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<jats:title>Abstract</jats:title> <jats:p>The structure of shocks and turbulence are strongly modified during the acceleration of cosmic rays (CRs) at a shock wave. The pressure and the collisionless viscous stress decelerate the incoming thermal gas and thus modify the shock structure. A CR streaming instability ahead of the shock generates the turbulence on which CRs scatter. The turbulent magnetic field in turn determines the CR diffusion coefficient and further affects the CR energy spectrum and pressure distribution. The dissipation of turbulence contributes to heating the thermal gas. Within a multicomponent fluid framework, CRs and thermal gas are treated as fluids and are closely coupled to the turbulence. The system equations comprise the gas dynamic equations, the CR pressure evolution equation, and the turbulence transport equations, and we adopt typical parameters for the hot ionized interstellar medium. It is shown that the shock has no discontinuity but possesses a narrow but smooth transition. The self-generated turbulent magnetic field is much stronger than both the large-scale magnetic field and the preexisting turbulent magnetic field. The resulting CR diffusion coefficient is substantially suppressed and is more than three orders smaller near the shock than it is far upstream. The results are qualitatively consistent with certain observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study the spectral evolution of the black hole candidate EXO 1846−031 during its 2019 outburst, in the 1–150 keV band, with the Hard X-ray Modulation Telescope. The continuum spectrum is well modeled with an absorbed disk-blackbody plus cutoff power law, in the hard, intermediate, and soft states. In addition, we detect an ≈6.6 keV Fe emission line in the hard intermediate state. Throughout the soft intermediate and soft states, the fitted inner disk radius remains almost constant; we suggest that it has settled at the innermost stable circular orbit (ISCO). However, in the hard and hard intermediate states, the apparent inner radius was unphysically small (smaller than the ISCO), even after accounting for the Compton scattering of some of the disk photons by the corona in the fit. We argue that this is the result of a high hardening factor, <jats:italic>f</jats:italic> <jats:sub>col</jats:sub> ≈ 2.0–2.7, in the early phases of the outburst evolution, well above the canonical value of 1.7 suitable for a steady disk. We suggest that the inner disk radius was already close to the ISCO in the low/hard state. Furthermore, we propose that this high value of the hardening factor in the relatively hard state was probably caused by the additional illuminating of the coronal irradiation onto the disk. Additionally, we estimate the spin parameter using the continuum-fitting method, over a range of plausible black hole masses and distances. We compare our results with the spin measured using the reflection-fitting method and find that the inconsistency of the two results is partly caused by different choices of <jats:italic>f</jats:italic> <jats:sub>col</jats:sub>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Advection is believed to be the dominant cooling mechanism in optically thin advection-dominated accretion flows (ADAFs). When outflow is considered, however, the first impression is that advection should be of opposite sign in the inflow and the outflow, due to the opposite direction of radial motion. Then how is the energy balance achieved simultaneously? We investigate the problem in this paper, analyzing the profiles of different components of advection with self-similar solutions of ADAFs in spherical coordinates (<jats:italic>r</jats:italic> <jats:italic>θ</jats:italic> <jats:italic>ϕ</jats:italic>). We find that for <jats:italic>n</jats:italic> &lt; 3<jats:italic>γ</jats:italic>/2 − 1, where <jats:italic>n</jats:italic> is the density index in <jats:italic>ρ</jats:italic> ∝ <jats:italic>r</jats:italic> <jats:sup>−<jats:italic>n</jats:italic> </jats:sup> and <jats:italic>γ</jats:italic> is the heat capacity ratio, the radial advection is a heating mechanism in the inflow and a cooling mechanism in the outflow. It becomes 0 for <jats:italic>n</jats:italic> = 3<jats:italic>γ</jats:italic>/2 − 1, and turns to a cooling mechanism in the inflow and a heating mechanism in the outflow for <jats:italic>n</jats:italic> &gt; 3<jats:italic>γ</jats:italic>/2 − 1. The energy conservation is only achieved when the latitudinal (<jats:italic>θ </jats:italic>direction) advection is considered, which takes an appropriate value to maintain energy balance, so that the overall effect of advection, no matter the parameter choices, is always a cooling mechanism that cancels out the viscous heating everywhere. For the extreme case of <jats:italic>n</jats:italic> = 3/2, latitudinal motion stops, viscous heating is balanced solely by radial advection, and no outflow is developed.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We explore how thermal Rossby waves propagate within the gravitationally stratified atmosphere of a low-mass star with an outer convective envelope. Under the conditions of slow, rotationally constrained dynamics, we derive a local dispersion relation for atmospheric waves in a fully compressible stratified fluid. This dispersion relation describes the zonal and radial propagation of acoustic waves and gravito-inertial waves. Thermal Rossby waves are just one class of prograde-propagating gravito-inertial wave that manifests when the buoyancy frequency is small compared to the rotation rate of the star. From this dispersion relation, we identify the radii at which waves naturally reflect and demonstrate how thermal Rossby waves can be trapped radially in a waveguide that permits free propagation in the longitudinal direction. We explore this trapping further by presenting analytic solutions for thermal Rossby waves within an isentropically stratified atmosphere that models a zone of efficient convective heat transport. We find that, within such an atmosphere, waves of short zonal wavelength have a wave cavity that is radially thin and confined within the outer reaches of the convection zone near the star’s equator. The same behavior is evinced by the thermal Rossby waves that appear at convective onset in numerical simulations of convection within rotating spheres. Finally, we suggest that stable thermal Rossby waves could exist in the lower portion of the Sun’s convection zone, despite that region’s unstable stratification. For long wavelengths, the Sun’s rotation rate is sufficiently rapid to stabilize convective motions, and the resulting overstable convective modes are identical to thermal Rossby waves.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The gamma-ray bursts (GRBs) with distinct thermal components are rarely detected, especially in cases with thermal components throughout the prompt phase. Recently, Fermi/GBM, Swift/BAT, and Swift/XRT detected the special long-duration GRB 190109A, which has four pulses in the prompt gamma-ray emission, i.e, Pulse I (−4 to 20 s), Pulse II (20–50 s), Pulse III (50–90 s), and Pulse IV (90–120 s). GRB 190109A exhibits a very hard low-energy index (<jats:italic>α</jats:italic> ∼ 1) in the Band function relative to the typical GRBs (<jats:italic>α</jats:italic> ∼ − 1). In the whole burst prompt emission, we find distinct thermal emissions in the time-resolved spectra throughout four pulses. The blackbody (BB) temperature <jats:italic>kT</jats:italic> varies from 24.7 to 8.2 keV for Pulse I to Pulse IV. We also obtain the relation of <jats:italic>F</jats:italic> ∝ <jats:italic>kT</jats:italic> <jats:sup>−0.40</jats:sup> for the early phase (Pulse I) and <jats:italic>F</jats:italic> ∝ <jats:italic>kT</jats:italic> <jats:sup>3.33±0.76</jats:sup> for the late phase (Pulses II–IV), respectively. The significant deviation of the <jats:italic>kT</jats:italic> − <jats:italic>F</jats:italic> relation in the early epochs from that in the late epochs likely suggests that the BB spectra origin of the early phase (Pulse I) may have disparate physical processes from those of the late phase (Pulses II–IV). For instance, it may be the transition from cocoon surroundings by a jet to the photosphere of the matter-dominated jet. A jet break is found in the late X-ray afterglow, which is in keeping with the standard external shock afterglow model in the interstellar medium circumburst.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The reflex motion and distortion of the Milky Way (MW) halo caused by the infall of a massive Large Magellanic Cloud (LMC) has been demonstrated to result in an excess of orbital poles of dark matter halo particles toward the LMC orbital pole. This was suggested to help explain the observed preference of MW satellite galaxies to coorbit along the Vast Polar Structure (VPOS). We test this idea by correcting the positions and velocities of the MW satellites for the Galactocentric-distance-dependent shifts inferred from a LMC-infall simulation. While this should substantially reduce the observed clustering of orbital poles if it were mainly caused by the LMC, we instead find that the strong clustering remains preserved. We confirm the initial study’s main result with our simulation of an MW-LMC-like interaction, and use it to identify two reasons why this scenario is unable to explain the VPOS: (1) the orbital pole density enhancement in our simulation is very mild (∼10% within 50–250 kpc) compared to the observed enhancement (∼220%–300%), and (2) it is very sensitive to the specific angular momenta (AM) of the simulation particles, with the higher-AM particles being affected the least. Particles in simulated dark matter halos tend to follow more radial orbits (lower AM), so their orbital poles are more easily affected by small offsets in position and velocity caused by a LMC infall than objects with more tangential velocity (higher AM), such as the observed dwarf galaxies surrounding the MW. The origin of the VPOS thus remains unexplained.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We introduce the Phoenix Simulations, a suite of highly resolved cosmological simulations featuring hydrodynamics, primordial gas chemistry, primordial and enriched star formation and feedback, UV radiative transfer, and saved outputs with Δ<jats:italic>t</jats:italic> = 200 kyr. We observe 73,523 individual primordial stars within 3313 distinct regions forming 2110 second-generation enriched star clusters by <jats:italic>z</jats:italic> ≥ 12 within a combined 177.25 Mpc<jats:sup>3</jats:sup> volume across three simulations. The regions that lead to enriched star formation can contain ≳150 primordial stars, with 80% of regions having experienced combinations of primordial Type II, hypernovae, and/or pair-instability supernovae. Primordial supernovae enriched 0.8% of the volume, with 2% of enriched gas enriched by later-generation stars. We determine the extent of a primordial stellar region by its metal-rich or ionized hydrogen surrounding cloud; the metal-rich and ionized regions have time-dependent average radii <jats:italic>r</jats:italic> ≲ 3<jats:strike> </jats:strike>kpc. 7 and 17% of regions have <jats:italic>r</jats:italic> &gt; 7 kpc for metal-rich and ionized radii, respectively. We find that the metallicity distribution function of second-generation stars overlaps that of subsequent Population II star formation, spanning metal-deficient (∼7.94 × 10<jats:sup>−8</jats:sup> <jats:italic>Z</jats:italic> <jats:sub>⊙</jats:sub>) to supersolar (∼3.71 <jats:italic>Z</jats:italic> <jats:sub>⊙</jats:sub>), and that 30.5% of second-generation stars have <jats:italic>Z</jats:italic> &gt; 10<jats:sup>−2</jats:sup> <jats:italic>Z</jats:italic> <jats:sub>⊙</jats:sub>. We find that the metallicity of second-generation stars depends on progenitor configuration, with metals from pair-instability supernovae contributing to the most metal-rich clusters; these clusters form promptly after the supernova event. Finally, we create an interpretable regression model to predict the radius of the metal-rich influence of Population III star systems within the first 7–18 Myr after the first Population III stars form in the region.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the first very long baseline interferometric (VLBI) observations of the blazar OJ 287 carried out jointly with the Global Millimeter VLBI Array (GMVA) and the phased Atacama Large Millimeter/submillimeter Array (ALMA) at 3.5 mm on 2017 April 2. The participation of phased ALMA has not only improved the GMVA north–south resolution by a factor of ∼3, but has also enabled fringe detections with signal-to-noise ratios up to 300 at baselines longer than 2 G<jats:italic>λ</jats:italic>. The high sensitivity has motivated us to image the data with newly developed regularized maximum likelihood imaging methods, revealing the innermost jet structure with unprecedentedly high angular resolution. Our images reveal a compact and twisted jet extending along the northwest direction, with two bends within the inner 200 <jats:italic>μ</jats:italic>as, resembling a precessing jet in projection. The component at the southeastern end shows a compact morphology and high brightness temperature, and is identified as the VLBI core. An extended jet feature that lies at ∼200 <jats:italic>μ</jats:italic>as northwest of the core shows a conical shape, in both total and linearly polarized intensity, and a bimodal distribution of the linear polarization electric vector position angle. We discuss the nature of this feature by comparing our observations with models and simulations of oblique and recollimation shocks with various magnetic field configurations. Our high-fidelity images also enabled us to search for possible jet features from the secondary supermassive black hole (SMBH) and test the SMBH binary hypothesis proposed for this source.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We numerically integrate the equations of motion of a large number of GeV protons, released impulsively near the Sun, in order to study their time–intensity behavior at the location of an observer at 1 au. This is relevant to the interpretation of Ground Level Enhancements (GLEs) detected by neutron monitors on Earth. Generally, the observed time–intensity profiles reveal a single sharp rise, followed by slow decay. However, in the 1989 October 22 GLE event, there was an initial sharp spike followed by a secondary smaller spike in the particle intensity. We consider whether the propagation of the high-energy protons in a large-scale turbulent interplanetary magnetic field (IMF) can lead to this unusual time–intensity profile. The IMF model includes large-scale magnetic turbulence and a heliospheric current sheet. Ad-hoc scattering is used to mimic the effect of smaller-scale fluctuations resulting in pitch-angle scattering. Proton fluxes as a function of time and location for an observer are determined for various turbulence parameters, IMF polarities, and the size of the particle source near the Sun. We find that the fluctuating IMF leads to considerable variation in the arrival location of the particles crossing 1 au, and the time–intensity profile depends significantly on the observer's location and can have multiple peaks. An alternate explanation for the unusual structure in the 1989 October 22 GLE event is provided. Our findings show that the large-scale turbulent IMF enhances the access of the high-energy protons to the HCS at the early time of the event, which leads to efficient cross-field transport.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report Very Long Baseline Array observations of 22 GHz H<jats:sub>2</jats:sub>O and 43 GHz SiO masers toward the Mira variable RR Aql. By fitting the SiO maser emission to a circular ring, we estimate the absolute stellar position of RR Aql and find agreement with Gaia astrometry to within the joint uncertainty of ≈1 mas. Using the maser astrometry we measure a stellar parallax of 2.44 ± 0.07 mas, corresponding to a distance of <jats:inline-formula> <jats:tex-math> <?CDATA ${410}_{-11}^{+12}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>410</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>11</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>12</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac69e0ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> pc. The maser parallax deviates significantly from the Gaia EDR3 parallax of 1.95 ± 0.11 mas, indicating a 3.8<jats:italic>σ</jats:italic> tension between radio and optical measurements. This tension is most likely caused by optical photocenter variations limiting the Gaia astrometric accuracy for this Mira variable. Combining infrared magnitudes with parallaxes for RR Aql and other Miras, we fit a period–luminosity relation using a Bayesian approach with Markov Chain Monte Carlo sampling and a strong prior for the slope of −3.60 ± 0.30 from the Large Magellanic Cloud. We find a <jats:italic>K</jats:italic>-band zero-point (defined at logP(days) = 2.30) of −6.79 ± 0.15 mag using very long baseline interferometry (VLBI) parallaxes and −7.08 ± 0.29 mag using Gaia parallaxes. The Gaia zero-point is statistically consistent with the more accurate VLBI value.</jats:p>