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<jats:title>Abstract</jats:title> <jats:p>We report the results from our study of the blazar S5 1803+784 carried out using quasi-simultaneous <jats:italic>B</jats:italic>, <jats:italic>V</jats:italic>, <jats:italic>R</jats:italic>, and <jats:italic>I</jats:italic> observations from 2020 May to 2021 July on 122 nights. Our observing campaign detected a historically bright optical flare during MJD 59,063.5−MJD 59,120.5. We also found the source in its brightest (<jats:italic>R</jats:italic> <jats:sub>mag</jats:sub> = 13.617) and faintest (<jats:italic>R</jats:italic> <jats:sub>mag</jats:sub> = 15.888) states to date. On 13 nights, covering both flaring and nonflaring periods, we searched for intraday variability using the power-enhanced <jats:italic>F</jats:italic>-test and the nested ANOVA test. We found significant variability in 2 of these 13 nights. However, no such variability was detected during the flaring period. From correlation analysis, we observed that the emission in all optical bands were strongly correlated with a time lag of ∼0 days. To get insights into its dominant emission mechanisms, we generated the optical spectral energy distributions of the source on 79 nights and estimated the spectral indices by fitting a simple power law. The spectral index varied from 1.392 to 1.911 and showed significant variations with time and <jats:italic>R</jats:italic>-band magnitude. We detected a mild bluer-when-brighter (BWB) trend during the whole monitoring period and a much stronger BWB trend during the flare. We also carried out a periodicity search using four different methods and found no significant periodicity during our observation period. Based on the analysis during the flaring state of the source one can say that the emissions most likely originate from the jet rather than from the accretion disk.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the results of a 2019–2021 monitoring campaign with Swift and associated target-of-opportunity observations with XMM-Newton and NuSTAR, examining the spectral and timing behavior of the highly variable ultraluminous X-ray source (ULX) NGC 925 ULX-3. We find that the source exhibits a 127–128-day periodicity, with fluxes typically ranging from 1 × 10<jats:sup>−13</jats:sup> to 8 × 10<jats:sup>−13</jats:sup> erg s<jats:sup>−1</jats:sup> cm<jats:sup>−2</jats:sup>. We do not find strong evidence for a change in period over the time that NGC 925 ULX-3 has been observed, although the source may have been in a much lower flux state when first observed with Chandra in 2005. We do not detect pulsations, and we place an upper limit on the pulsed fraction of ∼40% in the XMM-Newton band, consistent with some previous pulsation detections at low energies in other ULXs. The source exhibits a typical ULX spectrum that turns over in the NuSTAR band and can be fitted using two thermal components. These components have a high temperature ratio that may indicate the lack of extreme inner disk truncation by a magnetar-level magnetic field. We examine the implications for a number of different models for superorbital periods in ULXs, finding that a neutron star with a magnetic field of ∼10<jats:sup>12</jats:sup> G may be plausible for this source. The future detection of pulsations from this source would allow for the further testing and constraining of such models.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Magnetic switchbacks, or sudden reversals in the magnetic field’s radial direction, are one of the more striking observations of the Parker Solar Probe (PSP) in its mission thus far. While their precise production mechanisms are still unknown, the two main theories are via interchange reconnection events and in situ generation. In this work, density and abundance variations of alpha particles are studied inside and outside individual switchbacks. We find no consistent compositional differences in the alpha particle abundance ratio, <jats:italic>n</jats:italic> <jats:sub> <jats:italic>α</jats:italic> <jats:italic>p</jats:italic> </jats:sub>, inside versus outside switchbacks, nor do we observe any signature when separating the switchbacks according to <jats:italic>V</jats:italic> <jats:sub> <jats:italic>α</jats:italic> <jats:italic>p</jats:italic> </jats:sub>/<jats:italic>V</jats:italic> <jats:sub> <jats:italic>pw</jats:italic> </jats:sub>, the ratio of the alpha–proton differential speed to the wave phase speed (the speed at which the switchback is traveling). We argue that these measurements cannot be used to rule in favor of one production mechanism over the other, due to the distance between PSP and the postulated interchange reconnection events. In addition, we examine the 3D velocity fluctuations of protons and alpha particles within individual switchbacks. While switchbacks are always associated with increases in proton velocity, alpha velocities may be enhanced, unchanged, or decrease. This is due to the interplay between <jats:italic>V</jats:italic> <jats:sub> <jats:italic>pw</jats:italic> </jats:sub> and <jats:italic>V</jats:italic> <jats:sub> <jats:italic>α</jats:italic> <jats:italic>p</jats:italic> </jats:sub>, with the Alfvénic motion of the alpha particles vanishing as the difference ∣<jats:italic>V</jats:italic> <jats:sub> <jats:italic>pw </jats:italic> </jats:sub>– <jats:italic>V</jats:italic> <jats:sub> <jats:italic>α</jats:italic> <jats:italic>p</jats:italic> </jats:sub>∣ decreases. We show how the Alfvénic motion of both the alphas and the protons through switchbacks can be understood as an approximately rigid arm rotation about the location of the wave frame, and illustrate that the wave frame can therefore be estimated using particle measurements alone, via sphere fitting.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>To understand how well galaxies, gas, and intracluster stars trace dark matter in and around galaxy clusters, we use the IllustrisTNG cosmological hydrodynamical simulation and compare the spatial distribution of dark matter with that of baryonic components in clusters. To quantify the global morphology of the density distribution of each component in clusters, we fit an ellipse to the density contour of each component and derive shape parameters at different radii. We find that the ellipticity of dark matter is better correlated with that of galaxy mass-weighted number density, rather than with that of galaxy number density or galaxy velocity dispersion. We thus use the galaxy mass-weighted number density map as representative of the galaxy maps. Among three different density maps from galaxies, gas, and intracluster stars, the ellipticity of dark matter is best reproduced by that of the galaxy map over the entire radii. The <jats:italic>virialized</jats:italic> galaxy clusters show a better correlation of spatial distribution between dark matter and other components than the <jats:italic>unvirialized</jats:italic> clusters, suggesting that it requires some time for each component to follow the spatial distribution of dark matter after merging events. Our results demonstrate that galaxies are still good tracers of dark matter distribution even in the nonlinear regime corresponding to the scales in and around galaxy clusters, being consistent with the case where galaxies trace well the matter distribution on cosmologically large scales.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We show the results of a study using the spectral synthesis technique study for the full MaNGA sample showing their chemical enrichment history (ChEH) as well as the evolution of the stellar mass–metallicity relation (MZR) over cosmic time. We find that the more massive galaxies became enriched first and the lower-mass galaxies did so later, producing a change in the MZR that becomes shallower in time. Separating the sample into morphology and star-forming status bins, some particularly interesting results appear: The mass dependence of the MZR becomes less relevant for later morphological types, to the extent that it inverts for Sd/Irr galaxies, suggesting that morphology is at least as important a factor as mass in the chemical evolution. The MZR for the full sample shows a flattening at the high-mass end and another in the low-mass range, but the former only appears for retired galaxies, while the latter only appears for star-forming galaxies. We also find that the average metallicity gradient is currently negative for all mass bins, but for low-mass galaxies, it was inverted at some point in the past, before which all galaxies had a positive gradient. We also compare how diverse the ChEHs are in the different bins we considered, as well as what primarily drives the diversity: By how much galaxies become enriched, or how quickly they do so.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Triple stars and compact objects are ubiquitously observed in nature. Their long-term evolution is complex; in particular, the von Zeipel–Lidov–Kozai (ZLK) mechanism can potentially lead to highly eccentric encounters of the inner binary. Such encounters can lead to a plethora of interacting binary phenomena, as well as stellar and compact-object mergers. Here we find implicit analytical formulae for the maximal eccentricity, <jats:inline-formula> <jats:tex-math> <?CDATA ${e}_{\max }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>max</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac7958ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, of the inner binary undergoing ZLK oscillations, where both the test-particle limit (parameterized by the inner-to-outer angular momentum ratio <jats:italic>η</jats:italic>) and the double-averaging approximation (parameterized by the period ratio, <jats:italic>ϵ</jats:italic> <jats:sub>SA</jats:sub>) are relaxed, for circular outer orbits. We recover known results in both limiting cases (either <jats:italic>η</jats:italic> or <jats:italic>ϵ</jats:italic> <jats:sub>SA</jats:sub> → 0) and verify the validity of our model using numerical simulations. We test our results with two accurate numerical <jats:italic>N</jats:italic>-body codes, <jats:sc>rebound</jats:sc> for Newtonian dynamics and <jats:sc>tsunami</jats:sc> for general-relativistic dynamics, and find excellent correspondence. We discuss the implications of our results for stellar triples and both stellar and supermassive triple black hole mergers.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Based on the observations from the Super Dual Auroral Radar Network at the Zhongshan Station (−74.9 MLAT, 97.2 MLON) and GOES satellites X-ray sensor, we present the first statistical study of the dayside ionospheric short-wave fadeout (SWF) events on the Southern Hemispheric high latitude from the years 2010–2019 and provide a normal characteristic of SWF with onset of 6 minutes 54 s, blackout of 20 minutes 24 s, and recovery of 39 minutes 36 s, respectively. All the SWF events in this work are selected to be caused by extreme flares. The statistical analysis shows both short-type and long-type SWF onset phases. Onset/blackout phase duration of long events is highly correlated with flare duration (0.79, 0.60), the SWF is mainly driven by the flare radiation profile, and the soft X-ray flux rise rate is higher for short-onset events than for most long-onset events, which is the main reason for the difference between the two types of events. In addition, the effect of ionospheric sluggishness on long-onset events also needs to be considered. The relationship between each phase’s durations of long SWFs and the effective peak X-ray flux is not obvious. However, the correlation between the integrated effective X-ray flux and the onset/blackout phase duration of long events is significant.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Magnetic fields play an important role in the evolution of molecular clouds and star formation. Using the velocity gradient technique (VGT) model, we measured the magnetic field in Orion A using the <jats:sup>12</jats:sup>CO, <jats:sup>13</jats:sup>CO, and C<jats:sup>18</jats:sup>O(1-0) emission lines at a scale of ∼0.07 pc. The measured B field shows an east–west orientation that is perpendicular to the integral shaped filament of Orion A at large scale. The VGT magnetic fields obtained from <jats:sup>13</jats:sup>CO and C<jats:sup>18</jats:sup>O are in agreement with the B field that is measured from the Planck 353 GHz dust polarization at a scale of ∼0.55 pc. Removal of density effects by using a velocity decomposition algorithm can significantly improve the accuracy of the VGT in tracing magnetic fields with the <jats:sup>12</jats:sup>CO(1-0) line. The magnetic field strengths of seven subclouds, OMC-1, OMC-2, OMC-3, OMC-4, OMC-5, L 1641-N, and NGC 1999, have also been estimated with the Davis–Chandrasekhar–Fermi and the Two Mach Numbers technique, and these are found to be in agreement with previous results obtained from dust polarization at far-infrared and submillimeter wavelengths. At smaller scales, the VGT prove a good method to measure magnetic fields.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>By adopting the intermediate and power-law scale factors, we study the tachyon inflation with constant sound speed. We perform some numerical analysis on the perturbation and non-Gaussianity parameters in this model and compare the results with observational data. By using the constraints on the scalar spectral index and tensor-to-scalar ratio obtained from Planck2018 TT, TE, and EE+lowE+lensing+BAO+BK14 data; the constraints on the running of the scalar spectral index obtained from Planck2018 TT, TE, and EE+lowEB+lensing data; and the constraints on tensor spectral index obtained from Planck2018 TT, TE, and EE+lowE+lensing+BK14+BAO+LIGO and Virgo2016 data, we find the observationally viable ranges of the model’s parameters at both 68% CL and 95% CL. We also analyze the non-Gaussian features of the model in the equilateral and orthogonal configurations. Based on Planck2018 TTT, EEE, TTE, and EET data, we find constraints on the sound speed of 0.276 ≤ <jats:italic>c</jats:italic> <jats:sub> <jats:italic>s</jats:italic> </jats:sub> ≤ 1 at 68% CL, 0.213 ≤ <jats:italic>c</jats:italic> <jats:sub> <jats:italic>s</jats:italic> </jats:sub> ≤ 1 at 95% CL, and 0.186 ≤ <jats:italic>c</jats:italic> <jats:sub> <jats:italic>s</jats:italic> </jats:sub> ≤ 1 at 97% CL.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The recent NICER measurement of the radius of the neutron star PSR J0740+6620, and the inferred small variation of radii from 1.4 to 2.1 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, reveal key features of the equation of state of neutron star matter. The pressure rises rapidly in the regime of baryon density <jats:italic>n</jats:italic> ∼ 2–4 times nuclear saturation density, <jats:italic>n</jats:italic> <jats:sub>0</jats:sub>—the region where we expect hadronic matter to be undergoing transformation into quark matter—and the pressure in the nuclear regime is greater than predicted by microscopic many-body variational calculations of nuclear matter. To incorporate these insights into the microscopic physics from the nuclear to the quark matter regimes, we construct an equation of state, QHC21, within the framework of quark–hadron crossover. We include nuclear matter results primarily based on the state-of-the-art chiral effective field theory, but also note results of using nuclear matter variational calculations based on empirical nuclear forces. We employ explicit nuclear degrees of freedom only up to <jats:italic>n</jats:italic> ∼ 1.5 <jats:italic>n</jats:italic> <jats:sub>0</jats:sub>, in order to explore the possibility of further physical degrees of freedom than nucleonic here. The resulting QHC21, which has a peak in sound velocity in ∼2–4 <jats:italic>n</jats:italic> <jats:sub>0</jats:sub>, is stiffer than the earlier QHC19 below 2 <jats:italic>n</jats:italic> <jats:sub>0</jats:sub>, predicting larger radii in substantial agreement with the NICER data.</jats:p>