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<jats:title>Abstract</jats:title> <jats:p>The reconnection front (RF), one of the most efficient accelerators of particles in the terrestrial magnetosphere, is a sharp plasma boundary resulting from transient magnetic reconnection. It has been both theoretically predicted and observationally confirmed that electron-scale substructures can develop at the RFs. How such electron-scale structures modulate the electron energization and transport has not been fully explored. Based on high-resolution data from MMS spacecraft and particle tracing simulations, we investigate and compare the electron acceleration across two typical RFs with or without rippled electron-scale structures. Both observations and simulations reveal that high-energy electron flux behind the RF increases more dramatically if the electrons encounter a rippled RF surface, as compared to a smooth RF surface. The main acceleration mechanism is electron surfing acceleration, in which electrons are trapped by the ripples, due to the large local magnetic field gradient, and therefore undergo surfing motion along the motional electric field.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We analyze stellar proper motions in the COSMOS field to assess the presence of bulk motions. At bright magnitudes (<jats:italic>G</jats:italic>-band 18.5–20.76 AB), we use the proper motions of 1010 stars in the Gaia DR2 catalog. At the faint end, we compute proper motions of 11,519 pointlike objects at <jats:italic>i</jats:italic>-band magnitudes 19–25 AB using Hubble ACS and Subaru HSC data, which span two epochs about 11 yr apart. In order to measure these proper motions with unprecedented accuracy at faint magnitudes, we developed a foundational set of astrometric tools that will be required for joint survey processing of data from the next generation of optical/infrared surveys. The astrometric grids of Hubble ACS and Subaru HSC mosaics were corrected at the catalog level using proper motion–propagated and parallax-corrected Gaia DR2 sources. These astrometric corrections were verified using compact extragalactic sources. Upon comparison of our measured proper motions with Gaia DR2, we estimate the uncertainties in our measurements to be ∼2–3 mas yr<jats:sup>−1</jats:sup> axis<jats:sup>−1</jats:sup>, down to 25.5 AB mag. We correct proper motions for the mean motion of the Sun, and we find that late-type main-sequence stars predominantly in the thin disk in the COSMOS field have space velocities mainly toward the Galactic center. We detect candidate high-velocity (≥220 km s<jats:sup>−1</jats:sup>) stars, six of them at ∼0.4–6 kpc, from the Gaia sample, and five of them at ∼20 kpc, from the faint star HSC and ACS sample. The sources from the faint star sample may be candidate halo members of the Sangarius stream.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The radius and surface composition of an exploding massive star, as well as the explosion energy per unit mass, can be measured using early ultraviolet (UV) observations of core-collapse supernovae (CC SNe). We present the results from a simultaneous Galaxy Evolution Explorer (GALEX) and Palomar Transient Factory (PTF) search for early UV emission from SNe. We analyze five CC SNe for which we obtained near-UV (NUV) measurements before the first ground-based <jats:italic>R</jats:italic>-band detection. We introduce SOPRANOS, a new maximum likelihood fitting tool for models with variable temporal validity windows, and use it to fit the Sapir &amp; Waxman shock-cooling model to the data. We report four Type II SNe with progenitor radii in the range of <jats:italic>R</jats:italic> <jats:sub>*</jats:sub> ≈ 600–1100 <jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub> and a shock velocity parameter in the range of <jats:italic>v</jats:italic> <jats:sub> <jats:italic>s</jats:italic>*</jats:sub> ≈ 2700–6000 km s<jats:sup>−1</jats:sup> (<jats:italic>E</jats:italic>/<jats:italic>M</jats:italic> ≈ 2–8 × 10<jats:sup>50</jats:sup> erg/<jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) and one Type IIb SN with <jats:italic>R</jats:italic> <jats:sub>*</jats:sub> ≈ 210 <jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub> and <jats:italic>v</jats:italic> <jats:sub> <jats:italic>s</jats:italic>*</jats:sub> ≈ 11,000 km s<jats:sup>−1</jats:sup> (<jats:italic>E</jats:italic>/<jats:italic>M</jats:italic> ≈ 1.8 × 10<jats:sup>51</jats:sup> erg/<jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>). Our pilot GALEX/PTF project thus suggests that a dedicated, systematic SN survey in the NUV band, such as the wide-field UV explorer ULTRASAT mission, is a compelling method to study the properties of SN progenitors and SN energetics.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The systematic targeting of extended Ly<jats:italic>α</jats:italic> emission around high-redshift quasars resulted in the discovery of rare and bright Enormous Ly<jats:italic>α</jats:italic> Nebulae (ELANe) associated with multiple active galactic nuclei (AGNs). We initiate here “a multiwavelength study of ELAN environments” (AMUSE<jats:sup>2</jats:sup>) focusing on the ELAN around the <jats:italic>z</jats:italic> ∼ 3 quasar SDSS J1040+1020, aka the Fabulous ELAN. We report on VLT/HAWK-I, APEX/LABOCA, JCMT/SCUBA-2, SMA/850<jats:italic>μ</jats:italic>m, and ALMA CO(5-4), and 2 mm observations and compare them to previously published VLT/MUSE data. The continuum and line detections enable a first estimate of the star formation rates, dust, stellar, and molecular gas masses in four objects associated with the ELAN (three AGNs and one Ly<jats:italic>α</jats:italic> emitter), confirming that the quasar host is the most star-forming (star formation rate of ∼500 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> yr<jats:sup>−1</jats:sup>) and massive galaxy (<jats:italic>M</jats:italic> <jats:sub>star</jats:sub> ∼ 10<jats:sup>11</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) in the system, and thus can be assumed as central. All four embedded objects have similar molecular gas reservoirs (<jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{{{\rm{H}}}_{2}}\sim {10}^{10}$?> </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:msub> <mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:msub> <mml:mo>∼</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac5a4dieqn1.gif" xlink:type="simple" /> </jats:inline-formula> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>), resulting in short depletion timescales. This fact together with the estimated total dark matter halo mass, <jats:italic>M</jats:italic> <jats:sub>DM</jats:sub> = (0.8–2) × 10<jats:sup>13</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, imply that this ELAN will evolve into a giant elliptical galaxy. Consistently, the constraint on the baryonic mass budget for the whole system indicates that the majority of baryons should reside in a massive warm/hot reservoir (up to 10<jats:sup>12</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>), needed to complete the baryons count. Additionally, we discuss signatures of gas infall on the compact objects as traced by Ly<jats:italic>α</jats:italic> radiative transfer effects and the evidence for the alignment between the satellites’ spins and their directions to the central.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Using the cross-matched data of Gaia EDR3 and the Two Micron All Sky Survey Point Source Catalog, a sample of RC stars with parallax accuracies better than 20% is identified and used to reveal the nearby spiral pattern traced by old stars. As shown in the overdensity distribution of RC stars, there is an arc-like feature extending from <jats:italic>l</jats:italic> ∼ 90° to ∼243°, which passes close to the Sun. This feature is probably an arm segment traced by old stars, indicating the galaxy potential in the vicinity of the Sun. With a comparison to the spiral arms depicted by young objects, we found that there are considerable offsets between the two different components of the Galactic spiral arms. The spiral arm traced by RC stars tends to have a larger pitch angle, and hence a more loosely wound pattern.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The TRAPPIST-1 system is home to at least seven terrestrial planets and is a target of interest for future James Webb Space Telescope (JWST) observations. Additionally, these planets will be of interest to future missions making observations in the ultraviolet (UV). Although several of these planets are located in the traditional habitable zone, where liquid water could exist on the surface, TRAPPIST-1h is interesting to explore as a potentially habitable ocean world analog. In this study, we evaluate the observability of a Titan-like atmosphere on TRAPPIST-1h. The ability of the JWST or a future UV mission to detect specific species in the atmosphere at TRAPPIST-1h will depend on how far each species extends from the surface. In order to understand the conditions required for detection, we evaluate the input parameters used in one-dimensional models to simulate the structure of Titan-like atmospheres. These parameters include surface temperature and pressure, temperature profile as a function of distance from the surface, composition of the minor species relative to N<jats:sub>2</jats:sub>, and the eddy diffusion coefficient. We find that JWST simulated spectra for cloud- and haze-free atmospheres are most sensitive to surface temperature, temperature gradients with altitude, and surface pressure. The importance of temperature gradients in JWST observations shows that a simple isothermal scale height is not ideal for determining temperature or atmospheric mean molecular mass in transit spectra from exoplanet atmospheres. We demonstrate that UV transmission spectra are sensitive to the upper atmosphere, where the exobase can be used to approximate the vertical extent of the atmosphere.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate the temporal evolution of the yearly total mass-loss rate (YTMLR) from the Sun through coronal mass ejections (CMEs) over solar cycles 23 and 24. The mass determination of CMEs can be subject to significant uncertainty. To minimize this problem, we have used extensive statistical analysis. For this purpose, we employed data included in the Coordinated Data Analysis Workshop (CDAW) catalog. We estimated the contributions to mass loss from the Sun from different subsamples of CMEs (selected on the basis of their masses, angular widths, and position angles). The temporal variations of the YTMLR were compared to those of the sunspot number (SSN), X-ray flare flux, and the Disturbance Storm Time (Dst) index. We show that the CME mass included in the CDAW catalog reflects with high accuracy the actual mass-loss rate from the Sun through CMEs. Additionally, it is shown that the CME mass distribution in the log-lin representation reflects the Gaussian distribution very well. This means that the CMEs included in the CDAW catalog form one coherent population of ejections that have been correctly identified. Unlike the CME occurrence rate, it turns out that the YTMLR is a very good indicator of solar activity (e.g., SSN) and space weather (e.g., Dst index) consequences. These results are very important, since the YTMLR, unlike the mass loss through solar wind, significantly depends on solar cycles.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Gamma-ray astronomy has become one of the main experimental ways to test the modified dispersion relations (MDRs) of photons in vacuum, obtained in some attempts to formulate a theory of quantum gravity. The MDRs in use imply time delays that depend on the energy and that increase with distance following some function of redshift. The use of transient, or variable, distant and highly energetic sources already allows us to set stringent limits on the energy scale related to this phenomenon, usually thought to be of the order of the Planck energy, but robust conclusions on the existence of MDR-related propagation effects still require the analysis of a large population of sources. In order to gather the biggest sample of sources possible for MDR searches at teraelectronvolt energies, the H.E.S.S., MAGIC, and VERITAS collaborations enacted a joint task force to combine all their relevant data to constrain the quantum gravity energy scale. In the present article, the likelihood method used to combine the data and provide a common limit is described in detail and tested through simulations of recorded data sets for a gamma-ray burst, three flaring active galactic nuclei, and two pulsars. Statistical and systematic errors are assessed and included in the likelihood as nuisance parameters. In addition, a comparison of two different formalisms for distance dependence of the time lags is performed for the first time. In a second article, to appear later, the method will be applied to all relevant data from the three experiments.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Supersonic flows in the interstellar medium (ISM) are believed to be a key driver of the molecular cloud formation and evolution. Among molecular clouds’ properties, the ratio between the solenoidal and compressive modes of turbulence plays important roles in determining the star formation efficiency. We use numerical simulations of supersonic converging flows of the warm neutral medium (WNM) resolving the thermal instability to calculate the early phase of molecular cloud formation, and we investigate the turbulence structure and the density probability distribution function (density PDF) of the multiphase ISM. We find that both the solenoidal and compressive modes have their power spectrum similar to the Kolmogorov spectrum. The solenoidal (compressive) modes account for ≳80% (≲20%) of the total turbulence power. When we consider both the cold neutral medium (CNM) and the thermally unstable neutral medium (UNM) up to <jats:italic>T</jats:italic> ≲ 400 K, the density PDF follows the lognormal distribution, whose width <jats:inline-formula> <jats:tex-math> <?CDATA ${\sigma }_{s}^{}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>σ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>s</mml:mi> </mml:mrow> <mml:mrow /> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac5a54ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> is well explained by the known relation from the isothermal turbulence as <jats:inline-formula> <jats:tex-math> <?CDATA ${\sigma }_{s}^{}=\mathrm{ln}(1\,+{b}^{2}{{ \mathcal M }}^{2})$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>σ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>s</mml:mi> </mml:mrow> <mml:mrow /> </mml:msubsup> <mml:mo>=</mml:mo> <mml:mi>ln</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mn>1</mml:mn> <mml:mspace width="0.15em" /> <mml:mo>+</mml:mo> <mml:msup> <mml:mrow> <mml:mi>b</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:msup> <mml:mrow> <mml:mi mathvariant="italic"></mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mo stretchy="false">)</mml:mo> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac5a54ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> (where <jats:italic>b</jats:italic> is the parameter representing the turbulence mode ratio and <jats:inline-formula> <jats:tex-math> <?CDATA ${ \mathcal M }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="italic"></mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac5a54ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> is the turbulent Mach number). The density PDF of the CNM component alone (<jats:italic>T</jats:italic> ≤ 50 K), however, exhibits a narrower <jats:inline-formula> <jats:tex-math> <?CDATA ${\sigma }_{s}^{}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>σ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>s</mml:mi> </mml:mrow> <mml:mrow /> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac5a54ieqn4.gif" xlink:type="simple" /> </jats:inline-formula> by a factor of ∼2. These results suggest that observational estimations of <jats:italic>b</jats:italic> based on the CNM density PDF requires the internal turbulence within each CNM clump but not the interclump relative velocity, the latter of which is instead powered by the WNM/UNM turbulence.</jats:p>