adsabs/SciX_UAT_keywords huggingface dataset:
FLEET: A Redshift-agnostic Machine Learning Pipeline to Rapidly Identify Hydrogen-poor Superluminous Supernovae

Over the past decade wide-field optical time-domain surveys have increased the discovery rate of transients to the point that ≲10% are being spectroscopically classified. Despite this, these surveys have enabled the discovery of new and rare types of transients, most notably the class of hydrogen-poor superluminous supernovae (SLSN-I), with about 150 events confirmed to date. Here we present a machine-learning classification algorithm targeted at rapid identification of a pure sample of SLSN-I to enable spectroscopic and multiwavelength follow-up. This algorithm is part of the Finding Luminous and Exotic Extragalactic Transients (FLEET) observational strategy. It utilizes both light-curve and contextual information, but without the need for a redshift, to assign each newly discovered transient a probability of being a SLSN-I. This classifier can achieve a maximum purity of about 85% (with 20% completeness) when observing a selection of SLSN-I candidates. Additionally, we present two alternative classifiers that use either redshifts or complete light curves and can achieve an even higher purity and completeness. At the current discovery rate, the FLEET algorithm can provide about 20 SLSN-I candidates per year for spectroscopic follow-up with 85% purity; with the Legacy Survey of Space and Time we anticipate this will rise to more than $\sim {10}^{3}$ events per year.

Keywords: supernovae; core-collapse supernovae; surveys
Diagnosing the Circumburst Environment with Multiband Gamma-Ray Burst Radio Afterglows

It has been widely recognized that gamma-ray burst (GRB) afterglows arise from interactions between the GRB outflow and circumburst medium, while their evolution follows the behaviors of relativistic shock waves. Assuming the distribution of circumburst medium follows a general power-law form, that is, n = A * R -k , where R denotes the distance from the burst, it is obvious that the value of the density-distribution index k can affect the behaviors of the afterglow. In this paper, we analyze the temporal and spectral behaviors of GRB radio afterglows with arbitrary k values. In the radio band, a standard GRB afterglow produced by a forward shock exhibits a late-time flux peak, and the relative peak fluxes, as well as peak times at different frequencies, show dependencies on k. Thus, with multiband radio-peak observations, one can determine the density profile of the circumburst medium by comparing the relations between peak flux/time and frequency at each observing band. Also, the effects of transrelativistic shock waves, as well as jets in afterglows, are discussed. By analyzing 31 long and 1 short GRB with multiband data of radio afterglows, we find that nearly half of them can be explained with a uniform interstellar medium (k = 0), ~1/5 can be constrained to exhibiting a stellar-wind environment (k = 2), while less than ~1/3 of the samples show 0 < k < 2.

Keywords: burst astrophysics
Planetary Orbit Eccentricity Trends (POET). I. The Eccentricity-Metallicity Trend for Small Planets Revealed by the LAMOST-Gaia-Kepler Sample

Orbital eccentricity is one of the basic planetary properties, whose distribution may shed light on the history of planet formation and evolution. Here, in a series of works on Planetary Orbit Eccentricity Trends (dubbed POET), we study the distribution of planetary eccentricities and their dependence on stellar/planetary properties. In this paper, the first work of the POET series, we investigate whether and how the eccentricities of small planets depend on stellar metallicities (e.g., [Fe/H]). Previous studies on giant planets have found a significant correlation between planetary eccentricities and their host metallicities. Nevertheless, whether such a correlation exists for small planets (e.g., super-Earths and sub-Neptunes) remains unclear. Here, benefiting from the large and homogeneous LAMOST-Gaia-Kepler sample, we characterize the eccentricity distributions of 244 (286) small planets in single (multiple) transiting systems with the TDR method. We confirm the eccentricity-metallicity trend whereby the eccentricities of single small planets increase with stellar metallicities. Interestingly, a similar trend between eccentricity and metallicity is also found in the radial velocity sample. We also found that the mutual inclination of multiple transiting systems increases with metallicity, which predicts a moderate eccentricity-metallicity rising trend. Our results of the correlation between eccentricity (inclination) and metallicity for small planets support the core accretion model for planet formation, and they could be footprints of self (and/or external) excitation processes during the history of planet formation and evolution.

Keywords: exoplanets; planet hosting stars
Estimating Distances from Parallaxes. V. Geometric and Photogeometric Distances to 1.47 Billion Stars in Gaia Early Data Release 3

Stellar distances constitute a foundational pillar of astrophysics. The publication of 1.47 billion stellar parallaxes from Gaia is a major contribution to this. Despite Gaia's precision, the majority of these stars are so distant or faint that their fractional parallax uncertainties are large, thereby precluding a simple inversion of parallax to provide a distance. Here we take a probabilistic approach to estimating stellar distances that uses a prior constructed from a three-dimensional model of our Galaxy. This model includes interstellar extinction and Gaia's variable magnitude limit. We infer two types of distance. The first, geometric, uses the parallax with a direction-dependent prior on distance. The second, photogeometric, additionally uses the color and apparent magnitude of a star, by exploiting the fact that stars of a given color have a restricted range of probable absolute magnitudes (plus extinction). Tests on simulated data and external validations show that the photogeometric estimates generally have higher accuracy and precision for stars with poor parallaxes. We provide a catalog of 1.47 billion geometric and 1.35 billion photogeometric distances together with asymmetric uncertainty measures. Our estimates are quantiles of a posterior probability distribution, so they transform invariably and can therefore also be used directly in the distance modulus ( $5{\mathrm{log}}_{10}r\,-\,5$ ). The catalog may be downloaded or queried using ADQL at various sites (see http://www.mpia.de/~calj/gedr3_distances.html), where it can also be cross-matched with the Gaia catalog.

Keywords: catalogs; galaxy structure; bayesian statistics; parallax; stellar parallax; photometric parallax; distance indicators; astrometry; markov chain monte carlo; absolute magnitude
Constraining the Equation of State of Hybrid Stars Using Recent Information from Multidisciplinary Physics

At the ultrahigh densities existing in the core of neutron stars (NSs), it is expected that a phase transition from baryonic to deconfined quark matter may occur. Such a phase transition would affect the underlying equation of state (EoS) as well as the observable astrophysical properties of NSs. Comparison of EoS model predictions with astronomical data from multimessenger signals then provides us an opportunity to probe the behavior of dense matter. In this work, we restrict the allowed parameter space of EoS models in NSs for both nucleonic (relativistic mean field model) and quark matter (MIT bag model) sectors by imposing state-of-the-art constraints from nuclear calculations, multimessenger astrophysical data, and perturbative quantum chromodynamics (pQCD). We systematically investigate the effect of each constraint on the parameter space of uncertainties using a cutoff filter scheme, as well as the correlations among the parameters and with NS astrophysical observables. Using the constraints, we obtain limits for maximum NS mass, maximum central density, as well as for NS radii and tidal deformability. Although pQCD constraints are only effective at very high densities, they significantly reduce the parameter space of the quark model. We also conclude that astrophysical data supports high values of the bag parameter B and disfavors the existence of a pure quark matter core in hybrid stars.

Keywords: neutron stars; neutron star cores; gravitational waves; high energy astrophysics; particle astrophysics
No Redetections of blc1 in 39 hr of Reobservation Campaigns of Proxima Centauri

In 2019 April, radio observations of Proxima Centauri were performed with the Ultra-Wideband Low Receiver on the Parkes Telescope. A narrowband radio search of these data revealed a technosignature signal-of-interest reported as "blc1" at 982.002 MHz. After the initial discovery of blc1 in the data in 2020 October, we performed a series of reobservations over the next 6 months, totaling 39 hr of on-sky time. We do not redetect blc1, or find any other signals-of-interest, within ±1 MHz of 982.002 MHz in this data set. Taken in context, this null result implies that blc1 was transient radio frequency interference, makes it less consistent with a periodic transmission, and makes it less consistent with interstellar scintillation.

Keywords: radio astronomy; technosignatures; search for extraterrestrial intelligence; astrobiology
Caltech-NRAO Stripe 82 Survey (CNSS). V. AGNs That Transitioned to Radio-loud State

A recent multiyear Caltech-NRAO Stripe 82 Survey revealed a group of objects that appeared as new radio sources after >5-20 yr of absence. They are transient phenomena with respect to the Faint Images of the Radio Sky at Twenty Centimeters survey and constitute the first unbiased sample of renewed radio activity. Here we present a follow-up, radio, optical, and X-ray study of them. The group consists of 12 sources, both quasars and galaxies with wide redshift (0.04 < z < 1.7) and luminosity ( $22\lt {\mathrm{log}}_{10}[{L}_{1.4\mathrm{GHz}}/{\rm{W}}\,{\mathrm{Hz}}^{-1}]\gt 24.5$ ) distributions. Their radio properties in the first phase of activity, namely the convex spectra and compact morphology, allow them all to be classified as gigahertz-peaked spectrum (GPS) sources. We conclude that the spectral changes are a consequence of the evolution of newly born radio jets. Our observations show that over the next few years of activity the GPS galaxies keep the convex shape of the spectrum, while GPS quasars rapidly transform into flat-spectrum sources, which may result in them not being recognized as young sources. The wide range of bolometric luminosities, black hole masses, and jet powers among the transient sources indicates even greater population diversity in the group of young radio objects. We also suggest that small changes of the accretion disk luminosity (accretion rate) may be sufficient to ignite low-power radio activity that evolves on the scale of decades.

Keywords: active galaxies; agn host galaxies; radio galaxies; quasars; radio loud quasars; radio quiet quasars; supermassive black holes; active galactic nuclei; galaxy evolution
First Detection of the GI-type of Intrinsic Alignments of Galaxies Using the Self-calibration Method in a Photometric Galaxy Survey

Weak gravitational lensing is one of the most promising cosmological probes to constrain dark matter, dark energy, and the nature of gravity at cosmic scales. Intrinsic alignments (IAs) of galaxies have been recognized as one of the most serious systematic effects facing gravitational lensing. Such alignments must be isolated and removed to obtain a pure lensing signal. Furthermore, the alignments are related to the processes of galaxy formation, so their extracted signal can help in understanding such formation processes and improving their theoretical modeling. We report in this Letter the first detection of the gravitational shear-intrinsic shape (GI) correlation and the intrinsic shape-galaxy density (Ig) correlation using the self-calibration method in a photometric redshift survey. These direct measurements are made from the KiDS-450 photometric galaxy survey with a significance of 3.65σ in the third bin for the Ig correlation, and 3.51σ for the GI cross-correlation between the third and fourth bins. The self-calibration method uses the information available from photometric surveys without needing to specify an IA model and will play an important role in validating IA models and IA mitigation in future surveys such as the Rubin Observatory Legacy Survey of Space and Time, Euclid, and WFIRST.

Keywords: observational cosmology; weak gravitational lensing
Physical Characteristics of Unstructured Coronal Clouds

Active regions in the inner solar corona, when observed in X-ray emission, consist of bright, hot loops surrounded by unstructured clouds. The emission from the clouds extends to a height of ≈4-5 × 104 km at temperatures of ≈2-3 MK. These "hot clouds" are variable, but persist for many days and do not appear to connect directly to the active region streamers or other large-scale structures observed higher in the corona. We present an observational analysis of these diffuse structures to establish basic plasma parameters such as magnetic field strength, particle density, and temperature. The values of β, the ratio of the plasma pressure to the magnetic field pressure, were found to be generally less than unity, though often approaching unity in the upper portions of the active region, where the hot clouds are located. The magnetic field may therefore only partially confine these regions and inhibit flare-like instabilities that could otherwise be driven by gradients of plasma pressure and current density.

Keywords: the sun
ALMA CO Observations of the Gamma-Ray Supernova Remnant RX J1713.7-3946: Discovery of Shocked Molecular Cloudlets and Filaments at 0.01 pc Scales

RX J1713.7-3946 is a unique core-collapse supernova remnant (SNR) that emits bright TeV gamma-rays and synchrotron X-rays caused by cosmic rays, in addition to interactions with interstellar gas clouds. We report here on results of Atacama Large Millimeter/submillimeter Array 12CO(J = 1-0) observations toward the northwestern shell of the SNR. We newly found three molecular complexes consisting of dozens of shocked molecular cloudlets and filaments with typical radii of ∼0.03-0.05 pc and densities of ∼104 cm-3. These cloudlets and filaments are located not only along synchrotron X-ray filaments, but also in the vicinity of X-ray hotspots with month- or year-scale time variations. We argue that X-ray hotspots and filaments were generated by shock-cloudlet interactions through magnetic-field amplification up to mG. The interstellar medium density contrast of ∼105, coexistence of molecular cloudlets and low-density diffuse medium of ∼0.1 cm-3, is consistent with such a magnetic field amplification as well as a wind-bubble scenario. The small-scale cloud structures also affect hadronic gamma-ray spectra considering the magnetic field amplification on surface and inside clouds.

Keywords: supernova remnants; interstellar medium; cosmic ray sources; gamma-ray sources; x-ray sources
The Spectrum and Term Analysis of Singly Ionized Manganese

An extensive analysis of the Mn spectrum was carried out using high-resolution Fourier transform (FT) and grating spectroscopy of Mn-Ne and Mn-Ar hollow cathode discharge sources, over the range 82-5500 nm (1820-121,728 cm-1). Spectral wavelengths for a total of 6019 Mn II lines have been measured, of which 1345 are obtained through FT spectroscopy. These wavelengths are given to at least an order of magnitude lower uncertainty than previous measurements. These lines were used to identify 6256 Mn II transitions and improve the values of 505 previously published energy levels with typical uncertainties of a few thousandths of a cm-1, representing an order-of-magnitude reduction in uncertainty. We have verified and improved an additional 57 Mn II energy levels, previously established through observation of stellar spectra alone, using our FT spectra. In addition, 52 new energy level values have been established. The number of classified lines reported is approximately 50% more than previously published. The new accurate data for 614 energy levels and 6019 lines will allow a more reliable analysis of Mn II spectral lines in astrophysical spectra.

Keywords: atomic spectroscopy; line positions; spectroscopy; laboratory astrophysics; spectral line identification; experimental techniques; spectral line lists; stellar atmospheric opacity; stellar spectral lines; atomic data benchmarking
Formulating Mass-loss Rates for Sun-like Stars: A Hybrid Model Approach

We observe an enhanced stellar wind mass-loss rate from low-mass stars exhibiting higher X-ray flux. This trend, however, does not align with the Sun, where no evident correlation between X-ray flux and mass-loss rate is present. To reconcile these observations, we propose a hybrid model for the stellar wind from solar-type stars, incorporating both Alfvén wave dynamics and flux emergence-driven interchange reconnection, an increasingly studied concept guided by the latest heliospheric observations. For establishing a mass-loss rate scaling law, we perform a series of magnetohydrodynamic simulations across varied magnetic activities. Through a parameter survey concerning the surface (unsigned) magnetic flux (Φsurf) and the open-to-surface magnetic flux ratio (ξ open = Φopen/Φsurf), we derive a scaling law of the mass-loss rate given by ${\dot{M}}_{w}/{\dot{M}}_{w,\odot }\,={\left({{\rm{\Phi }}}^{\mathrm{surf}}/{{\rm{\Phi }}}_{\odot }^{\mathrm{surf}}\right)}^{0.52}{\left({\xi }^{\mathrm{open}}/{\xi }_{\odot }^{\mathrm{open}}\right)}^{0.86}$ , where ${\dot{M}}_{w,\odot }=2.0\times {10}^{-14}\ {M}_{\odot }\ {\mathrm{yr}}^{-1}$ , ${{\rm{\Phi }}}_{\odot }^{\mathrm{surf}}=3.0\times {10}^{23}\ \mathrm{Mx}$ , and ${\xi }_{\odot }^{\mathrm{open}}=0.2$ . By comparing cases with and without flux emergence, we find that the increase in the mass-loss rate with the surface magnetic flux can be attributed to the influence of flux emergence. Our scaling law demonstrates an agreement with solar wind observations spanning 40 yr, exhibiting superior performance when compared to X-ray-based estimations. Our findings suggest that flux emergence may play a significant role in the stellar winds of low-mass stars, particularly those originating from magnetically active stars.

Keywords: stellar winds; solar wind; magnetohydrodynamical simulations; alfven waves; solar magnetic reconnection
Multiwavelength Observations of the Blazar VER J0521+211 during an Elevated TeV Gamma-Ray State

We report on a long-lasting, elevated gamma-ray flux state from VER J0521+211 observed by VERITAS, MAGIC, and Fermi-LAT in 2013 and 2014. The peak integral flux above 200 GeV measured with the nightly binned light curve is (8.8 ± 0.4) × 10-7 photons m-2 s-1, or ~37% of the Crab Nebula flux. Multiwavelength observations from X-ray, UV, and optical instruments are also presented. A moderate correlation between the X-ray and TeV gamma-ray fluxes was observed, and the X-ray spectrum appeared harder when the flux was higher. Using the gamma-ray spectrum and four models of the extragalactic background light (EBL), a conservative 95% confidence upper limit on the redshift of the source was found to be z ≤ 0.31. Unlike the gamma-ray and X-ray bands, the optical flux did not increase significantly during the studied period compared to the archival low-state flux. The spectral variability from optical to X-ray bands suggests that the synchrotron peak of the spectral energy distribution (SED) may become broader during flaring states, which can be adequately described with a one-zone synchrotron self-Compton model varying the high-energy end of the underlying particle spectrum. The synchrotron peak frequency of the SED and the radio morphology of the jet from the MOJAVE program are consistent with the source being an intermediate-frequency-peaked BL Lac object.

Keywords: active galactic nuclei; high energy astrophysics; blazars; bl lacertae objects; relativistic jets; gamma-rays; non-thermal radiation sources
Unprecedented Molecular Diversity Revealed in Meteoritic Insoluble Organic Matter: The Paris Meteorite's Case

The insoluble organic matter (IOM) contained in carbonaceous chondrites has witnessed a diverse suite of processes possibly starting from the evolution of the parent molecular cloud down to the protosolar nebula and finally to asteroidal processes that occurred on the chondrites' parent bodies. Laser desorption coupled with ultra-high-resolution mass spectrometry reveals that the IOM of the Paris meteorite releases a large diversity of molecules. Various molecular families ranging from hydrogenated amorphous carbon to CHNOS aromatic molecules were detected with heteroatoms (nitrogen, oxygen, and sulfur) mainly incorporated within aromatic structures. Molecules bearing nitrogen atoms present a significant variation in aromaticity. These unprecedented results allow the proposal that small molecules bearing heteroatoms could be trapped in the large macromolecular network of the IOM by hydrophobic interactions. This molecular diversity could originate from different sources, such as the soluble organic matter, the hydrothermal alteration inside the Paris's parent body, or even generated during the IOM extraction procedure. It has to be noted that some of the molecular diversity may reflect fragmentation and rearrangement of the IOM constituents during the laser desorption ionization, although care was taken to minimize such damage.

Keywords: meteorites; carbonaceous chondrites; meteorite composition; mass spectrometry
The Megamaser Cosmology Project. XIII. Combined Hubble Constant Constraints

We present a measurement of the Hubble constant made using geometric distance measurements to megamaser-hosting galaxies. We have applied an improved approach for fitting maser data and obtained better distance estimates for four galaxies previously published by the Megamaser Cosmology Project: UGC 3789, NGC 6264, NGC 6323, and NGC 5765b. Combining these updated distance measurements with those for the maser galaxies CGCG 074-064 and NGC 4258, and assuming a fixed velocity uncertainty of 250 km s-1 associated with peculiar motions, we constrain the Hubble constant to be H0 = 73.9 ± 3.0 km s-1 Mpc-1 independent of distance ladders and the cosmic microwave background. This best value relies solely on maser-based distance and velocity measurements, and it does not use any peculiar velocity corrections. Different approaches for correcting peculiar velocities do not modify H0 by more than ±1σ, with the full range of best-fit Hubble constant values spanning 71.8-76.9 km s-1 Mpc-1. We corroborate prior indications that the local value of H0 exceeds the early-universe value, with a confidence level varying from 95% to 99% for different treatments of the peculiar velocities.

Keywords: hubble constant; observational cosmology; megamasers; water masers; very long baseline interferometry
Searching for Broadband Pulsed Beacons from 1883 Stars Using Neural Networks

The search for extraterrestrial intelligence at radio frequencies has largely been focused on continuous-wave narrowband signals. We demonstrate that broadband pulsed beacons are energetically efficient compared to narrowband beacons over longer operational timescales. Here, we report the first extensive survey searching for such broadband pulsed beacons toward 1883 stars as a part of the Breakthrough Listen's search for advanced intelligent life. We conducted 233 hr of deep observations across 4-8 GHz using the Robert C. Byrd Green Bank Telescope and searched for three different classes of signals with artificial (or negative) dispersion. We report a detailed search-leveraging a convolutional neural network classifier on high-performance GPUs-deployed for the very first time in a large-scale search for signals from extraterrestrial intelligence. Due to the absence of any signal-of-interest from our survey, we place a constraint on the existence of broadband pulsed beacons in our solar neighborhood: ≲1 in 1000 stars have transmitter power densities ≳105 W Hz-1 repeating ≤500 s at these frequencies.

Keywords: technosignatures; search for extraterrestrial intelligence; radio transient sources