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<jats:title>Abstract</jats:title> <jats:p>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.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Compact astrophysical objects have been considered in the literature as dark matter (DM) probes, via the observational effects of annihilating captured DM. In this paper we investigate the role of stellar velocity on multiscatter-capture rates and find that the capture rates of DM by a star moving with respect to the DM halo rest frame are suppressed by a predictable amount. We develop and validate an analytical expression for the capture rate suppression factor. This suppression factor can be used to directly reevaluate projected bounds on the DM–nucleon cross section, for any given stellar velocity, as we explicitly show using Population III stars as DM probes. These objects (Population III stars) are particularly interesting candidates, since they form at high redshifts, in very high DM-density environments. We find that previous results, obtained under the assumption of a star at rest with respect to the DM rest frame, are essentially unchanged when considering the possible orbital velocities for those central stars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present results of a wide-field (approximately 60 × 90 pc) Atacama Large Millimeter/submillimeter Array mosaic of CO(2–1) and <jats:sup>13</jats:sup>CO(2–1) emission from the molecular cloud associated with the 30 Doradus star-forming region in the Large Magellanic Cloud (LMC). Three main emission complexes, including two forming a bow-tie-shaped structure extending northeast and southwest from the central R136 cluster, are resolved into complex filamentary networks. Consistent with previous studies, we find that the central region of the cloud has higher line widths at a fixed size relative to the rest of the molecular cloud and to other LMC clouds, indicating an enhanced level of turbulent motions. However, there is no clear trend in gravitational boundedness (as measured by the virial parameter) with distance from R136. Structures observed in <jats:sup>13</jats:sup>CO are spatially coincident with filaments and are close to a state of virial equilibrium. In contrast, <jats:sup>12</jats:sup>CO structures vary greatly in virialization, with low CO surface brightness structures outside of the main filamentary network being predominantly unbound. The low surface brightness structures constitute ∼10% of the measured CO luminosity; they may be shredded remnants of previously star-forming gas clumps, or alternatively the CO-emitting parts of more massive, CO-dark structures.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>It is well known that magnetic field strength (<jats:italic>B</jats:italic>) in the solar corona can be calculated using the Alfvén Mach number (<jats:italic>M</jats:italic> <jats:sub> <jats:italic>A</jats:italic> </jats:sub>) and Alfvén speed (<jats:italic>v</jats:italic> <jats:sub> <jats:italic>A</jats:italic> </jats:sub>) of the magnetohydrodynamic shock waves associated with coronal type II radio bursts. We show that observations of weak circularly polarized emission associated with the harmonic component of the type II bursts provide independent and consistent estimates of <jats:italic>B</jats:italic>. For the coronal type II burst observed on 2021 October 9, we obtained <jats:italic>B</jats:italic> ≈1.5 G and ≈1.9 G at a heliocentric distance (<jats:italic>r</jats:italic>) of ≈1.8 <jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub>, using the above two techniques, respectively.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The core collapses of massive stars at the ends of their lives will produce powerful streams of neutrinos, which provide an important contribution to the <jats:sup>26</jats:sup>Al yield during the explosion stage. In this work, the contribution of the process <jats:inline-formula> <jats:tex-math> <?CDATA ${}^{26}\mathrm{Mg}{({\nu }_{e},{e}^{-})}^{26}\mathrm{Al}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mrow /> <mml:mrow> <mml:mn>26</mml:mn> </mml:mrow> </mml:msup> <mml:mi>Mg</mml:mi> <mml:msup> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>ν</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> </mml:msub> <mml:mo>,</mml:mo> <mml:msup> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> </mml:mrow> </mml:msup> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mrow> <mml:mn>26</mml:mn> </mml:mrow> </mml:msup> <mml:mi>Al</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6ef8ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> to the radioactive <jats:sup>26</jats:sup>Al in the Milky Way is studied based on a simple model. By combining the calculation of the neutrino-nucleus cross section and some hypotheses about core-collapse supernova explosions, the ratio of <jats:sup>26</jats:sup>Al and <jats:sup>26</jats:sup>Mg of the <jats:italic>ν</jats:italic> <jats:sub> <jats:italic>e</jats:italic> </jats:sub>-process is estimated. An analytical relationship between the <jats:sup>26</jats:sup>Mg yield and the initial mass and metallicity of massive stars is then obtained, making it easy to estimate the <jats:sup>26</jats:sup>Mg and <jats:sup>26</jats:sup>Al yields analytically. Due to the simplicity of the model, we can move away from complex calculations and into a careful study of the effects of some important factors, such as the radius of the O/Ne shell, the shock velocity, the neutrino spectrum, the Galactic mass and metallicity distribution, and so on. The uncertainties of the <jats:sup>26</jats:sup>Al yield contributed from these factors are discussed in detail. This study will facilitate an intuitive understanding of the buried implicit assumptions in previous studies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Microlensing imprints by typical stellar-mass lenses on gravitational waves are challenging to identify in the LIGO–Virgo frequency band because such effects are weak. However, stellar-mass lenses are generally embedded in lens galaxies such that strong lensing accompanies microlensing. Therefore, events that are strongly lensed in addition to being microlensed may significantly improve the inference of the latter. We present a proof-of-principle demonstration of how one can use parameter estimation results from one strongly lensed signal to enhance the inference of the microlensing effects of the other signal with the Bayesian inference method currently used in gravitational-wave astronomy. We expect this to significantly enhance our future ability to detect the weak imprints from stellar-mass objects on gravitational-wave signals from colliding compact objects.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Event Horizon Telescope (EHT) collaboration recently unveiled the first image of the supermassive black hole M87*, which exhibited a ring of angular diameter <jats:italic>θ</jats:italic> <jats:sub> <jats:italic>d</jats:italic> </jats:sub> = 42 ± 3 <jats:italic>μ</jats:italic>as, a circularity deviation of Δ<jats:italic>C</jats:italic> ≤ 0.1, and also inferred a black hole mass of <jats:italic>M</jats:italic> = (6.5 ± 0.7) × 10<jats:sup>9</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. This provides a new window onto tests of theories of gravity in the strong-field regime, including probes of violations of the no-hair theorem. It is widely believed that the Kerr metric describes astrophysical black holes, as encapsulated in the critical but untested no-hair theorem. Modeling Horndeski gravity black holes—with an additional hair parameter <jats:italic>h</jats:italic> besides the mass <jats:italic>M</jats:italic> and spin <jats:italic>a</jats:italic> of the Kerr black hole—as the supermassive black hole M87*, we observe that to be a viable astrophysical black hole candidate, the EHT result constrains the (<jats:italic>a</jats:italic>, <jats:italic>h</jats:italic>) parameter space. However, a systematic bias analysis indicates that rotating Horndeski black hole shadows may or may not capture Kerr black hole shadows, depending on the parameter values; the latter is the case over a substantial part of the constrained parameter space, allowing Horndeski gravity and general relativity to be distinguishable in the said space, and opening up the possibility of potential modifications to the Kerr metric.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Very Long Baseline Interferometry (VLBI) astrometry is a well established technique for achieving ±10 <jats:italic>μ</jats:italic>as parallax accuracies at frequencies well above 10 GHz. At lower frequencies, uncompensated interferometer delays associated with the ionosphere play the dominant role in limiting the astrometric accuracy. Multiview is a novel VLBI calibration method, which uses observations of multiple quasars to accurately model and remove time-variable, directional-dependent changes to the interferometer delay. Here we extend the Multiview technique by phase-referencing data to the target source (“inverse Multiview”) and test its performance. Multiple observations with a four-antenna VLBI array operating at 8.3 GHz show single-epoch astrometric accuracies near 20 <jats:italic>μ</jats:italic>as for target–reference quasar separations up to about 7°. This represents an improvement in astrometric accuracy by up to an order of magnitude compared to standard phase-referencing.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Extreme-ultraviolet late phase (ELP) refers to the second extreme-ultraviolet (EUV) radiation enhancement observed in certain solar flares, which usually occurs tens of minutes to several hours after the peak of soft X-ray emission. The coronal loop system that hosts the ELP emission is often different from the main flaring arcade, and the enhanced EUV emission therein may imply an additional heating process. However, the origin of the ELP remains rather unclear. Here we present the analysis of a C1.4 flare that features such an ELP, which is also observed in microwave wavelengths by the Expanded Owens Valley Solar Array. Similar to the case of the ELP, we find a gradual microwave enhancement that occurs about 3 minutes after the main impulsive phase microwave peaks. Radio sources coincide with both foot points of the ELP loops and spectral fits on the time-varying microwave spectra demonstrate a clear deviation of the electron distribution from the Maxwellian case, which could result from injected nonthermal electrons or nonuniform heating to the footpoint plasma. We further point out that the delayed microwave enhancement suggests the presence of an additional heating process, which could be responsible for the evaporation of heated plasma that fills the ELP loops, producing the prolonged ELP emission.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Dust plays a pivotal role in determining the observed spectral energy distribution (SED) of galaxies. Yet our understanding of dust attenuation is limited and our observations suffer from the dust–metallicity–age degeneracy in SED fitting (single galaxies), large individual variances (ensemble measurements), and the difficulty in properly dealing with uncertainties (statistical considerations). In this study, we create a population Bayesian model to rigorously account for correlated variables and non-Gaussian error distributions and demonstrate the improvement over a simple Bayesian model. We employ a flexible 5D linear interpolation model for the parameters that control dust attenuation curves as a function of stellar mass, star formation rate (SFR), metallicity, redshift, and inclination. Our setup allows us to determine the complex relationships between dust attenuation and these galaxy properties simultaneously. Using <jats:monospace>Prospector</jats:monospace> fits of nearly 30,000 3D–Hubble Space Telescope galaxies, we find that the attenuation slope (<jats:italic>n</jats:italic>) flattens with increasing optical depth (<jats:italic>τ</jats:italic>), though less so than in previous studies. <jats:italic>τ</jats:italic> increases strongly with SFR, though when <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}(\mathrm{SFR})\lesssim 0$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mi>SFR</mml:mi> <mml:mo stretchy="false">)</mml:mo> <mml:mo>≲</mml:mo> <mml:mn>0</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6c80ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, <jats:italic>τ</jats:italic> remains roughly constant over a wide range of stellar masses. Edge-on galaxies tend to have larger <jats:italic>τ</jats:italic> than face-on galaxies, but only for <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}({M}_{* })\gtrsim 10$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>*</mml:mo> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo>≳</mml:mo> <mml:mn>10</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6c80ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>, reflecting the lack of triaxiality for low-mass galaxies. Redshift evolution of dust attenuation is strongest for low-mass, low-SFR galaxies, with higher optical depths but flatter curves at high redshift. Finally, <jats:italic>n</jats:italic> has a complex relationship with stellar mass, highlighting the intricacies of the star–dust geometry. We have publicly released <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="uri" xlink:href="http://software" xlink:type="simple">software</jats:ext-link> for users to access our population model.</jats:p>