implies that another rebrightening should happen between 2025 May and August, and if the star survived the second encounter, a third shutoff is predicted to occur between 2027 January and July. Finally, low-level accretion from the less-bound debris tail (which is completely unbound/does not contribute to accretion in a nonrepeating TDE) can result in a faint X-ray plateau that could be detectable until the next rebrightening.

Keywords: X-ray astronomy, Supermassive black holes, Tidal disruption, Transient sources, Ultraviolet astronomy, Time domain astronomy, Astrophysical black holes
Discovery of an Apparent Red, High-velocity Type Ia Supernova at z = 2.9 with JWST. We present the James Webb Space Telescope (JWST) discovery of SN 2023adsy, a transient object located in a host galaxy JADES-GS+53.13485‑27.82088 with a host spectroscopic redshift of 2.903 ± 0.007. The transient was identified in deep (JWST)/NIRCam imaging from the JWST Advanced Deep Extragalactic Survey (JADES) program. Photometric and spectroscopic follow-up with NIRCam and NIRSpec, respectively, confirm the redshift and yield UV-NIR light-curve, NIR color, and spectroscopic information all consistent with a Type Ia classification. Despite its classification as a likely SN Ia, SN 2023adsy is both fairly red (c ∼ 0.9) despite a host galaxy with low extinction and has a high Ca II velocity (19,000 ± 2000 km s‑1) compared to the general population of SNe Ia. While these characteristics are consistent with some Ca-rich SNe Ia, particularly SN 2016hnk, SN 2023adsy is intrinsically brighter than the low-z Ca-rich population. Although such an object is too red for any low-z cosmological sample, we apply a fiducial standardization approach to SN 2023adsy and find that the SN 2023adsy luminosity distance measurement is in excellent agreement (≲1σ) with ΛCDM. Therefore unlike low-z Ca-rich SNe Ia, SN 2023adsy is standardizable and gives no indication that SN Ia standardized luminosities change significantly with redshift. A larger sample of distant SNe Ia is required to determine if SN Ia population characteristics at high z truly diverge from their low-z counterparts and to confirm that standardized luminosities nevertheless remain constant with redshift.

Keywords: Cosmology, Type Ia supernovae, Supernovae, High-redshift galaxy clusters
An HI-absorption-selected Cold Rotating Disk Galaxy at z ≈ 2.193. We have used the Atacama Large Millimeter/submillimeter Array to map CO(3─2) emission from a galaxy, DLA-B1228g, associated with the high-metallicity damped Lyα absorber at z ≍ 2.1929 toward the QSO PKS B1228─113. At an angular resolution of ≍0.″32 × 0.″24, DLA-B1228g shows extended CO(3─2) emission with a deconvolved size of ≍0.″78 × 0.″18, i.e., a spatial extent of ≍6.4 kpc. We detect extended stellar emission from DLA-B1228g in a Hubble Space Telescope Wide Field Camera 3 F160W image and find that Hα emission is detected in a Very Large Telescope SINFONI image from only one side of the galaxy. While the clumpy nature of the F160W emission and the offset between the kinematic and physical centers of the CO(3─2) emission are consistent with a merger scenario, this appears unlikely due to the lack of strong Hα emission, the symmetric double-peaked CO(3─2) line profile, the high molecular gas depletion timescale, and the similar velocity dispersions in the two halves of the CO(3─2) image. Kinematic modeling reveals that the CO(3─2) emission is consistent with arising from an axisymmetric rotating disk with an exponential profile, a rotation velocity of v rot = 328 ± 7 km s−1, and a velocity dispersion of σ  v  = 62 ± 7 km s−1. The high value of the ratio v rot/σ  v , ≍5.3, implies that DLA-B1228g is a rotation-dominated cold disk galaxy, the second case of a high-z HI-absorption-selected galaxy identified with a cold rotating disk. We obtain a dynamical mass of M dyn = (1.5 ± 0.1) × 1011 M ⊙, similar to the molecular gas mass of ≍1011 M ⊙ inferred from earlier CO(1─0) studies; this implies that the galaxy is baryon-dominated in its inner regions.

Keywords: Radio interferometry, High-redshift galaxies
Fragmentation in Gravitationally Unstable Collapsar Disks and Subsolar Neutron Star Mergers. Although stable neutron stars (NSs) can in principle exist down to masses M ns ≈ 0.1 M ⊙, standard models of stellar core-collapse predict a robust lower limit M ns ≳ 1.2 M ⊙, roughly commensurate with the Chandrasekhar mass M Ch of the progenitor's iron core (electron fraction Y  e  ≈ 0.5). However, this limit may be circumvented in sufficiently dense neutron-rich environments (Y  e  &lt; 0.5) for which  MCh∝Ye2  is reduced to ≲1 M ⊙. Such physical conditions could arise in the black hole accretion disks formed from the collapse of rapidly rotating stars ("collapsars"), as a result of gravitational instabilities and cooling-induced fragmentation, similar to models for planet formation in protostellar disks. We confirm that the conditions to form subsolar-mass NS (ssNS) may be marginally satisfied in the outer regions of massive neutrino-cooled collapsar disks. If the disk fragments into multiple ssNSs, their subsequent coalescence offers a channel for precipitating subsolar mass LIGO/Virgo gravitational-wave mergers that does not implicate primordial black holes. The model makes several additional predictions: (1) ∼Hz frequency Doppler modulation of the ssNS-merger gravitational-wave signals due to the binary's orbital motion in the disk; (2) at least one additional gravitational-wave event (coincident within ≲hours), from the coalescence of the ssNS-merger remnant(s) with the central black hole; (3) an associated gamma-ray burst and supernova counterpart, the latter boosted in energy and enriched with r-process elements from the NS merger(s) embedded within the exploding stellar envelope ("kilonovae inside a supernova").

Keywords: Neutron stars, Gamma-ray bursts, Accretion, Gravitational wave sources
Observation of a Fully-formed Forward─Reverse Shock Pair due to the Interaction between Two Coronal Mass Ejections at 0.5 au. We report direct observations of a fast magnetosonic forward─reverse shock pair observed by Solar Orbiter on 2022 March 8 at the short heliocentric distance of 0.5 au. The structure, sharing some features with fully-formed stream interaction regions, is due to the interaction between two successive coronal mass ejections (CMEs), never previously observed to give rise to a forward─reverse shock pair. The scenario is supported by remote observations from extreme ultraviolet cameras and coronagraphs, where two candidate eruptions compatible with the in situ signatures have been found. In the interaction region, we find enhanced energetic particle activity, strong nonradial flow deflections, and evidence of magnetic reconnection. At 1 au, well radially aligned Wind observations reveal a complex event, with characteristic observational signatures of both stream interaction region and CME─CME interaction, thus demonstrating the importance of investigating the complex dynamics governing solar eruptive phenomena.

Keywords: The Sun, Interplanetary shocks, Solar coronal mass ejections, Heliosphere
Metal-poor Stars in the MW Disk: Resonant Cooling of Vertical Oscillations of Halo Stars in Barred Galaxies. Using numerical simulations of a barred disk galaxy embedded in nonspinning and spinning dark matter (DM) halos, we present a novel mechanism of "cooling" the vertical oscillations of DM particles, which acquire disk kinematics. The underlying mechanism consists of resonant interactions between halo particles and the stellar bar, facilitated by a chaotic phase space of the system. The cooling mechanism acts both on dynamical and secular timescales, from ∼0.5 Gyr to a few Gyr. The stellar bar acts to absorb the kinetic energy of the vertical motions. Using a Milky Way (MW)–type stellar halo, we estimate the population of metal-poor disk stars trapped by the MW disk and analyze its kinematics. We find that the population of metal-poor MW disk stars with ∣z∣ ≲ 3 kpc detected by the Gaia DR3 and other surveys can have their origin in the stellar halo. The cooled population also migrates radially outwards by exchanging energy and angular momentum with the spinning bar, and prograde-moving stars have a different distribution from retrograde ones. Next, we calculated the ratio of the prograde-to-retrograde orbits of the cooled population and found that this ratio varies radially, with the fast-spinning stellar halo resulting in the shallower radial increase of this ratio outside of the corotation. The nonspinning stellar halo shows a monotonic increase of this ratio with radius outside the corotation. Together with the analyzed radial migration of these halo stars, the cooling phenomenon of halo metal-poor stars can explain their current disk population and has corollaries for the chemical evolution of disk galaxies in general.

Keywords: Galaxy formation, Galaxy bars, Galaxy dynamics, Galaxy disks, Galaxy stellar halos, Galaxy evolution
Corvus A: A Low-mass, Isolated Galaxy at 3.5 Mpc. We report the discovery of Corvus A, a low-mass, gas-rich galaxy at a distance of approximately 3.5 Mpc, identified in DR10 of the Dark Energy Camera Legacy Imaging Survey during the initial phase of our ongoing SEmi-Automated Machine LEarning Search for Semi-resolved galaxies (SEAMLESS). Jansky Very Large Array observations of Corvus A detect H I line emission at a radial velocity of 523 ± 2 km s‑1. Magellan/Megacam imaging reveals an irregular and complex stellar population with both young and old stars. We detect UV emission in Neil Gehrels Swift observations, indicative of recent star formation. However, there are no signs of H II regions in Hα imaging from Steward Observatory's Kuiper telescope. Based on the Megacam color–magnitude diagram we measure the distance to Corvus A via the tip of the red giant branch standard candle as 3.48 ± 0.24 Mpc. This makes Corvus A remarkably isolated, with no known galaxy within ∼1 Mpc. Based on this distance, we estimate the H I and stellar mass of Corvus A to be  logMHI/M⊙=6.59  and  logM*/M⊙=6.0 , respectively. Although there are some signs of rotation, the H I distribution of Corvus A appears to be close to face on, analogous to that of Leo T, and we therefore do not attempt to infer a dynamical mass from its H I line width. Higher-resolution synthesis imaging is required to confirm this morphology and to draw robust conclusions from its gas kinematics.

Keywords: Dwarf irregular galaxies, Galaxy distances, Galaxy stellar content, Galaxy environments
Detecting Gravitational-wave Bursts from Black Hole Binaries in the Galactic Center with LISA. Stellar-mass black hole binaries (BHBs) in galactic nuclei are gravitationally perturbed by the central supermassive black hole (SMBH) of the host galaxy, potentially inducing strong eccentricity oscillations through the eccentric Kozai–Lidov mechanism. These highly eccentric binaries emit a train of gravitational-wave (GW) bursts detectable by the Laser Interferometer Space Antenna (LISA)—a planned space-based GW detector—with signal-to-noise ratios up to ∼100 per burst. In this work, we study the GW signature of BHBs orbiting our galaxy's SMBH, Sgr A*, which are consequently driven to very high eccentricities. We demonstrate that an unmodeled approach using a wavelet decomposition of the data effectively yields the time-frequency properties of each burst, provided that the GW frequency peaks between 10‑3 and 10‑1 Hz. The wavelet parameters may be used to infer the eccentricity of the binary, measuring  log10(1‑e)  within an error of 20%. Our proposed search method can thus constrain the parameter space to be sampled by complementary Bayesian inference methods, which use waveform templates or orthogonal wavelets to reconstruct and subtract the signal from LISA data.

Keywords: Supermassive black holes, Galactic center, Stellar dynamics, Stellar mass black holes, Gravitational wave astronomy, Eccentricity