adsabs/SciX_UAT_keywords huggingface dataset:
Polarized Anisotropic Synchrotron Emission and Absorption and Its Application to Black Hole Imaging

Low-collisionality plasma in a magnetic field generically develops anisotropy in its distribution function with respect to the magnetic field direction. Motivated by the application to radiation from accretion flows and jets, we explore the effect of temperature anisotropy on synchrotron emission. We derive analytically and provide numerical fits for the polarized synchrotron emission and absorption coefficients for a relativistic bi-Maxwellian plasma (we do not consider Faraday conversion/rotation). Temperature anisotropy can significantly change how the synchrotron emission and absorption coefficients depend on observing angle with respect to the magnetic field. The emitted linear polarization fraction does not depend strongly on anisotropy, while the emitted circular polarization does. We apply our results to black hole imaging of Sgr A* and M87* by ray tracing a GRMHD simulation and assuming that the plasma temperature anisotropy is set by the thresholds of kinetic-scale anisotropy-driven instabilities. We find that the azimuthal asymmetry of the 230 GHz images can change by up to a factor of 3, accentuating (T ⊥ > T ∥) or counteracting (T ⊥ < T ∥) the image asymmetry produced by Doppler beaming. This can change the physical inferences from observations relative to models with an isotropic distribution function, e.g., by allowing for larger inclination between the line of sight and spin direction in Sgr A*. The observed image diameter and the size of the black hole shadow can also vary significantly due to plasma temperature anisotropy. We describe how the anisotropy of the plasma can affect future multifrequency and photon ring observations. We also calculate kinetic anisotropy-driven instabilities (mirror, whistler, and firehose) for relativistically hot plasmas.

Keywords: accretion; astrophysical black holes; supermassive black holes; black holes; low-luminosity active galactic nuclei; plasma physics; plasma astrophysics; gravitational lensing; radiative processes; radiative transfer
Surveying the Giant H II Regions of the Milky Way with SOFIA. IV. Sgr D, W42, and a Reassessment of the Giant H II Region Census

This is the fourth paper exploring the infrared properties of giant H II regions with the FORCAST instrument on the Stratospheric Observatory For Infrared Astronomy (SOFIA). Our survey utilizes the census of 56 Milky Way giant H II regions identified by Conti & Crowther, and in this paper we present the 20 and 37 μm imaging data we obtained from SOFIA for sources Sgr D and W42. Based upon the SOFIA data and other multiwavelength data, we derive and discuss the detailed physical properties of the individual compact sources and subregions as well as the large-scale properties of Sgr D and W42. However, improved measurements have revealed much closer distances to both regions than previously believed, and consequently, both sources are not powerful enough to be considered giant H II regions any longer. Motivated by this, we revisit the census of giant H II regions, performing a search of the last two decades of literature to update each source with the most recent and/or most accurate distance measurements. Based on these new distance estimates, we determine that 14 sources in total (25%) are at sufficiently reliable and closer distances that they are not powerful enough to be considered giant H II regions. We briefly discuss the observational and physical characteristics specific to Sgr D and W42 and show that they have properties distinct from the giant H II regions previously studied as a part of this survey.

Keywords: h ii regions; infrared sources; star forming regions; young star clusters
JWST/NIRCam Imaging of Young Stellar Objects. II. Deep Constraints on Giant Planets and a Planet Candidate Outside of the Spiral Disk Around SAO 206462

We present JWST/NIRCam F187N, F200W, F405N, and F410M direct imaging data of the disk surrounding SAO 206462. Previous images show a very structured disk, with a pair of spiral arms thought to be launched by one or more external perturbers. The spiral features are visible in three of the four filters, with the nondetection in F410M due to the large detector saturation radius. We detect with a signal-to-noise ratio of 4.4 a companion candidate that, if on a coplanar circular orbit, would orbit SAO 206462 at a separation of ∼300 au, 2.25σ away from the predicted separation for the driver of the eastern spiral. No other companion candidates were detected. At the location predicted by simulations of both spirals generated by a single massive companion, the NIRCam data exclude objects more massive than ∼2.2 M J assuming the BEX evolutionary models. In terms of temperatures, the data are sensitive to objects with T eff ∼ 650–850 K, when assuming planets emit like blackbodies (R p between 1 and 3R J). From these results, we conclude that if the spirals are driven by gas giants, these must be either cold or embedded in circumplanetary material. In addition, the NIRCam data provide tight constraints on ongoing accretion processes. In the low extinction scenario we are sensitive to mass accretion rates of the order $\dot{M}\sim {10}^{-9}{M}_{{\rm{J}}}$ yr‑1. Thanks to the longer wavelengths used to search for emission lines, we reach unprecedented sensitivities to processes with $\dot{M}\sim {10}^{-7}{M}_{{\rm{J}}}$ yr‑1 even toward highly extincted environments (A V ≈ 50 mag).

Keywords: exoplanet formation; protoplanetary disks; direct imaging
Enhanced Magnetic Field Amplification by Ion-beam Weibel Instability in Weakly Magnetized Astrophysical Shocks

We examine the evolution of ion-beam Weibel instability at strong collisionless shocks in weakly magnetized media. We find that a finite background magnetic field substantially affects both the linear and nonlinear phases of the instability, depending on whether the background electrons behave magnetized or not. Particle-in-cell simulations for magnetized electrons identify a dynamo-like mechanism of magnetic field amplification, which eventually leads to spontaneous magnetic reconnection. We conclude that this scenario is applicable to typical young supernova remnant shocks.

Keywords: shocks; supernova remnants; plasma physics; cosmic ray sources
Evidence Suggesting That 'Oumuamua Is the 30 Myr Old Product of a Molecular Cloud

The appearance of interstellar objects (ISOs) in the solar system-and specifically the arrival of 1I/'Oumuamua-points to a significant number density of free-floating bodies in the solar neighborhood. We review the details of 'Oumuamua's pre-encounter Galactic orbit, which intersected the solar system at very nearly its maximum vertical and radial excursion relative to the Galactic plane. These kinematic features are strongly emblematic of nearby young stellar associations. We obtain an a priori order-of-magnitude age estimate for 'Oumuamua by comparing its orbit to the orbits of 50,899 F-type stars drawn from Gaia DR2; a diffusion model then suggests a ~35 Myr dynamical age. We compare 'Oumuamua's orbit with the trajectories of individual nearby moving groups, confirming that its motion is fully consistent with membership in the Carina (CAR) moving group with an age of ~30 Myr. We conduct Monte Carlo simulations that trace the orbits of test particles ejected from the stars in the CAR association. The simulations indicate that in order to uniformly populate the ~106 pc3 volume occupied by CAR members with the inferred number density, n = 0.2 au-3, of ISOs implied by Pan-STARRS's detection of 'Oumuamua, the required ejection mass is M ~ 500 MJup per known star within the CAR association. This suggests that the Pan-STARRS observation is in significant tension with scenarios that posit 'Oumuamua's formation and ejection from a protostellar disk.

Keywords: interstellar objects; molecular clouds; orbits; comets; asteroids; asteroid dynamics
Solar Observations by Angelo Secchi. I. Digitization of Original Documents and Analysis of Group Numbers over the Period of 1853-1878

Angelo Secchi, an Italian Jesuit and prominent scientist of the 19th century, and one of the founders of modern astrophysics, observed the Sun regularly at the Collegio Romano in Rome, Italy, for more than 25 yr. Results from his observations are reported in articles published in the scientific journals of the time, as well as in drawings and personal notebooks that are stored in the historical archive of the Istituto Nazionale di Astrofisica Osservatorio Astronomico di Roma. The latter material, which reports solar observations performed from 1853-1878, includes original documents from Secchi and from a few of his close collaborators. The above unique material has recently been digitized for preservation purposes and for allowing the scientific exploitation of data not easily accessible so far. A total of more than 5400 digital images have been produced. Here we present the archival material and the new digital data derived from it. We also present results obtained from our primary analysis of the new digital data. In particular, we produced new measurements of the group number from 1853-1878, which will be available for future recalibration of the group number series.

Keywords: sunspot groups
Source-count Distribution of Gamma-Ray Blazars

With 10 years of operation and an exceptional data set, the Fermi-Large Area Telescope allows us to unveil the detailed composition of the extragalactic γ-ray sky above 100 MeV. In this paper, we derive the intrinsic source-count distribution (logN-logS) of extragalactic sources (I.e., blazars) at $| b| \gt 20^\circ $ via the efficiency correction method. With this approach, we are able to measure the distribution down to a photon flux of $\sim {10}^{-10}\,\mathrm{ph}\,{\mathrm{cm}}^{-2}\,{{\rm{s}}}^{-1}$ and to an energy flux of ∼10-12 $\,\mathrm{erg}\,{\mathrm{cm}}^{-2}\,{{\rm{s}}}^{-1}$ . In both cases, the logN-logS becomes flatter at low fluxes. Moreover, we show that this logN-logS is representative of the blazar population (assuming the majority of unassociated sources are blazars) and allows us to constrain its evolution quite effectively. Among recently proposed evolutionary models, we find that the Pure Density Evolution model best describes the evolutionary properties of the blazar population and that their integrated emission accounts for $\sim {50}_{-5}^{+10} \% $ of the total extragalactic γ-ray background.

Keywords: blazars; cosmological evolution; active galactic nuclei; active galaxies; gamma-ray sources
Light Curve Analysis of Nine Algol (EA) Eclipsing Binaries Discovered During the Dauban Survey

The Dauban Survey was a project focused on photometric observations in the Milky Way. This project was a collaboration between Francois Kugel and Jerome Caron utilizing the Observatoire de Chante-Perdix Dauban (MPC A77) in France between 2012 September 17 and 2014 July 20. Over this period, a total of 7826 known variable stars and 5521 new, unknown variable stars were detected. In particular, 497 new variables were published in the AAVSO VSX database. These included Mira Ceti, cataclysmic variables, RR Lyrae, cepheids, and nine EA eclipsing systems. It is the nine EA eclipsing binaries that are the focus of this research.

Keywords: eclipsing binary stars
Tilted Dark Halos Are Common and Long-lived, and Can Warp Galactic Disks

In the Lambda cold dark matter paradigm, the dark halo governs the gravitational potential within which a galaxy can form and evolve. In this Letter we show that the present-day inner (r < 50 kpc) dark halo can be significantly misaligned with the stellar disk. To this end, we use the TNG50 run from the cosmological magnetohydrodynamic IllustrisTNG simulation suite. Such "tilted" dark halos can arise from a variety of processes including major mergers, massive flybys, or interactions with satellite companions. Furthermore, we show that tilted dark halos (1) are well traced by tilted stellar halos, (2) can maintain their tilt for >5 Gyr in isolated evolution, and (3) can generate warps in the outer disks that are stable over many Gyr. A tilted dark halo holds clues to important events in the formation history of a galaxy, and could help explain the abundance of warped disks in galaxy observations, including the Milky Way.

Keywords: galaxy dark matter halos
Detecting and Characterizing Young Quasars. II. Four Quasars at z 6 with Lifetimes < 104 Yr

The extents of proximity zones of high-redshift quasars enable constraints on the timescales of quasar activity, which are fundamental for understanding the growth of the supermassive black holes (SMBHs) that power the quasars' emission. In this study, we obtain precise estimates for the ultraviolet (UV) luminous lifetimes of 10 quasars at 5.8 < z < 6.5. These objects were preselected to have short lifetimes based on preliminary measurements of their proximity zone sizes and were then targeted for high-quality follow-up submillimeter, optical, and infrared observations required to increase the measurements' precision and securely determine their lifetimes. By comparing these proximity zone sizes to mock quasar spectra generated from radiative transfer simulations at a range of different lifetimes, we deduce extremely short lifetimes tQ < 104 yr for four objects in our sample, whereas the remaining quasars are consistent with longer lifetimes of tQ ≳ 105 yr. These young objects with small proximity zones represent ≲10% of the quasar population as a whole. We compare our results in detail to other studies on timescales of quasar activity, which point toward an average lifetime of tQ ~ 106 yr for the quasar population. This is consistent with finding newly turned-on quasars approximately ~1%-10% of the time. These young quasars represent a unique opportunity to study triggering and feedback mechanisms of SMBHs, since the onset of their UV-luminous quasar phase happened only recently, and therefore traces of this process might still be observable.

Keywords: quasars; supermassive black holes; reionization; early universe; intergalactic medium
Rapid Variability in the Wind from the White Dwarf Merger Candidate J005311

We analyze time-series spectroscopy of the white dwarf merger candidate J005311 and confirm the unique nature of its optical spectrum. We detect an additional broad emission feature peaking at 343 nm that was predicted in the Gvaramadze et al. (2019) models. Comparing ten spectra taken with the Large Binocular Telescope, we find significant variability in the profile of the strong O VI 381.1/383.4 nm emission feature. This appears to be caused by rapidly shifting subpeaks generated by clumpiness in the stellar wind of J005311. This line variability is similar to what is seen in many Wolf-Rayet stars. However, in J005311, the rate of motion of the subpeaks appears exceedingly high as they can reach 16,000 km s-1 in less than two hours.

Keywords: white dwarf stars; wolf-rayet stars; stellar mergers; evolved stars; stellar winds
NICER Monitoring of Supersoft X-Ray Sources

We monitored four supersoft sources-two persistent ones, CAL 83 and MR Vel, and the recent novae YZ Ret (Nova Ret 2020), and V1674 Her (Nova Her 2021)-with NICER. The two persistent supersoft X-ray sources (SSS) were observed with unvaried X-ray flux level and spectrum, respectively, 13 and 20 yr after the last observations. Short-period modulations of the SSS appear where the spectrum of the luminous central source was fully visible (in CAL 83 and V1674 Her) and were absent in YZ Ret and MR Vel, in which the flux originated in photoionized or shocked plasma, while the white dwarf (WD) was not observable. We thus suggest that the pulsations occur on, or very close to, the WD surface. The pulsations of CAL 83 were almost unvaried after 15 yr, including an irregular drift of the ≃67 s period by 2.1 s. Simulations, including previous XMM-Newton data, indicate actual variations in period length within hours, rather than an artifact of the variable amplitude of the pulsations. Large amplitude pulsations with a period of 501.53 ± 0.30 s were always detected in V1674 Her, as long as the SSS was observable. This period seems to be due to rotation of a highly magnetized WD. We cannot confirm the maximum effective temperature of (≃145,000 K) previously inferred for this nova, and discuss the difficulty in interpreting its spectrum. The WD appears to present two surface zones, one of which does not emit SSS flux.

Keywords: novae
Discovery of a New Gamma-Ray Source, LHAASO J0341+5258, with Emission up to 200 TeV

We report the discovery of a new unidentified extended γ-ray source in the Galactic plane named LHAASO J0341+5258 with a pretrial significance of 8.2 standard deviations above 25 TeV. The best-fit position is R.A. = 55°34 ± 0°11 and decl. = 52°97 ± 0°07. The angular size of LHAASO J0341+5258 is 0°29 ± 0°06stat ± 0°02sys. The flux above 25 TeV is about 20% of the flux of the Crab Nebula. Although a power-law fit of the spectrum from 10 to 200 TeV with the photon index α = 2.98 ± 0.19stat ± 0.02sys is not excluded, the LHAASO data together with the flux upper limit at 10 GeV set by the Fermi-LAT observation, indicate a noticeable steepening of an initially hard power-law spectrum with a cutoff at ≈50 TeV. We briefly discuss the origin of ultra-high-energy gamma rays. The lack of an energetic pulsar and a young supernova remnant inside or in the vicinity of LHAASO J0341+5258 challenge, but do not exclude, both the leptonic and hadronic scenarios of gamma-ray production.

Keywords: particle astrophysics
The Bow Shock and Kinematics of PSR J1959+2048

Pulsar Hα bow shocks provide rare opportunities to constrain the energetics and kinematics of the relativistic pulsar wind. We have acquired optical imaging and integral field unit spectroscopy of the bow shock of the millisecond pulsar PSR J1959+2048, measuring the shock symmetry axis at a position angle = 213.2 ± 0.°2 and showing that this slow nonradiative shock has a broad-to-narrow line component ratio I b /I n = 4. The data show that the pulsar's velocity lies 2.°2 out of the plane of the sky. Coupled with a new fit for its timing proper motion, giving μ tot = 30.05 mas yr-1 and a Very Long Baseline Array (VLBA) interferometric parallax measurement giving $d={2.57}_{-0.77}^{+1.84}$ kpc (90% range), we have unusually complete information on the pulsar kinematics. The bow shock constraints on the wind momentum flux imply that, at the best-fit parallax distance, the pulsar moment of inertia must be very large and/or the Hα efficiency at its modest shock velocity must be very high.

Keywords: pulsar wind nebulae
The Sloan Digital Sky Survey Reverberation Mapping Project: Mg II Lag Results from Four Years of Monitoring

We present reverberation mapping results for the Mg II λ2800 Å broad emission line in a sample of 193 quasars at $0.35\lt z\lt 1.7$ with photometric and spectroscopic monitoring observations from the Sloan Digital Sky Survey Reverberation Mapping project during 2014-2017. We find significant time lags between the Mg II and continuum lightcurves for 57 quasars, and define a "gold sample" of 24 quasars with the most reliable lag measurements. We estimate false-positive rates for each lag that range from 1% to 24%, with an average false-positive rate of 11% for the full sample and 8% for the gold sample. There are an additional ∼40 quasars with marginal Mg II lag detections, which may yield reliable lags after additional years of monitoring. The Mg II lags follow a radius-luminosity relation with a best-fit slope that is consistent with $\alpha =0.5$ , but with an intrinsic scatter of 0.36 dex that is significantly larger than found for the Hβ radius-luminosity relation. For targets with SDSS-RM lag measurements of other emission lines, we find that our Mg II lags are similar to the Hβ lags and ∼2-3 times larger than the C IV lags. This work significantly increases the number of Mg II broad-line lags and provides additional reverberation-mapped black hole masses, filling the redshift gap at the peak of supermassive black hole growth between the Hβ and C IV emission lines in optical spectroscopy.

Keywords: active galaxies; galaxy nuclei; quasars; active galactic nuclei
High Spatial Resolution Observations of Molecular Lines toward the Protoplanetary Disk around TW Hya with ALMA

We present molecular line observations of 13CO and C18O J = 3 - 2, CN N = 3 - 2, and CS J = 7 - 6 lines in the protoplanetary disk around TW Hya at a high spatial resolution of ~9 au (angular resolution of 0"15), using the Atacama Large Millimeter/Submillimeter Array. A possible gas gap is found in the deprojected radial intensity profile of the integrated C18O line around a disk radius of ~58 au, slightly beyond the location of the au-scale dust clump at ~52 au, which resembles predictions from hydrodynamic simulations of planet-disk interaction. In addition, we construct models for the physical and chemical structure of the TW Hya disk, taking account of the dust surface density profile obtained from high spatial resolution dust continuum observations. As a result, the observed flat radial profile of the CN line intensities is reproduced due to a high dust-to-gas surface density ratio inside ~20 au. Meanwhile, the CO isotopologue line intensities trace high temperature gas and increase rapidly inside a disk radius of ~30 au. A model with either CO gas depletion or depletion of gas-phase oxygen elemental abundance is required to reproduce the relatively weak CO isotopologue line intensities observed in the outer disk, consistent with previous atomic and molecular line observations toward the TW Hya disk. Further observations of line emission of carbon-bearing species, such as atomic carbon and HCN, with high spatial resolution would help to better constrain the distribution of elemental carbon abundance in the disk gas.

Keywords: protoplanetary disks; planetary system formation; molecular gas; submillimeter astronomy
Ghostly Strong Lyα Absorbers: Tracers of Gas Flows in the Close Vicinity of Quasars?

We have searched the Sloan Digital Sky Survey Data Release 12 for ghostly strong Lyα (DLA) systems. These systems, located at the redshift of the quasars, show strong absorption from low-ionization atomic species but reveal no H I Lyα absorption. Our search has, for the first time, resulted in a sample of 30 homogeneously selected ghostly absorbers with z QSO > 2.0. Thirteen of the ghostly absorbers exhibit absorption from other H I Lyman series lines. The lack of Lyα absorption in these absorbers is consistent with them being dense and compact with projected sizes smaller than the broad-line region of the background quasar. Although uncertain, the estimated median H I column density of these absorbers is logN(H I) ∼ 21.0. We compare the properties of ghostly absorbers with those of eclipsing DLAs that are high-column-density absorbers, located within 1500 km s-1 of the quasar emission redshift and showing strong Lyα emission in their DLA trough. We discover an apparent sequence in the observed properties of these DLAs, with ghostly absorbers showing wider H I kinematics, stronger absorptions from high-ionization species, C II and Si II excited states, and a higher level of dust extinction. Since we estimate that all these absorbers have similar metallicities, logZ/{Z}⊙ ∼ -1.0, we conclude that ghostly absorbers are part of the same population as eclipsing DLAs, except that they are denser and located closer to the central active galactic nuclei.

Keywords: interstellar absorption; interstellar line absorption; quasars; active galactic nuclei; quasar absorption line spectroscopy; intergalactic medium; interstellar dust extinction; circumgalactic medium; extragalactic astronomy; galaxy structure; galactic winds