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<jats:title>Abstract</jats:title> <jats:p>The dielectric function of interstellar dust material is modeled using observations of extinction and polarization in the infrared, together with estimates for the mass of interstellar dust. The “astrodust” material is assumed to be a mix of amorphous silicates and other materials, including hydrocarbons producing an absorption feature at 3.4 <jats:italic>μ</jats:italic>m. The detailed shape of the 10 <jats:italic>μ</jats:italic>m polarization profile depends on the assumed porosity and grain shape, but the 10 <jats:italic>μ</jats:italic>m spectropolarimetric data are not yet good enough to clearly favor one shape over another, nor to constrain the porosity. The expected 3.4 <jats:italic>μ</jats:italic>m feature polarization is consistent with existing upper limits, provided the 3.4 <jats:italic>μ</jats:italic>m absorption is preferentially located in grain surface layers; a separate population of non-aligned carbonaceous grains is not required. We predict the 3.4 <jats:italic>μ</jats:italic>m polarization feature to be (Δ<jats:italic>p</jats:italic>)<jats:sub>3.4 <jats:italic>μ</jats:italic>m</jats:sub>/<jats:italic>p</jats:italic>(10 <jats:italic>μ</jats:italic>m) ≈ 0.016, just below current upper limits. Polarization by the same grains at submillimeter wavelengths is also calculated.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We provide a simple geometric explanation for the source of switchbacks and associated large and one-sided transverse flows in the solar wind observed by the Parker Solar Probe (PSP). The more radial, sub-Parker spiral structure of the heliospheric magnetic field observed previously by Ulysses, ACE, and STEREO is created within rarefaction regions where footpoint motion from the source of fast into slow wind at the Sun creates a magnetic fieldline connection across solar wind speed shear. Conversely, when footpoints move from the source of slow wind into faster wind, a super-Parker spiral field structure is formed: below the Alfvén critical point, one-sided transverse field-aligned flows develop; above the Alfvén critical point, the field structure contracts between adjacent solar wind flows, and the radial field component decreases in magnitude with distance from the Sun, eventually reversing into a switchback. The sub-Parker and super-Parker spirals behave functionally as opposites. Observations from PSP confirm the paucity of switchbacks within rarefaction regions and immediately outside these rarefaction regions, we observe numerous switchbacks in the magnetic field that are directly associated with abrupt transients in solar wind speed. The magnetic field strength, the radial component of the magnetic field, the speed gradients, radial Alfvén speed, and the ratio of the sound speed to the radial Alfvén speed all conform to predictions based on the sub-Parker and super-Parker spirals within rarefaction regions and solar wind speed enhancements (spikes or jets), respectively. Critically, the predictions associated with the super-Parker spiral naturally explain the observations of switchbacks being associated with unexpectedly large and one-sided tangential flows.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In Wada et al. (2019), we proposed for the first time that a new class of planets, <jats:italic>blanets</jats:italic>, can be formed around supermassive black holes in the galactic center. Here, we investigate the dust coagulation processes and physical conditions of the blanet formation outside the snowline (<jats:italic>r</jats:italic> <jats:sub>snow</jats:sub> ∼ several parsecs) in more detail, especially considering the effect of the radial drift of the dust aggregates. We found that a dimensionless parameter <jats:inline-formula> <jats:tex-math> <?CDATA $\alpha ={v}_{t}^{2}/{c}_{s}^{2}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabd40aieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, where <jats:italic>v</jats:italic> <jats:sub> <jats:italic>t</jats:italic> </jats:sub> is the turbulent velocity and <jats:italic>c</jats:italic> <jats:sub> <jats:italic>s</jats:italic> </jats:sub> is the sound velocity, describing the turbulent viscosity should be smaller than 0.04 in the circumnuclear disk to prevent the destruction of the aggregates due to collision. The formation timescale of blanets <jats:italic>τ</jats:italic> <jats:sub>GI</jats:sub> at <jats:italic>r</jats:italic> <jats:sub>snow</jats:sub> is, <jats:italic>τ</jats:italic> <jats:sub>GI</jats:sub> ≃ 70–80 Myr for <jats:italic>α</jats:italic> = 0.01 − 0.04 and <jats:italic>M</jats:italic> <jats:sub>BH</jats:sub> = 10<jats:sup>6</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. The mass of the blanets ranges from ∼20<jats:italic>M</jats:italic> <jats:sub> <jats:italic>E</jats:italic> </jats:sub> to 3000<jats:italic>M</jats:italic> <jats:sub> <jats:italic>E</jats:italic> </jats:sub> in <jats:italic>r</jats:italic> &lt; 4 pc for <jats:italic>α</jats:italic> = 0.02 (<jats:italic>M</jats:italic> <jats:sub> <jats:italic>E</jats:italic> </jats:sub> is the Earth mass), which is in contrast with 4<jats:italic>M</jats:italic> <jats:sub>E</jats:sub>–6<jats:italic>M</jats:italic> <jats:sub>E</jats:sub> for the case without the radial drift. Our results suggest that blanets could be formed around relatively low-luminosity active galactic nuclei (<jats:italic>L</jats:italic> <jats:sub>bol</jats:sub> ∼ 10<jats:sup>42</jats:sup> erg s<jats:sup>−1</jats:sup>) during their lifetime (≲10<jats:sup>8</jats:sup> yr).</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We have extended the membership and determined the 3D structure of the large (0.19 pc) HH 269 sequence of shocks in the Orion Nebula. All of the components lie along a track that is highly tilted to the plane of the sky and emerge from within the Orion-S embedded molecular cloud. Their source is probably either the highly obscured mm 9 source associated with a high N<jats:sub>2</jats:sub>H<jats:sup>+</jats:sup> density core (more likely) or the more distant star COUP 632 (less likely). The former must be located in the photon dominated region (PDR) underlying the ionized surface of the Orion-S Cloud, while the latter would be embedded within the Orion-S Cloud. The flows seem to be episodic, with intervals of 1900–2600 yr or 700–2600 yr if COUP 632 is the source.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present ALMA observations of CO isotopologues and high-density molecular tracers (HCN, HCO<jats:sup>+</jats:sup>, CN, etc.) in NGC 7465, an unusually gas-rich early-type galaxy that acquired its cold gas recently. In the inner 300 pc, the molecular gas kinematics are misaligned with respect to all other galaxy components; as the gas works its way inward, it is torqued into polar orbits about the stellar kinematically decoupled core (KDC), indicating that the stellar KDC is not related to the current gas accretion event. The galaxy also exhibits unusually high <jats:sup>12</jats:sup>CO/<jats:sup>13</jats:sup>CO line ratios in its nucleus but typical <jats:sup>13</jats:sup>CO/C<jats:sup>18</jats:sup>O ratios. Our calculations show that this result does not necessarily indicate an unusual [<jats:sup>12</jats:sup>CO/<jats:sup>13</jats:sup>CO] abundance ratio but rather that <jats:sup>12</jats:sup>CO (1–0) is optically thin due to high temperatures and/or large line widths associated with the inner decoupled, misaligned molecular structure. Line ratios of the higher-density tracers suggest that the densest phase of molecular gas in NGC 7465 has a lower density than is typical for nearby galaxies, possibly as a result of the recent gas accretion. All of the observed molecular properties of NGC 7465 are consistent with it having acquired its molecular (and atomic) gas from a spiral galaxy. Further detailed studies of the CO isotopologues in other early-type galaxies would be valuable for investigating the histories of those that may have acquired their gas from dwarfs. Finally, these ALMA data also show an unidentified line source that is probably a background galaxy similar to those found at <jats:italic>z</jats:italic> = 1–3 in blind CO surveys.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We model the Neupert effect that relates flare heating energy with the observed soft X-ray (SXR) emission. The traditional form of the Neupert effect refers to the correlation between the time-integrated hard X-ray or microwave light curve and the SXR light curve. In this paper, we instead use as the proxy for heating energy the ultraviolet (UV) emission at the footpoints of flare loops and modify the model of the Neupert effect by taking into account the discrete nature of flare heating, as well as cooling. In the modified empirical model, spatially resolved UV light curves from the transition region or upper chromosphere are each convolved with a kernel function characterizing the decay of the flare loop emission. Contributions by all loops are summed to compare with the observed total SXR emission. The model has successfully reproduced the observed SXR emission from its rise to decay. To estimate the heating energies in flare loops, we also employ the UV footpoint calorimeter (UFC) method that infers heating rates in flare loops from these UV light curves and models the evolution of flare loops with a zero-dimensional hydrodynamic code. The experiments show that a multitude of impulsive heating events do not well reproduce the observed flare SXR light curve, but a two-phase heating model leads to better agreement with observations. Comparison of the two models of the Neupert effect further allows us to calibrate the UFC method and improve the estimate of heating rates in flare loops continuously formed by magnetic reconnection throughout the flare evolution.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the detailed optical evolution of a Type Ib SN 2015dj in NGC 7371, using data spanning up to ∼170 days after discovery. SN 2015dj shares similarity in light-curve shape with SN 2007gr and peaks at <jats:italic>M</jats:italic> <jats:sub> <jats:italic>V</jats:italic> </jats:sub> = −17.37 ± 0.02 mag. Analytical modeling of the quasi bolometric light curve yields 0.06 ± 0.01 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> of <jats:sup>56</jats:sup>Ni, ejecta mass <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{\mathrm{ej}}={1.4}_{-0.5}^{+1.3}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabdf5cieqn1.gif" xlink:type="simple" /> </jats:inline-formula> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, and kinetic energy <jats:inline-formula> <jats:tex-math> <?CDATA ${E}_{{\rm{k}}}={0.7}_{-0.3}^{+0.6}\times {10}^{51}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabdf5cieqn2.gif" xlink:type="simple" /> </jats:inline-formula> erg. The spectral features show a fast evolution and resemble those of spherically symmetric ejecta. The analysis of nebular phase spectral lines indicates a progenitor mass between 13–20 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, suggesting a binary scenario.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Central compact objects (CCOs) are young neutron stars emitting thermal X-rays with bolometric luminosities <jats:italic>L</jats:italic> <jats:sub>X</jats:sub> in the range of 10<jats:sup>32</jats:sup>–10<jats:sup>34</jats:sup> erg s<jats:sup>−1</jats:sup>. Gourgouliatos, Hollerbach, and Igoshev recently suggested that peculiar emission properties of CCOs can be explained by tangled magnetic field configurations formed in a stochastic dynamo during the proto–neutron star stage. In this case the magnetic field consists of multiple small-scale components with negligible contribution of global dipolar field. We study numerically three-dimensional magnetothermal evolution of tangled crustal magnetic fields in neutron stars. We find that all configurations produce complicated surface thermal patterns that consist of multiple small hot regions located at significant separations from each other. The configurations with initial magnetic energy of (2.5–10) × 10<jats:sup>47</jats:sup> erg have temperatures of hot regions that reach ≈ 0.2 keV, to be compared with the bulk temperature of ≈ 0.1 keV in our simulations with no cooling. A factor of two in temperature is also seen in observations of CCOs. The hot spots produce periodic modulations in light curve with typical amplitudes of ≤9%–11%. Therefore, the tangled magnetic field configuration can explain thermal emission properties of some CCOs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the discovery of a luminous X-ray transient, serendipitously detected by Swift’s X-ray Telescope on 2020 February 5, located in the nucleus of the galaxy SDSS J143359.16+400636.0 at <jats:italic>z</jats:italic> = 0.099 (luminosity distance <jats:italic>D</jats:italic> <jats:sub>L</jats:sub> = 456 Mpc). The transient was observed to reach a peak luminosity of ∼10<jats:sup>44</jats:sup> erg s<jats:sup>−1</jats:sup> in the 0.3–10 keV X-ray band, which was ∼20 times more than the peak optical/UV luminosity. Optical, UV, and X-ray light curves from the Zwicky Transient Facility and Swift show a decline in flux from the source consistent with <jats:italic>t</jats:italic> <jats:sup>−5/3</jats:sup>, and observations with NuSTAR and Chandra show a soft X-ray spectrum with photon index Γ = 2.9 ± 0.1. The X-ray/UV properties are inconsistent with well-known active galactic nucleus properties and have more in common with known X-ray tidal disruption events (TDEs), leading us to conclude that it was likely a TDE. The broadband spectral energy distribution can be described well by a disk blackbody model with an inner disk temperature of <jats:inline-formula> <jats:tex-math> <?CDATA ${7.3}_{-0.8}^{+0.3}\times {10}^{5}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabde34ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> K, with a large fraction (&gt;40%) of the disk emission upscattered into the X-ray band. An optical spectrum taken with Keck/LRIS after the X-ray detection reveals LINER line ratios in the host galaxy, suggesting low-level accretion onto the supermassive black hole prior to the event, but no broad lines or other indications of a TDE were seen. The stellar velocity dispersion implies that the mass of the supermassive black hole powering the event is log(<jats:italic>M</jats:italic> <jats:sub>BH</jats:sub>/<jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) = 7.41 ± 0.41, and we estimate that at peak the Eddington fraction of this event was ∼50%. This likely TDE was not identified by wide-field optical surveys or optical spectroscopy, indicating that more events like this would be missed without wide-field UV or X-ray surveys.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We have examined 13 pointed observations of the TeV-emitting high synchrotron peak blazar PKS 2155−304, taken by the Suzaku satellite throughout its operational period. We found that the blazar showed large-amplitude intraday variabilities in the soft (0.8–1.5 keV) and the hard (1.5–8.0 keV) bands in the light curves. Spectral variability on intraday timescales is estimated using the hardness ratio. The blazar usually becomes harder when brighter and vice versa, following the typical behavior of high synchrotron peak blazars. The power spectral density analyses of 11 out of 13 light curves in the total energy (0.8–8.0 keV) are found to be dominated by red noise, with power-law spectral indices that span a large range, from −2.81 to −0.88. Discrete correlation function analyses of all the 13 light curves between the soft and the hard bands show that they are well correlated and peak at, or very close to, zero lag. This indicates that the emissions in soft and hard bands are probably cospatial and emitted from the same population of leptons. Considering fluxes versus variability timescales, we found no correlation on intraday timescales, implying that X-ray emission from PKS 2155−304 is not dominated by simple changes in the Doppler factor. We briefly discuss the most likely emission mechanisms responsible for the observed flux and spectral variabilities and place constraints on magnetic field strength and Lorentz factors of the electrons emitting the X-rays in the most likely scenario.</jats:p>