Sazuna/UAT_keywords huggingface dataset:
A NICER View of Spectral and Profile Evolution for Three X-Ray-emitting Millisecond Pulsars. We present two years of Neutron star Interior Composition Explorer (NICER) X-ray observations of three energetic rotation-powered millisecond pulsars (MSPs): PSRs B1937+21, B1821-24, and J0218+4232. We fit Gaussians and Lorentzians to the pulse profiles for different energy sub-bands of the soft X-ray regime to measure the energy dependence of pulse separation and width. We find that the separation between pulse components of PSR J0218+4232 decreases with increasing energy at &gt;3σ confidence. The 95% upper limit on pulse separation evolution for PSRs B1937+21 and B1821-24 is less than 2 milliperiods per keV. Our phase-resolved spectral results provide updated constraints on the non-thermal X-ray emission of these three pulsars. The photon indices of the modeled X-ray emission spectra for each pulse component of PSR B1937+21 are inconsistent with each other at the 90% confidence level, suggesting different emission origins for each pulse. We find that the PSR B1821-24 and PSR J0218+4232 emission spectra are invariant with phase at the 90% confidence level. We describe the implications of our profile and spectral results in the context of equatorial current sheet emission models for these three MSPs with non-thermal, magnetospheric X-ray emission.

Keywords: Neutron stars, X-ray astronomy, Millisecond pulsars
Prospects for Directly Imaging Young Giant Planets at Optical Wavelengths. In this work, we investigate the properties of young giant planet spectra in the optical and suggest that future space-based direct imaging missions should be considering young planets as a valuable and informative science case. While young planets are dimmer in the optical than in the infrared, they can still be brighter in the optical than a mature planet of similar mass. Therefore, an instrument designed to characterize mature planets should also be suitable for high-precision photometric imaging and spectroscopy of young self-luminous planets in a wavelength range and at a contrast ratio not currently attainable from the ground. We identify known young self-luminous companions that are feasible targets for coronagraphic instrument on the Wide Field Infrared Survey Telescope (WFIRST-CGI) and compute spectra for them, including a treatment of scattering and reflected light at optical wavelengths. Using these results, we highlight potentially diagnostic spectral features that will be present in the WFIRST-CGI wavelengths. Expanding to direct imaging missions beyond WFIRST-CGI, we also use evolutionary models across a grid of masses and planet-star separations as inputs to compute spectra of hypothetical objects, exploring when reflected light may contribute to a degree comparable to that of thermal emission from the residual heat of formation.

Keywords: Substellar companion stars, Exoplanets, Direct imaging, Extrasolar gaseous giant planets, Exoplanet atmospheres
Understanding the Origin of the Magnetic Field Morphology in the Wide-binary Protostellar System BHR 71. We present 1.3 mm Atacama Large Millimeter/submillimeter Array observations of polarized dust emission toward the wide-binary protostellar system BHR 71 IRS1 and IRS2. IRS1 features what appears to be a natal, hourglass-shaped magnetic field. In contrast, IRS2 exhibits a magnetic field that has been affected by its bipolar outflow. Toward IRS2, the polarization is confined mainly to the outflow cavity walls. Along the northern edge of the redshifted outflow cavity of IRS2, the polarized emission is sandwiched between the outflow and a filament of cold, dense gas traced by N2D+, toward which no dust polarization is detected. This suggests that the origin of the enhanced polarization in IRS2 is the irradiation of the outflow cavity walls, which enables the alignment of dust grains with respect to the magnetic field - but only to a depth of ∼300 au, beyond which the dust is cold and unpolarized. However, in order to align grains deep enough in the cavity walls, and to produce the high polarization fraction seen in IRS2, the aligning photons are likely to be in the mid- to far-infrared range, which suggests a degree of grain growth beyond what is typically expected in very young, Class 0 sources. Finally, toward IRS1 we see a narrow, linear feature with a high (10%-20%) polarization fraction and a well-ordered magnetic field that is not associated with the bipolar outflow cavity. We speculate that this feature may be a magnetized accretion streamer; however, this has yet to be confirmed by kinematic observations of dense-gas tracers.

Keywords: Interstellar dust, Compact radiation sources, Astrochemistry, Interstellar magnetic fields, Young stellar objects, Star formation, Dust continuum emission, Wide binary stars, Protostars, Polarimetry
Optical Polarimetry of the Tidal Disruption Event AT2019DSG. We present time-series imaging polarimetry observations of a nearby tidal disruption event (TDE) AT2019DSG at z = 0.0512 to probe the disruption mechanism and shed light on the accretion process. We obtain linear polarimetry using the Alhambra Faint Object Spectrograph and Camera on board the 2.5 m Nordic Optical Telescope. Our observations showed a polarization at the 9.2% ± 2.7% level early on, decreasing to less than 2.7% (at the 68% confidence level) one month later. While the high level of polarization in the early epoch is similar to that of Swift J164449.3+573451 and Swift J2058+0516, the low level of polarization in the later epoch is in agreement with that of OGLE16aaa. Our results thus show the temporal evolution of optical polarization from a TDE. As the degree of polarization changes over time, it is unlikely to be attributed to host galaxy dust, but may originate from a non-isotropic accreting disk, or associated with the relativistic jet emission.

Keywords: Tidal disruption, Polarimetry
The Typical Massive Quiescent Galaxy at z ∼ 3 is a Post-starburst. We have obtained spectroscopic confirmation with Hubble Space Telescope WFC3/G141 of a first sizeable sample of nine quiescent galaxies at 2.4 &lt; z &lt; 3.3. Their average near-UV/optical rest-frame spectrum is characterized by low attenuation (AV ∼ 0.6 mag) and a strong Balmer break, larger than the 4000 Å break, corresponding to a fairly young age of ∼300 Myr. This formally classifies a substantial fraction of classically selected quiescent galaxies at z ∼ 3 as post-starbursts, marking their convergence to the quenching epoch. The rapid spectral evolution with respect to z ∼ 1.5 quiescent galaxies is not matched by an increase of residual star formation, as judged from the weak detection of [O II]λ3727 emission, pointing to a flattening of the steep increase in gas fractions previously seen from z ∼ 0 to 1.8. However, radio 3 GHz stacked emission implies either much stronger dust-obscured star formation or substantial further evolution in radio-mode AGN activity with respect to z ∼ 1.5.

Keywords: Galaxy quenching, Quenched galaxies, Galaxy evolution
GW190425: Observation of a Compact Binary Coalescence with Total Mass ∼ 3.4 M<SUB>⊙</SUB>. On 2019 April 25, the LIGO Livingston detector observed a compact binary coalescence with signal-to-noise ratio 12.9. The Virgo detector was also taking data that did not contribute to detection due to a low signal-to-noise ratio, but were used for subsequent parameter estimation. The 90% credible intervals for the component masses range from 1.12 to 2.52 M⊙ (1.46-1.87 M⊙ if we restrict the dimensionless component spin magnitudes to be smaller than 0.05). These mass parameters are consistent with the individual binary components being neutron stars. However, both the source-frame chirp mass 1.44-0.02+0.02 M⊙ and the total mass 3.4-0.1+0.3 M⊙ of this system are significantly larger than those of any other known binary neutron star (BNS) system. The possibility that one or both binary components of the system are black holes cannot be ruled out from gravitational-wave data. We discuss possible origins of the system based on its inconsistency with the known Galactic BNS population. Under the assumption that the signal was produced by a BNS coalescence, the local rate of neutron star mergers is updated to 250-2810 Gpc-3yr-1.

Keywords: Neutron stars, Gravitational waves
The Birth of Binary Direct-collapse Black Holes. Supermassive primordial stars forming during catastrophic baryon collapse in atomically cooling halos at z ∼ 15-20 may be the origin of the first quasars in the universe. However, no simulation to date has followed the evolution of these halos at resolutions that are high enough or for times that are long enough to determine if collapse actually produces supermassive stars (SMSs). Here we report new cosmological simulations of baryon collapse in atomically cooled halos for times that are long enough for SMSs to form and die as direct-collapse black holes (DCBHs). We find that the high infall rates required to build up such stars persist until the end of their lives and could fuel the rapid growth of their BHs thereafter. Our simulations also demonstrate that binary and even small multiples of SMSs can form in low-spin and high-spin halos, respectively. This discovery raises the exciting possibility of detecting gravitational waves from DCBH mergers with LISA and tidal disruption events in the near-infrared with the James Webb Space Telescope and ground-based telescopes in the coming decade.

Keywords: Supermassive black holes, High-redshift galaxies, Early universe, Quasars
Extension of the Electron Diffusion Region in a Guide Field Magnetic Reconnection at Magnetopause. The structure of the electron diffusion region (EDR) in different plasma regimes is an outstanding question related to magnetic reconnection. Here we report a long EDR that extended at least 20 ion inertial lengths downstream of an X line at the Earth's magnetopause, which was observed by the Magnetospheric Multiscale mission. This EDR was detected in the exhaust of an asymmetric magnetic reconnection with a moderate guide field, the reconnection rate of which was ∼0.1. It corresponds to strong positive energy dissipation (J\cdot E' &gt;0) and enhancement of electron nongyrotropy. The energy dissipation was contributed by the electron jet and non-ideal electric field along the outflow direction, which suggests that the EDR probably plays more important roles in the energy conversion in magnetic reconnection than previously thought. Our result could be a significant step toward fully understanding the structure of the EDR.

Keywords: Space plasmas, Solar magnetic reconnection, Planetary boundary layers, Plasma physics
The FAST Discovery of an Eclipsing Binary Millisecond Pulsar in the Globular Cluster M92 (NGC 6341). We report the discovery of an eclipsing binary millisecond pulsar in the globular cluster M92 (NGC 6341) with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). PSR J1717+4308A, or M92A, has a pulse frequency of 316.5 Hz (3.16 ms) and a dispersion measure of 35.45 pc cm-3. The pulsar is a member of a binary system with an orbital period of 0.20 days around a low-mass companion that has a median mass of ∼0.18 M⊙. From observations so far, at least two eclipsing events have been observed in each orbit. The longer one lasted for ∼5000 s in the orbital phase range 0.1-0.5. The other lasted for ∼500 s and occurred between 1000 and 2000 s before or after the longer eclipsing event. The lengths of these two eclipsing events also change. These properties suggest that J1717+4308A is a "red-back" system with a low-mass main-sequence or sub-giant companion. Timing observations of the pulsar and further searches of the data for additional pulsars are ongoing.

Keywords: Globular star clusters, Pulsar timing method, Millisecond pulsars, Eclipsing binary stars, Binary pulsars
TESS Spots a Hot Jupiter with an Inner Transiting Neptune. Hot Jupiters are rarely accompanied by other planets within a factor of a few in orbital distance. Previously, only two such systems have been found. Here, we report the discovery of a third system using data from the Transiting Exoplanet Survey Satellite (TESS). The host star, TOI-1130, is an eleventh magnitude K-dwarf in Gaia G-band. It has two transiting planets: a Neptune-sized planet (3.65 ± 0.10 R\oplus) with a 4.1 days period, and a hot Jupiter (1.50-0.22+0.27 RJ) with an 8.4 days period. Precise radial-velocity observations show that the mass of the hot Jupiter is 0.974-0.044+0.043 MJ. For the inner Neptune, the data provide only an upper limit on the mass of 0.17 MJ (3σ). Nevertheless, we are confident that the inner planet is real, based on follow-up ground-based photometry and adaptive-optics imaging that rule out other plausible sources of the TESS transit signal. The unusual planetary architecture of and the brightness of the host star make TOI-1130 a good test case for planet formation theories, and an attractive target for future spectroscopic observations.

Keywords: Extrasolar rocky planets, Exoplanets, Hot Jupiters, Exoplanet astronomy, Extrasolar gaseous giant planets
The Branching Ratio of LIGO Binary Black Holes. Formation of binary black holes (BBHs) detected by gravitational-wave observations could be broadly divided into two categories: those formed through field binary evolution and those assembled dynamically in dense stellar systems. The branching ratio of the BBHs refers to the contribution of each channel. The dynamical assembly channel would predict a symmetric distribution in the effective spins of the BBHs while field formation predicts BBHs to have positive effective spins. By modeling these two populations based on their effective spin distribution we show that in the 10 BBHs detected by LIGO/Virgo the contribution of the dynamically assembled BBHs is more than about 50% with 90% confidence. This result is based on the assumption that the field binaries are born with positive effective spins not restricted to have small values.

Keywords: LIGO, Black hole physics, High energy astrophysics
LISA and the Existence of a Fast-merging Double Neutron Star Formation Channel. Using a Milky Way (MW) double neutron star (DNS) merger rate of 210 Myr-1, as derived by the Laser Interferometer Gravitational-Wave Observatory (LIGO), we demonstrate that the Laser Interferometer Space Antenna (LISA) will detect on average 240 (330) DNSs within the MW for a 4 yr (8 yr) mission with a signal-to-noise ratio greater than 7. Even adopting a more pessimistic rate of 42 Myr-1, as derived by the population of Galactic DNSs, we find a significant detection of 46 (65) MW DNSs. These DNSs can be leveraged to constrain formation scenarios. In particular, without prior information on a particular system's position and orbital period, traditional NS-discovery methods using radio telescopes alone are insensitive to DNSs with Porb ≲ 1 hr (merger times ≲10 Myr). If a fast-merging channel exists that forms DNSs at these short orbital periods, LISA affords, perhaps, the best opportunity to observationally identify and characterize these systems; we show that toy models for possible formation scenarios leave imprints on DNS orbital eccentricities, which may be measured by LISA for values as small as ∼10-2.

Keywords: Neutron stars, Gravitational wave detectors, Binary pulsars, Gravitational waves
Fast Radio Bursts as Strong Waves Interacting with the Ambient Medium. Fast radio bursts (FRBs) are mysterious radio transients whose physical origin is still unknown. Within a few astronomical units near an FRB source, the electric field of the electromagnetic wave is so large that the electron oscillation velocity becomes relativistic, which makes the classical Thomson scattering theory and the linear plasma theory invalid. We discuss FRBs as strong waves interacting with the ambient medium, in terms of both electron motion properties and plasma properties. Several novel features are identified. (1) The cross section of Thomson scattering is significantly enhanced for the scattering photons. (2) On the other hand, because of the nonlinear plasma properties in strong waves, the near-source plasma is more transparent and has a smaller effective dispersion measure (DM) contribution to the observed value. For a repeating FRB source, the brighter bursts would have somewhat smaller DMs contributed by the near-source plasma. (3) The radiation beam undergoes relativistic self-focusing in a dense plasma, the degree of self-focusing (or squeezing) depends on the plasma density. Such a squeezing effect would affect the collimation angle and the true event rate of FRBs. (4) When an FRB propagates in a nearby ambient plasma, a wakefield wave in the plasma will be generated by the ponderomotive force of the FRB, and accelerates electrons in the ambient medium. However, such an effect is too weak to be observationally interesting.

Keywords: Plasma physics, Interstellar plasma, Radio transient sources
Nekhoroshev Estimates for the Survival Time of Tightly Packed Planetary Systems. N-body simulations of nonresonant, tightly packed planetary systems have found that their survival time (I.e., time to first close encounter) grows exponentially with their interplanetary spacing and planetary masses. Although this result has important consequences for the assembly of planetary systems by giant collisions and their long-term evolution, this underlying exponential dependence is not understood from first principles, and previous attempts based on orbital diffusion have only yielded power-law scalings. We propose a different picture, where large deviations of the system from its initial conditions is due to a few slowly developing high-order resonances. Thus, we show that the survival time of the system T can be estimated using a heuristic motivated by Nekhoroshev's theorem, and obtain a formula for systems away from overlapping two-body mean-motion resonances as T/P={c1 a/Δa \exp (c2 Δa/a/μ,SUP&gt;1/4), where P is the average Keplerian period, a is the average semimajor axis, Δa ≪ a is the difference between the semimajor axes of neighboring planets, μ is the planet-to-star mass ratio, and c1 and c2 are dimensionless constants. We show that this formula is in good agreement with numerical N-body experiments for c1 = 5 × 10-4 and c2 = 8.

Keywords: Exoplanet dynamics, Few-body systems, Planetary system formation
The Search for Europa's Plumes: No Surface Patterns or Changes 1979-2007?. With the apparent detections of eruptive plumes of water vapor at Europa, we use low-resolution global imaging maps of the surface obtained in 1979, 1996-1998, and 2007 by Voyager, Galileo (GLL), and New Horizons to search for plume-related deposits on the surface or changes to them. These imaging data were acquired using different imaging filters, and at different observation geometries. Though not ideal, these maps reveal no obvious albedo or color patterns or surface changes related to plume activity that can be identified with confidence on the surface of Europa over this 28 yr time period. Either plume activity was relatively continuous over these time periods and produced neither distinctive color nor photometric patterns or observable changes, plume activity produces vapor-only "stealth" deposits that are not apparent in currently available data sets, or these are not plumes in the expected sense. We also examine the proposed E12 GLL plume site at 5°S, 115°E, which was observed by GLL at pixel scales of 0.23-1.6 km pixel-1 before and as little as 4 months after the E12 magnetometer observations. We observe no unusual or anomalous photometric features or changes at this or any other sites, including the Hubble Space Telescope site at 17°S, 72-96°E. Prominent dark double ridges flanked by diffuse dark reddish deposits, and sporadic chaos formation events, are among the best-candidate eruptive sites on Europa, but none are linked with the proposed plume detection sites. Novel approaches to plume deposit detection may be required during the Europa Clipper mission.

Keywords: Tidal interaction, Galilean satellites, Habitable planets, Planetary science
The Critical Role of Collisionless Plasma Energization on the Structure of Relativistic Magnetic Reconnection. During magnetically dominated relativistic reconnection, inflowing plasma depletes the initial relativistic pressure at the X-line and collisionless plasma heating inside the diffusion region is insufficient to overcome this pressure loss. The resulting significant pressure drop causes a collapse at the X-line, essentially a localization mechanism of the diffusion region necessary for fast reconnection. The extension of this low-pressure region (into the outflow) further explains the bursty nature of antiparallel reconnection because a once opened outflow exhaust can also collapse, which repeatedly triggers secondary tearing islands. However, a stable single X-line reconnection can be achieved when an external guide field exists, since the reconnecting magnetic field component rotates out of the reconnection plane at outflows, providing additional magnetic pressure to keep the exhaust open.

Keywords: Plasma astrophysics, Plasma physics
The Birth of a Massive First-star Binary. We study the formation of massive Population III binary stars using a newly developed radiation hydrodynamics code with the adaptive mesh refinement and adaptive ray-tracing methods. We follow the evolution of a typical primordial star-forming cloud obtained from a cosmological hydrodynamics simulation. Several protostars form as a result of disk fragmentation and grow in mass by the gas accretion, which is finally quenched by the radiation feedback from the protostars. Our code enables us, for the first time, to consider the feedback by both the ionizing and dissociating radiation from the multiple protostars, which is essential for self-consistently determining their final masses. At the final step of the simulation, we observe a very wide (≳104 au) binary stellar system consisting of 60 and 70 M⊙ stars. One of the member stars also has two smaller mass (10 M⊙) companion stars orbiting at 200 and 800 au, making up a mini-triplet system. Our results suggest that massive binary or multiple systems are common among Population III stars.

Keywords: Star formation, Early universe, Population III stars
Periodic Fast Radio Bursts with Neutron Star Free Precession. The CHIME/FRB collaboration recently reported the detection of a 16 day periodicity in the arrival times of radio bursts from FRB 180916.J0158+65. We study the possibility that the observed periodicity arises from free precession of a magnetized neutron star, and put constraints on different components of the star's magnetic fields. Using a simple geometric model, where radio bursts are emitted from a rotating neutron star magnetosphere, we show that the emission pattern as a function of time can match that observed from FRB 180916.J0158+65.

Keywords: Neutron stars, Magnetospheric radio emissions, Compact radiation sources, Radio bursts, Magnetars
Thunder and Lightning: Using Neutron-star Mergers as Simultaneous Standard Candles and Sirens to Measure Cosmological Parameters. With the detection of gravitational wave (GW) GW170817 and its associated electromagnetic (EM) counterparts from a binary neutron star (NS) merger, the "standard siren" method for Hubble-constant measurements is expected to play a role in the Hubble-constant tension in the next few years. One intriguing proposal put forward in multiple studies is to use an NS merger's optical counterpart, known as a kilonova, as a standard candle, because its absolute magnitude can in principle be calculated from simulations. In this work, I detail the statistical framework for performing joint standard-candle and standard-siren measurements using GWs, EM follow-up data, and simulations of EM counterparts. I then perform an example analysis using GW170817 and its optical counterpart AT2017gfo to illustrate the method and the method's limitations. Crucially, the inferences using this method are only as robust as the EM counterpart models, so significant theoretical advances are needed before this method can be employed for precision cosmology.

Keywords: Neutron stars, Gravitational waves, Hubble constant, Cosmological parameters