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<jats:title>Abstract</jats:title> <jats:p>Pox 186 is an exceptionally small dwarf starburst galaxy hosting a stellar mass of ∼10<jats:sup>5</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. Undetected in H <jats:sc>i</jats:sc> (<jats:italic>M</jats:italic> &lt; 10<jats:sup>6</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) from deep 21 cm observations and with an [O <jats:sc>iii</jats:sc>]/[O <jats:sc>ii</jats:sc>] (5007/3727) ratio of 18.3 ± 0.11, Pox 186 is a promising candidate Lyman continuum emitter. It may be a possible analog of low-mass reionization-era galaxies. We present a spatially resolved kinematic study of Pox 186 and identify two distinct ionized gas components: a broad one with <jats:italic>σ</jats:italic> &gt; 400 km s<jats:sup>−1</jats:sup> and a narrow one with <jats:italic>σ</jats:italic> &lt; 30 km s<jats:sup>−1</jats:sup>. We find strikingly different morphologies between the two components and direct evidence of outflows as seen in the high-velocity gas. Possible physical mechanisms driving the creation of high-velocity gas seen in [O <jats:sc>iii</jats:sc>] are discussed, from outflow geometry to turbulent mixing between a hot (10<jats:sup>6</jats:sup> K) star-cluster wind and cooler (10<jats:sup>4</jats:sup> K) gas clouds. We find a modest mass-outflow rate of 0.022 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup> with a small mass-loading factor of 0.5, consistent with other low-mass galaxies. Finally, we compare the mass-loading factor of Pox 186 with extrapolations from numerical simulations and discuss possible reasons for the apparent discrepancy between them.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a detailed spectral analysis of the joint XMM-Newton and NuSTAR observations of the active galactic nuclei (AGNs) in the Seyfert 1.5 Galaxy ESO 362-G18. The broadband (0.3–79 keV) spectrum shows the presence of a power-law continuum with a soft excess below 2 keV, iron K<jats:italic>α</jats:italic> emission (∼6.4 keV), and a Compton hump (peaking at ∼20 keV). We find that the soft excess can be modeled by two different possible scenarios: a warm (<jats:italic>kT</jats:italic> <jats:sub>e</jats:sub> ∼ 0.2 keV) and optically thick (<jats:italic>τ</jats:italic> ∼ 34) Comptonizing corona, or with a relativistically blurred reflection off a high-density (<jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}[{n}_{{\rm{e}}}/{\mathrm{cm}}^{-3}]\gt 18.3$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabf430ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) inner disk. These two models cannot be easily distinguished solely from their fit statistics. However, the low temperature (<jats:italic>kT</jats:italic> <jats:sub>e</jats:sub> ∼ 20 keV) and the thick optical depth (<jats:italic>τ</jats:italic> ∼ 5) of the hot corona required by the warm corona scenario are uncommon for AGNs. We also fit a “hybrid” model, which includes both disk reflection and a warm corona. Unsurprisingly, as this is the most complex of the models considered, this provides the best fit, and more reasonable coronal parameters. In this case, the majority of the soft excess flux arises in the warm corona component. However, based on recent simulations of warm coronae, it is not clear whether such a structure can really exist at the low accretion rates relevant for ESO 362-G18 (<jats:inline-formula> <jats:tex-math> <?CDATA $\dot{m}\sim 0.015$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabf430ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>). This may therefore argue in favor of a scenario in which the soft excess is instead dominated by the relativistic reflection. Based on this model, we find that the data would require a compact hot corona (<jats:italic>h</jats:italic> ∼ 3 <jats:italic>R</jats:italic> <jats:sub>Horizon</jats:sub>) around a rapidly spinning (<jats:italic>a</jats:italic> <jats:sub>⋆</jats:sub> &gt; 0.927) black hole.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study the effects of additional cooling due to the emission of a dark matter candidate particle, the dark photon, on the final phases of the evolution of a 15 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> star and resulting modifications of the pre-supernova neutrino signal. For a substantial portion of the dark photon parameter space the extra cooling speeds up Si burning, which results in a reduced number of neutrinos emitted during the last day before core collapse. This reduction can be described by a systematic acceleration of the relevant timescales and the results can be estimated semi-analytically in good agreement with the numerical simulations. Outside the semi-analytic regime we find more complicated effects. In a narrow parameter range, low-mass dark photons lead to an increase in the number of emitted neutrinos because of additional shell-burning episodes that delay core collapse. Furthermore, relatively strong couplings produce a thermonuclear runaway during O burning, which could result in a complete disruption of the star but requires more detailed simulations to determine the outcome. Our results show that pre-supernova neutrino signals are a potential probe of the dark photon parameter space.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We presented a multiwavelength study of the AFGL 333-Ridge. The molecular line data reveals that the AFGL 333-Ridge has two independent velocity components at −50.5 and −48.0 km s<jats:sup>−1</jats:sup>. In the position–velocity diagram, the bridge feature connects with two parts that are spatially correlated but separated in velocity. This observational evidence supports the scenario that the two velocity components have collided and merged into one molecular cloud. The majority of Class I young stellar objects (YSOs) are distributed within the collision region, suggesting that the cloud–cloud collision has induced the YSOs’ formation in the ridge. Using the radio recombination line (RRL) data obtained by the Five-hundred-meter Aperture Spherical radio Telescope, the RRL velocities of three H <jats:sc>ii</jats:sc> regions are consistent with that of the AFGL 333-Ridge. By comparing the three H <jats:sc>ii</jats:sc> regions’ dynamical ages with the collision timescale of the two components, we conclude that the influence of the three H <jats:sc>ii</jats:sc> regions may not drive the two clouds to merge. The formation of the AFGL 333-Ridge is probably due to the expansion of the giant H <jats:sc>ii</jats:sc> region W4.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>One possible progenitor of short gamma-ray bursts (GRBs) is thought to be from a double neutron star (NS) merger, and the remnant of such a merger may be a supramassive NS, which is supported by rigid rotation and through its survival of hundreds of seconds before collapsing into a black hole (BH). If this is the case, an optical/infrared transient (namely merger-nova) is generated from the ejected materials and it is powered by radioactive decay from <jats:italic>r</jats:italic>-process, spin-down energy from a supramassive NS, as well as the magnetic wind from a newborn BH. In this paper, we systematically search for the signature of a supramassive NS central engine by analyzing the X-ray emission of short GRBs with internal plateau observed by Swift, and we find that five candidates of short GRBs have such a feature with redshift measurement. Then, we calculate the possible merger-nova emission from those candidates given the typical model parameters by considering the above three energy sources, and compare its brightness with the sensitivity of some optical telescopes. We find that the merger-nova emission of GRB 060801 in <jats:italic>K</jats:italic>-, <jats:italic>r</jats:italic>-, and <jats:italic>U</jats:italic>-bands with variations of <jats:italic>M</jats:italic> <jats:sub>ej</jats:sub> (10<jats:sup>−4</jats:sup>–10<jats:sup>−2</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>), <jats:italic>κ</jats:italic> (0.1–10 cm<jats:sup>2</jats:sup> g<jats:sup>−1</jats:sup>), and <jats:italic>β</jats:italic> (0.1–0.3) is very difficult to detect using the Vera C. Rubin, Panoramic Survey Telescope and Rapid Response System (Pan-STARRS), the Zwicky Transient Facility, and the Roman Space Telescope (Roman), except for the case of large ejecta mass <jats:italic>M</jats:italic> <jats:sub>ej</jats:sub> = 10<jats:sup>−2</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. However, we are very hopeful to detect the merger-nova emission of GRBs 090515, 100625A, and 101219A using more sensitive instruments, such as Vera C. Rubin, Pan-STARRS, and Roman. Moreover, the merger-nova emission of GRB 160821B is bright enough to detect in our calculations, and it is also consistent with current real observations of merger-nova emission.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We study the nature of energy release and transfer for two sub-A class solar microflares observed during the second Focusing Optics X-ray Solar Imager (FOXSI-2) sounding rocket flight on 2014 December 11. FOXSI is the first solar-dedicated instrument to utilize focusing optics to image the Sun in the hard X-ray (HXR) regime, sensitive to energies of 4–20 keV. Through spectral analysis of the microflares using an optically thin isothermal plasma model, we find evidence for plasma heated to ∼10 MK and emission measures down to ∼10<jats:sup>44</jats:sup> cm<jats:sup>−3</jats:sup>. Though nonthermal emission was not detected for the FOXSI-2 microflares, a study of the parameter space for possible hidden nonthermal components shows that there could be enough energy in nonthermal electrons to account for the thermal energy in microflare 1, indicating that this flare is plausibly consistent with the standard thick-target model. With a solar-optimized design and improvements in HXR focusing optics, FOXSI-2 offers approximately five times greater sensitivity at 10 keV than the Nuclear Spectroscopic Telescope Array for typical microflare observations and allows for the first direct imaging spectroscopy of solar HXRs with an angular resolution at scales relevant for microflares. Harnessing these improved capabilities to study small-scale events, we find evidence for spatial and temporal complexity during a sub-A class flare. This analysis, combined with contemporaneous observations by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory, indicates that these microflares are more similar to large flares in their evolution than to the single burst of energy expected for a nanoflare.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Habitable-zone Planet Finder (HPF) is a fiber-fed precise radial velocity (RV) spectrograph at the 10 m Hobby–Eberly Telescope (HET). Due to its fixed-altitude design, the HET pupil changes appreciably across a track, leading to significant changes of the fiber far-field illumination. HPF’s fiber scrambler is designed to suppress the impact of these illumination changes on the RVs—but the residual impact on the RV measurements has yet to be probed on-sky. We use GJ 411, a bright early type (M2) M dwarf to probe the effects of far-field input trends due to these pupil variations on HPF RVs. These large changes (∼2x) in the pupil area and centroid present a harsh test of HPF’s far-field scrambling. Our results show that the RVs are effectively decoupled from these extreme far-field input changes due to pupil centroid offsets, attesting to the effectiveness of the scrambler design. This experiment allows us to test the impact of these changes with large pupil variation on-sky, something we would not easily be able to do at a conventional optical telescope. While the pupil and illumination changes expected at these other telescopes are small, scaling from our results enables us to estimate and bound these effects, and show that they are controllable even for the new and next generation of RV instruments in their quest to beat down instrumental noise sources toward the goal of a few <jats:inline-formula> <jats:tex-math> <?CDATA $\,\mathrm{cm}\,{{\rm{s}}}^{-1}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mspace width="0.25em" /> <mml:mi>cm</mml:mi> <mml:mspace width="0.25em" /> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabec83ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Supermassive black hole binaries are likely to accrete interstellar gas through a circumbinary disk. Shortly before merger, the inner portions of this circumbinary disk are subject to general relativistic effects. To study this regime, we approximate the spacetime metric of close orbiting black holes by superimposing two boosted Kerr–Schild terms. After demonstrating the quality of this approximation, we carry out very long-term general relativistic magnetohydrodynamic simulations of the circumbinary disk. We consider black holes with spin dimensionless parameters of magnitude 0.9, in one simulation parallel to the orbital angular momentum of the binary, but in another anti-parallel. These are contrasted with spinless simulations. We find that, for a fixed surface mass density in the inner circumbinary disk, aligned spins of this magnitude approximately reduce the mass accretion rate by 14% and counter-aligned spins increase it by 45%, leaving many other disk properties unchanged.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The location of the obscuring “torus” in an active galactic nucleus (AGN) is still an unresolved issue. The line widths of X-ray fluorescence lines originating from the torus, particularly Fe K<jats:italic>α</jats:italic>, carry key information on the radii of line-emitting regions. Utilizing XCLUMPY, an X-ray clumpy torus model, we develop a realistic model of emission line profiles from an AGN torus where we take into account line broadening due to the Keplerian motion around the black hole. Then, we apply the updated model to the best available broadband spectra (3–100 keV) of the Circinus galaxy observed with Suzaku, XMM-Newton, Nuclear Spectroscopic Telescope Array, and Chandra, including 0.62 Ms Chandra/HETG data. We confirm that the torus is Compton-thick (hydrogen column density along the equatorial plane is <jats:inline-formula> <jats:tex-math> <?CDATA ${N}_{{\rm{H}}}^{\mathrm{Equ}}={2.16}_{-0.16}^{+0.24}\times {10}^{25}\ {\mathrm{cm}}^{-2}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabf0a2ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>), geometrically thin (torus angular width <jats:inline-formula> <jats:tex-math> <?CDATA $\sigma \,={10.3}_{-0.3}^{+0.7}\,{\rm{d}}{\rm{e}}{\rm{g}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabf0a2ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>), viewed edge-on (inclination <jats:inline-formula> <jats:tex-math> <?CDATA $i={78.3}_{-0.9}^{+0.4}\,{\rm{d}}{\rm{e}}{\rm{g}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabf0a2ieqn3.gif" xlink:type="simple" /> </jats:inline-formula>), and has supersolar abundance (<jats:inline-formula> <jats:tex-math> <?CDATA ${1.52}_{-0.06}^{+0.04}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabf0a2ieqn4.gif" xlink:type="simple" /> </jats:inline-formula> times solar). Simultaneously analyzing the Chandra/HETG first-, second-, and third-order spectra with consideration of the spatial extent of the Fe K<jats:italic>α</jats:italic> line-emitting region, we constrain the inner radius of the torus to be <jats:inline-formula> <jats:tex-math> <?CDATA ${1.9}_{-0.8}^{+3.1}\times {10}^{5}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabf0a2ieqn5.gif" xlink:type="simple" /> </jats:inline-formula> times the gravitational radius, or <jats:inline-formula> <jats:tex-math> <?CDATA ${1.6}_{-0.9}^{+1.5}\times {10}^{-2}\ \mathrm{pc}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabf0a2ieqn6.gif" xlink:type="simple" /> </jats:inline-formula> for a black hole mass of (1.7 ± 0.3) × 10<jats:sup>6</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. This is about three times smaller than that estimated from the dust sublimation radius, suggesting that the inner side of the dusty region of the torus is composed of dust-free gas.</jats:p>