Sazuna/UAT_keywords huggingface dataset:
Early Science from GOTHAM: Project Overview, Methods, and the Detection of Interstellar Propargyl Cyanide (HCCCH<SUB>2</SUB>CN) in TMC-1. We present an overview of the GBT Observations of TMC-1: Hunting Aromatic Molecules Large Program on the Green Bank Telescope. This and a related program were launched to explore the depth and breadth of aromatic chemistry in the interstellar medium at the earliest stages of star formation, following our earlier detection of benzonitrile (c-C6H5CN) in TMC-1. In this work, details of the observations, use of archival data, and data reduction strategies are provided. Using these observations, the interstellar detection of propargyl cyanide (HCCCH2CN) is described, as well as the accompanying laboratory spectroscopy. We discuss these results, and the survey project as a whole, in the context of investigating a previously unexplored reservoir of complex, gas-phase molecules in pre-stellar sources. A series of companion papers describe other new astronomical detections and analyses.

Keywords: Interstellar molecules, Polycyclic aromatic hydrocarbons, Chemical abundances, Astrochemistry, Dense interstellar clouds, Dark interstellar clouds, Interstellar medium
Solar Longitude Distribution of High-energy Proton Flares: Fluences and Spectra. The distribution of the longitudes of solar flares associated with the high-energy proton events called ground level events (GLEs) can be approximated by a Gaussian with a peak at ∼W60, with a full range from ∼E90 to ∼W150. The longitudes of flares associated with the top third (24 of 72) of GLEs in terms of their &gt;430 MeV fluences (F430) are primarily distributed over E20-W100 with a skew toward disk center. This 120° span in longitude is comparable to the latitudinal spans of powerful coronal mass ejections (CMEs) from limb flares. Only 5 of 24 strong GLEs are located within the W40-80 zone of good magnetic connection to Earth. GLEs with hard spectra, i.e., a spectral index SI30/200(= log(F30/F200)) &lt; 1.5, also tend to avoid W40-80 source regions. Three-fourths of such events (16 of 21) arise in flares outside this range. The above tendencies favor a CME-driven shock source over a flare-resident acceleration process for high-energy solar protons. GLE spectra show a trend, with broad scatter, from hard spectra for events originating in eruptive flares beyond the west limb to soft spectra for GLEs with sources near central meridian. This behavior can be explained in terms of: (1) dominant near-Sun quasi-perpendicular shock acceleration of protons for far western (&gt;W100) GLEs; (2) quasi-parallel shock acceleration for well-connected (W40-80) GLEs, and (3) proton acceleration/trapping at CME-driven bow shocks from central meridian (E20-W20) that strike the Earth.

Keywords: Solar energetic particles, Solar coronal mass ejection shocks, Solar flares, Solar coronal mass ejections
Short Gamma-Ray Bursts and the Decompression of Neutron Star Matter in Tidal Streams. Short gamma-ray bursts (sGRBs) are generally thought to result from the merger of two neutron stars or the merger of a neutron star with a black hole. It is becoming standard practice to model these mergers with hydrodynamical simulations that employ equations of state that are derived, for example, for determining the behavior of matter in core-collapse supernovae, and which therefore make use of the assumption that the matter is hot and in nuclear statistical equilibrium (NSE). In this Letter we draw attention to the fact that the hydrodynamical timescale (roughly the gravitational timescale of the neutron star) may be several orders of magnitude shorter than the timescale on which such equilibrium can be reestablished in the tidal debris ejected during an sGRB, and that on the initial decompression timescales the unshocked tidal ejecta may remain sufficiently cool that the employed equations of state are not appropriate for modeling the dynamics of this part of the flow. On timescales short compared with the timescale on which NSE can be (re)established, the equation of state can remain relatively stiff and thus the stream of tidal debris can remain narrow and vulnerable to gravitational instability, as has recently been suggested. These findings suggest that estimates of the type and abundances of heavy elements formed in short gamma-ray bursts need to be revisited. We suggest that the most direct method of testing the physical and dynamical properties of tidal ejecta in sGRBs will come from modeling of their lightcurves, which provides the cleanest source of information on the system dynamics.

Keywords: Neutron stars, Gravitational instability, Nuclear astrophysics, Particle astrophysics
Properties and Astrophysical Implications of the 150 M<SUB>⊙</SUB> Binary Black Hole Merger GW190521. The gravitational-wave signal GW190521 is consistent with a binary black hole (BBH) merger source at redshift 0.8 with unusually high component masses, ${85}_{-14}^{+21}$ M⊙ and ${66}_{-18}^{+17}$ M⊙, compared to previously reported events, and shows mild evidence for spin-induced orbital precession. The primary falls in the mass gap predicted by (pulsational) pair-instability supernova theory, in the approximate range 65-120 M⊙. The probability that at least one of the black holes in GW190521 is in that range is 99.0%. The final mass of the merger ( ${142}_{-16}^{+28}$ M⊙) classifies it as an intermediate-mass black hole. Under the assumption of a quasi-circular BBH coalescence, we detail the physical properties of GW190521's source binary and its post-merger remnant, including component masses and spin vectors. Three different waveform models, as well as direct comparison to numerical solutions of general relativity, yield consistent estimates of these properties. Tests of strong-field general relativity targeting the merger-ringdown stages of the coalescence indicate consistency of the observed signal with theoretical predictions. We estimate the merger rate of similar systems to be ${0.13}_{-0.11}^{+0.30}\,{{\rm{Gpc}}}^{-3}\,{{\rm{yr}}}^{-1}$ . We discuss the astrophysical implications of GW190521 for stellar collapse and for the possible formation of black holes in the pair-instability mass gap through various channels: via (multiple) stellar coalescences, or via hierarchical mergers of lower-mass black holes in star clusters or in active galactic nuclei. We find it to be unlikely that GW190521 is a strongly lensed signal of a lower-mass black hole binary merger. We also discuss more exotic possible sources for GW190521, including a highly eccentric black hole binary, or a primordial black hole binary.

Keywords: Intermediate-mass black holes, High energy astrophysics, Gravitation, Stellar populations, Gravitational wave sources, Gravitational wave astronomy, Galaxy photometry, Gravitational collapse, LIGO, Astrophysical black holes
Identification of Two Distinct Electron Populations in an Impulsive Solar Energetic Electron Event. We examine the release times of energetic electrons in the 2001 April 25 event. An M2.7 flare occurred on 2001 April 25, from AR 09433, located at N18W09. The flare was observed in X-rays by GOES and the Yohkoh spacecraft. The Yohkoh observation also included hard X-ray (HXR) images for all four energy channels: L, M1, M2, and H. We use Yohkoh observation times as a proxy for the release time of energetic electrons that propagated downward, which are responsible for the HXRs. In situ &gt;∼25 keV electrons were observed by the Wind spacecraft. For these electrons, we obtain the release time at the Sun using the recently developed Fractional Velocity Dispersion Analysis method. We find that the release times of outward-propagating energetic electrons are clearly delayed from those that propagated downward. Furthermore, these delayed releases are energy dependent. The implication of this delay on the underlying acceleration and trapping process of the &gt;∼25 keV electrons at solar flares is discussed.

Keywords: Solar energetic particles, Solar flares, Solar magnetic reconnection
Localized Amplification of Magnetic Field in the Solar Photosphere Associated with a Rapid Moving Pore. In the Sun, the flows of hot plasma drive a dynamo that generates a global magnetic field as well as smaller-scale local fields. The existence of a magnetic field in turn affects the motion of plasma so that complex dynamic characteristics can be observed. In this Letter, we give an analysis on the localized amplification of magnetic fields in front of a moving pore. Moving with the pore, the formation of semicircular penumbra-like structures and enhancement of horizontal fields can be observed simultaneously. The increasing horizontal magnetic fields in a penumbra-like area probably did not come from the pore, since the penumbra-like structures were not connected to the pore and a magnetic gap existed. The possibility of flux emergence can also be safely excluded. We further report that horizontal magnetic fields in the front of a moving pore are amplified in accordance with the MHD induction equation after necessary yet reasonable simplification. All characteristics show that the flows driven by the moving pore can lead to the amplification of the magnetic fields around its front. The observations are from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory.

Keywords: Solar active region velocity fields, Solar photosphere, Penumbra, Sunspot flow, Sunspots, Solar dynamo, Solar active regions, Solar magnetic fields
The High Helium Abundance and Charge States of the Interplanetary CME and Its Material Source on the Sun. Identifying the source of the material within coronal mass ejections (CMEs) and understanding CME onset mechanisms are fundamental issues in solar and space physics. Parameters relating to plasma composition, such as charge states and He abundance (AHe), may be different for plasmas originating from differing processes or regions on the Sun. Thus, it is crucial to examine the relationship between in situ measurements of CME composition and activity on the Sun. We study the CME that erupted on 2014 September 10, in association with an X1.6 flare, by analyzing Atmospheric Imaging Assembly imaging and Interface Region Imaging Spectrograph (IRIS) spectroscopic observations and its in situ signatures detected by Wind and Advanced Composition Explorer. We find that during the slow expansion and intensity increase of the sigmoid, plasma temperatures of 9 MK, and higher, first appear at the footpoints of the sigmoid, associated with chromospheric brightening. Then the high-temperature region extends along the sigmoid. IRIS observations confirm that this extension is caused by transportation of hot plasma upflow. Our results show that chromospheric material can be heated to 9 MK, and above, by chromospheric evaporation at the sigmoid footpoints before flare onset. The heated chromospheric material can transport into the sigmoidal structure and supply mass to the CME. The aforementioned CME mass supply scenario provides a reasonable explanation for the detection of high charge states and elevated AHe in the associated interplanetary CME. The observations also demonstrate that the quasi-steady evolution in the precursor phase is dominated by magnetic reconnection between the rising flux rope and the overlying magnetic field structure.

Keywords: Solar flares, Solar abundances, Solar coronal mass ejections, Solar corona, Solar-terrestrial interactions
Accelerating and Supersonic Density Fluctuations in Coronal Hole Plumes: Signature of Nascent Solar Winds. Slow magnetoacoustic waves in a static background provide a seismological tool to probe the solar atmosphere in the analytic frame. By analyzing the spatiotemporal variation of the electron number density of plume structure in coronal holes above the limb for a given temperature, we find that the density perturbations accelerate with supersonic speeds in the distance range from 1.02 to 1.23 solar radii. We interpret them as slow magnetoacoustic waves propagating at about the sound speed with accelerating subsonic flows. The average sonic height of the subsonic flows is calculated to be 1.27 solar radii. The mass flux of the subsonic flows is estimated to be 44.1% relative to the global solar wind. Hence, the subsonic flow is likely to be the nascent solar wind. In other words, the evolution of the nascent solar wind in plumes at the low corona is quantified for the first time from imaging observations. Based on the interpretation, propagating density perturbations present in plumes could be used as a seismological probe of the gradually accelerating solar wind.

Keywords: Solar coronal seismology, Solar wind, Solar coronal plumes
Optical Spectrum of the Adamantane Radical Cation. Known for their stable structural and thermal properties, diamondoids and particularly their radical cations are viable candidates as carriers for diffuse interstellar bands. While previous research has mainly focused on neutral diamondoids and their derivatives, little is known about their radical cations, which may form in interstellar environments by ionizing radiation. We report the first experimental optical spectrum of the simplest diamondoid cation, the adamantane radical cation ( ${{\rm{C}}}_{10}{{{\rm{H}}}_{16}}^{+}$ ), obtained via electronic photodissociation spectroscopy of cryogenic ions in the 310-1000 nm range. The main fragmentation channels are H loss at low energies and C3H7 loss at higher energies. The optical spectrum reveals a broad band spanning the range of 420-850 nm, assigned to the D2(2E) ← D0(2A1) transition using time-dependent density functional theory calculations. Despite a vibrational temperature below 20 K, we observe no vibrational structure because of lifetime broadening and/or Franck-Condon congestion. A second band system originating at 345 nm that shows vibrational progressions is attributed to the overlapping D5(2A1)/D6(2E) ← D0(2A1) transitions split by the Jahn-Teller effect. The lifetime deduced from the widths of these vibronic bands is ∼30 fs. Comparison of the spectrum with known diffuse interstellar bands suggests that ${{\rm{C}}}_{10}{{{\rm{H}}}_{16}}^{+}$ is not likely to be a carrier. However, the strong absorption features in the UV to near-IR show promise in the investigation of higher-order diamondoids as potential candidates.

Keywords: Interstellar molecules, Diffuse interstellar bands, Laboratory astrophysics, Molecular spectroscopy, Astrochemistry, Interstellar medium, Electron impact ionization
Plasmoid Ejection by Alfvén Waves and the Fast Radio Bursts from SGR 1935+2154. Using numerical simulations we show that low-amplitude Alfvén waves from a magnetar quake propagate to the outer magnetosphere and convert to "plasmoids" (closed magnetic loops) that accelerate from the star, driving blast waves into the magnetar wind. Quickly after its formation, the plasmoid becomes a thin relativistic pancake. It pushes out the magnetospheric field lines, and they gradually reconnect behind the pancake, generating a variable wind far stronger than the normal spindown wind of the magnetar. Repeating ejections drive blast waves in the amplified wind. We suggest that these ejections generate the simultaneous X-ray and radio bursts detected from SGR 1935+2154. A modest energy budget of the magnetospheric perturbation ∼1040 erg is sufficient to produce the observed bursts. Our simulation predicts a narrow (a few milliseconds) X-ray spike from the magnetosphere, arriving almost simultaneously with the radio burst emitted far outside the magnetosphere. This timing is caused by the extreme relativistic motion of the ejecta.

Keywords: Neutron stars, Shocks, Radio bursts, Non-thermal radiation sources, Magnetars, Radio transient sources
'Oumuamua as a Cometary Fractal Aggregate: The "Dust Bunny" Model. The first known interstellar object, 1I/2017 U1 'Oumuamua, displayed such unusual properties that its origin remains a subject of much debate. We propose that 'Oumuamua's properties could be explained as those of a fractal dust aggregate (a "dust bunny") formed in the inner coma of a fragmenting exo-Oort cloud comet. Such fragments could serve as accretion sites by accumulating dust particles, resulting in the formation of a fractal aggregate. The fractal aggregate eventually breaks off from the fragment due to hydrodynamic stress. With their low density and tenuously bound orbits, most of these cometary fractal aggregates are then ejected into interstellar space by radiation pressure.

Keywords: Oort cloud, Long period comets, Comets, Coma dust
A First-principle Model for Polarization Swings during Reconnection-powered Flares. We show that magnetic reconnection in a magnetically dominated fast-cooling plasma can naturally produce bright flares accompanied by rotations in the synchrotron polarization vector. With particle-in-cell simulations of reconnection, we find that flares are powered by efficient particle acceleration at the interface of merging magnetic flux ropes, or "plasmoids." The accelerated particles stream through the post-merger plasmoid toward the observer, thus progressively illuminating regions with varying plane-of-sky field direction, and so leading to a rotation in the observed polarization vector. Our results provide evidence for magnetic reconnection as the physical cause of high-energy flares from the relativistic jets of blazars (which recent observations have shown to be frequently associated with polarization rotations), and provide a first-principle physical mechanism for such flares.

Keywords: Blazars, Relativistic jets, Polarimetry
PIC Simulations of Microinstabilities and Waves at Near-Sun Solar Wind Perpendicular Shocks: Predictions for Parker Solar Probe and Solar Orbiter. Microinstabilities and waves excited at moderate-Mach-number perpendicular shocks in the near-Sun solar wind are investigated by full particle-in-cell simulations. By analyzing the dispersion relation of fluctuating field components directly issued from the shock simulation, we obtain key findings concerning wave excitations at the shock front: (1) at the leading edge of the foot, two types of electrostatic (ES) waves are observed. The relative drift of the reflected ions versus the electrons triggers an electron cyclotron drift instability (ECDI) that excites the first ES wave. Because the bulk velocity of gyro-reflected ions shifts to the direction of the shock front, the resulting ES wave propagates oblique to the shock normal. Immediately, a fraction of incident electrons are accelerated by this ES wave and a ring-like velocity distribution is generated. They can couple with the hot Maxwellian core and excite the second ES wave around the upper hybrid frequency. (2) From the middle of the foot all the way to the ramp, electrons can couple with both incident and reflected ions. ES waves excited by ECDI in different directions propagate across each other. Electromagnetic (EM) waves (X mode) emitted toward upstream are observed in both regions. They are probably induced by a small fraction of relativistic electrons. Results shed new insight on the mechanism for the occurrence of ES wave excitations and possible EM wave emissions at young coronal mass ejection-driven shocks in the near-Sun solar wind.

Keywords: Space plasmas, Interplanetary shocks, Plasma astrophysics, Plasma physics
Alternative High-plasma Beta Regimes of Electron Heat-flux Instabilities in the Solar Wind. Heat transport in the solar wind is dominated by suprathermal electron populations, i.e., a tenuous halo and a field-aligned beam/strahl, with high energies and antisunward drifts along the magnetic field. Their evolution may offer plausible explanations for the rapid decrease of the heat flux with the solar wind expansion, and self-generated instabilities, or so-called "heat flux instabilities" (HFIs), are typically invoked to explain this evolution. This Letter provides a unified description of the full spectrum of HFIs, as prescribed by the linear kinetic theory for high beta conditions (βe ≫ 0.1) and different relative drifts (U) of the suprathermals. HFIs of different natures are examined, i.e., electromagnetic, electrostatic or hybrid, propagating parallel or obliquely to the magnetic field, etc., as well as their regimes of interplay (co-existence) or dominance. These alternative regimes of HFIs complement each other and may be characteristic of different relative drifts of suprathermal electrons and various conditions in the solar wind, e.g., in the slow or fast winds, streaming interaction regions, and interplanetary shocks. Moreover, these results strongly suggest that heat flux regulation may not involve just one but several HFIs, concomitantly or successively in time. Conditions for a single, well-defined instability with major effects on the suprathermal electrons and, implicitly, the heat flux, seem to be very limited. Whistler HFIs are more likely to occur but only for minor drifts (as also reported by recent observations), which may explain a modest implication in their regulation, shown already in quasilinear studies and numerical simulations.

Keywords: Space plasmas, Solar wind, Plasma astrophysics
Understanding FRB 200428 in the Synchrotron Maser Shock Model: Consistency and Possible Challenge. Recently, the discovery of Galactic FRB 200428 associated with an X-ray burst (XRB) of SGR 1935+2154 has built a bridge between FRBs and magnetar activities. In this Letter, we assume that the XRB occurs in the magnetar magnetosphere. We show that the observational properties of FRB 200428 and the associated XRB are consistent with the predictions of synchrotron maser emission at ultrarelativistic magnetized shocks, including radiation efficiency, similar energy occurrence frequency distributions, and simultaneous arrive times. It requires that the upstream medium is a mildly relativistic baryonic shell ejected by a previous flare. The energy injection by flares responsible for the radio bursts will produce a magnetar wind nebula, which has been used to explain the persistent radio source associated with FRB 121102. We find that the radio continuum around SGR 1935+2154 can be well understood in the magnetar wind nebula model, by assuming the same energy injection rate $\dot{E}\propto {t}^{-1.37}$ as FRB 121102. The required baryonic mass is also estimated form the observations of FRB 121102 by the Green Bank Telescope and the Five-hundred-meter Aperture Spherical Telescope. By assuming the same radiation efficiency $\eta \sim {10}^{-5}$ , the total baryonic mass ejected from the central magnetar is about 0.005 solar mass. This value is much larger than the typical mass of a magnetar outer crust, but is comparable to the total mass of a magnetar crust.

Keywords: Soft gamma-ray repeaters, Magnetars, Radio bursts, Radio transient sources