adsabs/SciX_UAT_keywords huggingface dataset:
Radiation and Polarization Signatures from Magnetic Reconnection in Relativistic Jets. I. A Systematic Study

Blazars are relativistic magnetized plasma outflows from supermassive black holes that point very close to our line of sight. Their emission is nonthermal-dominated and highly variable across the entire electromagnetic spectrum. Relativistic magnetic reconnection has been proposed as the driver of particle acceleration during blazar flares. While recent particle-in-cell (PIC) simulations have self-consistently studied the evolution of magnetic reconnection and particle acceleration therein, the resulting radiation signatures have not been systematically explored. In particular, the polarization signatures, which directly reflect the characteristic strongly dynamical evolution of magnetic field during reconnection, have not been carefully investigated. In this paper, we present a systematic study of radiation and polarization signatures arising from magnetic reconnection in blazars, based on combined PIC and polarized radiation transfer simulations with various physical parameters. We identify a harder-when-brighter trend in the spectral evolution. Moreover, higher-frequency bands (ultraviolet to X-ray) tend to flare earlier than lower-frequency bands (infrared to optical) in the synchrotron spectral component. Most importantly, polarization signatures appear more variable with higher frequencies. We find that the variation in temporal polarization depends strongly on the guide field strength. Specifically, reconnection with a significant guide field component leads to a very high polarization degree that contradicts typical blazar observations, while large polarization angle rotations are unique signatures of magnetic reconnection between nearly antiparallel magnetic field lines. These rotations are at least 90° and can extend to >180°, and they may be in either direction. These results imply that blazars that have shown large polarization angle rotations intrinsically have more nearly antiparallel magnetic field morphology.

Keywords: blazars; active galactic nuclei; jets; non-thermal radiation sources; polarimetry
Models of Rotating Infall for the B335 Protostar

Models of the protostellar source, B335, are developed using axisymmetric three-dimensional models to resolve conflicts found in one-dimensional models. The models are constrained by a large number of observations, including ALMA, Herschel, and Spitzer data. Observations of the protostellar source B335 with ALMA show redshifted absorption against a central continuum source indicative of infall in the HCO+ and HCN J = 4 → 3 transitions. The data are combined with a new estimate of the distance to provide strong constraints to three-dimensional radiative transfer models including a rotating, infalling envelope, outflow cavities, and a very small disk. The models favor ages since the initiation of collapse between 3 × 104 and 4 × 104 yr for both the continuum and the lines, resolving a conflict found in one-dimensional models. The models underpredict the continuum emission seen by ALMA, suggesting an additional component such as a pseudo-disk. The best-fitting model is used to convert variations in the 4.5 μm flux in recent years into a model for a variation of a factor of 5-7 in luminosity over the last 8 yr.

Keywords: star formation; interstellar clouds
Evidence for Two Distinct Populations of Kilonova-associated Gamma-Ray Bursts

Identification of gamma-ray burst (GRB) progenitors based on the duration of their prompt emission (T 90) has faced several roadblocks recently. Long-duration GRBs (with T 90 > 2 s) have traditionally been thought to be originating from the collapse of massive stars and the short-duration ones (with T 90 < 2 s) from compact binary mergers. However, recent observations of a long GRB associated with a kilonova (KN) and a short GRB with supernova association demand a more detailed classification of the GRB population. In this Letter, we focus on GRBs associated with KNe, believed to be originating from mergers of binaries involving neutron stars (NSs). We make use of the GRB prompt-emission light curves of the Swift/BAT 2022 GRB catalog and employ machine-learning algorithms to study the classification of GRB progenitors. Our analysis reveals that there are five distinct clusters of GRBs, of which the KN-associated GRBs are located in two separate clusters, indicating they may have been produced by different progenitors. We argue that these clusters may be due to subclasses of binary neutron star and/or NS-black hole mergers. We also discuss the implications of these findings for future gravitational-wave observations and how those observations may help in understanding these clusters better.

Keywords: gamma-ray bursts; gamma-ray transient sources
Possible Implications of Relatively High Levels of Initial 60Fe in Iron Meteorites for the Noncarbonaceous-Carbonaceous Meteorite Dichotomy and Solar Nebula Formation

Cook et al. found that iron meteorites have an initial abundance ratio of the short-lived isotope 60Fe to the stable isotope 56Fe of 60Fe/56Fe ~ (6.4 ± 2.0) × 10-7. This appears to require the injection of live 60Fe from a Type II supernova (SN II) into the presolar molecular cloud core, as the observed ratio is over a factor of 10 times higher than would be expected to be found in the ambient interstellar medium (ISM) as a result of galactic chemical evolution. The supernova triggering and injection scenario offers a ready explanation for an elevated initial 60Fe level, and in addition provides a physical mechanism for explaining the noncarbonaceous-carbonaceous (NC-CC) dichotomy of meteorites. The NC-CC scenario hypothesizes the solar nebula first accreted material that was enriched in supernova-derived nuclides, and then later accreted material depleted in supernova-derived nuclides. While the NC-CC dichotomy refers to stable nuclides, not short-lived isotopes like 60Fe, the SN II triggering hypothesis provides an explanation for the otherwise unexplained change in nuclides being accreted by the solar nebula. Three-dimensional hydrodynamical models of SN II shock-triggered collapse show that after triggering collapse of the presolar cloud core, the shock front sweeps away the local ISM while accelerating the resulting protostar/disk to a speed of several kilometers per second, sufficient for the protostar/disk system to encounter within ~1 Myr the more distant regions of a giant molecular cloud complex that might be expected to have a depleted inventory of supernova-derived nuclides.

Keywords: planet formation; star formation; hydrodynamics; protoplanetary disks; supernova remnants
A Short Gamma-Ray Burst from a Protomagnetar Remnant

The contemporaneous detection of gravitational waves and gamma rays from GW170817/GRB 170817A, followed by kilonova emission a day after, confirmed compact binary neutron star mergers as progenitors of short-duration gamma-ray bursts (GRBs) and cosmic sources of heavy r-process nuclei. However, the nature (and life span) of the merger remnant and the energy reservoir powering these bright gamma-ray flashes remains debated, while the first minutes after the merger are unexplored at optical wavelengths. Here, we report the earliest discovery of bright thermal optical emission associated with short GRB 180618A with extended gamma-ray emission-with ultraviolet and optical multicolor observations starting as soon as 1.4 minutes post-burst. The spectrum is consistent with a fast-fading afterglow and emerging thermal optical emission 15 minutes post-burst, which fades abruptly and chromatically (flux density F ν ∝ t -α , α = 4.6 ± 0.3) just 35 minutes after the GRB. Our observations from gamma rays to optical wavelengths are consistent with a hot nebula expanding at relativistic speeds, powered by the plasma winds from a newborn, rapidly spinning and highly magnetized neutron star (i.e., a millisecond magnetar), whose rotational energy is released at a rate L th ∝ t -(2.22±0.14) to reheat the unbound merger-remnant material. These results suggest that such neutron stars can survive the collapse to a black hole on timescales much larger than a few hundred milliseconds after the merger and power the GRB itself through accretion. Bright thermal optical counterparts to binary merger gravitational wave sources may be common in future wide-field fast-cadence sky surveys.

Keywords: high energy astrophysics; time domain astronomy; gamma-ray bursts; magnetars; polarimetry
SN 2020bvc: A Broad-line Type Ic Supernova with a Double-peaked Optical Light Curve and a Luminous X-Ray and Radio Counterpart

We present optical, radio, and X-ray observations of SN 2020bvc (=ASASSN-20bs, ZTF 20aalxlis), a nearby ( $z=0.0252;$ d = 114 Mpc) broad-line (BL) Type Ic supernova (SN) and the first double-peaked Ic-BL discovered without a gamma-ray burst (GRB) trigger. Our observations show that SN 2020bvc shares several properties in common with the Ic-BL SN 2006aj, which was associated with the low-luminosity gamma-ray burst (LLGRB) 060218. First, the 10 GHz radio luminosity ( ${L}_{\mathrm{radio}}\approx {10}^{37}\,\mathrm{erg}\,{{\rm{s}}}^{-1}$ ) is brighter than ordinary core-collapse SNe but fainter than LLGRB SNe such as SN 1998bw (associated with LLGRB 980425). We model our VLA observations (spanning 13-43 days) as synchrotron emission from a mildly relativistic (v ≳ 0.3c) forward shock. Second, with Swift and Chandra, we detect X-ray emission (LX ≈ 1041 erg ${{\rm{s}}}^{-1}$ ) that is not naturally explained as inverse Compton emission or part of the same synchrotron spectrum as the radio emission. Third, high-cadence (6× night-1) data from the Zwicky Transient Facility (ZTF) show a double-peaked optical light curve, the first peak from shock cooling of extended low-mass material (mass ${M}_{e}\lt {10}^{-2}\,{M}_{\odot }$ at radius Re > 1012 cm) and the second peak from the radioactive decay of ${}^{56}\mathrm{Ni}$ . SN 2020bvc is the first double-peaked Ic-BL SN discovered without a GRB trigger, so it is noteworthy that it shows X-ray and radio emission similar to LLGRB SNe. For four of the five other nearby (z ≲ 0.05) Ic-BL SNe with ZTF high-cadence data, we rule out a first peak like that seen in SN 2006aj and SN 2020bvc, i.e., that lasts ≈1 day and reaches a peak luminosity M ≈ -18. Follow-up X-ray and radio observations of Ic-BL SNe with well-sampled early optical light curves will establish whether double-peaked optical light curves are indeed predictive of LLGRB-like X-ray and radio emission.

Keywords: radio transient sources; high energy astrophysics; transient sources; core-collapse supernovae; supernovae; type ic supernovae; x-ray transient sources; gamma-ray bursts
An Ionized Outflow in Orion-KL Source I?

We present images at 6 and 14 GHz of Source I (SrcI) in the Kleinmann-Low Nebula in Orion. At higher frequencies, from 43 to 340 GHz, images of this source are dominated by thermal emission from dust in a 100 au diameter circumstellar disk, but at 6 and 14 GHz the emission is elongated along the minor axis of the disk, aligned with the SiO bipolar outflow from the central object. Gaussian fits to the 6, 14, 43, and 99 GHz images find a component along the disk minor axis whose flux and length vary with frequency consistent with free-free emission from an ionized outflow. The data favor a broad outflow from a disk wind, rather than a narrow ionized jet. SrcI was undetected in higher-resolution 5 GHz e-MERLIN observations obtained in 2021. The 5-6 GHz structure of SrcI may be resolved out by the high sidelobe structure of the e-MERLIN synthesized beam, or be time variable.

Keywords: radio continuum emission
The Maximum Isotropic Equivalent Energy of Gamma-Ray Bursts

In the cannonball model of gamma-ray bursts (GRBs), a highly relativistic jet of plasmoids of ordinary stellar matter that is ejected during stellar collapse or shortly after by fallback matter, produces simultaneously a GRB and a cosmic-ray burst by scattering light and charged particles in its path. This association and the observed knee at ~1 TeV in the energy spectrum of Galactic cosmic-ray electrons imply a maximum peak energy ~2.25 MeV in the energy spectrum of GRBs in the 1 keV-10 MeV band. Such a peak energy and the Amati correlation in GRBs imply a maximum isotropic equivalent energy release of ~3.8 × 1054 erg in GRBs, in the 1 keV-10 MeV band. Both predictions are in good agreement with up-to-date observations.

Keywords: high energy astrophysics
Exploring the Galactic Warp through Asymmetries in the Kinematics of the Galactic Disk

Previous analyses of large databases of Milky Way stars have revealed the stellar disk of our Galaxy to be warped and that this imparts a strong signature on the kinematics of stars beyond the solar neighborhood. However, due to the limitation of accurate distance estimates, many attempts to explore the extent of these Galactic features have generally been restricted to a volume near the Sun. By combining the Gaia DR2 astrometric solution, StarHorse distances, and stellar abundances from the APOGEE survey, we present the most detailed and radially expansive study yet of the vertical and radial motions of stars in the Galactic disk. We map velocities of stars with respect to their Galactocentric radius, angular momentum, and azimuthal angle and assess their relation to the warp. A decrease in vertical velocity is discovered at Galactocentric radius R = 13 kpc and angular momentum Lz = 2800 kpc km s-1. Smaller ripples in vertical and radial velocity are also discovered superposed on the main trend. We also discovered that trends in the vertical velocity with azimuthal angle are not symmetric about the peak, suggesting the warp is lopsided. To explain the global trend in vertical velocity, we built a simple analytical model of the Galactic warp. Our best fit yields a starting radius of ${8.87}_{-0.09}^{+0.08}\ \mathrm{kpc}$ and precession rate of ${13.57}_{-0.18}^{+0.20}\ \mathrm{km}\ {{\rm{s}}}^{-1}\ {\mathrm{kpc}}^{-1}$ . These parameters remain consistent across stellar age groups, a result that supports the notion that the warp is the result of an external, gravitationally induced phenomenon.

Keywords: milky way disk; milky way dynamics; galaxy structure
Dust Production of Interstellar Comet 2I/Borisov Throughout Perihelion

The recently discovered comet 2I/Borisov quickly became a prime target for comet observers during its perihelion approach in 2019 December, after it was discovered to be the first comet of interstellar origin. We present our observations and measurements of the dust production between 2019 October, when the interstellar comet became bright enough for small aperture telescopes, and 2020 January, when the comet entered the plane of the Milky Way. We observed the comet for 24 nights using three telescopes in the public iTelescope network. The telescopes spanned both the Northern and Southern hemispheres, were of similar aperture size (0.43-0.51 m), and employed a Johnson-Cousins RC filter. Using these data, we measure an A(0°)fρ range of 94 ± 14 to 139 ± 34 cm, a dust production rate Qdust range of 11.2 ± 4.4 to 16.4 ± 7.3 kg s-1, and a dust-brightness profile-parameter range of -0.95 ± 0.11 to -1.81 ± 0.20 for the interstellar comet. This work revealed low dust production rates from the comet that remained consistent throughout its apparition, with no notable brightening or increase in dust production throughout the observing campaign.

Keywords: comets; interstellar objects; coma dust; comae
Breaking Correlation in the Inflow Parameters of Interstellar Neutral Gas in Direct-sampling Observations

We analyze the reasons for the correlation between the temperature, direction, and speed of the interstellar neutral gas inflow into the heliosphere, obtained in analyses of observations performed by an onboard Interstellar Boundary Explorer (IBEX) instrument, IBEX-Lo. We point out that this correlation is the combined result of the inability to measure the speed of the atoms that enter the instrument and the restriction of the observations to a short orbital arc around the Sun performed by the instrument during observation. We demonstrate that without the capability to measure the speed, but with the ability to perform observations along longer orbital arcs, or from at least two distant locations on the orbit around the Sun, it is possible to break the parameter correlation. This, however, requires the capability of adjusting the boresight of the instrument relative to the spacecraft rotation axis, such as that of the planned camera on board the Interstellar Mapping and Acceleration Probe (IMAP), IMAP-Lo.

Keywords: interstellar atomic gas; heliosphere; interstellar medium; interstellar objects
Detectability of Optical Transients with Timescales of Subseconds

We search for optical transient sources with durations of ∼0.1 to ∼1.3 s using a data set obtained in the Organized Autotelescopes for Serendipitous Event Survey (OASES) observation campaign. Since the OASES observations were carried out using two independent wide-field and high-cadence observation systems monitored the same field simultaneously, the obtained data set provides a unique opportunity to develop a robust detection method for subsecond optical transients. In the data set of a selected field around the ecliptic and the Galactic plane, we find no astronomical event candidate that satisfies our detection criteria. From the nondetection result, we derive an upper limit on the event rate of subsecond transients around the ecliptic and the Galactic plane for the first time, obtaining ∼0.090 and ∼0.38 hr-1 deg-2 for m = 12 and 13 Vmag, respectively. In addition, future prospects of the subsecond-scale transient event surveys are discussed.

Keywords: time domain astronomy; transient sources; astronomical methods
Probing the Sea of Cosmic Rays by Measuring Gamma-Ray Emission from Passive Giant Molecular Clouds with HAWC

The study of high-energy gamma rays from passive giant molecular clouds (GMCs) in our Galaxy is an indirect way to characterize and probe the paradigm of the "sea" of cosmic rays in distant parts of the Galaxy. By using data from the High Altitude Water Cerenkov (HAWC) Observatory, we measure the gamma-ray flux above 1 TeV of a set of these clouds to test the paradigm. We selected high galactic latitude clouds that are in HAWC's field of view and that are within 1 kpc distance from the Sun. We find no significant excess emission in the cloud regions, nor when we perform a stacked log-likelihood analysis of GMCs. Using a Bayesian approach, we calculate 95% credible interval upper limits of the gamma-ray flux and estimate limits on the cosmic-ray energy density of these regions. These are the first limits to constrain gamma-ray emission in the multi-TeV energy range (>1 TeV) using passive high galactic latitude GMCs. Assuming that the main gamma-ray production mechanism is due to proton-proton interaction, the upper limits are consistent with a cosmic-ray flux and energy density similar to that measured at Earth.

Keywords: galactic cosmic rays; gamma-rays; high energy astrophysics
The Hitchhiker's Guide to the Galaxy Catalog Approach for Dark Siren Gravitational-wave Cosmology

We outline the "dark siren" galaxy catalog method for cosmological inference using gravitational wave (GW) standard sirens, clarifying some common misconceptions in the implementation of this method. When a confident transient electromagnetic counterpart to a GW event is unavailable, the identification of a unique host galaxy is in general challenging. Instead, as originally proposed by Schutz, one can consult a galaxy catalog and implement a dark siren statistical approach incorporating all potential host galaxies within the localization volume. Trott & Huterer recently claimed that this approach results in a biased estimate of the Hubble constant, H 0, when implemented on mock data, even if optimistic assumptions are made. We demonstrate explicitly that, as previously shown by multiple independent groups, the dark siren statistical method leads to an unbiased posterior when the method is applied to the data correctly. We highlight common sources of error possible to make in the generation of mock data and implementation of the statistical framework, including the mismodeling of selection effects and inconsistent implementations of the Bayesian framework, which can lead to a spurious bias.

Keywords: gravitational wave astronomy; hubble constant; cosmology
Solar Wind Discontinuity Transformation at the Bow Shock

Solar wind plasma at the Earth's orbit carries transient magnetic field structures including discontinuities. Their interaction with the Earth's bow shock can significantly alter discontinuity configuration and stability. We investigate such an interaction for the most widespread type of solar wind discontinuities—rotational discontinuities (RDs). We use a set of in situ multispacecraft observations and perform kinetic hybrid simulations. We focus on the RD current density amplification that may lead to magnetic reconnection. We show that the amplification can be as high as two orders of magnitude and is mainly governed by three processes: the transverse magnetic field compression, global thinning of RD, and interaction of RD with low-frequency electromagnetic waves in the magnetosheath, downstream of the bow shock. The first factor is found to substantially exceed simple hydrodynamic predictions in most observed cases, the second effect has a rather moderate impact, while the third causes strong oscillations of the current density. We show that the presence of accelerated particles in the bow shock precursor highly boosts the current density amplification, making the postshock magnetic reconnection more probable. The pool of accelerated particles strongly affects the interaction of RDs with the Earth's bow shock, as it is demonstrated by observational data analysis and hybrid code simulations. Thus, shocks should be distinguished not by the inclination angle, but rather by the presence of foreshocks populated with shock reflected particles. Plasma processes in the RD-shock interaction affect magnetic structures and turbulence in the Earth's magnetosphere and may have implications for the processes in astrophysics.

Keywords: planetary bow shocks; interplanetary discontinuities
A Study of the Soft X-Ray Emission Lines in NGC 4151. I. Kinematic Properties of the Plasma Wind

We present our analysis of the narrow emission lines produced in the plasma regions within the bright active galactic nucleus of NGC 4151, from an ORBYTS research-with-schools public engagement project. Our goal was to test whether the properties of these plasma regions changed between XMM-Newton observations spanning 15 yr from 2000 to 2015, by measuring the outflow velocities and distances. From this study, we found that NGC 4151 has at least two to three plasma regions. There is no evidence of the outflowing wind properties changing as the velocities and distances are consistent throughout the observations.

Keywords: active galactic nuclei
X-Ray Observations of Type Ia Supernova 2018cqj

I report on Chandra X-ray observations of SN 2018cqj, a low luminosity Type Ia supernova that showed an Hα line in its optical spectrum. No X-ray emission was detected at the location of the SN, with an upper limit to the X-ray luminosity of 2 × 1039 erg s-1.

Keywords: circumstellar matter; supernovae; type ia supernovae; x-ray sources