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<jats:title>Abstract</jats:title> <jats:p>We perform an expansion study of the Balmer-dominated outer shock of the SNR 0519−69.0 in the LMC by using a combination of new Hubble Space Telescope (HST) WFC3 imagery obtained in 2020 and archival ACS images from 2010 and 2011. Thanks to the very long time baseline, our proper motion measurements are of unprecedented accuracy. We find a wide range of shock velocities, with the fastest shocks averaging 5280 km s<jats:sup>−1</jats:sup> and the slowest grouping of shocks averaging just 1670 km s<jats:sup>−1</jats:sup>. We compare the H<jats:italic>α</jats:italic> images from HST with X-ray images from Chandra and mid-IR images from Spitzer, finding a clear anticorrelation between the brightness of the remnant in a particular location and the velocity of the blast wave at that location, supporting the idea that the bright knots of X-ray and IR emission result from an interaction with a dense inhomogeneous circumstellar medium. We find no evidence for X-ray emission, thermal or nonthermal, associated with the fastest shocks, as expected if the fastest velocities are the result of the blast wave encountering the lower density ambient medium of the LMC. We derive an age of the remnant of ≤670 ± 70 yr, consistent with results derived from previous investigations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The positive-to-negative transition of spectral lag is an uncommon feature reported in a small number of gamma-ray bursts (GRBs). An application of such a feature has been made to constrain the critical quantum gravity energy (<jats:italic>E</jats:italic> <jats:sub>QG</jats:sub>) of the light photons under the hypothesis that the Lorentz invariance might be violated. Motivated by previous case studies, this paper systematically examined the up-to-date GRB sample observed by Fermi Gamma-ray Burst Monitor for the lag transition feature to establish a comprehensive physical limit on the Lorentz invariance violation (LIV). This search resulted in 32 GRBs with redshift available, which exhibit the lag transition phenomenon. We first fit each of the lag–<jats:italic>E</jats:italic> relations of the 32 GRBs with an empirical smoothly broken power-law function, and found that the lag transition occurs typically at about 400 keV. We then implemented the LIV effect into the fit, which enabled us to constrain the lower limit of the linear and quadratic values of <jats:italic>E</jats:italic> <jats:sub>QG</jats:sub>, which are typically distributed at 1.5 × 10<jats:sup>14</jats:sup> and 8 × 10<jats:sup>5</jats:sup> GeV, respectively.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Wide-field Infrared Survey Explorer all-sky survey has discovered a new population of hot dust-obscured galaxies (Hot DOGs), which have been confirmed to be dusty quasars. Previous statistical studies have found significant overdensities of submillimeter and mid-IR-selected galaxies around Hot DOGs, indicating they may reside in dense regions. Here we present the near-infrared (<jats:italic>J</jats:italic> and <jats:italic>K</jats:italic> <jats:sub> <jats:italic>s</jats:italic> </jats:sub> bands) observations over a <jats:inline-formula> <jats:tex-math> <?CDATA $7\buildrel{\,\prime}\over{.} 5\times 7\buildrel{\,\prime}\over{.} 5$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>7</mml:mn> <mml:mo>.′</mml:mo> <mml:mn>5</mml:mn> <mml:mo>×</mml:mo> <mml:mn>7</mml:mn> <mml:mo>.′</mml:mo> <mml:mn>5</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac8162ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> field centered on a Hot DOG W1835+4355 at <jats:italic>z</jats:italic> ∼ 2.3 using the wide-field infrared camera on the Palomar 200 inch telescope. We use the color criterion <jats:italic>J</jats:italic> − <jats:italic>K</jats:italic> <jats:sub> <jats:italic>s</jats:italic> </jats:sub> &gt; 2.3 for objects with <jats:inline-formula> <jats:tex-math> <?CDATA ${K}_{S}\lt 20$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mi>K</mml:mi> <mml:mi>S</mml:mi> </mml:msub> <mml:mo>&lt;</mml:mo> <mml:mn>20</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac8162ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>, to select distant red galaxies (DRGs). We find a significant excess of number density of DRGs in the W1835+4355 field compared to three control fields, by a factor of about two. The overdensity of red galaxies around W1835+4355 is consistent with the multiwavelength environment of Hot DOGs, suggesting that Hot DOGs may be a good tracer for dense regions at high redshift. We find that W1835+4355 does not reside in the densest region of the dense environment traced by itself. A possible scenario is that W1835+4355 is undergoing a merging process, which lowers the local number density of galaxies in its surrounding region.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The first solar encounters by the Parker Solar Probe revealed the magnetic field to be dominated by short field reversals in the radial direction, referred to as “switchbacks.” While radial velocity and proton temperature were shown to increase inside the switchbacks, ∣<jats:italic>B</jats:italic>∣ exhibits very brief dropouts only at the switchback boundaries. Brief intensifications in spectral density measurements near the electron plasma frequency, <jats:italic>f</jats:italic> <jats:sub>pe</jats:sub>, were also observed at these boundaries, indicating the presence of plasma waves triggered by current systems in the form of electron beams. We perform a correlative study using observations from the Parker FIELDS Radio Frequency Spectrometer and Fluxgate Magnetometer to compare occurrences of spectral density intensifications at the electron plasma frequency (<jats:italic>f</jats:italic> <jats:sub>pe</jats:sub> emissions) and ∣<jats:italic>B</jats:italic>∣ dropouts at switchback boundaries during Parker’s first and second solar encounters. We find that only a small fraction of minor ∣<jats:italic>B</jats:italic>∣ dropouts are associated with <jats:italic>f</jats:italic> <jats:sub>pe</jats:sub> emissions. This fraction increases with ∣<jats:italic>B</jats:italic>∣ dropout size until all dropouts are associated with <jats:italic>f</jats:italic> <jats:sub>pe</jats:sub> emissions. Brief spikes in the differential electron flux measured by the SWEAP Solar Probe Analyzer for Electron sensors also occur in conjunction with nearly all <jats:italic>f</jats:italic> <jats:sub>pe</jats:sub> emissions. This suggests that in the presence of strong ∣<jats:italic>B</jats:italic>∣ dropouts, electron currents that create the perturbation in ∣<jats:italic>B</jats:italic>∣ along the boundaries are also stimulating plasma waves such as Langmuir waves.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Electron-scale magnetic peaks (ESMPs) with spatial sizes less than one local ion gyroradius have been recently revealed to exist in the terrestrial magnetosheath and solar wind at 1 au. Whether they widely exist in the astrophysical plasma is unclear. Here, we investigate the magnetic peaks with a period of 0.1–100 s upstream of Mercury’s bow shock by using the magnetic field data from the MESSENGER spacecraft. Based on the distribution of their durations, these magnetic peaks can be divided into two groups: one with durations less than 0.6 s and the other with durations larger than 0.6 s. The durations in each group obey a log-normal distribution. The magnetic peaks with durations less than 0.6 s are inferred to be electron scale, suggesting that ESMPs exist in the solar wind at Mercury’s orbit. The median duration of these ESMPs is ∼0.3 s. The ESMPs have a larger occurrence rate near the bow shock and prefer to occur when the ambient interplanetary magnetic field (IMF) can be connected to the bow shock, which suggests that the foreshock could be one source region of these ESMPs. Their occurrence rate also tends to be larger when the IMF strength is weaker. Our observations also suggest that some ESMPs originate from the upstream solar wind. The properties of the ESMPs found here could help to shed light on their generation mechanisms and their roles in the astrophysical plasma.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The three-rung distance ladder, which calibrates Type Ia supernovae (SNe Ia) through stellar distances linked to geometric measurements, provides the highest precision direct measurement of the Hubble constant. In light of the Hubble tension, it is important to test the individual components of the distance ladder. For this purpose, we report a measurement of the Hubble constant from 35 extragalactic Cepheid hosts measured by the SH0ES team, using their distances and redshifts at <jats:italic>cz</jats:italic> ≤ 3300 km s<jats:sup>−1</jats:sup>, instead of any more distant SNe Ia, to measure the Hubble flow. The Cepheid distances are calibrated geometrically in the Milky Way, NGC 4258, and the Large Magellanic Cloud. Peculiar velocities are a significant source of systematic uncertainty at <jats:italic>z</jats:italic> ∼ 0.01, and we present a formalism for both mitigating and quantifying their effects, making use of external reconstructions of the density and velocity fields in the nearby universe. We identify a significant source of uncertainty originating from different assumptions about the selection criteria of this sample, whether distance or redshift limited, as it was assembled over three decades. Modeling these assumptions yields central values ranging from <jats:italic>H</jats:italic> <jats:sub>0</jats:sub> = 71.7 to 76.4 km s<jats:sup>−1</jats:sup> Mpc<jats:sup>−1</jats:sup>. Combining the four best-fitting selection models yields <jats:inline-formula> <jats:tex-math> <?CDATA ${H}_{0}={72.9}_{-2.2}^{+2.4}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>H</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>72.9</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2.2</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>2.4</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac80bdieqn1.gif" xlink:type="simple" /> </jats:inline-formula> as a fiducial result, at 2.4<jats:italic>σ</jats:italic> tension with Planck. While SNe Ia are essential for a precise measurement of <jats:italic>H</jats:italic> <jats:sub>0</jats:sub>, unknown systematics in these supernovae are unlikely to be the source of the Hubble tension.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate the use of bright single pulses from the Crab pulsar to determine separately the dispersion measure (DM) for the Main Pulse and Interpulse components. We develop two approaches using cross-correlation functions (CCFs). The first method computes the CCF of the total intensity of each of the 64 frequency channels with a reference channel and converts the time lag of maximum correlation into a DM. The second method separately computes the CCF between every pair of channels for each individual bright pulse and extracts an average DM from the distribution of all channel-pair DMs. Both methods allow the determination of the DM with a relative uncertainty of better than 10<jats:sup>−5</jats:sup> and provide robust estimates for the uncertainty of the best-fit value. We find differences in DM between the Main Pulse, the Low Frequency Interpulse, and the High Frequency Interpulse using both methods in a frequency range from 4 to 6 GHz. Earlier observations of the High Frequency Interpulse carried out by Hankins et al. (2016) resulted in DM<jats:sub>HFIP</jats:sub>–DM<jats:sub>MP</jats:sub> of 0.010 ± 0.016 pc cm<jats:sup>−3</jats:sup>. Our results indicate a DM<jats:sub>HFIP</jats:sub>–DM<jats:sub>MP</jats:sub> of 0.0127 ± 0.0011 pc cm<jats:sup>−3</jats:sup> (with DM<jats:sub>comp</jats:sub> being the DM value of the respective emission component), confirming earlier results with an independent method. During our studies we also find a relation between the brightness of single pulses in the High Frequency Interpulse and their DM. We also discuss the application of the developed methods on the identification of substructures in the case of Fast Radio Bursts.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Both observations and simulations suggest that the solar filament eruption is closely related to magnetic flux emergence. It is thought that the eruption is triggered by magnetic reconnection between the filament and the emerging flux. However, the details of such a reconnection are rarely presented. In this study, we report the detailed reconnection between a filament and its nearby emerging fields, which led to the reconfiguration and subsequent partial eruption of the filament located over the polarity inversion line of active region 12816. Before the reconnection, we observed repeated brightenings in the filament at a location that overlies a site of magnetic flux cancellation. Plasmoids form at this brightening region, and propagate bidirectionally along the filament. These indicate the tether-cutting reconnection that results in the formation and eruption of a flux rope. To the northwest of the filament, magnetic fields emerge, and reconnect with the context ones, resulting in repeated jets. Afterwards, other magnetic fields emerge near the northwestern filament endpoints, and reconnect with the filament, forming the newly reconnected filament and loops. A current sheet repeatedly occurs at the interface, with the mean temperature and emission measure of 1.7 MK and 1.1×10<jats:sup>28</jats:sup> cm<jats:sup>−5</jats:sup>. Plasmoids form in the current sheet, and propagate along it and further along the newly reconnected filament and loops. The newly reconnected filament then erupts, while the unreconnected filament remains stable. We propose that besides the orientation of emerging fields, some other parameters, such as the position, distance, strength, and area, are also crucial for triggering the filament eruption.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We consider fallback accretion after an ultrastripped supernova (USSN) that accompanies formation of a binary neutron star (BNS) or a neutron star–black hole binary (NS–BH). The fallback matter initially accretes directly to the nascent NS, while it starts to accrete to the circumbinary disk, typically 0.1–1 day after the onset of the USSN explosion. The circumbinary disk mass further accretes, forming mini disks around each compact object, with a super-Eddington rate up to a few years. We show that such a system constitutes a binary ultraluminous X-ray source, and a fraction of the X-rays can emerge through the USSN ejecta. We encourage follow-up observations of USSNe within ≲100 Mpc and ∼100–1000 days after the explosion using Chandra, XMM Newton, and NuSTAR, which could detect the X-ray counterpart with time variations representing the properties of the nascent compact binary, e.g., the orbital motion of the binary, the spin of the NS, and/or the quasiperiodic oscillation of the mini disks.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Electromagnetic follow-up of gravitational-wave detections is very resource intensive, taking up hours of limited observation time on dozens of telescopes. Creating more efficient schedules for follow-up will lead to a commensurate increase in counterpart location efficiency without using more telescope time. Widely used in operations research and telescope scheduling, mixed-integer linear programming is a strong candidate to produce these higher-efficiency schedules, as it can make use of powerful commercial solvers that find globally optimal solutions to provided problems. We detail a new target-of-opportunity scheduling algorithm designed with Zwicky Transient Facility in mind that uses mixed-integer linear programming. We compare its performance to <jats:monospace>gwemopt</jats:monospace>, the tuned heuristic scheduler used by the Zwicky Transient Facility and other facilities during the third LIGO–Virgo gravitational-wave observing run. This new algorithm uses variable-length observing blocks to enforce cadence requirements and to ensure field observability, along with having a secondary optimization step to minimize slew time. We show that by employing a hybrid method utilizing both this scheduler and <jats:monospace>gwemopt</jats:monospace>, the previous scheduler used, in concert, we can achieve an average improvement in detection efficiency of 3%–11% over <jats:monospace>gwemopt</jats:monospace> alone for a simulated binary neutron star merger data set consistent with LIGO–Virgo’s third observing run, highlighting the potential of mixed-integer target of opportunity schedulers for future multimessenger follow-up surveys.</jats:p>