Sazuna/UAT_keywords huggingface dataset:
The TeV Cosmic-Ray Bump: A Message from the Epsilon Indi or Epsilon Eridani Star?. A recently observed bump in the cosmic-ray (CR) spectrum from 0.3 to 30 TV is likely caused by a stellar bow shock that reaccelerates preexisting CRs, which further propagate to the Sun along the magnetic field lines. Along their way, these particles generate an Iroshnikov-Kraichnan (I-K) turbulence that controls their propagation and sustains the bump. Ad hoc fitting of the bump shape requires six adjustable parameters. Our model requires none, merely depending on three physical unknowns that we constrain using the fit. These are the shock Mach number, M, its size, l⊥, and the distance to it, ζobs. Altogether, they define the bump rigidity R0. With M ≍ 1.5-1.6 and R0 ≍ 4.4 TV, the model fits the data with ≍0.08% accuracy. The fit critically requires the I-K spectrum predicted by the model and rules out the alternatives. These attributes of the fit make an accidental agreement highly unlikely. In turn, the R0 and M derived from the fit impose the distance-size relation on the shock: ζobs(pc) ∼ ${10}^{2}\sqrt{{l}_{\perp }(\mathrm{pc})}$ . For sufficiently large bow shocks, l⊥ = 10-3-10-2 pc, we find the distance of ζobs = 3-10 pc. Three promising stars in this range are the Scholz's Star at 6.8 pc, Epsilon Indi at 3.6 pc, and Epsilon Eridani at 3.2 pc. Based on their current positions and velocities, we propose that Epsilon Indi and Epsilon Eridani can produce the observed spectral bump. Moreover, Epsilon Eridani's position is only ∼6°7 off of the magnetic field direction in the solar neighborhood, which also changes the CR arrival direction distribution. Given the proximity of these stars, the bump appearance may change in a relatively short time.

Keywords: Secondary cosmic rays, Stellar bow shocks, Galactic cosmic rays, Interstellar magnetic fields, Interstellar scattering
Coherent Curvature Radio Emission and Polarization from Pulsars. We have developed a collective plasma radio emission model for the radio pulsars based on the implications of the tangent model. The secondary pair (electron-positron) plasma particles get arranged into a phased array like an antenna due to plasma waves and radiate in phase. We have reproduced the polarization profiles by considering different viewing conditions in the pulsars having an oblique dipolar magnetic field. We find that when there is a resonance between the radio and the plasma waves, the flux of emitted radio waves gets enhanced. We numerically estimated the collective radio emission due to relativistic plasma. The model predicts the correlation between the sign reversal circular polarization and the polarization angle swing and the brightness temperature in the range ∼1031-1033 K.

Keywords: Radio pulsars
An HST Survey of Protostellar Outflow Cavities: Does Feedback Clear Envelopes?. We study protostellar envelope and outflow evolution using Hubble Space Telescope NICMOS or WFC3 images of 304 protostars in the Orion molecular clouds. These near-IR images resolve structures in the envelopes delineated by the scattered light of the central protostars with 80 au resolution, and they complement the 1.2 μm to 870 μm spectral energy distributions (SEDs) obtained with the Herschel Orion Protostar Survey program. Based on their 1.60 μm morphologies, we classify the protostars into five categories: nondetections, point sources without nebulosity, bipolar cavity sources, unipolar cavity sources, and irregulars. We find point sources without associated nebulosity are the most numerous, and show through monochromatic Monte Carlo radiative transfer modeling that this morphology occurs when protostars are observed at low inclinations or have low envelope densities. We also find that the morphology is correlated with the SED-determined evolutionary class, with Class 0 protostars more likely to be nondetections, Class I protostars to show cavities, and flat-spectrum protostars to be point sources. Using an edge detection algorithm to trace the projected edges of the cavities, we fit power laws to the resulting cavity shapes, thereby measuring the cavity half-opening angles and power-law exponents. We find no evidence for the growth of outflow cavities as protostars evolve through the Class I protostar phase, in contradiction with previous studies of smaller samples. We conclude that the decline of mass infall with time cannot be explained by the progressive clearing of envelopes by growing outflow cavities. Furthermore, the low star formation efficiency inferred for molecular cores cannot be explained by envelope clearing alone.

Keywords: Early stellar evolution, Stellar feedback, Stellar jets, Molecular clouds, Protostars, Near infrared astronomy
Variability of Late-time Radio Emission in the Superluminous Supernova PTF10hgi. We report the time variability of the late-time radio emission in a Type I superluminous supernova (SLSN), PTF10hgi, at z = 0.0987. The Karl G. Jansky Very Large Array 3 GHz observations at 8.6 and 10 yr after the explosion both detected radio emission with a ∼40% decrease in flux density in the second epoch. This is the first report of a significant variability of the late-time radio light curve in an SLSN. Through combination with previous measurements in two other epochs, we constrained both the rise and decay phases of the radio light curve over three years, peaking at approximately 8-9 yr after the explosion with a peak luminosity of L3 GHz = 2 × 1021 W Hz-1. Possible scenarios for the origin of the variability are an active galactic nucleus (AGN) in the host galaxy, an afterglow caused by the interaction between an off-axis jet and circumstellar medium, and a wind nebula powered by a newly born magnetar. Comparisons with models show that the radio light curve can be reproduced by both the afterglow model and magnetar wind nebula model. Considering the flat radio spectrum at 1-15 GHz and an upper limit at 0.6 GHz obtained in previous studies, plausible scenarios are a low-luminosity flat-spectrum AGN or a magnetar wind nebula with a shallow injection spectral index.

Keywords: Very Large Array, Extragalactic radio sources, Radio continuum emission, Radio astronomy, Supernovae, Radio transient sources
The Solar-cycle Variations of the Anisotropy of Taylor Scale and Correlation Scale in the Solar Wind Turbulence. The field-aligned anisotropy of the solar wind turbulence, which is quantified by the ratio of the parallel to the perpendicular correlation (and Taylor) length scales, is determined by simultaneous two-point correlation measurements during the time period 2001-2017. Our results show that the correlation scale along the magnetic field is the largest, and the correlation scale in the field-perpendicular directions is the smallest, at both solar maximum and solar minimum. However, the Taylor scale reveals inconsistent results for different stages of the solar cycles. During the years 2001-2004, the Taylor scales are slightly larger in the field-parallel directions, while during the years 2004-2017, the Taylor scales are larger in the field-perpendicular directions. The correlation coefficient between the sunspot number and the anisotropy ratio is employed to describe the effects of solar activity on the anisotropy of solar wind turbulence. The results show that the correlation coefficient regarding the Taylor scale anisotropy (0.65) is larger than that regarding the correlation scale anisotropy (0.43), which indicates that the Taylor scale anisotropy is more sensitive to the solar activity. The Taylor scale and the correlation scale are used to calculate the effective magnetic Reynolds number, which is found to be systematically larger in the field-parallel directions than in the field-perpendicular directions. The correlation coefficient between the sunspot number and the magnetic Reynolds number anisotropy ratio is -0.75. Our results will be meaningful for understanding the solar wind turbulence anisotropy and its long-term variability in the context of solar activity.

Keywords: Solar cycle, Space plasmas, Magnetohydrodynamics, Interplanetary turbulence, Solar wind, Sunspots, Solar activity
LOFAR Detection of 110-188 MHz Emission and Frequency-dependent Activity from FRB 20180916B. The object FRB 20180916B is a well-studied repeating fast radio burst source. Its proximity (∼150 Mpc), along with detailed studies of the bursts, has revealed many clues about its nature, including a 16.3 day periodicity in its activity. Here we report on the detection of 18 bursts using LOFAR at 110-188 MHz, by far the lowest-frequency detections of any FRB to date. Some bursts are seen down to the lowest observed frequency of 110 MHz, suggesting that their spectra extend even lower. These observations provide an order-of-magnitude stronger constraint on the optical depth due to free-free absorption in the source's local environment. The absence of circular polarization and nearly flat polarization angle curves are consistent with burst properties seen at 300-1700 MHz. Compared with higher frequencies, the larger burst widths (∼40-160 ms at 150 MHz) and lower linear polarization fractions are likely due to scattering. We find ∼2-3 rad m-2 variations in the Faraday rotation measure that may be correlated with the activity cycle of the source. We compare the LOFAR burst arrival times to those of 38 previously published and 22 newly detected bursts from the uGMRT (200-450 MHz) and CHIME/FRB (400-800 MHz). Simultaneous observations show five CHIME/FRB bursts when no emission is detected by LOFAR. We find that the burst activity is systematically delayed toward lower frequencies by about 3 days from 600 to 150 MHz. We discuss these results in the context of a model in which FRB 20180916B is an interacting binary system featuring a neutron star and high-mass stellar companion.

Keywords: Neutron stars, High energy astrophysics, Radio transient sources
Identifying the Coronal Source Regions of Solar Wind Streams from Total Solar Eclipse Observations and in situ Measurements Extending over a Solar Cycle. This letter capitalizes on a unique set of total solar eclipse observations acquired between 2006 and 2020 in white light, Fe XI 789.2 nm (Tfexi = 1.2 ± 0.1 MK), and Fe XIV 530.3 nm (Tfexiv = 1.8 ± 0.1 MK) emission complemented by in situ Fe charge state and proton speed measurements from Advanced Composition Explorer/SWEPAM-SWICS to identify the source regions of different solar wind streams. The eclipse observations reveal the ubiquity of open structures invariably associated with Fe XI emission from Fe10+ and hence a constant electron temperature, Tc = Tfexi, in the expanding corona. The in situ Fe charge states are found to cluster around Fe10+, independently of the 300-700 km s-1 stream speeds, referred to as the continual solar wind. Thus, Fe10+ yields the fiducial link between the continual solar wind and its Tfexi sources at the Sun. While the spatial distribution of Fe XIV emission from Fe13+ associated with streamers changes throughout the solar cycle, the sporadic appearance of charge states &gt;Fe11+ in situ exhibits no cycle dependence regardless of speed. These latter streams are conjectured to be released from hot coronal plasmas at temperatures ≥Tfexiv within the bulge of streamers and from active regions, driven by the dynamic behavior of prominences magnetically linked to them. The discovery of continual streams of slow, intermediate, and fast solar wind characterized by the same Tfexi in the expanding corona places new constraints on the physical processes shaping the solar wind.

Keywords: Solar cycle, Total eclipses, Solar prominences, Solar wind, Solar coronal heating, Solar magnetic fields, Solar coronal mass ejections, Solar corona, Solar coronal streamers
<SUP>22</SUP>Ne Phase Separation as a Solution to the Ultramassive White Dwarf Cooling Anomaly. The precise astrometric measurements of the Gaia Data Release 2 have opened the door to detailed tests of the predictions of white dwarf cooling models. Significant discrepancies between theory and observations have been identified, the most striking affecting ultramassive white dwarfs. Cheng et al. found that a small fraction of white dwarfs on the so-called Q branch must experience an extra cooling delay of ∼8 Gyr not predicted by current models. 22Ne phase separation in a crystallizing C/O white dwarf can lead to a distillation process that efficiently transports 22Ne toward its center, thereby releasing a considerable amount of gravitational energy. Using state-of-the-art Monte Carlo simulations, we show that this mechanism can largely resolve the ultramassive cooling anomaly if the delayed population consists of white dwarfs with moderately above-average 22Ne abundances. We also argue that 22Ne phase separation can account for the smaller cooling delay currently missing for models of white dwarfs with more standard compositions.

Keywords: Stellar interiors, Degenerate matter, Plasma physics, White dwarf stars, Cosmochronology, Stellar evolution
Reactivation of the High Magnetic Field Pulsar PSR J1846-0258 with Magnetar-like Bursts. We report on the 2020 reactivation of the energetic high magnetic field pulsar PSR J1846-0258 and its pulsar wind nebula (PWN) after 14 yr of quiescence with new Chandra and Green Bank Telescope observations. The emission of short-duration bursts from J1846-0258 was accompanied by an enhancement of X-ray persistent flux and significant spectral softening, similar to those observed during its first bursting episode in 2006. The 2020 pulsar spectrum is described by a power-law model with a photon index Γ = 1.7 ± 0.3 in comparison to a Γ = 1.2 ± 0.1 before outburst, and shows evidence of an emerging thermal component with blackbody temperature kT = 0.7 ± 0.1 keV. The 0.5-10 keV unabsorbed flux increased from ${5.4}_{-0.5}^{+0.4}$ × 10-12 erg cm-2 s-1 in quiescence to ${1.3}_{-0.2}^{+0.3}$ × 10-11 erg cm-2 s-1 following the outburst. We did not detect any radio pulsations from the pulsar at 2 GHz, and we place an upper limit of 7.1 μJy and 55 mJy for the coherent pulsed emission and single pulses, respectively. The 2020 PWN spectrum, characterized by a photon index of 1.92 ± 0.04 and X-ray luminosity of (1.2 ± 0.1) × 1035 erg s-1 at a distance of 5.8 kpc, is consistent with those observed before the outburst. An analysis of regions closer to the pulsar shows small-scale time variabilities and brightness changes over the 20 yr period from 2000 to 2020, while the photon indices did not change. We conclude that the outburst in PSR J1846-0258 is a combination of crustal and magnetospheric effects, with no significant burst-induced variability in its PWN based on the current observations.

Keywords: Magnetars, Rotation powered pulsars
Subproton-scale Intermittency in Near-Sun Solar Wind Turbulence Observed by the Parker Solar Probe. High time-resolution solar wind magnetic field data are employed to study statistics describing intermittency near the first perihelion (∼35.6 R⊙) of the Parker Solar Probe mission. A merged data set employing two instruments on the FIELDS suite enables broadband estimation of higher-order moments of magnetic field increments, with five orders established with reliable accuracy. The duration, cadence, and low noise level of the data permit evaluation of scale dependence of the observed intermittency from the inertial range to deep subproton scales. The results support multifractal scaling in the inertial range, and monofractal but non-Gaussian scaling in the subproton range, thus clarifying suggestions based on data near Earth that had remained ambiguous due to possible interference of the terrestrial foreshock. The physics of the transition to monofractality remains unclear but we suggest that it is due to a scale-invariant population of current sheets between ion and electron inertial scales; the previous suggestion of incoherent kinetic-scale wave activity is disfavored as it presumably leads re-Gaussianization that is not observed.

Keywords: Interplanetary turbulence, Space plasmas, Magnetohydrodynamics, Solar wind
Exploring the Nature of EUV Waves in a Radiative Magnetohydrodynamic Simulation. Coronal extreme-ultraviolet (EUV) waves are large-scale disturbances propagating in the corona, whose physical nature and origin have been discussed for decades. We report the first three-dimensional (3D) radiative magnetohydrodynamic simulation of a coronal EUV wave and the accompanying quasi-periodic wave trains. The numerical experiment is conducted with the MURaM code and simulates the formation of solar active regions through magnetic flux emergence from the convection zone to the corona. The coronal EUV wave is driven by the eruption of a magnetic flux rope that also gives rise to a C-class flare. It propagates in a semicircular shape with an initial speed ranging from about 550 to 700 km s-1, which corresponds to an average Mach number (relative to fast magnetoacoustic waves) of about 1.2. Furthermore, the abrupt increase of the plasma density, pressure, and tangential magnetic field at the wave front confirms fast-mode shock nature of the coronal EUV wave. Quasi-periodic wave trains with a period of about 30 s are found as multiple secondary wavefronts propagating behind the leading wave front and ahead of the erupting magnetic flux rope. We also note that the true wave front in the 3D space can be very inhomogeneous; however, the line-of-sight integration of EUV emission significantly smoothes the sharp structures in 3D and leads to a more diffuse wave front.

Keywords: Radiative magnetohydrodynamics, Solar extreme ultraviolet emission, Solar coronal waves, Solar corona, Solar activity
Reconstructing 3D Magnetic Topology of On-disk Prominence Bubbles from Stereoscopic Observations. Bubbles, the semi-circular voids below quiescent prominences (filaments), have been extensively investigated in the past decade. However, to this point the magnetic nature of bubbles has been unverifiable due to the lack of on-disk photospheric magnetic field observations. Here for the first time, we find and investigate an on-disk prominence bubble around a filament barb on 2019 March 18 based on stereoscopic observations from the New Vacuum Solar Telescope (NVST), Solar Dynamics Observatory (SDO), and Spacecraft-A of the Solar TErrestrial RElations Observatory (STEREO-A). In high-resolution NVST Hα images, this bubble has a sharp arch-like boundary and a projected width of ∼26 Mm. Combining SDO and STEREO-A images, we further reconstruct 3D structure of the bubble boundary, whose maximum height is ∼15.6 Mm. The squashing factor Q map deduced from extrapolated 3D magnetic fields around the bubble depicts a distinct arch-shaped interface with a height of ∼11 Mm, which agrees well with the reconstructed 3D structure of the observed bubble boundary. Under the interface lies a set of magnetic loops, which is rooted on a surrounding photospheric magnetic patch. To be more persuasive, another on-disk bubble on 2019 June 10 is presented as a supplement. According to these results obtained from on-disk bubble observations, we suggest that the bubble boundary corresponds to the interface between the prominence dips (barb) and the underlying magnetic loops rooted nearby. Therefore, it is reasonable to speculate that the bubble can form around a filament barb below which there is a photospheric magnetic patch.

Keywords: Solar atmosphere, Solar filaments, Solar magnetic fields, Solar prominences
Universal Peaks Ratio in the Spectral Energy Density of Double Hump Blazars, Gamma-Ray Bursts, and Microquasars?. The peak frequencies of the two broad humps evident in the spectral energy density of blazars (SED) are time dependent and vary a lot between different blazars. However, their ratio in most blazars appears to be almost universal and equal to mec2/4(1 + z)ɛp to a good approximation, where me is the electron mass, ɛp is the peak energy of the cosmic microwave background radiation, and z is the redshift of the blazar. We discuss a possible origin of such a universal ratio in blazars: gamma-ray bursts (GRBs). We point out a possible connection between the knee in the energy spectrum of cosmic-ray electrons and the maximal peak energies of the two broad humps in the SED of high energy peaked blazars and GRBs. We also point out that a universal peak ratio in double hump blazars that belong to different classes in the BL Lac sequence may simply reflect different viewing angles of otherwise similar blazars.

Keywords: Blazars
The Inner Accretion Flow in the Resurgent Seyfert-1.2 AGN Mrk 817. Accretion disks and coronae around massive black holes have been studied extensively, and they are known to be coupled. Over a period of 30 yr, however, the X-ray (coronal) flux of Mrk 817 increased by a factor of 40 while its UV (disk) flux remained relatively steady. Recent high-cadence monitoring finds that the X-ray and UV continua in Mrk 817 are also decoupled on timescales of weeks and months. These findings could require mechanical beaming of the innermost accretion flow, and/or an absorber that shields the disk and/or broad line region (BLR) from the X-ray corona. Herein, we report on a 135 ks observation of Mrk 817 obtained with NuSTAR, complemented by simultaneous X-ray coverage via the Neil Gehrels Swift Observatory. The X-ray data strongly prefer a standard relativistic disk reflection model over plausible alternatives. Comparable fits with related models constrain the spin to lie in the range of 0.5 ≤ a ≤ 1, and the viewing angle to lie between 10° ≤ θ ≤ 22° (including 1σ statistical errors and small systematic errors related to differences between the models). The spectra also reveal strong evidence of moderately ionized absorption, similar to but likely less extreme than obscuring events in NGC 5548 and NGC 3783. Archival Swift data suggest that the absorption may be variable. Particularly if the column density of this absorber is higher along the plane of the disk, it may intermittently mask or prevent coupling between the central engine, disk, and BLR in Mrk 817.

Keywords: Active galaxies
Tiny-scale Structure Discovered toward PSR B1557-50. Optical depth variations in the Galactic neutral interstellar medium (ISM) with spatial scales from hundreds to thousands of astronomical units have been observed through H I absorption against pulsars and continuum sources, while extremely small structures with spatial scales of tens of astronomical units remain largely unexplored. The nature and formation of such tiny-scale atomic structures (TSAS) need to be better understood. We report a tentative detection of TSAS with a signal-to-noise ratio of 3.2 toward PSR B1557-50 in the second epoch of two Parkes sessions just 0.36 yr apart, which are the closest-spaced spectral observations toward this pulsar. One absorption component showing marginal variations has been identified. Based on the pulsar's proper motion of 14 mas yr-1 and the component's kinematic distance of 3.3 kpc, the corresponding characteristic spatial scale is 17 au, which is among the smallest sizes of known TSAS. Assuming a similar line-of-sight (LOS) depth, the tentative TSAS cloud detected here is overdense and overpressured relative to the cold neutral medium (CNM), and can radiatively cool fast enough to be in thermal equilibrium with the ambient environment. We find that turbulence is not sufficient to confine the overpressured TSAS. We explore the LOS elongation that would be required for the tentative TSAS to be at the canonical CNM pressure, and find that it is ∼5000—much larger than filaments observed in the ISM. We see some evidence of line width and temperature variations in the CNM components observed at the two epochs, as predicted by models of TSAS-like cloud formation colliding warm neutral medium flows.

Keywords: Distance measure, Pulsars, H I line emission, Interstellar absorption, Interstellar clouds, Cold neutral medium, Interstellar medium, Warm neutral medium, Radio pulsars