Sazuna/UAT_keywords huggingface dataset:
The Pulsar Science Collaboratory: Multiepoch Scintillation Studies of Pulsars. We report on findings from scintillation analyses using high-cadence observations of eight canonical pulsars with observing baselines ranging from 1–3 yr. We obtain scintillation bandwidth and timescale measurements for all pulsars in our survey and scintillation arc curvature measurements for four, and we detect multiple arcs for two. We find evidence of a previously undocumented scattering screen along the line of sight (LOS) to PSR J1645‑0317, as well as evidence that a scattering screen along the LOS to PSR J2313+4253 may reside somewhere within the Milky Way's Orion–Cygnus arm. We report evidence of a significant change in the scintillation pattern in PSR J2022+5154 from the previous two decades of literature, wherein both the scintillation bandwidth and timescale decreased by an order of magnitude relative to earlier observations at the same frequencies, potentially as a result of a different screen dominating the observed scattering. By augmenting the results of previous studies, we find general agreement with estimations of scattering delays from pulsar observations and predictions by the NE2001 electron density model but not for the newest data we have collected, providing some evidence of changes in the ISM along various LOSs over the timespans considered. In a similar manner, we find additional evidence of a correlation between a pulsar's dispersion measure and the overall variability of its scattering delays over time. The plethora of interesting science obtained through these observations demonstrates the capabilities of the Green Bank Observatory's 20 m telescope to contribute to pulsar-based studies of the interstellar medium.

Keywords: Interstellar medium, Interstellar scintillation, Pulsars, Radio pulsars
Signature of Triaxially Precessing Magnetars in Gamma-Ray Burst X-Ray Afterglows. The X-ray afterglows of some gamma-ray bursts (GRBs) exhibit plateaus, which can be explained by the internal dissipation of a newborn millisecond magnetar wind. In the early phase of these newborn magnetars, the magnetic inclination angle undergoes periodic changes due to precession, leading to periodic modulation of the injection luminosity due to magnetic dipole radiation. This may result in quasiperiodic oscillations on the plateaus. In this paper, we identify four GRBs with regular flux variations on their X-ray afterglow plateaus from Swift/X-Ray Telescope data before 2023 November, three of which exhibit periodicity. Based on the likelihood of supporting a precessing magnetar as the central engine, we classify them into three categories: Gold (GRB 060202 and GRB 180620A), Silver (GRB 050730), and Bronze (GRB 210610A). We invoke a model of magnetic dipole radiation emitted by a triaxially freely precessing magnetar whose spindown is dominated by electromagnetic radiation, to fit the light curves. Our model successfully reproduces the light curves of these four GRBs, including the regular flux variations on the plateaus and their periodicity (if present). Our work provides further evidence for early precession in newborn millisecond magnetars in GRBs.

Keywords: Magnetars, Gamma-ray bursts
X-Ray and Spectral Ultraviolet Observations of Periodic Pulsations in a Solar Flare Fan/Looptop. We present simultaneous X-ray and spectral ultraviolet observations of strikingly coherent oscillations in emission from a coronal looptop and fan structure, during the impulsive phase of a long-duration M-class solar flare. The ≈50 s oscillations are observed near in-phase by Solar Orbiter/STIX, GOES, and IRIS Fe XXI intensity, Doppler, and nonthermal velocity. For over 5 minutes of their approximate 35 minute duration, the oscillations are so periodic (2σ above the power-law background) that they are better described as "periodic pulsations" than the more widely documented "quasiperiodic pulsations" often observed during solar flares. By combining time-series analysis of the multi-instrument data sets with comparison to magnetohydrodynamic simulations, we attribute the oscillations to the magnetic tuning fork in the flare looptop–fan region, and betatron acceleration within the lower-altitude flare loops. These interpretations are possible due to the introduced Sliding Raster Method (SliRM) for analysis of slit spectrometer (e.g., IRIS) raster data, to increase the temporal cadence of the observations at the expense of spatial information.

Keywords: Solar flares, Solar magnetic reconnection, Solar ultraviolet emission, Ultraviolet spectroscopy, Solar flare spectra, Solar x-ray emission, Solar physics, Solar activity, Solar corona, Solar x-ray flares, Solar oscillations, Solar particle emission
A High-resolution Far-infrared Survey to Probe Black Hole–Galaxy Co-evolution. Far-infrared (FIR) surveys are critical to probing the co-evolution of black holes and galaxies, since of the order of half the light from accreting black holes and active star formation is emitted in the rest-frame IR over 0.5 ≲ z ≲ 10. For deep fields with areas of 1 deg2 or less, like the legacy surveys GOODS, COSMOS, and CANDELS, source crowding means that subarcsecond resolution is essential. In this paper, we show with a simulation of the FIR sky that observations made with a small telescope (2 m) at low angular resolution preferentially detect the brightest galaxies, and we demonstrate the scientific value of a space mission that would offer subarcsecond resolution. We envisage a facility that would provide high-resolution imaging and spectroscopy over the wavelength range 25–400 μm, and we present predictions for an extragalactic survey covering 0.5 deg2. Such a survey is expected to detect tens of thousands of star-forming galaxies and thousands of active galactic nuclei (AGNs), in multiple FIR lines (e.g., [C II], [O I], and [C I]) and continuum. At the longest wavelengths (200–400 μm), it would probe beyond the Epoch of Reionization, up to z ∼ 7–8. A combination of spectral resolution, line sensitivity, and broad spectral coverage would allow us to learn about the physical conditions (temperature, density, and metallicity) characterizing the interstellar medium of galaxies over the past ∼12 billion years and to investigate galaxy–AGN co-evolution.

Keywords: Extragalactic astronomy, Active galaxies, High-redshift galaxies, Infrared excess galaxies
Considerations for Photochemical Modeling of Possible Hycean Worlds. JWST is revolutionising the study of temperate sub-Neptunes, starting with the first detection of carbon-bearing molecules in the habitable-zone sub-Neptune K2-18 b. The retrieved abundances of CH4 and CO2 and nondetection of NH3 and CO in K2-18 b are consistent with prior predictions of photochemical models for a Hycean world with a habitable ocean. However, recent photochemical modeling raised the prospect that the observed abundances may be explained by a mini-Neptune scenario instead. In this study, we explore these scenarios using independent photochemical modeling with K2-18 b as a case study. We find the previous results to be sensitive to a range of model assumptions, such as the photochemical cross sections, incident stellar spectrum, surface pressure, UV albedo, and metallicity, significantly affecting the resulting abundances. We explore a wide model space to investigate scenarios that are compatible with the retrieved molecular abundances for K2-18 b. Our analysis shows that the previously favored mini-Neptune scenario is not compatible with most of the retrieved abundances, while the Hycean scenarios, both inhabited and uninhabited, provide better agreement. An uninhabited Hycean scenario explains most of the abundance constraints, except CH4, which is generally underabundant but dependent on the model assumptions. The inhabited Hycean scenario is compatible with all the abundances if the observed CH4 is assumed to be predominantly biogenic. Our results underscore the importance of systematic photochemical modeling and accurate interpretation of chemical abundance constraints for candidate Hycean worlds.

Keywords: Exoplanet atmospheric composition , Exoplanets, Mini Neptunes, Biosignatures, Habitable planets, Exoplanet atmospheres
Dust-obscured Galaxies in the XMM-SERVS Fields: Selection, Multiwavelength Characterization, and Physical Nature. Dust-obscured galaxies (DOGs) are enshrouded by dust and many are believed to host accreting supermassive black holes (SMBHs), which makes them unique objects for probing the coevolution of galaxies and SMBHs. We select and characterize DOGs in the 13 deg2 XMM-Spitzer Extragalactic Representative Volume Survey (XMM-SERVS), leveraging the superb multiwavelength data—from X-rays to radio. We select 3738 DOGs at z ≍ 1.6─2.1 in XMM-SERVS, while maintaining good data quality without introducing significant bias. This represents the largest DOG sample with thorough multiwavelength source characterization. Spectral energy distribution modeling shows DOGs are a heterogeneous population consisting of both normal galaxies and active galactic nuclei (AGNs). Our DOGs are massive ( ), 174 are detected in X-rays, and they are generally radio-quiet systems. X-ray detected DOGs are luminous and are moderately to heavily obscured in X-rays. Stacking analyses for the X-ray undetected DOGs show highly significant average detections. Critically, we compare DOGs with matched galaxy populations. DOGs have similar AGN fractions compared with typical galaxy populations. X-ray detected DOGs have higher M ⋆ and higher X-ray obscuration, but they are not more star-forming than typical X-ray AGNs. Our results potentially challenge the relevance of the merger-driven galaxy-SMBH coevolution framework for X-ray detected DOGs.

Keywords: Surveys, Active galactic nuclei, Galaxies
Do Neutron Star Ultraluminous X-Ray Sources Masquerade as Intermediate-mass Black Holes in Radio and X-Ray?. Ultraluminous X-ray sources (ULXs) were once largely believed to be powered by super-Eddington accretion onto stellar-mass black holes, although in some rare cases, ULXs also serve as potential candidates for (sub-Eddington) intermediate-mass black holes. However, a total of eight ULXs have now been confirmed to be powered by neutron stars, thanks to observed pulsations, and may act as contaminants for the radio/X-ray selection of intermediate-mass black holes. Here, we present the first comprehensive radio study of seven known neutron star ULXs using new and archival data from the Karl G. Jansky Very Large Array and the Australia Telescope Compact Array, combined with the literature. Across this sample, there is only one confident radio detection, from the Galactic neutron star ULX Swift J0243.6+6124. The other six objects in our sample are extragalactic, and only one has coincident radio emission, which we conclude is most likely contamination from a background H II region. We conclude that with current facilities, neutron star ULXs do not produce significant enough radio emission to cause them to be misidentified as radio-/X-ray-selected intermediate-mass black hole candidates. Thus, if background star formation has been properly considered, the current study indicates that a ULX with a compact radio counterpart is not likely to be a neutron star.

Keywords: Neutron stars, Ultraluminous x-ray sources, Compact objects
Effects of Background Solar Wind and Drag Force on the Propagation of Coronal-mass-ejection-driven Shocks. The propagation of interplanetary shocks, particularly those driven by coronal mass ejections (CMEs), is still an outstanding question in heliophysics and space weather forecasting. Here, we address the effects of the ambient solar wind on the propagation of two similar CME-driven shocks from the Sun to Earth. The two shock events (CME03, 2010 April 3; CME12, 2012 July 12) have the following properties. Both events (1) were driven by a halo CME (i.e., the source location is near the Sun–Earth line); (2) had a CME source in the southern hemisphere; (3) had a similar transit time (∼2 days) to Earth; (4) occurred in a nonquiet solar period; and (5) led to a severe geomagnetic storm. The initial (near the Sun) propagation speed, as measured by coronagraph images, was slower (by ∼300 km s‑1) for CME03 than CME12, but it took about the same amount of traveling time for both events to reach Earth. According to the in situ solar wind observations from the Wind spacecraft, the CME03-driven shock was associated with a faster solar wind upstream of the shock than the CME12-driven shock. This is also demonstrated in our global MHD simulations. Analysis of our simulation result indicates that the drag force indirectly plays an important role in the shock propagation. The present study suggests that in addition to the initial CME propagation speed near the Sun, the shock speed (in the inertial frame) and the ambient solar wind conditions—in particular, the solar wind speed—are key to timing the arrival of CME-driven shock events.

Keywords: Solar wind, Interplanetary shocks, Solar coronal mass ejections, Magnetohydrodynamical simulations
Gone with the Molecular Wind: Photoevaporation in the Compact Dust Disk around CX Tau. We present Keck NIRSPEC+AO high-resolution (R ∼ 25,000), mid-infrared (M-band: 4.6–5.2 μm) spectra of the protoplanetary disk CX Tau. CX Tau provides an ideal laboratory to study inner disk chemistry in a disk where the signs of radial drift of pebbles are present in the form of a compact mm dust disk and extended gas disk. Our data covers many 12CO v = 1–0 ro-vibrational transitions, in addition to 13CO and 12CO v = 2–1. We find no evidence for CO emission in the inner disk of CX Tau at the level of 8 × 1016 cm‑2, but do detect narrow, blueshifted absorption at ∼‑6 km s‑1. A rotation diagram analysis shows that the gas temperature ranges from about 10 to 350 K, with column densities ∼9 × 1015 and 3 × 1017 cm‑2, respectively. In addition to our Keck-NIRSPEC spectra, we create line maps from archival JWST-MIRI IFU data using custom JDISCS reduction techniques. These maps show spatially extended (∼500 au) H2 and [ Ne II]. The blueshifted CO absorption and extended H2 and [Ne II] are evidence of a photoevaporative disk wind. We estimate a wind mass-loss rate from the H2 S(1) line of ∼10‑9 M ⊙ yr‑1, which is approximately equal to the stellar accretion rate and suggests that CX Tau is in the early stages of disk dispersal.

Keywords: Infrared astronomy, T Tauri stars, Protoplanetary disks
Protoplanetary Disks around Sun-like Stars Appear to Live Longer When the Metallicity is Low. Previous Hubble Space Telescope observations of the star-forming cluster NGC 346 in the Small Magellanic Cloud (SMC) revealed a large population of pre-main-sequence (PMS) candidates, characterized by Hα excess emission in their photometry. However, without access to spectroscopy, the nature of these objects remained unclear. Using the NIRSpec instrument on board JWST, we studied a sample of these stars, with masses in the range of ∼0.9‑1.8 M ⊙, effective temperatures (T eff) in the range of 4500‑8000 K, and PMS ages between ∼0.1 and 30 Myr. Here, we present the first spectra of solar-mass PMS stars in the metal-poor SMC (Z = 1/8 Z ⊙) and discuss the physical properties of 10 representative sources with good signal-to-noise ratio. The observations indicate that even the oldest of these PMS candidates are still accreting gas with typical rates of ∼10‑8 M ⊙ yr‑1 for stars older than ∼10 Myr, confirming their PMS nature. The spectra also reveal near-infrared excess and molecular hydrogen excitation lines consistent with the presence of disks around these stars. These findings suggest that in a low-metallicity environment, circumstellar disks can live longer than previously thought. * Based on observations made with the NASA/ESA/CSA James Webb Space Telescope.

Keywords: Young star clusters, Small Magellanic Cloud, Pre-main sequence stars, Star formation, Stellar accretion, Spectroscopy
AstroSat View of the Neutron Star Low-mass X-Ray Binary GX 5-1. We present the spectral and timing study of the bright neutron star low-mass X-ray binary GX 5-1 using AstroSat/Large Area X-ray Proportional Counter (LAXPC) and Soft X-ray Telescope observations conducted in 2018. During the observation, the source traces out the complete horizontal branch (HB) and normal branch (NB) of the Z-track in the hardness–intensity diagram (HID). Understanding the spectral and temporal evolution of the source along the Z-track can probe the accretion process in the vicinity of a neutron star. Spectral analysis was performed in the 0.7–20 keV energy range for different segments in the HID using a multitemperature disk blackbody with an average temperature, kT in ∼ 0.47, and a thermal Comptonization model. It is found that the optical depth of the corona drops from ∼7.07 in HB to ∼2.61 in NB. The timing analysis using the LAXPC instrument indicates the presence of quasiperiodic oscillations in HB and NB of the Z-track. The observed QPO frequencies are similar to the characteristic frequencies of horizontal branch oscillations (HBOs) and normal branch oscillations (NBOs). The HBO frequency increases from ∼12 to 40 Hz toward the hard apex. NBOs are observed at ∼5 Hz. The timing studies conducted in soft and hard bands indicate the association of HBO and NBO origin with the nonthermal component. Further research could explore the implications of this relationship for understanding the dynamics of accretion onto neutron stars.

Keywords: X-ray astronomy, Neutron stars, Low-mass x-ray binary stars, Compact objects
Spectro-temporal Evolution of 4U 1702-429 Using AstroSat-NICER. We present the broadband spectral and timing properties of the atoll source 4U 1702-429 using two observations of AstroSat with the second one having simultaneous NICER data. For both observations, the spectra can be represented by a Comptonizing medium with a blackbody seed photon source that can be identified with the surface of the neutron star. A disk emission along with a distant reflection is also required for both spectra. For the first observation, the coronal temperature (∼7 keV) is smaller than the second (∼13 keV), and the disk is truncated at a larger radius, ∼150 km, compared to the second, ∼25 km, for an assumed distance of 7 kpc. A kHz quasiperiodic oscillation (QPO) at ∼800 Hz is detected in the first and is absent in the second observation. Modeling the energy-dependent rms and time lag of the kHz QPO reveals a corona size of ≤30 km. A similar model can explain the energy dependence of the broadband noise at ∼10 Hz for the second observation. The results suggest that kHz QPOs are associated with a compact corona surrounding the neutron star and may occur when the disk is truncated at large distances. We emphasize the need for more wide-band observations of the source to confirm these results.

Keywords: Accretion, X-ray binary stars, Stellar accretion disks
The Hubble Constant Anchor Galaxy NGC 4258: Metallicity and Distance from Blue Supergiants. A quantitative spectroscopic study of blue supergiant stars in the Hubble constant anchor galaxy NGC 4258 is presented. The non-LTE analysis of Keck I telescope LRIS spectra yields a central logarithmic metallicity (in units of the solar value) of [Z] = ‑0.05 ± 0.05 and a very shallow gradient of ‑(0.09 ± 0.11) r/r 25 with respect to galactocentric distance in units of the isophotal radius. Good agreement with the mass–metallicity relationship of star-forming galaxies based on stellar absorption line studies is found. A comparison with H II region oxygen abundances obtained from the analysis of strong emission lines shows reasonable agreement when the M. Pettini &amp; B. E. J. Pagel calibration is used, while the D. Zaritsky et al. calibration yields values that are 0.2–0.3 dex larger. These results allow us to put the metallicity calibration of the Cepheid period–luminosity relation in this anchor galaxy on a purely stellar basis. Interstellar reddening and extinction are determined using Hubble Space Telescope and JWST photometry. Based on extinction-corrected magnitudes, combined with the stellar effective temperatures and gravities we determine, we use the flux-weighted gravity–luminosity relationship to estimate an independent spectroscopic distance. We obtain a distance modulus m ‑ M = 29.38 ± 0.12 mag, in agreement with the geometrical distance derived from the analysis of the water maser orbits in the galaxy's central circumnuclear disk.

Keywords: Galaxy abundances
Suppression of Collisionless Magnetic Reconnection in the High Ion β, Strong Guide Field Limit. In magnetic reconnection, the ion bulk outflow speed and ion heating have been shown to be set by the available reconnecting magnetic energy, i.e., the energy stored in the reconnecting magnetic field (B  r ). However, recent simulations, observations, and theoretical works have shown that the released magnetic energy is inhibited by upstream ion plasma beta β  i —the relative ion thermal pressure normalized to magnetic pressure based on the reconnecting field—for antiparallel magnetic field configurations. Using kinetic theory and hybrid particle-in-cell simulations, we investigate the effects of β  i  on guide field reconnection. While previous works have suggested that guide field reconnection is uninfluenced by β  i , we demonstrate that the reconnection process is modified and the outflow is reduced for sufficiently large  . We develop a theoretical framework that shows that this reduction is consistent with an enhanced exhaust pressure gradient, which reduces the outflow speed as  . These results apply to systems in which guide field reconnection is embedded in hot plasmas, such as reconnection at the boundary of eddies in fully developed turbulence like the solar wind or the magnetosheath as well as downstream of shocks such as the heliosheath or the mergers of galaxy clusters.

Keywords: Solar magnetic reconnection, Plasma physics, Interplanetary turbulence, Plasma astrophysics, Magnetohydrodynamical simulations
Investigating the Intracluster Medium Viscosity Using the Tails of GASP Jellyfish Galaxies. The microphysics of the intracluster medium (ICM) in galaxy clusters is still poorly understood. Observational evidence suggests that the effective viscosity is suppressed by plasma instabilities that reduce the mean free path of particles. Measuring the effective viscosity of the ICM is crucial to understanding the processes that govern its physics on small scales. The trails of ionized interstellar medium left behind by the so-called jellyfish galaxies can trace the turbulent motions of the surrounding ICM and constrain its local viscosity. We present the results of a systematic analysis of the velocity structure function (VSF) of the Hα line for ten galaxies from the GASP sample. The VSFs show a sublinear power-law scaling below 10 kpc that may result from turbulent cascading and extends to 1 kpc, which is below the supposed ICM dissipation scales of tens of kpc expected in a fluid described by Coulomb collisions. Our result constrains the local ICM viscosity to be 0.3%─25% of the expected Spitzer value. Our findings demonstrate that either the ICM particles have a smaller mean free path than expected in a regime defined by Coulomb collisions or that we are probing effects due to collisionless physics in the ICM turbulence.

Keywords: Galaxy clusters, Intracluster medium, Plasma astrophysics, Galaxies