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<jats:title>Abstract</jats:title> <jats:p>A time–distance measurement technique is derived to isolate phase travel time anisotropy caused by subsurface horizontal magnetic fields; a method that uses the measured anisotropy to estimate the field’s orientation is also derived. A simulation of acoustic waves propagating in a uniform, inclined magnetic field with solar background structure is used to verify the derived technique. Then the procedure is applied to a numerical simulation of a sunspot for which the subsurface state is known to provide context for the results obtained from the study of several sunspots observed by the Helioseismic and Magnetic Imager. Significant anisotropies are detected, on the order of 1 minute, and the subsurface field’s azimuth is estimated and compared with the azimuth of the surface magnetic field. In all cases, the subsurface azimuth is found to be well aligned with that of the surface, and the results from the numerical simulation are used to interpret features in the detected travel time anisotropy.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Hot and warm Jupiters (HJs&amp;WJs) are gas-giant planets orbiting their host stars at short orbital periods, posing a challenge to their efficient in situ formation. Therefore, most HJs&amp;WJs are thought to have migrated from an initially farther-out birth location. Current migration models, i.e., disk migration (gas-dissipation driven) and eccentric migration (tidal evolution driven), fail to produce the occurrence rate and orbital properties of HJs&amp;WJs. Here we study the role of thermal evolution and its coupling to tidal evolution. We use <jats:monospace>AMUSE</jats:monospace>, a numerical environment, and <jats:monospace>MESA</jats:monospace>, planetary evolution modeling, to model in detail the coupled internal and orbital evolution of gas giants during their eccentric migration. In a companion paper, we use a simple semianalytic model, validated by our numerical model, and run a population-synthesis study. We consider the initially inflated radii of gas giants (expected following their formation), as well study the effects of the potentially slowed contraction and even reinflation of gas giants (due to tidal and radiative heating) on the eccentric migration. Tidal forces that drive eccentric migration are highly sensitive to the planetary structure and radius. Consequently, we find that this form of inflated eccentric migration operates on significantly (up to an order of magnitude) shorter timescales than previously studied eccentric-migration models. Therefore, inflated eccentric migration gives rise to the more rapid formation of HJs&amp;WJs, higher occurrence rates of WJs, and higher rates of tidal disruptions, compared with previous eccentric-migration models that consider constant ∼Jupiter radii for HJ and WJ progenitors. Coupled thermal–dynamical evolution of eccentric gas giants can therefore play a key role in their evolution.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>High dust density in the midplane of protoplanetary disks is favorable for efficient grain growth and can allow fast formation of planetesimals and planets, before disks dissipate. Vertical settling and dust trapping in pressure maxima are two mechanisms allowing dust to concentrate in geometrically thin and high-density regions. In this work, we aim to study these mechanisms in the highly inclined protoplanetary disk SSTC2D J163131.2-242627 (Oph 163131, <jats:italic>i</jats:italic> ∼ 84°). We present new high-angular-resolution continuum and <jats:sup>12</jats:sup>CO ALMA observations of Oph 163131. The gas emission appears significantly more extended in the vertical and radial direction compared to the dust emission, consistent with vertical settling and possibly radial drift. In addition, the new continuum observations reveal two clear rings. The outer ring, located at ∼100 au, is well-resolved in the observations, allowing us to put stringent constraints on the vertical extent of millimeter dust particles. We model the disk using radiative transfer and find that the scale height of millimeter-sized grains is 0.5 au or less at 100 au from the central star. This value is about one order of magnitude smaller than the scale height of smaller micron-sized dust grains constrained by previous modeling, which implies that efficient settling of the large grains is occurring in the disk. When adopting a parametric dust settling prescription, we find that the observations are consistent with a turbulent viscosity coefficient of about <jats:italic>α</jats:italic> ≲ 10<jats:sup>−5</jats:sup> at 100 au. Finally, we find that the thin dust scale height measured in Oph 163131 is favorable for planetary growth by pebble accretion: a 10 <jats:italic>M</jats:italic> <jats:sub>E</jats:sub> planet may grow within less than 10 Myr, even in orbits exceeding 50 au.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The merger of two galaxies, each hosting a supermassive black hole (SMBH) of mass 10<jats:sup>6</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> or more, could yield a bound SMBH binary. For the early-type galaxy NGC 4472, we study how astrometry with a next-generation Very Large Array could be used to monitor the reflex motion of the primary SMBH of mass <jats:italic>M</jats:italic> <jats:sub>pri</jats:sub>, as it is tugged on by the secondary SMBH of mass <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{\sec }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>sec</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac680bieqn1.gif" xlink:type="simple" /> </jats:inline-formula>. Casting the orbit of the putative SMBH binary in terms of its period <jats:italic>P</jats:italic>, semimajor axis <jats:italic>a</jats:italic> <jats:sub>bin</jats:sub>, and mass ratio <jats:inline-formula> <jats:tex-math> <?CDATA $q={M}_{\sec }/{M}_{\mathrm{pri}}\leqslant 1$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>q</mml:mi> <mml:mo>=</mml:mo> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>sec</mml:mi> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>M</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>pri</mml:mi> </mml:mrow> </mml:msub> <mml:mo>≤</mml:mo> <mml:mn>1</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac680bieqn2.gif" xlink:type="simple" /> </jats:inline-formula>, we find the following: (1) Orbits with fiducial periods of <jats:italic>P</jats:italic> = 4 yr and 40 yr could be spatially resolved and monitored. (2) For a 95% accuracy of 2 <jats:italic>μ</jats:italic>as per monitoring epoch, subparsec values of <jats:italic>a</jats:italic> <jats:sub>bin</jats:sub> could be accessed over a range of mass ratios notionally encompassing major <jats:inline-formula> <jats:tex-math> <?CDATA $\left(q\gt \tfrac{1}{4}\right)$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mfenced close=")" open="("> <mml:mrow> <mml:mi>q</mml:mi> <mml:mo>&gt;</mml:mo> <mml:mstyle displaystyle="false"> <mml:mfrac> <mml:mrow> <mml:mn>1</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> </mml:mfrac> </mml:mstyle> </mml:mrow> </mml:mfenced> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac680bieqn3.gif" xlink:type="simple" /> </jats:inline-formula> and minor <jats:inline-formula> <jats:tex-math> <?CDATA $\left(q\lt \tfrac{1}{4}\right)$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mfenced close=")" open="("> <mml:mrow> <mml:mi>q</mml:mi> <mml:mo>&lt;</mml:mo> <mml:mstyle displaystyle="false"> <mml:mfrac> <mml:mrow> <mml:mn>1</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>4</mml:mn> </mml:mrow> </mml:mfrac> </mml:mstyle> </mml:mrow> </mml:mfenced> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac680bieqn4.gif" xlink:type="simple" /> </jats:inline-formula> galaxy mergers. (3) If no reflex motion is detected for <jats:italic>M</jats:italic> <jats:sub>pri</jats:sub> after 1 (10) yr of monitoring, an SMBH binary with period <jats:italic>P</jats:italic> = 4 (40) yr and mass ratio <jats:italic>q</jats:italic> &gt; 0.01 (0.003) could be excluded. This would suggest no present-day evidence for a past major merger like that recently simulated, where scouring by a <jats:italic>q</jats:italic> ∼ 1 SMBH binary formed a stellar core with kinematic traits like those of NGC 4472. (4) Astrometric monitoring could independently check the upper limits on <jats:italic>q</jats:italic> from searches for continuous gravitational waves from NGC 4472.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present observations of ASASSN-20hx, a nearby ambiguous nuclear transient (ANT) discovered in NGC 6297 by the All-Sky Automated Survey for Supernovae (ASAS-SN). We observed ASASSN-20hx from −30 to 275 days relative to the peak UV/optical emission using high-cadence, multiwavelength spectroscopy and photometry. From Transiting Exoplanet Survey Satellite data, we determine that the ANT began to brighten on 2020 June 22.8 with a linear rise in flux for at least the first week. ASASSN-20hx peaked in the UV/optical 30 days later on 2020 July 22.8 (MJD = 59052.8) at a bolometric luminosity of <jats:italic>L</jats:italic> = (3.15 ± 0.04) × 10<jats:sup>43</jats:sup> erg s<jats:sup>−1</jats:sup>. The subsequent decline is slower than any TDE observed to date and consistent with many other ANTs. Compared to an archival X-ray detection, the X-ray luminosity of ASASSN-20hx increased by an order of magnitude to <jats:italic>L</jats:italic> <jats:sub> <jats:italic>x</jats:italic> </jats:sub> ∼ 1.5 × 10<jats:sup>42</jats:sup> erg s<jats:sup>−1</jats:sup> and then slowly declined over time. The X-ray emission is well fit by a power law with a photon index of Γ ∼ 2.3–2.6. Both the optical and near-infrared spectra of ASASSN-20hx lack emission lines, unusual for any known class of nuclear transient. While ASASSN-20hx has some characteristics seen in both tidal disruption events and active galactic nuclei, it cannot be definitively classified with current data.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>ZTF J213056.71+442046.5 is the prototype of a small class of recently discovered compact binaries composed of a white dwarf and a hot subdwarf that fills its Roche lobe. Its orbital period of only 39 minutes is the shortest known for the objects in this class. Evidence for a high orbital inclination (<jats:italic>i</jats:italic> = 86°) and for the presence of an accretion disk has been inferred from a detailed modeling of its optical photometric and spectroscopic data. We report the results of an XMM-Newton observation carried out on 2021 January 7. ZTF J213056.71+442046.5 was clearly detected by the Optical Monitor, which showed a periodic variability in the UV band (200–400 nm), with a light curve similar to that seen at longer wavelengths. Despite accretion on the white dwarf at an estimated rate of the order of 10<jats:sup>−9 </jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙ </jats:sub>yr<jats:sup>−1</jats:sup>, no X-rays were detected with the EPIC instrument, with a limit of ∼10<jats:sup>30</jats:sup> erg s<jats:sup>−1</jats:sup> on the 0.2–12 keV luminosity. We discuss possible explanations for the lack of a strong X-ray emission from this system.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Rapidly rotating neutron stars are promising sources for existing and upcoming gravitational-wave interferometers. While relatively dim, these systems are expected to emit continuously, allowing for signal to be accumulated through persistent monitoring over year-long timescales. If, at some point during the observational window, the source comes to lie behind a dense collection of stars, transient gravitational lensing may occur. Such events, though rare, would modulate the waveform, induce phase drifts, and ultimately affect parameter inferences concerning the nuclear equation of state and/or magnetic field structure of the neutron star. Importantly, the radiation wavelength will typically exceed the Schwarzschild radius of the individual perturbers in this scenario, implying that (micro)lensing occurs in the diffractive regime, where geometric optics does not apply. In this paper, we make use of numerical tools that borrow from Picard–Lefschetz theory to efficiently evaluate the relevant Fresnel–Kirchhoff integrals for <jats:italic>n</jats:italic> ≳ 10<jats:sup>2</jats:sup> microlenses. Modulated strain profiles are constructed both in general and for particular neutron star trajectories relative to some simulated macrolenses.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>One of the most common methods for inferring galaxy attenuation curves is via spectral energy distribution (SED) modeling, where the dust attenuation properties are modeled simultaneously with other galaxy physical properties. In this paper, we assess the ability of SED modeling to infer these dust attenuation curves from broadband photometry, and suggest a new flexible model that greatly improves the accuracy of attenuation curve derivations. To do this, we fit mock SEDs generated from the <jats:sc>simba</jats:sc> cosmological simulation with the <jats:sc>prospector</jats:sc> SED fitting code. We consider the impact of the commonly assumed uniform screen model and introduce a new nonuniform screen model parameterized by the fraction of unobscured stellar light. This nonuniform screen model allows for a nonzero fraction of stellar light to remain unattenuated, resulting in a more flexible attenuation curve shape by decoupling the shape of the UV attenuation curve from the optical attenuation curve. The ability to constrain the dust attenuation curve is significantly improved with the use of a nonuniform screen model, with the median offset in UV attenuation decreasing from −0.30 dex with a uniform screen model to −0.17 dex with the nonuniform screen model. With this increase in dust attenuation modeling accuracy, we also improve the star formation rates (SFRs) inferred with the nonuniform screen model, decreasing the SFR offset on average by 0.12 dex. We discuss the efficacy of this new model, focusing on caveats with modeling star-dust geometries and the constraining power of available SED observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Active galactic nuclei (AGN) can launch outflows of ionized gas that may influence galaxy evolution, and quantifying their full impact requires spatially resolved measurements of the gas masses, velocities, and radial extents. We previously reported these quantities for the ionized narrow-line region outflows in six low-redshift AGN, where the gas velocities and extents were determined from Hubble Space Telescope long-slit spectroscopy. However, calculating the gas masses required multicomponent photoionization models to account for radial variations in the gas densities, which span ∼6 orders of magnitude. To simplify this method for larger samples with less spectral coverage, we compare these gas masses with those calculated from techniques in the literature. First, we use a recombination equation with three different estimates for the radial density profiles. These include constant densities, those derived from [S <jats:sc>ii</jats:sc>], and power-law profiles based on constant values of the ionization parameter (<jats:italic>U</jats:italic>). Second, we use single-component photoionization models with power-law density profiles based on constant <jats:italic>U</jats:italic>, and allow <jats:italic>U</jats:italic> to vary with radius based on the [O <jats:sc>iii</jats:sc>]/H<jats:italic>β</jats:italic> ratios. We find that assuming a constant density of <jats:italic>n</jats:italic> <jats:sub>H</jats:sub> = 10<jats:sup>2</jats:sup> cm<jats:sup>−3</jats:sup> overestimates the gas masses for all six outflows, particularly at small radii where the outflow rates peak. The use of [S <jats:sc>ii</jats:sc>] marginally matches the total gas masses, but also overestimates at small radii. Overall, single-component photoionization models where <jats:italic>U</jats:italic> varies with radius are able to best match the gas mass and outflow rate profiles when there are insufficient emission lines to construct detailed models.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>There are currently many large-field surveys that are operational and are being planned including the powerful Vera C. Rubin Observatory Legacy Survey of Space and Time. These surveys will increase the number and diversity of transients dramatically. However, for some transients, like supernovae (SNe), we can gain more understanding by directed observations (e.g., shock breakout and <jats:italic>γ</jats:italic>-ray detections) than by simply increasing the sample size. For example, the initial emission from these transients can be a powerful probe of these explosions. Upcoming ground-based detectors are not ideally suited to observing the initial emission (shock emergence) of these transients. These observations require a large field-of-view X-ray mission with a UV follow-up within the first hour of shock breakout. The emission in the first 1 hr to even 1 day provides strong constraints on the stellar radius and asymmetries in the outer layers of stars, the properties of the circumstellar medium (e.g., inhomogeneities in the wind for core-collapse SNe and accreting companions in thermonuclear SNe), and the transition region between these two areas. This paper describes a simulation for the number of SNe that could be seen by a large field-of-view lobster-eye X-ray and UV observatory.</jats:p>