adsabs/SciX_UAT_keywords huggingface dataset:
3HWC: The Third HAWC Catalog of Very-high-energy Gamma-Ray Sources

We present a new catalog of TeV gamma-ray sources using 1523 days of data from the High-Altitude Water Cherenkov (HAWC) Observatory. The catalog represents the most sensitive survey of the northern gamma-ray sky at energies above several TeV, with three times the exposure compared to the previous HAWC catalog, 2HWC. We report 65 sources detected at ≥5σ significance, along with the positions and spectral fits for each source. The catalog contains eight sources that have no counterpart in the 2HWC catalog, but are within 1° of previously detected TeV emitters, and 20 sources that are more than 1° away from any previously detected TeV source. Of these 20 new sources, 14 have a potential counterpart in the fourth Fermi Large Area Telescope catalog of gamma-ray sources. We also explore potential associations of 3HWC sources with pulsars in the Australia Telescope National Facility (ATNF) pulsar catalog and supernova remnants in the Galactic supernova remnant catalog.

Keywords: gamma-ray astronomy; gamma-ray observatories; high energy astrophysics; cosmic ray sources
The Accretion History of AGN: A Newly Defined Population of Cold Quasars

Quasars are the most luminous of active galactic nuclei, and are perhaps responsible for quenching star formation in their hosts. The Stripe 82X catalog covers 31.3 deg2 of the Stripe 82 field, of which the 15.6 deg2 covered with XMM-Newton is also covered by Herschel/SPIRE. We have 2500 X-ray detected sources with multiwavelength counterparts, and 30% of these are unobscured quasars, with LX > 1044 erg s-1 and MB < -23. We define a new population of quasars that are unobscured, have X-ray luminosities in excess of 1044 erg s-1, have broad emission lines, and yet are also bright in the far-infrared, with a 250 μm flux density of S250 > 30 mJy. We refer to these Herschel-detected, unobscured quasars as "cold quasars." A mere 4% (21) of the X-ray- and optically selected unobscured quasars in Stripe 82X are detected at 250 μm. These cold quasars lie at z ∼ 1-3, have LIR > 1012 L⊙, and have star formation rates (SFRs) of ∼200-1400 M⊙ yr-1. Cold quasars are bluer in the mid-IR than the full quasar population, and 72% of our cold quasars have WISE W3 < 11.5 [Vega], while only 19% of the full quasar sample meets this criteria. Crucially, cold quasars have on average ∼nine times as much star formation as the main sequence of star-forming galaxies at similar redshifts. Although dust-rich, unobscured quasars have occasionally been noted in the literature before, we argue that they should be considered as a separate class of quasars due to their high SFRs. This phase is likely short-lived, as the central engine and immense star formation consume the gas reservoir. Cold quasars are type-1 blue quasars that reside in starburst galaxies.

Keywords: far infrared astronomy; quasars; starburst galaxies
Model-independent Constraints on Ultralight Dark Matter from the SPARC Data

Ultralight dark matter (ULDM) is currently one of the most popular classes of cosmological dark matter. The most important advantage is that ULDM with mass m ∼ 10-22 eV can account for the small-scale problems encountered in the standard cold dark matter model like the core-cusp problem, missing satellite problem, and the too-big-to-fail problem in galaxies. In this paper, we formulate a new simple model-independent analysis using the Spitzer Photometry and Accurate Rotation Curves data to constrain the range of ULDM mass. In particular, the most stringent constraint comes from the data of a galaxy ESO563-G021, which can conservatively exclude a ULDM mass range m = (0.14-3.11) × 10-22 eV. This model-independent excluded range is consistent with many bounds obtained by recent studies and it suggests that the ULDM proposal may not be able to alleviate the small-scale problems.

Keywords: dark matter; particle astrophysics; spiral galaxies
The Excitation Conditions of CN in TW Hya

We report observations of the cyanide anion, CN, in the disk around TW Hya covering the N = 1-0, N = 2-1, and N = 3-2 transitions. Using line-stacking techniques, 24 hyperfine transitions are detected out of the 30 within the observed frequency ranges. Exploiting the super-spectral resolution from the line-stacking method reveals the splitting of hyperfine components previously unresolved by laboratory spectroscopy. All transitions display a similar emission morphology, characterized by an azimuthally symmetric ring, peaking at ≈45 au (0"75), and a diffuse outer tail extending out to the disk edge at ≈200 au. Excitation analyses assuming local thermodynamic equilibrium (LTE) yield excitation temperatures in excess of the derived kinetic temperatures based on the local line widths for all fine-structure groups, suggesting assumptions of LTE are invalid. Using the 0D radiative transfer code RADEX, we demonstrate that such non-LTE effects may be present when the local H2 density drops to 107 cm-3 and below. Comparison with models of TW Hya find similar densities at elevated regions in the disk, typically z / r ≳ 0.2, consistent with model predictions where CN is formed via vibrationally excited H2 in the disk atmospheric layers where UV irradiation is less attenuated.

Keywords: submillimeter astronomy; radiative transfer; protoplanetary disks; astrochemistry
On the Detection and Characterization of Quasiperiodic Oscillations in Astronomical Time Series: Gamma-Ray Burst X-Ray Light Curves as a Test Case

The study of temporal properties of variable sources can elucidate their physical processes. In this context, we present a critical study comparing three approaches to periodic or quasiperiodic behavior: Gaussian process, power spectrum, and wavelet analysis, using celerite, Lomb–Scargle periodograms, and weighted wavelet Z-transforms, respectively. We use 15 Swift X-ray Telescope light curves of short gamma-ray bursts (sGRBs) as examples. A comprehensive analysis of two sGRB X-ray light curves is performed. The results reveal the importance of artifacts, largely in the form of false quasiperiodic oscillation signals, possibly introduced by preprocessing (such as detrending) or other aspects of the analysis. The exploration described in this paper can be helpful for future studies of variability in gamma-ray bursts, active galactic nuclei, and other astronomical sources.

Keywords: gamma-ray bursts
The Relation between the Cool-core Radius and the Host Galaxy Clusters: Thermodynamic Properties and Cluster Mass

We present a detailed study of cool-core systems in a sample of four galaxy clusters (RXCJ1504.1-0248, A3112, A4059, and A478) using archival X-ray data from the Chandra X-ray Observatory. Cool cores are frequently observed at the centers of galaxy clusters and are considered to be formed by radiative cooling of the intracluster medium (ICM). Cool cores are characterized by a significant drop in the ICM temperature toward the cluster center. We extract and analyze X-ray spectra of the ICM to measure the radial profiles of the ICM thermodynamic properties, including temperature, density, pressure, entropy, and radiative cooling time. We define the cool-core radius as the turnover radius in the ICM temperature profile and investigate the relation between the cool-core radius and the properties of the host galaxy clusters. In our sample, we observe that the radiative cooling time of the ICM at the cool-core radius exceeds 10 Gyr, with RXCJ1504.1-0248 exhibiting a radiative cooling time of Gyr at its cool-core radius. These results indicate that not only radiative cooling but also additional mechanisms, such as gas sloshing, may play an important role in determining the size of cool cores. Additionally, we might find that the best-fit relation between the cool-core radius and the cluster mass (M 500) is consistent with a linear relation. Our findings may suggest that cool cores are linked to the evolution of their host galaxy clusters.

Keywords: galaxy clusters; intracluster medium; x-ray astronomy
Expansion and Age of the Supernova Remnant G350.1-0.3: High-velocity Iron Ejecta from a Core-collapse Event

We report Chandra observations of the highly asymmetric core-collapse supernova remnant G350.1-0.3. We document expansion over 9 yr away from the roughly stationary central compact object, with sky-plane velocities up to 5000 d4.5 km s-1 (d4.5 is the distance in units of 4.5 kpc), redshifts ranging from 900 to 2600 km s-1, and three-dimensional space velocities approaching 6000 km s-1. Most of the bright emission comes from heavy-element ejecta particularly strong in iron. Iron-enhanced ejecta are seen at 4000-6000 km s-1, strongly suggesting that the supernova was not a common Type IIP event. While some fainter regions have roughly solar abundances, we cannot identify clear blast-wave features. Our expansion proper motions indicate that G350.1-0.3 is no more than about 600 yr old, independent of distance: the third youngest known core-collapse supernova in the Galaxy, and one of the most asymmetric.

Keywords: supernova remnants; core-collapse supernovae; ejecta; x-ray astronomy
Feasibility of Observing Gamma-Ray Polarization from Cygnus X-1 Using a CubeSat

Instruments flown on CubeSats are small. Meaningful applications of CubeSats in astronomical observations rely on the choice of a particular subject that is feasible for CubeSats. Here we report the result of a feasibility study for observing gamma-ray polarization from Cygnus X-1 using a small Compton polarimeter on board a 3U CubeSat. Silicon detectors and cerium bromide scintillators were employed in the instrument models that we discuss in this study. Through Monte Carlo simulations with a Geant4-based MEGAlib package, we found that, with a 10 Ms on-axis, zenith-direction observation in a low-inclination, low-altitude, Earth-orbit radiation background environment, the minimum detectable polarization degree can be down to about 10% in 160-250 keV, 20% in 250-400 keV, and 65% in 400-2000 keV. A 3U CubeSat dedicated to observing Cygnus X-1 can therefore yield useful information on the polarization state of gamma-ray emissions from the brightest persistent X-ray black hole binary in the sky.

Keywords: gamma-ray astronomy; gamma-ray telescopes; gamma-ray sources; astronomical instrumentation; polarimeters; gamma-ray detectors; astrophysical black holes
The Kiloparsec-scale Influence of the AGN in NGC 1068 with SALT RSS Fabry-Pérot Spectroscopy

We present Fabry-Pérot (FP) imaging and longslit spectroscopy of the nearby Seyfert II galaxy NGC 1068 using the Robert Stobie Spectrograph (RSS) on the Southern African Large Telescope (SALT) to observe the impact of the central active galactic nucleus (AGN) on the ionized gas in the galaxy on kiloparsec scales. With SALT RSS FP we are able to observe the Hα + [N II] emission line complex over a ~2.6 arcmin2 field of view. Combined with the longslit observation, we demonstrate the efficacy of FP spectroscopy for studying nearby Type II Seyfert galaxies and investigate the kiloparsec-scale ionized gas in NGC 1068. We confirm the results of previous work from the TYPHOON/Progressive Integral Step Method survey that the kiloparsec-scale ionized features in NGC 1068 are driven by AGN photoionization. We analyze the spatial variation of the AGN intensity to put forward an explanation for the shape and structure of the kiloparsec-scale ionization features. Using a toy model, we suggest the ionization features may be understood as a light echo from a burst of enhanced AGN activity ~2000 yr ago. *Based on observations made with the Southern African Large Telescope (SALT).

Keywords: seyfert galaxies; agn host galaxies
New Insights on 30 Dor B Revealed by High-quality Multiwavelength Observations

The supernova remnant (SNR) 30 Dor B is associated with the H II region ionized by the OB association LH99. The complex interstellar environment has made it difficult to study the physical structure of this SNR. We have used Hubble Space Telescope Hα images to identify SNR shocks and deep Chandra X-ray observations to detect faint diffuse emission. We find that 30 Dor B hosts three zones with very different X-ray surface brightnesses and nebular kinematics that are characteristic of SNRs in different interstellar environments and/or evolutionary stages. The ASKAP 888 MHz map of 30 Dor B shows counterparts to all X-ray emission features except the faint halo. The ASKAP 888 and 1420 MHz observations are used to produce a spectral index map, but its interpretation is complicated by the background thermal emission and the pulsar PSR J0537-6910's flat spectral index. The stellar population in the vicinity of 30 Dor B indicates a continuous star formation in the past 8-10 Myr. The observed very massive stars in LH99 cannot be coeval with the progenitor of 30 Dor B's pulsar. Adopting the pulsar's spin-down timescale, 5000 yr, as the age of the SNR, the X-ray shell would be expanding at ~4000 km s-1 and the post-shock temperature would be 1-2 orders of magnitude higher than that indicated by the X-ray spectra. Thus, the bright central region of 30 Dor B and the X-ray shell requires two separate SN events, and the faint diffuse X-ray halo perhaps other older SN events.

Keywords: interstellar medium; supernova remnants; magellanic clouds; large magellanic cloud
Confronting a Thin Disk-wind Launching Mechanism of Broad-line Emission in Active Galactic Nuclei with GRAVITY Observations of Quasar 3C 273

Quasars show a remarkable degree of atomic emission-line broadening, an observational feature which, in conjunction with a radial distance estimate for this emission from the nucleus, is often used to infer the mass of the central supermassive black hole. The radius estimate depends on the structure and kinematics of this so-called broad-line region, which is often modeled as a set of discrete emitting clouds. Here, we test an alternative kinematic disk-wind model of optically thick line emission originating from a geometrically thin accretion disk under Keplerian rotation around a supermassive black hole. We use this model to calculate broad emission-line profiles and interferometric phases to compare to GRAVITY data and previously published cloud modeling results. While we show that such a model can provide a statistically satisfactory fit to GRAVITY data for quasar 3C 273, we disfavor it as it requires 3C 273 be observed at high inclination, which observations of the radio jet orientation do not support.

Keywords: active galactic nuclei; quasars; reverberation mapping; interferometry; astronomy data modeling; theoretical models
TESS Phase Curve of the Hot Jupiter WASP-19b

We analyze the phase curve of the short-period transiting hot Jupiter system WASP-19, which was observed by the Transiting Exoplanet Survey Satellite (TESS) in Sector 9. WASP-19 is one of only five transiting exoplanet systems with full-orbit phase curve measurements at both optical and infrared wavelengths. We measure a secondary eclipse depth of ${470}_{-110}^{+130}$ ppm and detect a strong atmospheric brightness modulation signal with a semiamplitude of 319 ± 51 ppm. No significant offset is detected between the substellar point and the region of maximum brightness on the dayside. There is also no significant nightside flux detected, which is in agreement with the nightside effective blackbody temperature of ${1090}_{-250}^{+190}$ derived from the published Spitzer phase curves for this planet. Placing the eclipse depth measured in the TESS bandpass alongside the large body of previous values from the literature, we carry out the first atmospheric retrievals of WASP-19b's secondary eclipse spectrum using the SCARLET code. The retrieval analysis indicates that WASP-19b has a dayside atmosphere consistent with an isotherm at T = 2240 ± 40 K and a visible geometric albedo of 0.16 ± 0.04, indicating significant contribution from reflected starlight in the TESS bandpass and moderately efficient day-night heat transport.

Keywords: exoplanets; hot jupiters; broad band photometry
Optical Monitoring of the Didymos-Dimorphos Asteroid System with the Danish Telescope around the DART Mission Impact

The NASA's Double-Asteroid Redirection Test (DART) was a unique planetary defence and technology test mission, the first of its kind. The main spacecraft of the DART mission impacted the target asteroid Dimorphos, a small moon orbiting the asteroid Didymos (65803), on 2022 September 26. The impact brought up a mass of ejecta which, together with the direct momentum transfer from the collision, caused an orbital period change of 33 ± 1 minutes, as measured by ground-based observations. We report here the outcome of the optical monitoring campaign of the Didymos system from the Danish 1.54 m telescope at La Silla around the time of impact. The observations contributed to the determination of the changes in the orbital parameters of the Didymos-Dimorphos system, as reported by Thomas et al., but in this paper we focus on the ejecta produced by the DART impact. We present photometric measurements from which we remove the contribution from the Didymos-Dimorphos system using an H-G photometric model. Using two photometric apertures we determine the fading rate of the ejecta to be 0.115 ± 0.003 mag day-1 (in a 2″ aperture) and 0.086 ± 0.003 mag day-1 (5″) over the first week postimpact. After about 8 days postimpact we note the fading slows down to 0.057 ± 0.003 mag day-1 (2″ aperture) and 0.068 ± 0.002 mag day-1 (5″). We include deep-stacked images of the system to illustrate the ejecta evolution during the first 18 days, noting the emergence of dust tails formed from ejecta pushed in the antisolar direction, and measuring the extent of the particles ejected Sunward to be at least 4000 km.

Keywords: light curves; asteroid satellites; apollo group; planetary probes
Properties of the Lowest-metallicity Galaxies over the Redshift Range z = 0.2 to z = 1

Low-metallicity galaxies may provide key insights into the evolutionary history of galaxies. Galaxies with strong emission lines and high equivalent widths (rest-frame EW(Hβ) ≳ 30 Å) are ideal candidates for the lowest-metallicity galaxies to z ~ 1. Using a Keck/DEIMOS spectral database of about 18,000 galaxies between z = 0.2 and z = 1, we search for such extreme emission-line galaxies with the goal of determining their metallicities. Using the robust direct T e method, we identify eight new extremely metal-poor galaxies (XMPGs) with $12+\mathrm{log}$ O/H ≤7.65, including one at 6.949 ± 0.091, making it the lowest-metallicity galaxy reported to date at these redshifts. We also improve upon the metallicities for two other XMPGs from previous work. We investigate the evolution of Hβ using both instantaneous and continuous starburst models, finding that XMPGs are best characterized by continuous starburst models. Finally, we study the dependence on age of the buildup of metals and the emission-line strength.

Keywords: observational cosmology; galaxy abundances; starburst galaxies; galaxy evolution
Turbulence Characteristics of Switchback and Nonswitchback Intervals Observed by Parker Solar Probe

We use Parker Solar Probe (PSP) in situ measurements to analyze the characteristics of solar wind turbulence during the first solar encounter covering radial distances between 35.7R⊙ and 41.7R⊙. In our analysis we isolate so-called switchback (SB) intervals (folded magnetic field lines) from nonswitchback (NSB) intervals, which mainly follow the Parker spiral field. Using a technique based on conditioned correlation functions, we estimate the power spectra of Elsasser, magnetic, and bulk velocity fields separately in the SB and NSB intervals. In comparing the turbulent energy spectra of the two types of intervals, we find the following characteristics: (1) The decorrelation length of the backward-propagating Elsasser field z- is larger in the NSB intervals than the one in the SB intervals; (2) the magnetic power spectrum in SB intervals is steeper, with spectral index close to -5/3, than in NSB intervals, which have a spectral index close to -3/2; (3) both SB and NSB turbulence are imbalanced with NSB having the largest cross-helicity, (4) the residual energy is larger in the SB intervals than in NSB, and (5) the analyzed fluctuations are dominated by Alfvénic fluctuations that are propagating in the sunward (antisunward) direction for the SB (NSB) turbulence. These observed features provide further evidence that the switchbacks observed by PSP are associated with folded magnetic field lines giving insight into their turbulence nature.

Keywords: solar wind; interplanetary turbulence; magnetohydrodynamics; space plasmas; alfven waves; plasma physics; heliosphere
Late Engine Activity in Neutron Star Mergers and Its Cocoon: An Alternative Scenario for the Blue Kilonova

Follow-up observations of short gamma-ray bursts (sGRBs) have continuously unveiled late extended/plateau emissions, attributed to jet launch due to late engine activity, the nature of which remains enigmatic. Observations of GW170817 have confirmed that sGRBs are linked to neutron star (NS) mergers, and discovered a kilonova (KN) transient. Nevertheless, the origin of the early blue KN in GW170817 remains unclear. Here, we investigate the propagation of late jets in the merger ejecta. By analytically modeling jet dynamics, we determine the properties of the jet-heated cocoon, and estimate its cooling emission. Our results reveal that late jets generate significantly brighter cocoons compared to prompt jets, primarily due to reduced energy loss by adiabatic cooling. Notably, with typical late jets, emission from the cocoon trapped inside the ejecta can reproduce the blue KN emission. We estimate that the forthcoming Einstein Probe mission will detect the early cocoon emission at a rate of $\sim {2.1}_{-1.6}^{+3.2}$ yr‑1, and that optical/UV follow-ups in the LIGO-Virgo-KAGRA O5 run will be able to detect $\sim {1.0}_{-0.7}^{+1.5}$ cocoon emission events. As an electromagnetic counterpart, this emission provides an independent tool to probe NS mergers in the Universe, complementing insights from sGRBs and gravitational waves.

Keywords: gamma-ray bursts; neutron stars; hydrodynamics; relativistic fluid dynamics; relativistic jets; gravitational waves; x-ray transient sources
H I Narrow-line Self-absorptions toward the High-mass Star-forming Region G176.51+00.20

Using the Five-hundred-meter Aperture Spherical radio Telescope (FAST) 19-beam tracking observational mode, high-sensitivity and high-velocity-resolution H I spectral lines have been observed toward the high-mass star-forming region G176.51+00.20. This is a pilot study searching for H I narrow-line self-absorption (HINSA) toward high-mass star-forming regions where bipolar molecular outflows have been detected. This work is confined to the central seven beams of FAST. Two HINSA components are detected in all seven beams, which correspond to a strong CO emission region (SCER; with a velocity of ~-18 km s-1) and a weak CO emission region (WCER; with a velocity of ~-3 km s-1). The SCER detected in Beam 3 is probably more suitably classified as a WCER. In the SCER, the HINSA is probably associated with the molecular material traced by the CO. The fractional abundance of HINSA ranges from ~1.1 × 10-3 to ~2.6 × 10-2. Moreover, the abundance of HINSA in Beam 1 is lower than that in the surrounding beams (i.e., Beams 2 and 4-7). This possible ring could be caused by the ionization of H I or the relatively rapid conversion from H I to H2 in the higher-density inner region. In the WCER (including Beam 3 in the SCER), the HINSA is probably not associated with CO clouds, but with CO-dark or CO-faint gas.

Keywords: interstellar atomic gas; interstellar abundances; interstellar molecules; star formation; interstellar dynamics; jets