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<jats:title>Abstract</jats:title> <jats:p>We report new Northern Extended Millimeter Array observations of the [C <jats:sc>ii</jats:sc>]<jats:sub>158 <jats:italic>μ</jats:italic>m</jats:sub>, [N <jats:sc>ii</jats:sc>]<jats:sub>205 <jats:italic>μ</jats:italic>m</jats:sub>, and [O <jats:sc>i</jats:sc>]<jats:sub>146 <jats:italic>μ</jats:italic>m</jats:sub> atomic fine structure lines (FSLs) and dust continuum emission of J1148+5251, a <jats:italic>z</jats:italic> = 6.42 quasar, which probe the physical properties of its interstellar medium (ISM). The radially averaged [C <jats:sc>ii</jats:sc>]<jats:sub>158 <jats:italic>μ</jats:italic>m</jats:sub> and dust continuum emission have similar extensions (up to <jats:inline-formula> <jats:tex-math> <?CDATA $\theta ={2.51}_{-0.25}^{+0.46}\ \mathrm{arcsec}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>θ</mml:mi> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>2.51</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.25</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.46</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.33em" /> <mml:mi>arcsec</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac4e94ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, corresponding to <jats:inline-formula> <jats:tex-math> <?CDATA $r={9.8}_{-2.1}^{+3.3}\ \mathrm{kpc}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>r</mml:mi> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>9.8</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2.1</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>3.3</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.33em" /> <mml:mi>kpc</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac4e94ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>, accounting for beam convolution), confirming that J1148+5251 is the quasar with the largest [C <jats:sc>ii</jats:sc>]<jats:sub>158 <jats:italic>μ</jats:italic>m</jats:sub>-emitting reservoir known at these epochs. Moreover, if the [C <jats:sc>ii</jats:sc>]<jats:sub>158 <jats:italic>μ</jats:italic>m</jats:sub> emission is examined only along its NE–SW axis, a significant excess (&gt;5.8<jats:italic>σ</jats:italic>) of [C <jats:sc>ii</jats:sc>]<jats:sub>158 <jats:italic>μ</jats:italic>m</jats:sub> emission (with respect to the dust) is detected. The new wide-bandwidth observations enable us to accurately constrain the continuum emission, and do not statistically require the presence of broad [C <jats:sc>ii</jats:sc>]<jats:sub>158 <jats:italic>μ</jats:italic>m</jats:sub> line wings that were reported in previous studies. We also report the first detection of the [O <jats:sc>i</jats:sc>]<jats:sub>146 <jats:italic>μ</jats:italic>m</jats:sub> and (tentatively) [N <jats:sc>ii</jats:sc>]<jats:sub>205 <jats:italic>μ</jats:italic>m</jats:sub> emission lines in J1148+5251. Using FSL ratios of the [C <jats:sc>ii</jats:sc>]<jats:sub>158 <jats:italic>μ</jats:italic>m</jats:sub>, [N <jats:sc>ii</jats:sc>]<jats:sub>205 <jats:italic>μ</jats:italic>m</jats:sub>, [O <jats:sc>i</jats:sc>]<jats:sub>146 <jats:italic>μ</jats:italic>m</jats:sub>, and previously measured [C <jats:sc>i</jats:sc>]<jats:sub>369 <jats:italic>μ</jats:italic>m</jats:sub> emission lines, we show that J1148+5251 has similar ISM conditions compared to lower-redshift (ultra)luminous infrared galaxies. CLOUDY modeling of the FSL ratios excludes X-ray-dominated regions and favors photodissociation regions as the origin of the FSL emission. We find that a high radiation field (10<jats:sup>3.5–4.5</jats:sup> <jats:italic>G</jats:italic> <jats:sub>0</jats:sub>), a high gas density (<jats:italic>n</jats:italic> ≃ 10<jats:sup>3.5–4.5</jats:sup> cm<jats:sup>−3</jats:sup>), and an H <jats:sc>i</jats:sc> column density of 10<jats:sup>23</jats:sup> cm<jats:sup>−2</jats:sup> reproduce the observed FSL ratios well.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present analysis of the proper-motion (PM) field of the red clump stars in the Large Magellanic Cloud (LMC) disk using the Gaia Early Data Release 3 catalog. Using a kinematic model based on old stars with 3D velocity measurements, we construct the residual PM field by subtracting the center-of-mass motion and internal rotation motion components. The residual PM field reveals asymmetric patterns, including larger residual PMs in the southern disk. Comparisons of the observed residual PM field with those of five numerical simulations of an LMC analog that is subject to the tidal fields of the Milky Way and the Small Magellanic Cloud (SMC) show that the present-day LMC is not in dynamical equilibrium. We find that both the observed level of disk heating (PM residual rms of 0.057 ± 0.002 mas yr<jats:sup>−1</jats:sup>) and kinematic asymmetry are not reproduced by Milky Way tides or if the SMC impact parameter is larger than the size of the LMC disk. This measured level of disk heating provides a novel and important method to validate numerical simulations of the LMC–SMC interaction history. Our results alone put constraints on an impact parameter ≲10 kpc and impact timing &lt;250 Myr. When adopting the impact timing constraint of ∼140–160 Myr ago from previous studies, our results suggest that the most recent SMC encounter must have occurred with an impact parameter of ∼5 kpc. We also find consistent radial trends in the kinematically and geometrically derived disk inclination and line-of-node position angles, indicating a common origin.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The “equal-contrast technique” (ECT) methodology, developed by Singh et al. to generate uniform long time series of Ca-K images obtained during the 20th century from the Kodaikanal Observatory (KO), improved the correlation between the plage area and sunspot parameters. The same methodology can also be used on other observatory data taken with different instruments. We can combine such ECT-corrected images to reduce the gaps in the observations and make a long uniform data set to study short- and long-term variations. We apply this procedure to Mount Wilson Observatory (MWO) historical Ca-K data and recent Ca-K filtergrams obtained using narrowband filters at KO and the Mauna Loa Solar Observatory (MLSO). To determine the success of this method, the results of the analysis of the ECT images obtained from KO, MWO, and MLSO are compared. A comparison of the plage and active areas derived from KO and MWO images before and after the ECT procedure indicates an improvement in the correlation coefficients (CCs) between all the data sets after the ECT application. The CC for the combined monthly mean Ca-K plage area derived from the KO, MWO, and Precision Solar Photometric Telescope (at the MLSO) data with sunspot numbers is 0.96 for the period 1905–2015. The paper demonstrates that the time series of Ca-K data obtained from different instruments after applying the ECT procedure becomes uniform in contrast. The combined time series of KO and MWO spectroheliograms has 12 hr intervals compared to the ≈24 hr gap for a time series from a single observatory.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>This paper examines the short- and mid-term periodicities (≲2 yr) in the cosmic-ray flux along 55 yr, from 1964 to 2019. The cosmic-ray flux has been computed by averaging the counting rates, in typified units, of a set of selected neutron monitors. This builds a representative virtual neutron monitor, named the global neutron monitor. The relevant discovered periodicities are ∼13.5, ∼27, ∼46–64, ∼79–83 day; Rieger-type (∼134–190 days); ∼225–309 day; and ∼1.06–1.15, ∼1.31–1.40, and ∼1.75–2.20 yr periods. The same analyses have been applied to the sunspot number (SSN) with the aim to compare the discovered periodicities and look for possible origins of these periodicities. Two main results have been achieved: the periodicities of 77–83 days, 134–190 days (Rieger type), 225–309 days, ∼1.3 yr, and ∼1.7 yr could be related to the solar dynamo, and an inversely linear relationship has been found between the average of the SSN versus the duration time for each solar cycle of the ∼1.75–2.20 yr period.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Magnetic helicity is a measure of the entanglement of magnetic field lines used to characterize the complexity of solar active region (AR) magnetic fields. Previous attempts to use helicity-based indicators to predict solar eruptive/flaring events have shown promise but not been universally successful. Here we investigate the use of a quantity associated with the magnetic helicity, the magnetic winding, as a means to predict flaring activity. This quantity represents the fundamental entanglement of magnetic field lines and is independent of the magnetic field strength. We use vector magnetogram data derived from the Helioseismic Magnetic Imager (HMI) to calculate the evolution and distribution of the magnetic winding flux associated with five different ARs, three of them with little flaring activity/nonflaring (AR 11318, AR 12119, AR 12285) and two highly active with X-class flares (AR 11158, AR 12673). We decompose these quantities into “current-carrying” and “potential” parts. It is shown that the ARs that show flaring/eruptive activity have significant contributions to the winding input from the current-carrying part of the field. A significant and rapid input of current-carrying winding is found to be a precursor of flaring/eruptive activity, and, in conjunction with the helicity, sharp inputs of both quantities are found to precede individual flaring events by several hours. This suggests that the emergence/submergence of topologically complex current-carrying field is an important element for the ignition of AR flaring.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The observed durations of prompt gamma-ray emission from gamma-ray bursts (GRBs) are often used to infer the progenitors and energetics of the sources. Inaccurate duration measurements will have a significant impact on constraining the processes powering the bursts. The “tip-of-the-iceberg” effect describes how the observed signal is lost into background noise; lower instrument sensitivity leads to higher measurement bias. In this study, we investigate how observing conditions, such as the number of enabled detectors, background level, and incident angle of the source relative to the detector plane, affect the measured duration of GRB prompt emission observed with the Burst Alert Telescope on board the Neil Gehrels Swift Observatory (Swift/BAT). We generate “simple-pulse” light curves from an analytical fast rise exponential decay function and from a sample of eight real GRB light curves. We fold these through the Swift/BAT instrument response function to simulate light curves Swift/BAT would have observed for specific observing conditions. We find duration measurements are highly sensitive to observing conditions and the incident angle of the source has the highest impact on measurement bias. In most cases duration measurements of synthetic light curves are significantly shorter than the true burst duration. For the majority of our sample, the percentage of duration measurements consistent with the true duration is as low as ∼25%–45%. In this article, we provide quantification of the tip-of-the-iceberg effect on GRB light curves due to Swift/BAT instrumental effects for several unique light curves.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a dedicated search for new pulsating helium-atmosphere (DBV) white dwarfs from the Sloan Digital Sky Survey using the McDonald 2.1 m Otto Struve Telescope. In total we observed 55 DB and DBA white dwarfs with spectroscopic temperatures between 19,000 and 35,000 K. We find 19 new DBVs and place upper limits on variability for the remaining 36 objects. In combination with previously known DBVs, we use these objects to provide an update to the empirical extent of the DB instability strip. With our sample of new DBVs, the red edge is better constrained, as we nearly double the number of DBVs known between 20,000 and 24,000 K. We do not find any new DBVs hotter than PG 0112+104, the current hottest DBV is at <jats:italic>T</jats:italic> <jats:sub>eff</jats:sub> ≈ 31,000 K, but do find pulsations in four DBVs with temperatures between 27,000 and 30,000 K, improving empirical constraints on the poorly defined blue edge. We investigate the ensemble pulsation properties of all currently known DBVs, finding that the weighted mean period and total pulsation power exhibit trends with effective temperature that are qualitatively similar to the pulsating hydrogen-atmosphere white dwarfs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Recent studies have outlined the interest for the evaluation of transport coefficients in space plasmas, where the observed velocity distributions of plasma particles are conditioned not only by the binary collisions, e.g., at low energies, but also by the energization of particles from their interaction with wave turbulence and fluctuations, generating the suprathermal kappa-distributed populations. This paper provides a first estimate of the main transport coefficients based on regularized kappa distributions, which, unlike standard kappa distributions (SKDs), enable macroscopic parameterization without mathematical divergences or physical inconsistencies. All transport coefficients derived here, i.e., the diffusion and mobility coefficients, electric conductivity, thermoelectric coefficient, and thermal conductivity, are finite and well defined for all values of <jats:italic>κ</jats:italic> &gt; 0. Moreover, for low values of <jats:italic>κ</jats:italic> (i.e., below the SKD poles), the transport coefficients can be orders of magnitudes higher than the corresponding Maxwellian limits, meaning that significant underestimations can be made if suprathermal electrons are ignored.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In recent publications, the construction of explicit symplectic integrators for Schwarzschild- and Kerr-type spacetimes is based on splitting and composition methods for numerical integrations of Hamiltonians or time-transformed Hamiltonians associated with these spacetimes. Such splittings are not unique but have various options. A Hamiltonian describing the motion of charged particles around the Schwarzschild black hole with an external magnetic field can be separated into three, four, and five explicitly integrable parts. It is shown through numerical tests of regular and chaotic orbits that the three-part splitting method is the best of the three Hamiltonian splitting methods in accuracy. In the three-part splitting, optimized fourth-order partitioned Runge–Kutta and Runge–Kutta–Nyström explicit symplectic integrators exhibit the best accuracies. In fact, they are several orders of magnitude better than the fourth-order Yoshida algorithms for appropriate time steps. The first two algorithms have a small additional computational cost compared with the latter ones. Optimized sixth-order partitioned Runge–Kutta and Runge–Kutta–Nyström explicit symplectic integrators have no dramatic advantages over the optimized fourth-order ones in accuracy during long-term integrations due to roundoff errors. The idea of finding the integrators with the best performance is also suitable for Hamiltonians or time-transformed Hamiltonians of other curved spacetimes including Kerr-type spacetimes. When the numbers of explicitly integrable splitting sub-Hamiltonians are as small as possible, such splitting Hamiltonian methods would bring better accuracies. In this case, the optimized fourth-order partitioned Runge–Kutta and Runge–Kutta–Nyström methods are worth recommending.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The abundance of cold molecular gas plays a crucial role in models of galaxy evolution. While deep spectroscopic surveys of CO emission lines have been a primary tool for measuring this abundance, the difficulty of these observations has motivated alternative approaches to studying molecular gas content. One technique, line intensity mapping, seeks to constrain the average molecular gas properties of large samples of individually undetectable galaxies through the CO brightness power spectrum. Here we present constraints on the cross-power spectrum between CO intensity maps and optical galaxy catalogs. This cross-measurement allows us to check for systematic problems in CO intensity mapping data, and validate the data analysis used for the auto-power spectrum measurement of the CO Power Spectrum Survey. We place a 2<jats:italic>σ</jats:italic> upper limit on the band-averaged CO-galaxy cross-power of <jats:italic>P</jats:italic> <jats:sub>×</jats:sub> &lt; 540 <jats:italic>μ</jats:italic>K h<jats:sup>−3</jats:sup> Mpc<jats:sup>3</jats:sup>. Our measurement favors a nonzero 〈<jats:italic>T</jats:italic> <jats:sub>CO</jats:sub>〉 at around 90% confidence and gives an upper limit on the mean molecular gas density at <jats:italic>z</jats:italic> ∼ 2.6 of 7.7 × 10<jats:sup>8</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> Mpc<jats:sup>−3</jats:sup>. We forecast the expected cross-power spectrum by applying a number of literature prescriptions for the CO luminosity–halo mass relation to a suite of mock light cones. Under the most optimistic forecasts, the cross-spectrum could be detected with only moderate extensions of the data used here, while more conservative models could be detected with a factor of 10 increase in sensitivity. Ongoing CO intensity mapping experiments will target fields allowing for extensive cross-correlation analysis and should reach the sensitivity required to detect the cross-spectrum signal.</jats:p>