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<jats:title>Abstract</jats:title> <jats:p>Adopting the MPI-AMRVAC code, we present a 2.5-dimensional magnetohydrodynamic simulation, which includes thermal conduction and radiative cooling, to investigate the formation and evolution of the coronal rain phenomenon. We perform the simulation in initially linear force-free magnetic fields that host chromospheric, transition-region, and coronal plasma, with turbulent heating localized on their footpoints. Due to thermal instability, condensations start to occur at the loop top, and rebound shocks are generated by the siphon inflows. Condensations fragment into smaller blobs moving downwards, and as they hit the lower atmosphere, concurrent upflows are triggered. Larger clumps show us clear <jats:italic>coronal rain showers</jats:italic> as dark structures in synthetic EUV hot channels and as bright blobs with cool cores in the 304 Å channel, well resembling real observations. Following coronal rain dynamics for more than 10 hr, we carry out a statistical study of all coronal rain blobs to quantify their widths, lengths, areas, velocity distributions, and other properties. The coronal rain shows us continuous heating–condensation cycles, as well as cycles in EUV emissions. Compared to the previous studies adopting steady heating, the rain happens faster and in more erratic cycles. Although most blobs are falling downward, upward-moving blobs exist at basically every moment. We also track the movement of individual blobs to study their dynamics and the forces driving their movements. The blobs have a prominence-corona transition-region-like structure surrounding them, and their movements are dominated by the pressure evolution in the very dynamic loop system.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate the effects of winds on the observational properties of Type Ib and Ic supernova (SN Ib/Ic) progenitors using spectral models constructed with the non-LTE stellar atmospheric code CMFGEN. We consider SN Ib/Ic progenitor models of the final mass range of 2.16–9.09 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> having different surface temperatures and chemical compositions, and calculate the resulting spectra for various wind mass-loss rates and wind terminal velocities. We find that the progenitors having an optically thick wind would become brighter in the optical for a higher mass-loss rate (or a lower wind terminal velocity) because of the formation of the photosphere in the extended wind matter and the contribution from free–free and line emissions from the wind. As a result, for the standard Wolf-Rayet wind mass-loss rate, helium-deficient compact SN Ic progenitors would be brighter in the optical by ∼3 mag compared to the case without the wind effects. We also find that the color dependence on the photospheric temperature is non-monotonic because of the wind effects. Our results imply that inferring the progenitor mass, bolometric luminosity, and effective temperature from the optical observation using the standard stellar evolution model prediction can be misleading. By comparing our fiducial model predictions with the detection limits of the previous SN Ib/Ic progenitor searches, we conclude that a deep search with an optical absolute magnitude larger than ∼−4 is needed to directly identify most of the ordinary SN Ib/Ic progenitors. We discuss implications of our results for the observed SN Ib/Ic progenitor candidates for iPTF13bvn, SN 2019vyr, and SN 2017ein.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Venus’ mass and radius are similar to those of Earth. However, dissimilarities in atmospheric properties, geophysical activity, and magnetic field generation could hint toward significant differences in the chemical composition and interior evolution of the two planets. Although various explanations for the differences between Venus and Earth have been proposed, the currently available data are insufficient to discriminate among the different solutions. Here we investigate the possible range of models for Venus’ structure. We assume that core segregation happened as a single-stage event. The mantle composition is inferred from the core composition using a prescription for metal-silicate partitioning. We consider three different cases for the composition of Venus defined via the bulk Si and Mg content, and the core’s S content. Permissible ranges for the core size, mantle, and core composition as well as the normalized moment of inertia (MoI) are presented for these compositions. A solid inner core could exist for all compositions. We estimate that Venus’ MoI is 0.317–0.351 and its core size 2930–4350 km for all assumed compositions. Higher MoI values correspond to more oxidizing conditions during core segregation. A determination of the abundance of FeO in Venus’ mantle by future missions could further constrain its composition and internal structure. This can reveal important information on Venus’ formation and evolution, and, possibly, the reasons for the differences between Venus and our home planet.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present optical <jats:italic>UBVRI</jats:italic> photometry and low-to-medium resolution spectroscopic observations of type Iax supernova SN 2020sck spanning −5.5 days to +67 days from maximum light in the <jats:italic>B-</jats:italic>band. From the photometric analysis we find Δ<jats:italic>m</jats:italic> <jats:sub> <jats:italic>B</jats:italic> </jats:sub>(15) = 2.03 ± 0.05 mag and <jats:italic>M</jats:italic> <jats:sub> <jats:italic>B</jats:italic> </jats:sub> = −17.81 ± 0.22 mag. Radiation diffusion model fit to the quasi-bolometric light curve indicates 0.13 ± 0.02 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> of <jats:sup>56</jats:sup>Ni and 0.34 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> of ejecta are synthesized in the explosion. Comparing the observed quasi-bolometric light curve with the angle-averaged bolometric light curve of a three-dimensional pure deflagration explosion of <jats:italic>M</jats:italic> <jats:sub>ch</jats:sub> carbon-oxygen white dwarf, we find agreement with a model in which 0.16 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> of <jats:sup>56</jats:sup>Ni and 0.37 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> of ejecta is formed. By comparing the +1.4 days spectrum of SN 2020sck with synthetic spectrum generated using <jats:monospace>SYN++</jats:monospace>, we find absorption features due to C <jats:sc>ii</jats:sc>, C <jats:sc>iii</jats:sc>, and O <jats:sc>i</jats:sc>. These are unburned materials in the explosion and indicate a C–O white dwarf. One-dimensional radiative transfer modeling of the spectra with <jats:monospace>TARDIS</jats:monospace> shows higher density in the ejecta near the photosphere and a steep decrease in the outer layers with an ejecta composition dominated mostly by C, O, Si, Fe, and Ni. The star-formation rate of the host galaxy computed from the luminosity of the H<jats:italic>α</jats:italic> (<jats:italic>λ</jats:italic>6563) line is 0.09 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup>, indicating a relatively young stellar environment.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We analyze the structure and evolution of ribbons from the M7.3 SOL2014-04-18T13 flare using ultraviolet images from the Interface Region Imaging Spectrograph and the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA), magnetic data from the SDO/Helioseismic and Magnetic Imager, hard X-ray (HXR) images from the Reuven Ramaty High Energy Solar Spectroscopic Imager, and light curves from the Fermi/Gamma-ray Burst Monitor, in order to infer properties of coronal magnetic reconnection. As the event progresses, two flare ribbons spread away from the magnetic polarity inversion line. The width of the newly brightened front along the extension of the ribbon is highly intermittent in both space and time, presumably reflecting nonuniformities in the structure and/or dynamics of the flare current sheet. Furthermore, the ribbon width grows most rapidly in regions exhibiting concentrated nonthermal HXR emission, with sharp increases slightly preceding the HXR bursts. The light curve of the ultraviolet emission matches the HXR light curve at photon energies above 25 keV. In other regions the ribbon-width evolution and light curves do not temporally correlate with the HXR emission. This indicates that the production of nonthermal electrons is highly nonuniform within the flare current sheet. Our results suggest a strong connection between the production of nonthermal electrons and the locally enhanced perpendicular extent of flare ribbon fronts, which in turn reflects the inhomogeneous structure and/or reconnection dynamics of the current sheet. Despite this variability, the ribbon fronts remain nearly continuous, quasi-one-dimensional features. Thus, although the reconnecting coronal current sheets are highly structured, they remain quasi-two-dimensional and the magnetic energy release occurs systematically, rather than stochastically, through the volume of the reconnecting magnetic flux.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We reanalyze the mid-infrared (5–40 <jats:italic>μ</jats:italic>m) Spitzer spectra of 86 low-redshift (<jats:italic>z</jats:italic> &lt; 0.5) Palomar–Green quasars to investigate the nature of polycyclic aromatic hydrocarbon (PAH) emission and its utility as a star formation rate (SFR) indicator for the host galaxies of luminous active galactic nuclei (AGNs). We decompose the spectra with our recently developed template-fitting technique to measure PAH fluxes and upper limits, which we interpret using mock spectra that simulate the effects of AGN dilution. While luminous quasars can severely dilute and affect the detectability of emission lines, PAHs are intrinsically weak in some sources that are otherwise gas-rich and vigorously forming stars, conclusively demonstrating that powerful AGNs destroy PAH molecules. Comparing PAH-based SFRs with independent SFRs derived from the mid-infrared fine-structure neon lines and the total infrared luminosity reveals that PAHs can trace star formation activity in quasars with bolometric luminosities ≲10<jats:sup>46</jats:sup> erg s<jats:sup>−1</jats:sup>, but increasingly underestimate the SFR for more powerful quasars, typically by ∼0.5 dex. Relative to star-forming galaxies and low-luminosity AGNs, quasars have a comparable PAH 11.3<jats:italic> μ</jats:italic>m/7.7 <jats:italic>μ</jats:italic>m ratio but characteristically lower ratios of 6.2<jats:italic> μ</jats:italic>m/7.7 <jats:italic>μ</jats:italic>m, 8.6<jats:italic> μ</jats:italic>m<jats:italic>/</jats:italic>7.7 <jats:italic>μ</jats:italic>m, and 11.3<jats:italic> μ</jats:italic>m/17.0 <jats:italic>μ</jats:italic>m. We suggest that these trends indicate that powerful AGNs preferentially destroy small grains and enhance the PAH ionization fraction.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Past X-ray observations of the nearby Seyfert 2 MCG-03-58-007 revealed the presence of a powerful and highly variable disk wind, where two possible phases outflowing with <jats:italic>v</jats:italic> <jats:sub>out1</jats:sub>/<jats:italic>c</jats:italic> ∼ −0.07 and <jats:italic>v</jats:italic> <jats:sub>out2</jats:sub>/<jats:italic>c</jats:italic> ∼ −0.2 were observed. Multi-epoch X-ray observations, covering the period from 2010 to 2018, showed that the lower-velocity component is persistent, as it was detected in all the observations, while the faster phase outflowing with <jats:italic>v</jats:italic> <jats:sub>out2</jats:sub>/<jats:italic>c</jats:italic> ∼ −0.2 appeared to be more sporadic. Here we present the analysis of a new monitoring campaign of MCG-03-58-007 performed in 2019 May–June and consisting of four simultaneous XMM-Newton and NuSTAR observations. We confirm that the disk wind in MCG-03-58-007 is persistent, as it is detected in all the observations, and powerful, having a kinetic power that ranges between 0.5% and 10% of the Eddington luminosity. The highly ionized wind (log(<jats:italic>ξ</jats:italic>/erg cm s<jats:sup>−1</jats:sup>) ∼ 5) is variable in both the opacity and, remarkably in its velocity. This is the first time where we have observed a substantial variability of the outflowing velocity in a disk wind, which dropped from <jats:italic>v</jats:italic> <jats:sub>out</jats:sub>/<jats:italic>c</jats:italic> ∼ −0.2 (as measured in the first three observations) to <jats:italic>v</jats:italic> <jats:sub>out</jats:sub>/<jats:italic>c</jats:italic> ∼ −0.074 in just 16 days. We conclude that such a dramatic and fast variability of the outflowing velocity could be due to the acceleration of the wind, as recently proposed by Mizumoto et al. Here, the faster wind, seen in the first three observations, is already accelerated to <jats:italic>v</jats:italic> <jats:sub>out</jats:sub>/<jats:italic>c</jats:italic> ∼ −0.2, while in the last observation our line of sight intercepts only the slower, pre-accelerated streamline.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Uncertainty in the wide-angle point-spread function (PSF) at large angles (tens of arcseconds and beyond) is one of the dominant sources of error in a number of important quantities in observational astronomy. Examples include the stellar mass and shape of galactic halos and the maximum extent of starlight in the disks of nearby galaxies. However, modeling the wide-angle PSF has long been a challenge in astronomical imaging. In this paper, we present a self-consistent method to model the wide-angle PSF in images. Scattered light from multiple bright stars is fitted simultaneously with a background model to characterize the extended wing of the PSF using a Bayesian framework operating on a pixel-by-pixel level. The method is demonstrated using our software <jats:monospace>elderflower</jats:monospace> and is applied to data from the Dragonfly Telephoto Array to model its PSF out to 20′–25′. We compare the wide-angle PSF of Dragonfly to that of a number of other telescopes, including the SDSS PSF and show that, on scales of arcminutes, the scattered light in the Dragonfly PSF is markedly lower than that of other wide-field imaging telescopes. The energy in the wings of the Dragonfly PSF is sufficiently low that optical cleanliness plays an important role in defining the PSF. This component of the PSF can be modeled accurately, highlighting the power of our self-contained approach.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The correlation between the plasma density measured in space and the surface potential of an electrically conducting satellite body with biased electric field detectors has been recognized and used to provide density proxies. However, for Parker Solar Probe, this correlation has not produced quantitative density estimates over extended periods of time because it depends on the energy-dependent exponential variation of the photoemission spectrum, the electron temperature, the ratio of the biased surface area to the conducting spacecraft surface area, the spacecraft secondary or thermal emission, the spacecraft distance from the Sun, etc. In this paper the density as a function of time and frequency to frequencies as high as the electron gyrofrequency is determined through least-squares fits of a function of the spacecraft potential to the plasma density measured on the Parker Solar Probe. This function allows correction for the many effects on the spacecraft potential other than that due to the plasma density. Some examples of plasma density obtained from this procedure are presented.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the discovery of the fading radio transient FIRST J153350.8+272729. The source had a maximum observed 5 GHz radio luminosity of 8 × 10<jats:sup>39</jats:sup> erg s<jats:sup>−1</jats:sup> in 1986, but by 2019 had faded by a factor of nearly 400. It is located at the center of a galaxy (SDSS J153350.89+272729) at 147 Mpc, which shows weak Type II Seyfert activity. We show that a tidal disruption event (TDE) is the preferred scenario for FIRST J153350.8+272729, although it could plausibly be interpreted as the afterglow of a long-duration <jats:italic>γ</jats:italic>-ray burst. This is only the second TDE candidate to be first discovered at radio wavelengths. Its luminosity fills a gap between the radio afterglows of subrelativistic TDEs in the local universe, and relativistic TDEs at high redshifts. The unusual properties of FIRST J153350.8+272729 (ongoing nuclear activity in the host galaxy, high radio luminosity) motivate more extensive TDE searches in untargeted radio surveys.</jats:p>