Sazuna/UAT_keywords huggingface dataset:
Timing Results of 22 yr for PSR J0922+0638. We conducted a timing analysis of PSR J0922+0638 (B0919+06) using data from the Nanshan 26 m radio telescope and the MeerKAT telescope, spanning from 2001 January to 2023 March. During this 22 yr period, we discovered a previously unreported small glitch (glitch 1) before the well-known large glitch (glitch 2), occurring at MJD ∼ 53325(3), with a frequency jump amplitude of Δν/ν ∼ 0.79(6) × 10‑9. We also identified 10 slow glitch events, half of which were newly detected. These slow glitches occurred quasi-periodically, with an average interval of approximately 553(21) days, fractional frequency changes ranging from Δν/ν ∼ 1.13(1) × 10‑9 to 4.08(5)×10‑9, and a maximum fractional change in the first derivative of the frequency of  Δν̇/ν̇∼‑4.6×10‑3 . Additionally, our timing noise analysis reveals a change in the spectral index for noise power before and after glitch 2, with values of ‑6.0 and ‑5.3, respectively, likely due to this large glitch. Throughout the entire observation period, the first derivative of the spin frequency ( ν̇ ) showed a periodic structure. The possible modulation period was estimated to be 537(24) days before the 700 days data gap at MJD 56716 and 600(58) days afterward. We discuss the periodic oscillations in pulsar rotation as a possible manifestation of spin-down noise and quasi-periodic slow glitches.

Keywords: Neutron stars, Pulsars
Detailed Time-resolved Spectral and Temporal Investigations of SGR J1550–5418 Bursts Detected with Fermi Gamma-Ray Burst Monitor. We have conducted a time-resolved spectral analysis of magnetar bursts originating from SGR J1550‑5418. Our analysis utilizes a two-step methodology for temporal segmentation of the data. We first generated and fitted overlapping time segments. Subsequently, we obtained nonoverlapping time segments with varying lengths based on their spectral evolution patterns, employing a machine learning algorithm called k-means clustering. For the fitting process, we employed three distinct models, namely a modified blackbody (MBB-RCS), a double blackbody (BB+BB), and a power law with an exponential cutoff (COMPT) model. We found that nearly all of the time segments fit well with the COMPT model. Both the average peak energy in the νFν spectra (Epeak) and photon index parameters follow a Gaussian distribution with means ∼30 keV and ‑0.5, respectively. Furthermore, there is a strong positive correlation between the cooler and hotter temperature parameters of the BB+BB model, and both parameters show a Gaussian distribution with peaks ∼4 and 12 keV, respectively. Additionally, we found that the distribution of the temperature parameter of the MBB-RCS model can be fit with a skewed Gaussian function with a peak ∼9–10 keV. Lastly, we searched for quasiperiodic spectral oscillations (QPSOs) in the hardness ratio evolution of the bursts. We identified five potential QPSO candidates at frequencies ranging from ∼15 to ∼68 Hz. We discuss and compare these results with previous studies.

Keywords: Neutron stars, Magnetars, X-ray bursts
The Relationship of Stellar Radius Inflation to Rotation and Magnetic Starspots at 10─670 Myr. Active, low-mass stars are widely observed to have radii that are larger than predicted by standard stellar models. Proposed mechanisms for this radius inflation generally involve stellar magnetism, either in the form of added pressure support in the outer layers or suppression of convection via starspots. We have assembled a large sample of 261 low-mass stars in the young clusters Upper Scorpius, α Persei, Pleiades, and Praesepe (spanning ages 10─670 Myr) for which the data exist to empirically measure the stellar radii, rotation periods, and starspot covering fractions. We find a clear, strong relationship between the degree of radius inflation and stellar rotation as represented by the Rossby number; this inflation─rotation relationship bears striking resemblance to canonical activity─rotation relationships, including both the so-called linear and saturated regimes. We also demonstrate here for the first time that the radius inflation depends directly on the starspot covering fraction. We furthermore find that the stars' effective temperatures decrease with decreasing Rossby number as well, and that this temperature suppression balances the radius inflation so as to preserve the stellar bolometric luminosity. These relationships are consistent across the age range sampled here, which spans from the pre─main sequence to the zero-age main sequence. The favorable comparison of our findings to the predictions of modern starspot-based stellar evolution models suggests that, while rotation is clearly the underlying driver, magnetism may be the most likely direct cause of the radius inflation phenomenon.

Keywords: Starspots, Stellar properties, Stellar magnetic fields, Stellar radii, Stellar rotation, Stellar evolution
Discovery of Volatile Gas in the Giant Impact Disk Around the 150 Myr Old HD 23514. We report the discovery of CO2 gas emission around HD 23514, an F5V star in the ∼150 Myr old Pleiades cluster, hosting one of the rare giant-impact disks with unique mineralogy dominated by silica dust. We show that the dust feature remains stable over several decades, and that the submicron grains, which give rise to the ∼9 μm feature, are cospatial with the hot CO2 molecules within the sub-astronomical-unit vicinity of the star. Examining a Spitzer spectrum taken 15 yr earlier, we show that the CO2 emission was also present at 4.3σ significance. The existence of tiny silica grains and volatile gas requires special conditions to prevent the rapid loss caused by stellar radiation pressure and photodissociation. We explore several pathways explaining the observed properties and suggest that a past giant impact and/or stripping atmospheric event, involving large bodies with volatile content similar to carbonaceous chondritic material, can simultaneously explain both the silica and volatile emission. Our discovery provides an important context for the amount of volatiles that a newly formed planet or the largest planetesimals could retain during the giant impact phase in the early solar system evolution.

Keywords: Planetesimals, Circumstellar matter, Circumstellar grains, Circumstellar disks, Circumstellar dust, Debris disks, Circumstellar gas
A Plasma Torus around a Young Low-mass Star. A small fraction of red dwarfs younger than ∼100 million years show structured, periodic optical light curves suggestive of transiting opaque material that corotates with the star. However, the composition, origin, and even the existence of this material are uncertain. The main alternative hypothesis is that these complex periodic variables (CPVs) are explained by complex distributions of bright or dark regions on the stellar surfaces. Here we present time-series spectroscopy and photometry of a rapidly rotating (P = 3.9 hr) CPV, TIC 141146667. The spectra show sinusoidal time-varying Hα emission at twice to four times the star's equatorial velocity, providing direct evidence for cool (≲104 K) plasma clumps trapped in corotation around a CPV. These data support the idea that young, rapidly rotating M dwarfs can sustain warped tori of cool plasma, similar to other rapidly rotating magnetic stars. Outstanding questions include whether dust clumps in these plasma tori explain CPV light curves and whether the tori originate from the star or are fed by external sources. Rough estimates suggest that ≳10% of M dwarfs host similar structures during their early lives.

Keywords: Periodic variable stars, Stellar magnetic fields, Weak-line T Tauri stars, Circumstellar matter, Stellar rotation
Hundreds of TESS Exoplanets Might Be Larger than We Thought. The radius of a planet is a fundamental parameter that probes its composition and habitability. Precise radius measurements are typically derived from the fraction of starlight blocked when a planet transits its host star. The wide-field Transiting Exoplanet Survey Satellite (TESS) has discovered hundreds of new exoplanets, but its low angular resolution means that the light from a star hosting a transiting exoplanet can be blended with the light from background stars. If not fully corrected, this extra light can dilute the transit signal and result in a smaller measured planet radius. In a study of hundreds of TESS planet discoveries using deblended light curves from our validated methodology, we show that systematically incorrect planet radii are common in the literature: studies using various public TESS photometry pipelines have underestimated the planet radius by a weighted median of 6.1% ± 0.3%, leading to a ∼20% overestimation of planet density. The widespread presence of these biases in the literature has profoundly shaped—and potentially misrepresented—our understanding of the exoplanet population. Addressing these biases will refine the exoplanet mass─radius relation, reshape our understanding of exoplanet atmospheric and bulk composition, and potentially inform prevailing planet formation theories.

Keywords: Light curves, Transits, Exoplanets
Origins of Carbon Dust in a JWST-observed Primeval Galaxy at z ∼ 6.7. JADES-GS-z6-0, a high-redshift galaxy (z ∼ 6.7) recently observed as part of the James Webb Space Telescope Advanced Deep Extragalactic Survey (JADES), exhibits a distinct bump in its rest-frame ultraviolet (UV) spectrum indicative of a large quantity of hydrocarbon grains, a sign of rapid metal and dust enrichment in its interstellar medium (ISM). This galaxy serves as an ideal case for examining rapid dust formation processes in the early Universe. We investigated diverse dust production channels from a possible maximal formation redshift of zform ≍ 17, enabling dust contributions from asymptotic giant branch (AGB) stars over the longest possible timescale. Our model simultaneously reproduces key spectral features of JADES-GS-z6-0 such as its Balmer decrement, UV slope, and UV bump. The match is obtained by adopting a star formation history in which a burst at ∼600 Myr accounts for approximately 30% of the galaxy's final stellar mass. Our findings indicate two pathways for the formation of hydrocarbon grains, such as polycyclic aromatic hydrocarbons (PAHs): (1) efficient dust accretion within the ISM, necessitating a low depletion of metals into dust grains from Type II supernovae (≍10%), or (2) dust production predominantly by Type II supernovae, requiring a high depletion fraction (≍73%) without dust accretion. We further demonstrate that PAHs are unlikely to originate solely from AGB stars or from shattering of large grains in the ISM. The evolution of the UV slope with redshift points to a complex and bursty star formation history for galaxies observed by JADES.

Keywords: Theoretical models, High-redshift galaxies, Dust formation
The ∞ Galaxy: A Candidate Direct-collapse Supermassive Black Hole between Two Massive, Ringed Nuclei. We report the discovery of an unusual z = 1.14 object, dubbed the ∞ galaxy, in JWST imaging of the COSMOS field. Its rest-frame near-IR light is dominated by two compact nuclei with stellar masses of ∼1011 M⊙ and a projected separation of 10 kpc. Both nuclei have a prominent ring or shell around them, giving the galaxy the appearance of a figure eight or an ∞ symbol. The morphology resembles that of the nearby system II Hz 4, where the head-on collision of two galaxies with parallel disks led to the formation of collisional rings around both of their bulges. Keck spectroscopy, Very Large Array radio data, and Chandra X-ray data show that the ∞ galaxy hosts an actively accreting supermassive black hole (SMBH) with quasar-like radio and X-ray luminosity. Remarkably, the SMBH is not associated with either of the two nuclei but is in between them in both position and radial velocity. Furthermore, from excess emission in the NIRCAM F150W filter, we infer that the SMBH is embedded in an extended distribution of Hα-emitting gas, with a rest-frame equivalent width ranging from 400 Å to 2000 Å. The gas spans the entire width of the system and was likely shocked and compressed at the collision site in a galaxy-scale equivalent of what happened in the bullet cluster. We suggest that the SMBH formed within this gas in the immediate aftermath of the collision, when it was dense and highly turbulent. If corroborated with simulations and follow-up JWST spectroscopy, this would demonstrate that "direct" SMBH formation by a runaway gravitational collapse is possible in extreme conditions.

Keywords: Supermassive black holes, Active galaxies
Fine-tuned Supernova or Failed Explosion? Decoding the Origins of the G3425 Binary. A binary system (G3425) consisting of a massive unseen component and a red giant star on a nearly circular orbit was recently discovered. The formation of such a system is puzzling because orbital stability generally breaks down due to the large mass loss from the system caused by the supernova (SN) explosion while forming the unseen component. Analytical solutions of the variable-mass two-body problem suggest that the explosion should have occurred when the component was close to its apocenter to explain the near-circular remnant system. This provides a strong constraint on the total mass and orbital configuration of the progenitor system. The nearly circular orbit of G3425 rules out Type II SN scenarios and allows only for a fine-tuned SN Ib/c explosion to occur when the secondary was close to its apocenter. Such a scenario, although possible, is highly unlikely. However, the most likely scenario is a failed SN that produced a black hole (BH), for which no additional constraints on the position of the secondary are needed. We propose that the unseen component of G3425 is a mass-gap BH with a mass constrained between the theoretical minimum for failed SN progenitors (4 M⊙) and the observed upper limit (4.4 M⊙). Our analysis can be applied to any wide binary system containing an unseen component on a nearly circular orbit.

Keywords: Stellar mass black holes, Supernova dynamics, Stellar mass loss
Cosmic Clues from Amaterasu: Blazar-driven Ultrahigh-energy Cosmic Rays?. The detection of the Amaterasu event of energy 244 EeV by the Telescope Array, one of the most energetic ultrahigh-energy cosmic rays (UHECRs; E ≳ 0.1 EeV) observed to date, invites scrutiny of its potential source. We investigate whether the nearby blazar PKS 1717+177 at redshift z = 0.137, located within  2.°5  of the reconstructed arrival direction, could explain the event under a proton-primary hypothesis. Using a one-zone jet model, we fit the multiwavelength spectral energy distribution of the source, incorporating both leptonic and hadronic cascade emissions from photohadronic interactions inside the jet. Our model supports a cosmic-ray origin of the very-high-energy (ɛγ ≳ 100 GeV) γ-ray flux and predicts a subdominant neutrino flux, 1 one order of magnitude lower than from TXS 0506+056. Under Lorentz invariance violation, UHECRs escaping the blazar jet above a specific energy can propagate unattenuated over hundreds of Mpc due to an increase in energy loss length for certain parameter choices. In such a scenario, the Amaterasu event can have a plausible origin from this blazar. Our analysis indicates negligible deflection in the Galactic magnetic field, implying a strong extragalactic magnetic field is required. Our findings provide a compelling multimessenger framework linking UHECRs, γ-rays, and neutrinos and motivate targeted searches by current and future high-energy neutrino telescopes during increased γ-ray or X-ray activity of this blazar.

Keywords: High energy astrophysics, Blazars, Neutrino astronomy, Active galactic nuclei, Gamma-ray astronomy, Ultra-high-energy cosmic radiation
First Detection of Circular Polarization in Radio Continuum Toward a Massive Protostar. Polarization measurements provide strong constraints on magnetic fields in star-forming systems. While magnetic field estimates of a few kG have been obtained near the surfaces of low-mass protostars, there are no analogous measurements in the immediate vicinity of the surface of massive protostars. We report the measurement of radio continuum circular polarization (CP) toward a massive protostar, IRAS 18162–2048, for the first time, using Karl G. Jansky Very Large Array observations. The fractional CP varies between 3% and 5% across the observed frequency range of 4–6 GHz. We consider multiple hypotheses for the production of CP and propose (i) gyrosynchrotron emission and (ii) Faraday conversion due to turbulence in the magnetic medium—both driven by mildly relativistic electrons as plausible mechanisms. We estimate, for the first time, a magnetic field B ≳ 20–35 G close to the massive protostar. The Lorentz factor of the low-energy electrons is estimated to be in the range γmin ∼ 5–7 for gyrosynchrotron emission and 80–100 for Faraday conversion from our observations. The magnetic field estimate can provide important constraints to the formation models of massive stars.

Keywords: Polarimetry, Interstellar magnetic fields, Star formation, Interstellar synchrotron emission, Protostars, Radio astronomy
CAPERS Observations of Two UV-bright Galaxies at z &gt; 10. More Evidence for Bursting Star Formation in the Early Universe. We present the first results from the CANDELS-Area Prism Epoch of Reionization Survey (CAPERS), utilizing PRISM observations with the JWST/NIRSpec microshutter assembly in the PRIMER-UDS field. With just 14% of the total planned data volume, we spectroscopically confirm two new bright galaxies (MUV ∼ −20.4) at redshifts z = 10.562 ± 0.034 and z = 11.013 ± 0.028. We examine their physical properties, morphologies, and star formation histories, finding evidence for recent bursting star formation in at least one galaxy thanks to the detection of strong rest-frame equivalent width (EW0 ∼ 70 Å) Hγ emission. Combining our findings with previous studies of similarly bright objects at high z, we further assess the role of stochastic star formation processes in shaping early galaxy populations. Our analysis finds that the majority of bright (MUV ≲ −20) spectroscopically confirmed galaxies at z &gt; 10 were likely observed during a starburst episode, characterized by a median star formation rate (SFR) ratio of SFR10/SFR100 ∼ 2, although with substantial scatter of 0.24 dex. Our work also finds tentative evidence that z &gt; 10 galaxies are more preferentially in a bursting phase than similarly bright z ∼ 6 galaxies. We finally discuss the prospects of deeper spectroscopic observations of a statistically significant number of bright galaxies to quantify the true impact of bursting star formation on the evolution of the bright end of the UV luminosity function at these early epochs.

Keywords: Starburst galaxies, High-redshift galaxies, Galaxies
A Binary Origin for Ultralong-period Radio Pulsars. We propose a possible binary evolution model for the formation of ultralong-period pulsars. The model involves two key stages: first, a neutron star (NS) in wide binaries undergoes an effective spin-down phase through wind-fed accretion from its massive stellar companion; second, the supernova explosion of the companion leads to the disruption of the binary system and produces two isolated compact stars. One of the them is the first-born, slowly rotating NS, and our binary and spin evolution calculations show that the spin periods range from ≲0.1 to ≳108 s. This offers a possible formation channel for some of the long-period radio transients. We estimate that the formation rate of such systems in the Milky Way is approximately 10‑6 yr‑1.

Keywords: Accretion, Neutron stars, Pulsars
Observability of Isolated Stellar-mass Black Holes. Stellar-mass black holes (BHs) represent the natural end states of massive stars. It is estimated that 108 stellar-mass BHs are present in the Milky Way galaxy, a significant fraction of which are expected to be isolated. Despite their expected abundance, only about 20 have been detected so far—mostly in binary systems—with just one confirmed isolated black hole (IsoBH) identified via astrometric microlensing. In this study, we investigate the potential for detecting electromagnetic emissions from IsoBHs by generating synthetic model spectra of their emissions in different types of interstellar medium environments. These model spectra are then compared with current observational capabilities. We show that photons emitted by IsoBHs—especially those accreting material in dense environments or within the solar neighborhood—should be readily detectable. However, confidently identifying these sources remains highly challenging. We conclude that a number of IsoBHs must already exist in current astronomical catalogs but have not been identified as such. We outline possible strategies for the detection and identification of IsoBHs using the current and upcoming telescopes.

Keywords: Accretion, Black holes, Stellar mass black holes, Interstellar medium, Astrophysical black holes
EP 250108a/SN 2025kg: Observations of the Most Nearby Broad-line Type Ic Supernova Following an Einstein Probe Fast X-Ray Transient. With a small sample of fast X-ray transients (FXTs) with multiwavelength counterparts discovered to date, their progenitors and connections to γ-ray bursts (GRBs) and supernovae (SNe) remain ambiguous. Here, we present photometric and spectroscopic observations of SN 2025kg, the SN counterpart to the FXT EP 250108a. At z = 0.17641, this is the closest known SN discovered following an Einstein Probe (EP) FXT. We show that SN 2025kg's optical spectra reveal the hallmark features of a broad-lined Type Ic SN. Its light-curve evolution and expansion velocities are comparable to those of GRB-SNe, including SN 1998bw, and two past FXT-SNe. We present JWST/NIRSpec spectroscopy taken around SN 2025kg's maximum light, and find weak absorption due to He I 1.0830 μm and 2.0581 μm and a broad, unidentified emission feature at ∼4─4.5 μm. Further, we observe broadened Hα in optical data at 42.5 days that is not detected at other epochs, indicating interaction with H-rich material. From its light curve, we derive a 56Ni mass of 0.2─0.6 M⊙. Together with our companion Letter, our broadband data are consistent with a trapped or low-energy (≲1051 erg) jet-driven explosion from a collapsar with a zero-age main-sequence mass of 15─30 M⊙. Finally, we show that the sample of EP FXT-SNe supports past estimates that low-luminosity jets seen through FXTs are more common than successful (GRB) jets, and that similar FXT-like signatures are likely present in at least a few percent of the brightest Type Ic-BL SNe.

Keywords: X-ray transient sources, Gamma-ray bursts, Core-collapse supernovae