adsabs/SciX_UAT_keywords huggingface dataset:
A Possible Kilonova Powered by Magnetic Wind from a Newborn Black Hole

The merger of binary neutron stars (NS-NS) as the progenitor of short gamma-ray bursts (GRBs) has been confirmed by the discovery of the association of the gravitational-wave (GW) event GW170817 with GRB 170817A. However, the merger product of binary NS remains an open question. An X-ray plateau followed by a steep decay ("internal plateau") has been found in some short GRBs, implying that a supramassive magnetar operates as the merger remnant and then collapses into a newborn black hole (BH) at the end of the plateau. X-ray bump or second plateau following the "internal plateau" are considered as the expected signature from the fallback accretion onto this newborn BH through the Blandford-Znajek mechanism (BZ). At the same time, a nearly isotropic wind driven by the Blandford-Payne mechanism (BP) from the newborn BH's disk can produce a bright kilonova. Therefore, the bright kilonova observation for a short GRB with "internal plateau" (and followed by X-ray bump or second plateau) provides further evidence for this scenario. In this paper, we find that GRB 160821B is a candidate of such a case, and the kilonova emission of GRB 160821B is possibly powered by the BP wind from a newborn BH. Future GW detection of GRB 160821B-like events may provide further support to this scenario, enable us to investigate the properties of the magnetar and the newborn BH, and constrain the equation of state of neutron stars.

Keywords: accretion; black hole physics; gamma-ray bursts; neutron stars
Exploring γ-Ray Flares in the Long-term Light Curves of CTA 102 at GeV Energies

Blazar CTA 102 experienced an intense multiwavelength activity phase from 2015 to 2018; in particular, an unprecedented outburst was observed from 2016 October to 2017 February. In this work, we extract a 7 day binned γ-ray light curve from 2008 August to 2018 March in the energy range 0.1-300 GeV and identify three main outbursts. We study in detail the short-timescale variability of these three outbursts via an exponential function with parameterized rise and decay timescales. The obtained shortest rise and decay timescales are 0.70 ± 0.05 hr and 0.79 ± 0.27 hr, respectively. Based on these variability timescales, the physical parameters of the flaring region (e.g., the minimum Doppler factor and the emission region size) are constrained. The short-timescale flares exhibit a symmetric temporal profile within the error bars, implying that the rise and decay timescales are dominated by the light-crossing timescale or by disturbances caused by dense plasma blobs passing through the standing shock front in the jet region. We also find that the best-fitting form of the γ-ray spectra during the flare period is a power law with an exponential cutoff. The derived jet parameters from the spectral behavior and the temporal characteristics of the individual flares suggest that the γ-ray emission region is located upstream of the radio core. The extreme γ-ray flare of CTA 102 is likely to have been caused by magnetic reconnection.

Keywords: blazars; gamma-rays; active galactic nuclei; relativistic jets
Magnetic Winding as an Indicator of Flare Activity in Solar Active Regions

Magnetic helicity is a measure of the entanglement of magnetic field lines used to characterize the complexity of solar active region (AR) magnetic fields. Previous attempts to use helicity-based indicators to predict solar eruptive/flaring events have shown promise but not been universally successful. Here we investigate the use of a quantity associated with the magnetic helicity, the magnetic winding, as a means to predict flaring activity. This quantity represents the fundamental entanglement of magnetic field lines and is independent of the magnetic field strength. We use vector magnetogram data derived from the Helioseismic Magnetic Imager (HMI) to calculate the evolution and distribution of the magnetic winding flux associated with five different ARs, three of them with little flaring activity/nonflaring (AR 11318, AR 12119, AR 12285) and two highly active with X-class flares (AR 11158, AR 12673). We decompose these quantities into "current-carrying" and "potential" parts. It is shown that the ARs that show flaring/eruptive activity have significant contributions to the winding input from the current-carrying part of the field. A significant and rapid input of current-carrying winding is found to be a precursor of flaring/eruptive activity, and, in conjunction with the helicity, sharp inputs of both quantities are found to precede individual flaring events by several hours. This suggests that the emergence/submergence of topologically complex current-carrying field is an important element for the ignition of AR flaring.

Keywords: geomagnetic fields; magnetic fields; emerging flux tubes; solar coronal mass ejections; solar flares
Coherent Events at Ion Scales in the Inner Heliosphere: Parker Solar Probe Observations during the First Encounter

The Parker Solar Probe mission has shown the ubiquitous presence of strong magnetic field deflections, namely switchbacks, during its first perihelion where it was embedded in a highly Alfvénic slow stream. Here, we study the turbulent magnetic fluctuations around ion scales in three intervals characterized by a different switchback activity, identified by the behavior of the magnetic field radial component, Br. Quiet (Br does not show significant fluctuations), weakly disturbed (Br has strong fluctuations but no reversals), and highly disturbed (Br has full reversals) periods also show different behavior for ion quantities. However, the spectral analysis shows that each stream is characterized by the typical Kolmogorov/Kraichnan power law in the inertial range, followed by a break around the characteristic ion scales. This frequency range is characterized by strong intermittent activity, with the presence of noncompressive coherent events, such as current sheets, vortex-like structures, and wave packets identified as ion cyclotron modes. Although all these events have been detected in the three periods, they have different influences in each of them. Current sheets are dominant in the highly disturbed period, wave packets are the most common in the quiet interval; while, in the weakly disturbed period, a mixture of vortices and wave packets is observed. This work provides an insight into the heating problem in collisionless plasmas, fitting in the context of the new solar missions, and, especially for Solar Orbiter, which will allow an accurate magnetic connectivity analysis to link the presence of different intermittent events to the source region.

Keywords: space plasmas; interplanetary turbulence; solar wind
Bridging the Planet Radius Valley: Stellar Clustering as a Key Driver for Turning Sub-Neptunes into Super-Earths

Extrasolar planets with sizes between that of the Earth and Neptune (Rp = 1-4 R⊕) have a bimodal radius distribution. This "planet radius valley" separates compact, rocky super-Earths (Rp = 1.0-1.8 R⊕) from larger sub-Neptunes (Rp = 1.8-3.5 R⊕) hosting a gaseous hydrogen-helium envelope around their rocky core. Various hypotheses for this radius valley have been put forward, which all rely on physics internal to the planetary system: photoevaporation by the host star, long-term mass loss driven by the cooling planetary core, or the transition between two fundamentally different planet formation modes as gas is lost from the protoplanetary disk. Here we report the discovery that the planet radius distribution exhibits a strong dependence on ambient stellar clustering, characterized by measuring the position-velocity phase space density with Gaia. When dividing the planet sample into "field" and "overdensity" subsamples, we find that planetary systems in the field exhibit a statistically significant (p = 5.5 × 10-3) dearth of planets below the radius valley compared to systems in phase space overdensities. This implies that the large-scale stellar environment of a planetary system is a key factor setting the planet radius distribution. We discuss how models for the radius valley might be revised following our findings and conclude that a multiscale, multiphysics scenario is needed, connecting planet formation and evolution, star and stellar cluster formation, and galaxy evolution.

Keywords: stellar dynamics; star formation; planet formation; exoplanet formation; exoplanet systems; solar-planetary interactions
Non-local Thermodynamic Equilibrium Radiative Transfer Simulations of Sub-Chandrasekhar-mass White Dwarf Detonations

Type Ia supernovae (SNe Ia) span a range of luminosities and timescales, from rapidly evolving subluminous to slowly evolving overluminous subtypes. Previous theoretical work has, for the most part, been unable to match the entire breadth of observed SNe Ia with one progenitor scenario. Here, for the first time, we apply non-local thermodynamic equilibrium radiative transfer calculations to a range of accurate explosion models of sub-Chandrasekhar-mass white dwarf detonations. The resulting photometry and spectra are in excellent agreement with the range of observed nonpeculiar SNe Ia through 15 days after the time of B-band maximum, yielding one of the first examples of a quantitative match to the entire Phillips relation. The intermediate-mass element velocities inferred from theoretical spectra at maximum light for the more massive white dwarf explosions are higher than those of bright observed SNe Ia, but these and other discrepancies likely stem from the one-dimensional nature of our explosion models and will be improved upon by future non-local thermodynamic equilibrium radiation transport calculations of multidimensional sub-Chandrasekhar-mass white dwarf detonations.

Keywords: type ia supernovae; supernovae; white dwarf stars; radiative transfer
An Improved Measurement of the Secondary Cosmic Microwave Background Anisotropies from the SPT-SZ + SPTpol Surveys

We report new measurements of millimeter-wave power spectra in the angular multipole range 2000 ≤ ℓ ≤ 11,000 (angular scales $5^{\prime} \gtrsim \theta \gtrsim 1^{\prime} $ ). By adding 95 and 150 GHz data from the low-noise 500 deg2 SPTpol survey to the SPT-SZ three-frequency 2540 deg2 survey, we substantially reduce the uncertainties in these bands. These power spectra include contributions from the primary cosmic microwave background, cosmic infrared background, radio galaxies, and thermal and kinematic Sunyaev-Zel'dovich (SZ) effects. The data favor a thermal SZ (tSZ) power at 143 GHz of ${D}_{3000}^{\mathrm{tSZ}}=3.42\pm 0.54\,\,\mu {{\rm{K}}}^{2}$ and a kinematic SZ (kSZ) power of ${D}_{3000}^{\mathrm{kSZ}}=3.0\pm 1.0\,\,\mu {{\rm{K}}}^{2}$ . This is the first measurement of kSZ power at ≥3σ. However, different assumptions about the CIB or SZ models can reduce the significance down to 2.4σ in the worst case. We study the implications of the measured kSZ power for the epoch of reionization under the Calabrese et al. model for the kSZ power spectrum and find the duration of reionization to be ${\rm{\Delta }}{z}_{\mathrm{re}}={1.1}_{-0.7}^{+1.6}$ ( ${\rm{\Delta }}{z}_{\mathrm{re}}\lt 4.1$ at 95% confidence), when combined with our previously published tSZ bispectrum measurement. The upper limit tightens to ${\rm{\Delta }}{z}_{\mathrm{re}}\lt 3.2$ if the assumed homogeneous kSZ power is increased by 25% (∼0.5 μK2) and relaxes to ${\rm{\Delta }}{z}_{\mathrm{re}}\lt 5.2$ if the homogeneous kSZ power is decreased by the same amount.

Keywords: sunyaev-zeldovich effect; cosmic microwave background radiation; reionization
Lopsided Satellite Distributions around Isolated Host Galaxies

We investigate the spatial distribution of the satellites of bright, isolated host galaxies. In agreement with previous studies, we find that, on average, the satellites of red hosts are found preferentially close to their hosts' major axes, while the satellites of blue hosts are distributed isotropically. We compute the pairwise clustering of the satellites and find a strong tendency for pairs of satellites to be located on the same side of their host, resulting in lopsided spatial distributions. The signal is most pronounced for the satellites of blue hosts, where the number of pairs on the same side of their host exceeds the number of pairs on opposite sides of their host by a factor of 1.8 ± 0.1. For the satellites of red hosts, the number of pairs on the same side of their host exceeds the number of pairs on opposite sides of their host by a factor of 1.08 ± 0.03. Satellites that are far from their hosts (rp ≳ 300 kpc) show a strong preference for being located on the same side of their hosts; satellites that are near to their hosts (rp ≲ 100 kpc) show a weak preference for being located on opposite sides of their hosts. While lopsided distributions have been found previously for the satellites of bright pairs of galaxies, ours is the first study to find lopsided distributions for the satellites of isolated bright galaxies.

Keywords: dwarf galaxies; galaxy dark matter halos
TOI-561 b: A Low-density Ultra-short-period "Rocky" Planet around a Metal-poor Star

TOI-561 is a galactic thick-disk star hosting an ultra-short-period (0.45-day-orbit) planet with a radius of 1.37 R ⊕, making it one of the most metal-poor ([Fe/H] = -0.41) and oldest (≈10 Gyr) sites where an Earth-sized planet has been found. We present new simultaneous radial velocity (RV) measurements from Gemini-N/MAROON-X and Keck/HIRES, which we combined with literature RVs to derive a mass of M b = 2.24 ± 0.20 M ⊕. We also used two new sectors of TESS photometry to improve the radius determination, finding R b = 1.37 ± 0.04 R ⊕ and confirming that TOI-561 b is one of the lowest-density super-Earths measured to date (ρ b = 4.8 ± 0.5 g cm-3). This density is consistent with an iron-poor rocky composition reflective of the host star's iron and rock-building element abundances; however, it is also consistent with a low-density planet with a volatile envelope. The equilibrium temperature of the planet (~2300 K) suggests that this envelope would likely be composed of high mean molecular weight species, such as water vapor, carbon dioxide, or silicate vapor, and is likely not primordial. We also demonstrate that the composition determination is sensitive to the choice of stellar parameters and that further measurements are needed to determine whether TOI-561 b is a bare rocky planet, a rocky planet with an optically thin atmosphere, or a rare example of a nonprimordial envelope on a planet with a radius smaller than 1.5 R ⊕.

Keywords: exoplanets; extrasolar rocky planets; super earths; exoplanet surface composition; exoplanet atmospheric composition
Hard X-Ray Emission in Centaurus A

We use 13 yr of Swift/BAT observations to probe the nature and origin of the hard X-ray (14-195 KeV) emission in Centaurus A. Since the beginning of the Swift operation in 2004, significant X-ray variability in the 14-195 KeV band has been detected, with mild changes in the source spectrum. Spectral variations became more eminent after 2013, following a softer-when-brighter trend. Using the power spectral density (PSD) method, we find that the observed hard X-ray photon flux variations are consistent with a red-noise process of slope, -1.3, with no evidence for a break in the PSD. We find a significant correlation between the hard X-ray and 230 GHz radio flux variations, with no time delay longer than 30 days. The temporal and spectral analysis confirms that the X-ray emission generated by the accretion in the ADAF model is sub-dominant as compared with the emission arsiing from that produced by the inner regions of the radio jet.

Keywords: x-ray active galactic nuclei; active galactic nuclei; radio active galactic nuclei
Implications for Extraterrestrial Hydrocarbon Chemistry: Analysis of Acetylene (C2H2) and D2-acetylene (C2D2) Ices Exposed to Ionizing Radiation via Ultraviolet-Visible Spectroscopy, Infrared Spectroscopy, and Reflectron Time-of-flight Mass Spectrometry

The processing of the simple hydrocarbon ice, acetylene (C2H2/C2D2), via energetic electrons, thus simulating the processes in the track of galactic cosmic-ray particles penetrating solid matter, was carried out in an ultrahigh vacuum surface apparatus. The chemical evolution of the ices was monitored online and in situ utilizing Fourier transform infrared spectroscopy (FTIR) and ultraviolet-visible spectroscopy and, during temperature programmed desorption, via a quadrupole mass spectrometer with an electron impact ionization source (EI-QMS) and a reflectron time-of-flight mass spectrometer utilizing single-photon photoionization (SPI-ReTOF-MS) along with resonance-enhanced multiphoton photoionization (REMPI-ReTOF-MS). The confirmation of previous in situ studies of ethylene ice irradiation using FTIR was accomplished with the detection of five products: ethane (C2H6/C2D6), ethylene (C2H4/C2D4), diacetylene (C4H2/C4D2), vinylacetylene (C4H4/C4D4), and benzene (C6H6/C6D6). Alternatively to previous gas-phase analytical studies, the sensitive SPI-ReTOF-MS analysis detected 10 hydrocarbon groups of distinct degrees of saturation: CnH2n+2 (n = 4, 6-16), CnH2n (n = 2, 3, 6, 8-16), CnH2n-2 (n = 3, 4, 6, 8, 10-15), CnH2n-4 (n = 4-8, 10-14), CnH2n-6 (n = 4-10, 12-16), CnH2n-8 (n = 6-10, 12, 14-17), CnH2n-10 (n = 6-12, 14-17), CnH2n-12 (n = 8-14), CnH2n-14 (n = 8-16), and CnH2n-16 (n = 10-16). From these detected groups the REMPI-ReTOF-MS method was able to assign the isomer-specific production of five aromatic hydrocarbons: benzene (C6H6), phenylacetylene (C8H6), styrene (C8H8), naphthalene (C10H8), and phenanthrene (C14H10).

Keywords: saturnian satellites; spectroscopy; mass spectrometry; polycyclic aromatic hydrocarbons; astrochemistry; interstellar dust
Benchmark n ℓ-resolved Cross Sections of Single and Double Charge Exchange Processes in 1.67-20 keV u-1 C4+ Collisions with He

State-resolved charge exchange (CX) cross sections are of the utmost importance for modeling related photon emissions existing in a broad range of astrophysical environments. With the cold-target recoil-ion momentum spectroscopy, we determined with high accuracy the state-resolved single and double CX cross sections at the quantum orbital angular momentum level for solar wind ion C4+ collisions with He in an energy range of 1.67-20 keV u-1, which allow one to benchmark the CX calculations in great detail, and to test the applicability of the analytical n- and ℓ-distribution models widely adopted by the astrophysical community. We found that the present measurements are well reproduced by the most recent state-of-the-art atomic-orbital close-coupling calculations. However, the CX models failed to give a consistent description on the measured ℓ distributions. The present work reveals that the velocity and collision partner species dependence effects as well as electronic correlations for multielectron processes should be included in an improved model. Alternatively, in future modeling to interpret high-resolution astrophysical observations the more elaborate quantum-mechanical calculations may be resorted to with confidence.

Keywords: atomic data benchmarking; charge exchange recombination; collision physics; atomic physics
The Observability of Plasmoid-powered γ-Ray Flares with the Fermi Large Area Telescope

The exact mechanism for the production of fast γ-ray variability in blazars remains debated. Magnetic reconnection, in which plasmoids filled with relativistic particles and magnetic fields are formed, is a viable candidate to explain the broadband electromagnetic spectrum and variability of these objects. Using state-of-the-art magnetic reconnection simulations, we generate realistic γ-ray light curves that would be observed with the Fermi Large Area Telescope. A comparison with observed γ-ray flares from flat spectrum radio quasars (FSRQs) reveals that magnetic reconnection events lead to comparable flux levels and variability patterns, in particular, when the reconnection layer is slightly misaligned with the line of sight. Emission from fast plasmoids moving close to the line of sight could explain the fast variability on the timescales of minutes for which evidence has been found in observations of FSRQs. Our results motivate improvements in existing radiative transfer simulations as well as dedicated searches for fast variability as evidence for magnetic reconnection events.

Keywords: blazars; relativistic jets; gamma-ray astronomy; non-thermal radiation sources; time domain astronomy
The Zwicky Transient Facility Catalog of Periodic Variable Stars

The number of known periodic variables has grown rapidly in recent years. Thanks to its large field of view and faint limiting magnitude, the Zwicky Transient Facility (ZTF) offers a unique opportunity to detect variable stars in the northern sky. Here, we exploit ZTF Data Release 2 (DR2) to search for and classify variables down to r ∼ 20.6 mag. We classify 781,602 periodic variables into 11 main types using an improved classification method. Comparison with previously published catalogs shows that 621,702 objects (79.5%) are newly discovered or newly classified, including ∼700 Cepheids, ∼5000 RR Lyrae stars, ∼15,000 δ Scuti variables, ∼350,000 eclipsing binaries, ∼100,000 long-period variables, and about 150,000 rotational variables. The typical misclassification rate and period accuracy are on the order of 2% and 99%, respectively. 74% of our variables are located at Galactic latitudes, $| b| \lt 10^\circ $ . This large sample of Cepheids, RR Lyrae, δ Scuti stars, and contact (EW-type) eclipsing binaries is helpful to investigate the Galaxy's disk structure and evolution with an improved completeness, areal coverage, and age resolution. Specifically, the northern warp and the disk's edge at distances of 15-20 kpc are significantly better covered than previously. Among rotational variables, RS Canum Venaticorum and BY Draconis-type variables can be separated easily. Our knowledge of stellar chromospheric activity would benefit greatly from a statistical analysis of these types of variables.

Keywords: periodic variable stars; pulsating variable stars; cepheid variable stars; rr lyrae variable stars; delta scuti variable stars; long period variable stars; mira variable stars; eclipsing binary stars; galaxy structure; distance indicators
External Inverse-Compton Emission from Low-luminosity Gamma-Ray Bursts: Application to GRB 190829A

The detection of TeV gamma-ray bursts (GRBs) brought new opportunities for studying the physics of particle acceleration at relativistic shocks. The High Energy Stereoscopic System (H.E.S.S.) telescopes recently observed very-high-energy (VHE) emission from a nearby low-luminosity GRB, GRB 190829A. Follow-up observations with, e.g., Swift-XRT, revealed unusual flare activities at ~103 s, which can be caused by a long-lasting central engine. We show that the VHE emission during the H.E.S.S. observation time is naturally produced in the external inverse-Compton (EIC) scenario, where seed photons supplied by the flares or other late-time dissipations are upscattered to VHE energies by the nonthermal electrons accelerated at the external forward shock. Our calculations show that the EIC flare nearly coincides with the late-prompt flare, but extends ~3-4 times longer than the duration of the late-prompt flare. The preferred kinetic energy and initial Lorentz factor used in our model are ~1052 erg and ~20, respectively. Understanding the mechanisms of the VHE emission from low-luminosity GRBs will help us constrain the properties of the outflow and the central engine activities, as well as the particle acceleration mechanism.

Keywords: stellar jets; gamma-ray bursters; x-ray sources; radio sources; particle astrophysics