adsabs/SciX_UAT_keywords huggingface dataset:
Gamma-Ray and X-Ray Observations of the Periodic-repeater FRB 180916 during Active Phases

FRB 180916 is a most intriguing source capable of producing repeating fast radio bursts with a periodic 16.3 day temporal pattern. The source is well positioned in a star-forming region in the outskirts of a nearby galaxy at 150 Mpc distance. In this Letter we report on the X-ray and γ-ray observations of FRB 180916 obtained by AGILE and Swift. We focused especially on the recurrent 5 day time intervals of enhanced radio bursting. In particular, we report on the results obtained in the time intervals 2020 February 3-8, 2020 February 25, 2020 March 5-10, and 2020 March 22-28 during a multiwavelength campaign involving high-energy and radio observations of FRB 180916. We also searched for temporal coincidences at millisecond timescales between the 32 known radio bursts of FRB 180916 and X-ray and MeV events detectable by AGILE. We do not detect any simultaneous event or any extended X-ray and γ-ray emission on timescales of hours/days/weeks. Our cumulative X-ray (0.3-10 keV) flux upper limit of 5 × 10-14 erg cm-2 s-1 (obtained during 5 day active intervals from several 1-2 ks integrations) translates into an isotropic luminosity upper limit of LX,UL ∼ 1.5 × 1041 erg s-1. Deep γ-ray observations above 100 MeV over a many-year timescale provide an average luminosity upper limit one order of magnitude larger. These results provide the so-far most stringent upper limits on high-energy emission from the FRB 180916 source. Our results constrain the dissipation of magnetic energy from a magnetar-like source of radius Rm, internal magnetic field Bm, and dissipation timescale τd to satisfy the relation ${R}_{m,6}^{3}\,{B}_{m,16}^{2}\,{\tau }_{d,8}^{-1}\lesssim 1$ , where Rm,6 is Rm in units of 106 cm, Bm,16 is Bm in units of 1016 G, and τd,8 in units of 108 s.

Keywords: gamma-ray astronomy; x-ray astronomy; radio bursts; radio transient sources; gamma-ray transient sources
Panic at the ISCO: Time-varying Double-peaked Broad Lines from Evolving Accretion Disks Are Common among Optically Variable AGNs

About 3%–10% of Type I active galactic nuclei (AGNs) have double-peaked broad Balmer lines in their optical spectra originating from the motion of gas in their accretion disk. Double-peaked profiles arise not only in AGNs, but occasionally appear during optical flares from tidal disruption events and changing-state AGNs. In this paper, we identify 250 double-peaked emitters (DPEs) among a parent sample of optically variable broad-line AGNs in the Zwicky Transient Facility (ZTF) survey, corresponding to a DPE fraction of 19%. We model spectra of the broad Hα emission-line regions and provide a catalog of the fitted accretion disk properties for the 250 DPEs. Analysis of power spectra derived from the 5 yr ZTF light curves finds that DPE light curves have similar amplitudes and power-law indices to other broad-line AGNs. Follow-up spectroscopy of 12 DPEs reveals that ∼50% display significant changes in the relative strengths of their red and blue peaks over long 10–20 yr timescales, indicating that broad-line profile changes arising from spiral arm or hotspot rotation are common among optically variable DPEs. Analysis of the accretion disk parameters derived from spectroscopic modeling provides evidence that DPEs are not in a special accretion state, but are simply normal broad-line AGNs viewed under the right conditions for the accretion disk to be easily visible. We include inspiraling supermassive black hole binary candidate SDSSJ1430+2303 in our analysis, and discuss how its photometric and spectroscopic variability is consistent with the disk-emitting AGN population in the ZTF survey.

Keywords: active galactic nuclei; tidal disruption; galaxy accretion disks; radio active galactic nuclei
Gas Morphology of Milky Way–like Galaxies in the TNG50 Simulation: Signals of Twisting and Stretching

We present an in-depth analysis of gas morphologies for a sample of 25 Milky Way–like galaxies from the IllustrisTNG TNG50 simulation. We constrain the morphology of cold, warm, hot gas, and gas particles as a whole using a local shell iterative method and explore its observational implications by computing the hard-to-soft X-ray ratio, which ranges between 10‑3 and 10‑2 in the inner ∼50 kpc of the distribution and 10‑5–10‑4 at the outer portion of the hot gas distribution. We group galaxies into three main categories: simple, stretched, and twisted. These categories are based on the radial reorientation of the principal axes of the reduced inertia tensor. We find that a vast majority (77%) of the galaxies in our sample exhibit twisting patterns in their radial profiles. Additionally, we present detailed comparisons between (i) the gaseous distributions belonging to individual temperature regimes, (ii) the cold gas distributions and stellar distributions, and (iii) the gaseous distributions and dark matter (DM) halos. We find a strong correlation between the morphological properties of the cold gas and stellar distributions. Furthermore, we find a correlation between gaseous distributions with a DM halo that increases with gas temperature, implying that we may use the warm–hot gaseous morphology as a tracer to probe the DM morphology. Finally, we show gaseous distributions exhibit significantly more prolate morphologies than the stellar distributions and DM halos, which we hypothesize is due to stellar and active galactic nucleus feedback.

Keywords: magnetohydrodynamical simulations; galaxy dark matter halos; circumgalactic medium
A Method to Distinguish Quiescent and Dusty Star-forming Galaxies with Machine Learning

Large photometric surveys provide a rich source of observations of quiescent galaxies, including a surprisingly large population at z > 1. However, identifying large, but clean, samples of quiescent galaxies has proven difficult because of their near-degeneracy with interlopers such as dusty, star-forming galaxies. We describe a new technique for selecting quiescent galaxies based upon t-distributed stochastic neighbor embedding (t-SNE), an unsupervised machine-learning algorithm for dimensionality reduction. This t-SNE selection provides an improvement both over UVJ, removing interlopers that otherwise would pass color selection, and over photometric template fitting, more strongly toward high redshift. Due to the similarity between the colors of high- and low-redshift quiescent galaxies, under our assumptions, t-SNE outperforms template fitting in 63% of trials at redshifts where a large training sample already exists. It also may be able to select quiescent galaxies more efficiently at higher redshifts than the training sample.

Keywords: astronomy data analysis; computational astronomy; galaxy quenching; quenched galaxies; galaxy classification systems; star formation
Precise Mass Measurement of OGLE-2013-BLG-0132/MOA-2013-BLG-148: A Saturn-mass Planet Orbiting an M Dwarf

We revisit the planetary microlensing event OGLE-2013-BLG-0132/MOA-2013-BLG-148 using Keck adaptive optics imaging in 2013 with NIRC2 and in 2020, 7.4 yr after the event, with OSIRIS. The 2020 observations yield a source and lens separation of 56.91 ± 0.29 mas, which provides us with a precise measurement of the heliocentric proper motion of the event μ rel,hel = 7.695 ± 0.039 mas yr‑1. We measured the magnitude of the lens in the K band as K lens = 18.69 ± 0.04. Using these constraints, we refit the microlensing light curve and undertake a full reanalysis of the event parameters including the microlensing parallax π E and the distance to the source D S . We confirm the results obtained in the initial study by Mróz et al. and improve significantly upon the accuracy of the physical parameters. The system is an M dwarf of 0.495 ± 0.054 M ⊙ orbited by a cold, Saturn-mass planet of 0.26 ± 0.028 M Jup at projected separation r ⊥ = 3.14 ± 0.28 au. This work confirms that the planetary system is at a distance of 3.48 ± 0.36 kpc, which places it in the Galactic disk and not the Galactic bulge.

Keywords: gravitational microlensing; adaptive optics; m dwarf stars; exoplanet astronomy
The Puzzling Properties of the MACS1149-JD1 Galaxy at z = 9.11

We analyze new JWST NIRCam and NIRSpec data on the redshift 9.11 galaxy MACS1149-JD1 (hereafter JD1). Our NIRCam imaging data reveal that JD1 comprises three spatially distinct components. Our spectroscopic data indicate that JD1 appears dust free but is already enriched, $12+\mathrm{log}({\rm{O}}/{\rm{H}})={7.90}_{-0.05}^{+0.04}$ . We also find that the carbon and neon abundances in JD1 are below the solar abundance ratio. Particularly the carbon under-abundance is suggestive of recent star formation where Type II supernovae have already enriched the interstellar medium (ISM) in oxygen but intermediate mass stars have not yet enriched the ISM in carbon. A recent burst of star formation is also revealed by the star formation history derived from NIRCam photometry. Our data do not reveal the presence of a significant amount of old populations, resulting in a factor of ~7× smaller stellar mass than previous estimates. Thus, our data support the view that JD1 is a young galaxy.

Keywords: high-redshift galaxies
A Comparison of X-Ray Photon Indices among the Narrow- and Broad-line Seyfert 1 Galaxies

We present a detailed comparative systematic study using a sample of 221 narrow-line Seyfert 1 (NLSy1) galaxies in comparison to a redshift-matched sample of 154 broad-line Seyfert 1 (BLSy1) galaxies based on their observations using ROSAT and/or XMM-Newton in soft X-ray band (0.1-2.0 keV). A homogeneous analysis is carried out to estimate their soft X-ray photon indices ( ${{\rm{\Gamma }}}_{X}^{s}$ ) and its correlations with other parameters of nuclear activities such as Eddington ratios (REdd), bolometric luminosities (Lbol), black hole masses (MBH), and the widths of the broad component of Hβ lines (FWHM(Hβ)). In our analysis, we found clear evidence of the difference in the ${{\rm{\Gamma }}}_{X}^{s}$ and REdd distributions among NLSy1 and BLSy1 galaxies, with steeper ${{\rm{\Gamma }}}_{X}^{s}$ and higher REdd for the former. Such a difference also exists in the spectral index distribution in hard X-ray ( ${{\rm{\Gamma }}}_{X}^{h}$ ), based on the analysis of 53 NLSy1 and 46 BLSy1 galaxies in the 2-10 keV energy band. The difference in REdd distributions does exist even after applying the average correction for the difference in the inclination angle of NLSy1 and BLSy1 galaxies. We also estimated REdd, based on SED fitting of 34 NLSy1 and 30 BLSy1 galaxies over the 0.3-10 keV energy band, and found that results are still consistent with REdd estimates based on the optical bolometric luminosity. Our analysis suggests that the higher REdd in NLSy1 is responsible for its steeper X-ray spectral slope compared to the BLSy1, consistent with the disk-corona model as proposed for the luminous AGNs.

Keywords: galaxy physics; active galaxies; galaxy accretion disks; seyfert galaxies; x-ray surveys; active galactic nuclei
A Comprehensive Investigation of Metals in the Circumgalactic Medium of Nearby Dwarf Galaxies

Dwarf galaxies are found to have lost most of their metals via feedback processes; however, there still lacks consistent assessment on the retention rate of metals in their circumgalactic medium (CGM). Here we investigate the metal content in the CGM of 45 isolated dwarf galaxies with M * = 106.5-9.5 M ⊙ (M 200m = 1010.0-11.5 M ⊙) using the Hubble Space Telescope/Cosmic Origins Spectrograph. While H I (Lyα) is ubiquitously detected (89%) within the CGM, we find low detection rates (≈5%-22%) in C II, C IV, Si II, Si III, and Si IV, largely consistent with literature values. Assuming these ions form in the cool (T ≈ 104 K) CGM with photoionization equilibrium, the observed H I and metal column density profiles can be best explained by an empirical model with low gas density and high volume filling factor. For a typical galaxy with M 200m = 1010.9 M ⊙ (median of the sample), our model predicts a cool gas mass of M CGM,cool ~ 108.4 M ⊙, corresponding to ~2% of the galaxy's baryonic budget. Assuming a metallicity of 0.3 Z ⊙, we estimate that the dwarf galaxy's cool CGM likely harbors ~10% of the metals ever produced, with the rest either in more ionized states in the CGM or transported to the intergalactic medium. We further examine the EAGLE simulation and show that H I and low ions may arise from a dense cool medium, while C IV arises from a diffuse warmer medium. Our work provides the community with a uniform data set on dwarf galaxies' CGM that combines our recent observations, additional archival data and literature compilation, which can be used to test various theoretical models of dwarf galaxies.

Keywords: circumgalactic medium; dwarf galaxies; metal line absorbers
Polarization of the Cosmic Infrared Background Fluctuations

The cosmic infrared background (CIB) is slightly polarized. Polarization directions of individual galaxies could be aligned with tidal fields around galaxies, resulting in nonzero CIB polarization. We use a linear intrinsic alignment model to theoretically predict angular correlations of the CIB polarization fluctuations and find that electriclike and curl-like (B-mode) polarization modes are equally generated with power four orders of magnitude less than their intensity. The CIB B-mode signal is negligible and not a concerning foreground for the inflationary B-mode searches at nominal frequencies for cosmic microwave background measurements, but could be detected at submillimeter wavelengths by future space missions.

Keywords: cosmic background radiation; infrared galaxies; cosmic inflation
Discovery of the Closest Ultra-stripped Supernova: SN 2021agco in UGC 3855

We present the discovery and studies of the helium-rich, fast-evolving supernova (SN) 2021agco at a distance of ~40 Mpc. Its early-time flux is found to rise from half peak to the peak of -16.06 ± 0.42 mag in the r band within ${2.4}_{-1.0}^{+1.5}$ days, and the post-peak light curves also decline at a much faster pace relative to normal stripped-envelope supernovae (SNe) of Type Ib/Ic. The early-time spectrum of SN 2021agco (t ≈ 1.0 days after the peak) is characterized by a featureless blue continuum superimposed with a weak emission line of ionized C III, and the subsequent spectra show prominent He I lines. Both the photometric and spectroscopic evolution show close resemblances to SN 2019dge, which is believed to have an extremely stripped progenitor. We reproduce the multicolor light curves of SN 2021agco with a model combining shock-cooling emission with 56Ni decay. The best-fit results give an ejecta mass of ≈0.3 M ⊙ and a synthesized nickel mass of ≈2.2 × 10-2 M ⊙. The progenitor is estimated to have an envelope radius of R env ≈ 80 R ⊙ and a mass of M env ≈ 0.10 M ⊙. All these suggest that SN 2021agco can be categorized as an ultra-stripped SN Ib, representing the closest object of this rare subtype. This SN is found to explode in the disk of a Sab-type galaxy with an age of ~10.0 Gyr and low star-forming activity. Compared to normal SNe Ib/c, the host galaxies of SN 2021agco and other ultra-stripped SNe tend to have relatively lower metallicity, which complicates the properties of their progenitor populations.

Keywords: type ib supernovae; supernovae; transient sources
Precise Distance Measurement for a Near-Earth Asteroid by the Refined Rotational Reflex Velocity Method

The rotational reflex velocity (RRV) method was proposed by Heinze and Metchev in 2015 and was used to measure the distances of main-belt asteroids (MBAs). Later, Lin et al. generalized this method using spherical astronomy in 2016. The method measures the distances of MBAs using the observations from a single ground-based telescope over two nights. We refined this method and extend it further to the distance measurement of near-Earth asteroids (NEAs). In practice, we measure the distance of the potentially hazardous asteroid (99942) Apophis from the acquired CCD frames using the newly refined method. According to the requirement of the newly refined method, we also simulate the distance measurements of the four typical NEAs, (1221) Amor, (1862) Apollo, (2062) Aten, and (163693) Atira, on their discovery dates and follow-up dates. The measurement results of Apophis based on the newly refined RRV method show that the mean relative errors for the independent exposure frames on the successive two nights is ~0.08% (about a factor of 2 improvement in comparison with the research of Lin et al.) compared with the distance from JPL ephemeris. Our simulation results also show that this refined method can accurately and precisely measure the distances of newly discovered NEAs in an astrometric way without performing orbital determination. The accurate and precise distances of newly discovered asteroids help us to conveniently evaluate their impact risks within a shorter time, leaving us more time to take defense precautions.

Keywords: astrometry; astronomy image processing; astronomy data analysis; asteroids
The TW Hya Rosetta Stone Project. I. Radial and Vertical Distributions of DCN and DCO+

Molecular D/H ratios are frequently used to probe the chemical past of solar system volatiles. Yet it is unclear which parts of the solar nebula hosted an active deuterium fractionation chemistry. To address this question, we present 0"2-0"4 Atacama Large Millimeter/submillimeter Array (ALMA) observations of DCO+ and DCN 2-1, 3-2, and 4-3 toward the nearby protoplanetary disk around TW Hya, taken as part of the TW Hya Rosetta Stone project, augmented with archival data. DCO+ is characterized by an excitation temperature of ∼40 K across the 70 au radius pebble disk, indicative of emission from a warm, elevated molecular layer. Tentatively, DCN is present at even higher temperatures. Both DCO+ and DCN present substantial emission cavities in the inner disk, while in the outer disk the DCO+ and DCN morphologies diverge: most DCN emission originates from a narrow ring peaking around 30 au, with some additional diffuse DCN emission present at larger radii, while DCO+ is present in a broad structured ring that extends past the pebble disk. Based on a set of simple parametric disk abundance models, these emission patterns can be explained by a near-constant DCN abundance exterior to the cavity, and an increasing DCO+ abundance with radius. In conclusion, the ALMA observations reveal an active deuterium fractionation chemistry in multiple disk regions around TW Hya, but not in the cold planetesimal-forming midplane and in the inner disk. More observations are needed to explore whether deuterium fractionation is actually absent in these latter regions, and if its absence is a common feature or something peculiar to the old TW Hya disk.

Keywords: planet formation; protoplanetary disks; millimeter astronomy; astrochemistry; submillimeter astronomy; interstellar molecules; solar system formation
Identification of Superclusters and Their Properties in the Sloan Digital Sky Survey Using the WHL Cluster Catalog

Superclusters are the largest massive structures in the cosmic web, on tens to hundreds of megaparsec scales. They are the largest assembly of galaxy clusters in the Universe. Apart from a few detailed studies of such structures, their evolutionary mechanism is still an open question. In order to address and answer the relevant questions, a statistically significant, large catalog of superclusters covering a wide range of redshifts and sky areas is essential. Here, we present a large catalog of 662 superclusters identified using a modified friends-of-friends algorithm applied on the WHL (Wen-Han-Liu) cluster catalog within a redshift range of 0.05 ≤ z ≤ 0.42. We name the most massive supercluster at z ~ 0.25 as the Einasto Supercluster. We find that the median mass of superclusters is ~5.8 × 1015 M ⊙ and the median size ~65 Mpc. We find that the supercluster environment slightly affects the growth of clusters. We compare the properties of the observed superclusters with the mock superclusters extracted from the Horizon Run 4 cosmological simulation. The properties of the superclusters in the mocks and observations are in broad agreement. We find that the density contrast of a supercluster is correlated with its maximum extent with a power-law index, α ~ -2. The phase-space distribution of mock superclusters shows that, on average, ~90% of part of a supercluster has a gravitational influence on its constituents. We also show the mock halos' average number density and peculiar velocity profiles in and around the superclusters.

Keywords: superclusters; galaxy clusters; catalogs; large-scale structure of the universe
Neutron Tunneling: A New Mechanism to Power Explosive Phenomena in Neutron Stars, Magnetars, and Neutron Star Mergers

Neutron tunneling between neutron-rich nuclei in inhomogeneous dense matter encountered in neutron star crusts can release enormous energy on a short timescale to power explosive phenomena in neutron stars. In this work, we clarify aspects of this process that can occur in the outer regions of neutron stars when oscillations or cataclysmic events increase the ambient density. We use a time-dependent Hartree-Fock-Bogoliubov formalism to determine the rate of neutron diffusion and find that large amounts of energy can be released rapidly. The roles of nuclear binding, two-body interaction, and pairing in neutron diffusion times are investigated. We consider a one-dimensional quantum diffusion model and extend our analysis to study the impact of diffusion in three dimensions. We find that these novel neutron transfer reactions can generate energy in the amount of ≃ 1040-1044 erg under suitable conditions and assumptions.

Keywords: neutron stars; soft gamma-ray repeaters; gamma-ray sources
Flame Acceleration in SN Ia Induced by the Burning of Local Unreacted Islands

The mechanism of type Ia supernova explosions is still unsolved due to the uncertainties in the processes of flame acceleration and the associated deflagration to detonation transition. In carbon-oxygen (C-O) white dwarfs, due to the well known Rayleigh-Taylor (R-T) instability and turbulent vortices in the R-T fingers, there exist unburned islands embedded in the downstream of the main flame front. The burning of such islands can be modeled by the spherical inward-propagating two-step C-O flame, which will accelerate while propagating inward due to the stretch effect and the Zel'Dovich mechanism. In turbulent flows under proper conditions, such acceleration can be further strengthened by turbulent mixing, possibly making the burning of these islands speed up to be supersonic. The supersonic burning of the embedded islands is then a source of heating that speeds up the main flame. Here we derive the relationship between the flame's spontaneous inward-propagating speed and the flame radius in consuming the unburned islands based on the Zel'Dovich mechanism in both laminar and turbulent flows. The calculation results show that, in suitable turbulent situation, I.e., for a C-O white dwarf with density 3.5 × 107 g cm-3, Reynolds number 1.0 × 1013, and integral scale 110 km, the island flame speed reaches the sound speed when the flame radius is 1.5 times the flame thickness, and then remains supersonic. Such supersonic combustion generates shock waves, which heat and speed up the main flame, and possibly lead to the initiation of global detonation.

Keywords: hydrodynamics; shocks; type ia supernovae; astrophysical explosive burning