adsabs/SciX_UAT_keywords huggingface dataset:
Magnetar Giant Flare Origin for GRB 200415A Inferred from a New Scaling Relation

Soft gamma-ray repeaters (SGRs) are a mainly Galactic population and originate from neutron stars with intense (B ≃ 1015 G) magnetic fields (magnetars). Occasionally, a giant flare occurs with enormous intensity, displaying a short, hard spike followed by a weaker, oscillatory phase that exhibits the rotational period of the neutron star. If the magnetar giant flares occur in nearby galaxies, they would appear as cosmic, short-hard gamma-ray bursts (GRBs) without detecting the weak oscillatory phase. Recently, a short-hard GRB named GRB 200415A was detected, with a position coincident with the Sculptor Galaxy (NGC 253), raising the question of whether it is a classic short GRB or a magnetar giant flare. Here we show that magnetar giant flares follow a scaling relation between the spectral peak energy and the isotropic energy in 1 keV-10 MeV, i.e., ${E}_{{\rm{p}}}\propto {E}_{\mathrm{iso}}^{1/4}$ , and locate in a distinct region of the Ep-Eiso plane from that of classic short GRBs. The relation can be well understood in the model that giant flares arise from the photosphere emissions of relativistically expanding fireballs. GRB 200415A, together with two other candidate giant flares (GRB 051103 and GRB 070201) follow this relation, which strongly favors the giant flare origin of these GRBs. The GeV emission detected by Fermi/LAT from GRB 200415A at 18-285 s can also be explained in the giant flare scenario. The total energy in the GeV emission implies a baryon load of ∼1023 g in the giant flare fireball of GRB 200415A.

Keywords: magnetars; gamma-ray bursts
How Well is the International Celestial Reference System Maintained in Official IAU Implementations?

The International Celestial Reference Frame (ICRF) based on the VLBI-derived positions of 608 extragalactic radio sources was adopted by the International Astronomical Union (IAU) in 1998 as the first realization of the International Celestial Reference System (ICRS). Later, in 2009 and 2020, two extended ICRF versions, ICRF2 and ICRF3, respectively, were released. The latter is adopted by the IAU as the current implementation of the ICRF in the radio band. In the meantime, the Gaia mission delivered three versions of the optical ICRS realization in 2016, 2018, and 2022 with an accuracy similar to that achieved by VLBI-based ICRF. The Gaia-CRF catalogs were linked to the ICRF under no-rotation conditions and thus may suffer from ICRF systematic instability if the latter is substantial. In this work, a new analysis was performed to assess the long-term stability of radio and optical ICRS realizations. Based on the 16-parameter vector spherical harmonics expansion of the differences between the three ICRF catalogs, it can be concluded that the mutual orientation between them is at a level of a few tens of microarcseconds, while the components of the glide vector and E 2,0 term are several times greater. A comparison of the three Gaia-CRF catalogs with the ICRF3-SX showed that for the latest Gaia-CRF catalog, Gaia-CRF3, all rotational and deformation components are below 20 μas except for the E 2,0 term, which is several times greater. For both ICRF and Gaia-CRF catalogs, the evolution of the source position errors is also tracked.

Keywords: astronomical coordinate systems; astrometry; very long baseline interferometry; radio source catalogs; gaia
The Orbits and Dynamical Masses of the Castor System

Castor is a system of six stars in which the two brighter objects, Castor A and B, revolve around each other every ~450 yr and are both short-period spectroscopic binaries. They are attended by the more distant Castor C, which is also a binary. Here we report interferometric observations with the Center for High Angular Resolution Astronomy (CHARA) array that spatially resolve the companions in Castor A and B for the first time. We complement these observations with new radial velocity measurements of A and B spanning 30 yr, with the Hipparcos intermediate data, and with existing astrometric observations of the visual AB pair obtained over the past three centuries. We perform a joint orbital solution to solve simultaneously for the three-dimensional orbits of Castor A and B as well as the AB orbit. We find that they are far from being coplanar: the orbit of A is nearly at right angles (92°) relative to the wide orbit, and that of B is inclined about 59° compared to AB. We determine the dynamical masses of the four stars in Castor A and B to a precision better than 1%. We also determine the radii of the primary stars of both subsystems from their angular diameters measured with the CHARA array, and use them together with stellar evolution models to infer an age for the system of 290 Myr. The new knowledge of the orbits enables us to measure the slow motion of Castor C as well, which may assist future studies of the dynamical evolution of this remarkable sextuple system.

Keywords: astrometric binary stars; interferometric binary stars; spectroscopic binary stars; stellar evolution; visual binary stars; radial velocity
Molecules with ALMA at Planet-forming Scales (MAPS). XVII. Determining the 2D Thermal Structure of the HD 163296 Disk

Understanding the temperature structure of protoplanetary disks is key to interpreting observations, predicting the physical and chemical evolution of the disk, and modeling planet formation processes. In this study, we constrain the two-dimensional thermal structure of the disk around the Herbig Ae star HD 163296. Using the thermochemical code RAC2D, we derive a thermal structure that reproduces spatially resolved Atacama Large Millimeter/submillimeter Array observations (~0"12 (13 au)-0"25 (26 au)) of 12CO J = 2 - 1, 13CO J = 1 - 0, 2 - 1, C18O J = 1 - 0, 2 - 1, and C17O J = 1 - 0, the HD J = 1 - 0 flux upper limit, the spectral energy distribution (SED), and continuum morphology. The final model incorporates both a radial depletion of CO motivated by a timescale shorter than typical CO gas-phase chemistry (0.01 Myr) and an enhanced temperature near the surface layer of the the inner disk (z/r ≥ 0.21). This model agrees with the majority of the empirically derived temperatures and observed emitting surfaces derived from the J = 2 - 1 CO observations. We find an upper limit for the disk mass of 0.35 M⊙, using the upper limit of the HD J = 1 - 0 and J = 2 - 1 flux. With our final thermal structure, we explore the impact that gaps have on the temperature structure constrained by observations of the resolved gaps. Adding a large gap in the gas and small dust additionally increases gas temperature in the gap by only 5%-10%. This paper is part of the MAPS special issue of the Astrophysical Journal Supplement.

Keywords: protoplanetary disks; astrochemistry
An Eruptive Circular-ribbon Flare with Extended Remote Brightenings

We study an eruptive X1.1 circular-ribbon flare on 2013 November 10, combining multiwavelength observations with a coronal field reconstruction using a non-force-free field method. In the first stage, a filament forms via magnetic reconnection between two mildly twisted sheared arcades, which are embedded under the fan dome associated with a null point (NP). This reconnection seems to be driven by photospheric shearing and converging flows around the inner two arcade footpoints, consistent with the flare-related changes of the transverse field. The southern portion of the filament rises upward due to torus instability and pushes against the NP. The induced NP reconnection then generates the circular ribbon and the initial remote brightening in the west, as accelerated electrons precipitate along the fan and propagate outward along quasi-separatix surfaces with high values of the squashing factor (Q) in the envelope fields, which have a curtain-like shape here. In the second stage, the southern end of the flux rope breaks away from the surface, sequentially disrupts the dome and overlying fields, and erupts in a whipping-like fashion to become a partial halo coronal mass ejection. This leads to an enhanced flare emission and fast-moving remote brightenings at the footpoints of the magnetic curtain, which span a remarkably broad region and are also associated with coronal dimmings. This is a rare example of eruptive circular-ribbon flares, in which the evolution of a flux rope from its formation to successful eruption out of the dome and the resulting unusually extended remote brightenings are completely observed.

Keywords: solar magnetic fields; solar activity; solar flares; solar coronal mass ejections
NICER X-Ray Observations of Eta Carinae during Its Most Recent Periastron Passage

We report high-precision X-ray monitoring observations in the 0.4-10 keV band of the luminous, long-period colliding wind binary Eta Carinae, up to and through its most recent X-ray minimum/periastron passage in 2020 February. Eta Carinae reached its observed maximum X-ray flux on 2020 January 7, at a flux level of 3.30 ×10-10 ergs s-1 cm-2, followed by a rapid plunge to its observed minimum flux, 0.03 × 10-10 ergs s-1 cm-2, near 2020 February 17. The NICER observations show an X-ray recovery from the minimum of only ~16 days, the shortest X-ray minimum observed so far. We provide new constraints for the "deep" and "shallow" minimum intervals. Variations in the characteristic X-ray temperatures of the hottest observed X-ray emission indicate that the apex of the wind-wind "bow shock" enters the companion's wind acceleration zone about 81 days before the start of the X-ray minimum. There is a steplike increase in column density just before the X-ray minimum, probably associated with the presence of dense clumps near the shock apex. During the recovery and after, the column density shows a smooth decline, which agrees with previous N H measurements made by Swift at the same orbital phase, indicating that the changes in the mass-loss rate are only a few percent over the two cycles. Finally, we use the variations in the X-ray flux of the outer ejecta seen by NICER to derive a kinetic X-ray luminosity of the ejecta of ~1041 ergs s-1 near the time of the "Great Eruption."

Keywords: stellar winds; x-ray sources; stellar evolution
The Impact of Limited Time Resolution on the Forward-scattering Polarization in the Solar Sr I 4607 Å Line

Theoretical investigations predicted that high spatiotemporal resolution observations in the Sr I 4607 Å line must show a conspicuous scattering polarization pattern at the solar disk center, which encodes information on the unresolved magnetism of the intergranular photospheric plasma. Here we present a study of the impact of limited time resolution on the observability of such forward-scattering (disk-center) polarization signals. Our investigation is based on three-dimensional radiative transfer calculations in a time-dependent magnetoconvection model of the quiet solar photosphere, taking into account anisotropic radiation pumping and the Hanle effect. This type of radiative transfer simulation is computationally costly, which is why the time variation had not been investigated before for this spectral line. We compare our theoretical results with recent disk-center filter polarimetric observations in the Sr I 4607 Å line, showing that there is good agreement in the polarization patterns. We also show what we can expect to observe with the Visible Spectro-Polarimeter at the upcoming Daniel K. Inouye Solar Telescope.

Keywords: quiet sun; solar physics; solar atmosphere; solar magnetic fields; the sun
Orbital Decay of Hot Jupiters due to Weakly Nonlinear Tidal Dissipation

We study tidal dissipation in hot Jupiter host stars due to the nonlinear damping of tidally driven g-modes, extending the calculations of Essick & Weinberg to a wide variety of stellar host types. This process causes the planet's orbit to decay and has potentially important consequences for the evolution and fate of hot Jupiters. Previous studies either only accounted for linear dissipation processes or assumed that the resonantly excited primary mode becomes strongly nonlinear and breaks as it approaches the stellar center. However, the great majority of hot Jupiter systems are in the weakly nonlinear regime in which the primary mode does not break but instead excites a sea of secondary modes via three-mode interactions. We simulate these nonlinear interactions and calculate the net mode dissipation for stars that range in mass from 0.5M ⊙ ≤ M ⋆ ≤ 2.0M ⊙ and in age from the early main sequence to the subgiant phase. We find that the nonlinearly excited secondary modes can enhance the tidal dissipation by orders of magnitude compared to linear dissipation processes. For the stars with M ⋆ ≲ 1.0M ⊙ of nearly any age, we find that the orbital decay time is ≲100 Myr for orbital periods P orb ≲ 1 day. For M ⋆ ≳ 1.2M ⊙, the orbital decay time only becomes short on the subgiant branch, where it can be ≲10 Myr for P orb ≲ 2 days and result in significant transit time shifts. We discuss these results in the context of known hot Jupiter systems and examine the prospects for detecting their orbital decay with transit timing measurements.

Keywords: hot jupiters; tides; exoplanet migration; internal waves; hydrodynamics
Large-scale Multiconfiguration Dirac-Hartree-Fock Calculations for Astrophysics: n = 4 Levels in P-like Ions from Mn XI to Ni XIV

Using the multiconfiguration Dirac-Hartree-Fock and the relativistic configuration interaction methods, a consistent set of transition energies and radiative transition data for the lowest 546 (623, 701, and 745) states of the 3p43d, 3s3p23d2, 3s3p34p, 3s3p4, 3s23d3, 3s23p23d, 3s23p24d, 3s23p24s, 3p33d2, 3p5, 3s3p3d3, 3s3p33d, 3s3p34s, 3s23p3d2, 3s23p24p, and 3s23p3 configurations in Mn XI (Fe XII, Co XIII, and Ni XIV) is provided. The comparison between calculated excitation energies for the n = 4 states and available experimental values for Fe XII indicate that the calculations are highly accurate, with uncertainties of only a few hundred cm-1. Lines from these states are prominent in the soft X-rays. With the present calculations, several recent new identifications are confirmed. Other identifications involving 3p24d levels in Fe XII that were found to be questionable are discussed and a few new assignments are recommended. As some n = 4 states of the other ions also show large discrepancies between experimental and calculated energies, we reassess their identification. The present study provides highly accurate atomic data for the n = 4 states of P-like ions of astrophysical interest, for which experimental data are scarce.

Keywords: atomic data benchmarking; laboratory astrophysics
LAMOST Observations in 15 K2 Campaigns. I. Low-resolution Spectra from LAMOST DR6

The Large Sky Area Multi-object Fiber Spectroscopic Telescope (LAMOST)-K2 (LK2) project, initiated in 2015, aims to collect low-resolution spectra of targets in the K2 campaigns, similar to the LAMOST-Kepler project. By the end of 2018, a total of 126 LK2 plates had been observed by LAMOST. After cross-matching the catalog of the LAMOST data release 6 (DR6) with that of the K2 approved targets, we found 160,619 usable spectra of 84,012 objects, most of which had been observed more than once. The effective temperature, surface gravity, metallicity, and radial velocity from 129,974 spectra for 70,895 objects are derived through the LAMOST Stellar Parameter Pipeline (LASP). The internal uncertainties were estimated to be 81 K, 0.15 dex, 0.09 dex, and 5 km s-1, respectively, when derived from a spectrum with a signal-to-noise ratio in the g band (S/Ng) of 10. These estimates are based on results for targets with multiple visits. The external accuracies were assessed by comparing the parameters of targets in common with the APOGEE and Gaia surveys, for which we generally found linear relationships. A final calibration is provided, combining external and internal uncertainties for giants and dwarfs, separately. We foresee that these spectroscopic data will be used widely in different research fields, especially in combination with K2 photometry.

Keywords: astronomy databases; fundamental parameters of stars; catalogs
Mechanochemical Synthesis of Amorphous Silicates with an Enstatite and Forsterite Composition

The presence of amorphous silicate particles in interstellar and circumstellar space has been suggested based on the observation of 9.7 and 18 μm emission bands. We have successfully synthesized amorphous silicate samples of an enstatite and forsterite composition by the mechanical milling of mixed powder consisting of SiO2-MgO and SiO2-Mg(OH)2 reagent-grade particles under different rotation frequencies and milling times. These two types of starting materials are prepared to study the effect of the OH bond on synthesis and crystallization. The amorphous samples were characterized by X-ray diffraction and infrared spectroscopy. Amorphous samples with enstatite composition are synthesized from both SiO2-MgO and SiO2-Mg(OH)2 at 300 rpm and for 300 hr. Amorphous samples with forsterite composition are synthesized from both SiO2-MgO and SiO2-Mg(OH)2. The samples from SiO2-Mg(OH)2 require 400 rpm and a long milling time of 1600 hr. After crystallization, amorphous samples with an enstatite composition synthesized from SiO2-Mg(OH)2 mainly transform into forsterite with small amounts of amorphous silica SiO2 and enstatite depending on the rotation frequencies and milling time, while those from SiO2-MgO become enstatite. The amorphous samples with a forsterite composition are crystallized to forsterite from both starting materials. The presence of H2O or OH bonds significantly affects the final products after the crystallization of amorphous silicates of enstatite composition.

Keywords: infrared observatories; infrared spectroscopy; dust continuum emission
Atomic-scale Element and Isotopic Investigation of 25Mg-rich Stardust from an H-burning Supernova

We have discovered a presolar olivine from ALH 77307 with the highest 25Mg isotopic composition measured in a silicate to date (δ 25Mg = 3025.1‰ ± 38.3‰). Its isotopic compositions challenge current stellar models, with modeling of magnesium, silicon, and oxygen showing a closest match to formation in a supernova (SN) where hydrogen ingestion occurred in the pre-SN phase. Presolar grains within primitive astromaterials retain records of processes and environmental changes throughout stellar evolution. However, accessing these records has proved challenging due to the average grain size (∼150 nm) of presolar silicates, their sensitivity to extraction agents, and instrumental restrictions, limiting the range of isotopic and chemical signatures which can be studied per grain volume. Here, we present the first known detailed geochemical study of a presolar silicate from a hydrogen-burning SN, studied in 3D without contributions to the analysis volume and at unprecedented spatial resolutions (<1 nm), essential for constraining physical and chemical processes occurring within this recently proposed stellar environment. From our results, we infer either (i) condensation within an environment depleted of heavy elements compatible with the olivine lattice under the pressure and temperature conditions during condensation, or (ii) during periods of limited mixing either near the end of the pre-SN phase or from a collapse so rapid localized pockets of different gas compositions formed.

Keywords: hydrogen burning; stellar nucleosynthesis; cosmochemistry; type ii supernovae; isotopic abundances; atomic spectroscopy; chondrites
Black Hole Formation Accompanied by the Supernova Explosion of a 40 M ⊙ Progenitor Star

We have simulated the collapse and evolution of the core of a solar-metallicity 40 M ⊙ star and find that it explodes vigorously by the neutrino mechanism, despite its very high "compactness." Within ~1.5 s of explosion, a black hole forms. The explosion is very asymmetrical and has a total explosion energy of ~1.6 × 1051 erg. At black hole formation, its baryon mass is ~2.434 M ⊙ and gravitational mass is 2.286 M ⊙. Seven seconds after black hole formation, an additional ~0.2 M ⊙ is accreted, leaving a black hole baryon mass of ~2.63 M ⊙. A disk forms around the proto-neutron star, from which a pair of neutrino-driven jets emanates. These jets accelerate some of the matter up to speeds of ~45,000 km s-1 and contain matter with entropies of ~50. The large spatial asymmetry in the explosion results in a residual black hole recoil speed of ~1000 km s-1. This novel black hole formation channel now joins the other black hole formation channel between ~12 and ~15 M ⊙ discovered previously and implies that the black hole/neutron star birth ratio for solar-metallicity stars could be ~20%. However, one channel leaves black holes in perhaps the ~5-15 M ⊙ range with low kick speeds, while the other leaves black holes in perhaps the ~2.5-3.0 M ⊙ mass range with high kick speeds. However, even ~8.8 s after core bounce the newly formed black hole is still accreting at a rate of ~2 × 10-2 M ⊙ s-1, and whether the black hole eventually achieves a significantly larger mass over time is yet to be determined.

Keywords: core-collapse supernovae
CME-CME Interactions as Sources of CME Geoeffectiveness: The Formation of the Complex Ejecta and Intense Geomagnetic Storm in 2017 Early September

Coronal mass ejections (CMEs) are the primary sources of intense disturbances at Earth, where their geoeffectiveness is largely determined by their dynamic pressure and internal magnetic field, which can be significantly altered during interactions with other CMEs in interplanetary space. We analyze three successive CMEs that erupted from the Sun during 2017 September 4-6, investigating the role of CME-CME interactions as a source of the associated intense geomagnetic storm (Dst_{min}=-142 nT on September 7). To quantify the impact of interactions on the (geo)effectiveness of individual CMEs, we perform global heliospheric simulations with the European Heliospheric Forecasting Information Asset (EUHFORIA) model, using observation-based initial parameters with the additional purpose of validating the predictive capabilities of the model for complex CME events. The simulations show that around 0.45 au, the shock driven by the September 6 CME started compressing a preceding magnetic ejecta formed by the merging of two CMEs launched on September 4, significantly amplifying its Bz until a maximum factor of 2.8 around 0.9 au. The following gradual conversion of magnetic energy into kinetic and thermal components reduced the Bz amplification until its almost complete disappearance around 1.8 au. We conclude that a key factor at the origin of the intense storm triggered by the 2017 September 4-6 CMEs was their arrival at Earth during the phase of maximum Bz amplification. Our analysis highlights how the amplification of the magnetic field of individual CMEs in spacetime due to interaction processes can be characterized by a growth, a maximum, and a decay phase, suggesting that the time interval between the CME eruptions and their relative speeds are critical factors in determining the resulting impact of complex CMEs at various heliocentric distances (helioeffectiveness).

Keywords: solar coronal mass ejections; solar-terrestrial interactions; magnetohydrodynamics; solar wind