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<jats:title>Abstract</jats:title> <jats:p>Peculiar velocities of Type Ia supernova (SN Ia) host galaxies affect the dark-energy parameter constraints in a small but very specific way: the parameters are biased in a single direction in parameter space that is a priori knowable for a given SN Ia data set. We demonstrate the latter fact with a combination of inference from a cosmological <jats:italic>N</jats:italic>-body simulation with overwhelming statistics applied to the Pantheon SN Ia data set, then confirm it by simple quantitative arguments. We quantify small modifications to the current analyses that would ensure that the effect of cosmological parameters is essentially guaranteed to be negligible.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We use Parker Solar Probe (PSP) in situ measurements to analyze the characteristics of solar wind turbulence during the first solar encounter covering radial distances between 35.7<jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub> and 41.7<jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub>. In our analysis we isolate so-called switchback (SB) intervals (folded magnetic field lines) from nonswitchback (NSB) intervals, which mainly follow the Parker spiral field. Using a technique based on conditioned correlation functions, we estimate the power spectra of Elsasser, magnetic, and bulk velocity fields separately in the SB and NSB intervals. In comparing the turbulent energy spectra of the two types of intervals, we find the following characteristics: (1) The decorrelation length of the backward-propagating Elsasser field <jats:italic>z</jats:italic> <jats:sup>−</jats:sup> is larger in the NSB intervals than the one in the SB intervals; (2) the magnetic power spectrum in SB intervals is steeper, with spectral index close to −5/3, than in NSB intervals, which have a spectral index close to −3/2; (3) both SB and NSB turbulence are imbalanced with NSB having the largest cross-helicity, (4) the residual energy is larger in the SB intervals than in NSB, and (5) the analyzed fluctuations are dominated by Alfvénic fluctuations that are propagating in the sunward (antisunward) direction for the SB (NSB) turbulence. These observed features provide further evidence that the switchbacks observed by PSP are associated with folded magnetic field lines giving insight into their turbulence nature.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Since their discovery 20 years ago, the observed luminosity function of <jats:italic>z</jats:italic> ≳ 6 quasars has been suspected to be biased by gravitational lensing. Apart from the recent discovery of UHS J0439+1634 at <jats:italic>z</jats:italic> ≈ 6.52, no other strongly lensed <jats:italic>z</jats:italic> ≳ 6 quasar has been conclusively identified. The hyperluminous <jats:italic>z</jats:italic> ≈ 6.33 quasar SDSS J0100+2802, believed to host a supermassive black hole of ∼10<jats:sup>10</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, has recently been claimed to be lensed by a factor of ∼450, which would negate both its extreme luminosity and black hole mass. However, its Ly<jats:italic>α</jats:italic>-transparent proximity zone is the largest known at <jats:italic>z</jats:italic> &gt; 6, suggesting an intrinsically extreme ionizing luminosity. Here we show that the lensing hypothesis of <jats:italic>z</jats:italic> ≳ 6 quasars can be quantitatively constrained by their proximity zones. We first show that our proximity zone analysis can recover the strongly lensed nature of UHS J0439+1634, with an estimated magnification <jats:inline-formula> <jats:tex-math> <?CDATA $\mu ={28.0}_{-11.7}^{+18.4}{(}_{-18.3}^{+44.9})$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlabc61fieqn1.gif" xlink:type="simple" /> </jats:inline-formula> at 68% (95%) credibility that is consistent with previously published lensing models. We then show that the large proximity zone of SDSS J0100+2802 rules out lensing magnifications of <jats:italic>μ</jats:italic> &gt; 4.9 at 95% probability, and conclusively rule out the proposed <jats:italic>μ</jats:italic> &gt; 100 scenario. Future proximity zone analyses of existing <jats:italic>z</jats:italic> ≳ 6 quasar samples have the potential to identify promising strongly lensed candidates, constrain the distribution of <jats:italic>z</jats:italic> ≳ 6 quasar lensing, and improve our knowledge of the shape of the intrinsic quasar luminosity function.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report an energetic electron event observed by the Wind spacecraft in which electrons were first detected to propagate away from the Sun, and subsequently detected to propagate back toward the Sun. Using the recently developed fractional velocity dispersion analysis (FVDA), the path lengths corresponding to these two sequential electron signals were found to be ∼1.5 and ∼3.1 au. The inferred release times for both populations were found to be the same, within uncertainty. No bidirectional halo electrons were identified during the event, indicating that the electrons were not propagating within a closed magnetic field configuration (e.g., a magnetic flux rope). These observations suggest that the same energetic electrons were observed twice at 1 au, with the second time being due to reflection occurring beyond 1 au, by perhaps magnetic kinks caused by a coronal mass ejection–driven shock.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Differential rotation is the basis of the solar dynamo theory. Synoptic maps of He <jats:sc>I</jats:sc> intensity from Carrington rotations 2032–2135 are utilized to investigate the differential rotation of the solar chromosphere in the He <jats:sc>I</jats:sc> absorption line. The chromosphere is surprisingly found to rotate faster than the photosphere below it. The anomalous heating of the chromosphere and corona has been a big problem in modern astronomy. It is speculated that the small-scale magnetic elements with magnetic flux in the range of (2.9–32.0) × 10<jats:sup>18</jats:sup> Mx, which are anchored in the leptocline, heat the quiet chromosphere to present the anomalous temperature increase, causing it to rotate at the same rate as the leptocline. The differential of rotation rate in the chromosphere is found to be strengthened by strong magnetic fields, but in stark contrast, at the photosphere strong magnetic fields repress the differential of rotation rate. A plausible explanation is given for these findings.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We show observational evidence for a new form of collisionless shock in interplanetary space near Mars, small-scale shocks with periodic spacings. Pickup of new ionized hydrogen atoms in a magnetic field aligned with the solar wind direction causes the generation of a magnetosonic wave train through an ion beam instability. The waves have a frequency close to the local proton gyrofrequency. This is a similar physical process as for the formation of cometary plasma waves/turbulence. However, for the case of proton pickup near Mars, each individual magnetosonic wave cycle develops into a small-scale shock. So there is a string of fast mode shocks formed with proton gyroperiod spacings. These small-scale shocks display dissipation in the ions and dispersive whistlers. A fraction of ions trapped/reflected at the small-scale shocks are accelerated by the motional electric field. Observational results demonstrate that periodic shocks can perform the same functions as a single supercritical shock in a high-speed flow.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the first wideband monitoring observations of PSR J1803−3002A, a relatively bright millisecond pulsar (MSP) in the globular cluster NGC 6522 with a spin period of 7.1 ms and no known binary companion. These observations were performed using the Parkes 64 m radio telescope with the Ultra-Wideband Low receiver system, which covers 704–4032 MHz. We confirm that PSR J1803−3002A is an isolated MSP located near the cluster center and probe the emission properties of the pulsar over the wide observed band. The mean pulse profile consists of three components, with the outer components becoming more prominent at higher frequencies, and a mean spectral index for the pulsed emission of −1.66 ± 0.07 over the observed band. The fractional linear and circular polarization increase with increasing frequency, which is unusual for pulsars. We determine a Faraday rotation measure of −107 ± 6 rad m<jats:sup>−2</jats:sup> for the pulsar. PSR J1803−3002A is a distant pulsar in the Galactic plane, but our observations show no evidence of pulse broadening due to interstellar scattering. These results demonstrate the power of ultra-wideband receivers and signal processing systems.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A fast-mode shock can form in the front of reconnection outflows and has been suggested as a promising site for particle acceleration in solar flares. Recent developments in the study of magnetic reconnection have shown that numerous plasmoids can be produced in a large-scale current layer. Here we investigate the dynamical modulation of electron acceleration in the looptop region when plasmoids intermittently arrive at the shock by combining magnetohydrodynamics simulations with a particle kinetic model. As plasmoids interact with the shock, the looptop region exhibits various compressible structures that modulate the production of energetic electrons. The energetic electron population varies rapidly in both time and space. The number of 5–10 keV electrons correlates well with the compression area, while that of &gt;50 keV electrons shows good correlation with the strong compression area but only moderate correlation with shock parameters. We further examine the impacts of the first plasmoid, which marks the transition from a quasi-steady shock front to a distorted and dynamical shock. The number of energetic electrons is reduced by ∼20% at 15–25 keV and nearly 40% for 25–50 keV, while the number of 5–10 keV electrons increases. In addition, the electron energy spectrum above 10 keV evolves softer with time. We also find that double or even multiple distinct sources can develop in the looptop region when the plasmoids move across the shock. Our simulations have strong implications to the interpretation of nonthermal looptop sources, as well as the commonly observed fast temporal variations in flare emissions, including the quasi-periodic pulsations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>M31 and M33 serve as ideal places to study distributions of dust in the outskirts of spiral galaxies. In this Letter, using about 0.2 million stars selected from the LAMOST data and combining precise photometry and parallaxes from the Gaia DR2, we have constructed a two-dimensional foreground dust reddening map toward the M31 and M33 region (1112 ≤ <jats:italic>gl</jats:italic> ≤ 1362, −365 ≤ <jats:italic>gb</jats:italic> ≤ −165). The map has a typical spatial resolution of about 12′ and precision of 0.01 mag. The complex structure of dust clouds toward M31 is revealed. By carefully removing the foreground extinction from the dust reddening map of Schlegel et al., we thus have obtained a residual map to study dust distributions in the outskirts of M31 and M33. A large amount of dust is detected in the M31 halo out to a distance of over 100 kpc. Dust in the M31 disk is found to extend out to about 2.5 times its optical radius, with a distribution that is consistent with either an exponential disk with a scale length of 7.2 kpc or two disks with a scale length of 11.1 kpc within its optical radius and 18.3 kpc beyond its optical radius. Dust in the disk of M33 is also found to extend out to about 2.5 times its optical radius, its distribution beyond one optical radius is consistent with an exponential disk with a scale length of 5.6 kpc. Our results provide new clues to the distributions and cycling of dust in galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Binary neutron stars (BNSs) will spend ≃10–15 minutes in the band of Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO) and Virgo detectors at design sensitivity. Matched-filtering of gravitational-wave (GW) data could in principle accumulate enough signal-to-noise ratio (S/N) to identify a forthcoming event tens of seconds before the companions collide and merge. Here we report on the design and testing of an early-warning GW detection pipeline. Early-warning alerts can be produced for sources that are at low enough redshift so that a large enough S/N accumulates ∼10–60 s before merger. We find that about 7% (49%) of the total detectable BNS mergers will be detected 60 s (10 s) before the merger. About 2% of the total detectable BNS mergers will be detected before merger and localized to within 100 deg<jats:sup>2</jats:sup> (90% credible interval). Coordinated observing by several wide-field telescopes could capture the event seconds before or after the merger. LIGO–Virgo detectors at design sensitivity could facilitate observing at least one event at the onset of merger.</jats:p>