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<jats:title>Abstract</jats:title> <jats:p>We fit the mass and radial profile of the Orphan–Chenab Stream’s (OCS) dwarf-galaxy progenitor by using turnoff stars in the Sloan Digital Sky Survey and the Dark Energy Camera to constrain <jats:italic>N</jats:italic>-body simulations of the OCS progenitor falling into the Milky Way on the 1.5 PetaFLOPS MilkyWay@home distributed supercomputer. We infer the internal structure of the OCS’s progenitor under the assumption that it was a spherically symmetric dwarf galaxy composed of a stellar system embedded in an extended dark matter halo. We optimize the evolution time, the baryonic and dark matter scale radii, and the baryonic and dark matter masses of the progenitor using a differential evolution algorithm. The likelihood score for each set of parameters is determined by comparing the simulated tidal stream to the angular distribution of OCS stars observed in the sky. We fit the total mass of the OCS’s progenitor to (2.0 ± 0.3) × 10<jats:sup>7</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> with a mass-to-light ratio of <jats:italic>γ</jats:italic> = 73.5 ± 10.6 and (1.1 ± 0.2) × 10<jats:sup>6</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> within 300 pc of its center. Within the progenitor’s half-light radius, we estimate a total mass of (4.0 ± 1.0) × 10<jats:sup>5</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. We also fit the current sky position of the progenitor’s remnant to be (<jats:italic>α</jats:italic>, <jats:italic>δ</jats:italic>) = ((166.0 ± 0.9)°, (−11.1 ± 2.5)°) and show that it is gravitationally unbound at the present time. The measured progenitor mass is on the low end of previous measurements and, if confirmed, lowers the mass range of ultrafaint dwarf galaxies. Our optimization assumes a fixed Milky Way potential, OCS orbit, and radial profile for the progenitor, ignoring the impact of the Large Magellanic Cloud.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>As has been known nearly since the beginning of space research with satellites and rockets that the temperature of the atmosphere of our Sun rises rapidly from the photosphere at about 6000 K to the order of 10<jats:sup>6</jats:sup> K. The major heating of the solar wind apparently occurs in a narrow region, the transition region, just above the chromosphere, a region where remote sensing of atomic energy levels shows a temperature of 10<jats:sup>6</jats:sup> deg. However, since the early days of the recognition of the solar wind it has been recognized that there must also be further heating as the solar wind escapes the Sun, to overcome adiabatic cooling, and it is this heating that is the subject of the Parker Solar Probe mission, and of this work. As is well known, the solar wind is turbulent, which suggests that plasma instabilities play an important role in its behavior. The role of instabilities in shaping the solar wind was clearly shown by Kasper et al. and Hellinger et al. As shown in Figure 4 of Kasper or Figure 1 of Hellinger, the distribution function of the ions is limited by well-known instabilities. It seems that there ought to be an instability that is common and depends on omnipresent plasma characteristics. In this work it is assumed that such may be provided by the expansion of the solar wind magnetic field as it leaves the Sun.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Milky Way halo was predominantly formed by the merging of numerous progenitor galaxies. However, our knowledge of this process is still incomplete, especially in regard to the total number of mergers, their global dynamical properties and their contribution to the stellar population of the Galactic halo. Here, we uncover the Milky Way mergers by detecting groupings of globular clusters, stellar streams, and satellite galaxies in action (<jats:bold> <jats:italic>J</jats:italic> </jats:bold>) space. While actions fully characterize the orbits, we additionally use the redundant information on their energy (<jats:italic>E</jats:italic>) to enhance the contrast between the groupings. For this endeavor, we use Gaia EDR3‒based measurements of 170 globular clusters, 41 streams, and 46 satellites to derive their <jats:bold> <jats:italic>J</jats:italic> </jats:bold> and <jats:italic>E</jats:italic>. To detect groups, we use the ENLINK software, coupled with a statistical procedure that accounts for the observed phase-space uncertainties of these objects. We detect a total of <jats:italic>N</jats:italic> = 6 groups, including the previously known mergers Sagittarius, Cetus, Gaia‒Sausage/Enceladus, LMS-1/Wukong, Arjuna/Sequoia/I’itoi, and one new merger that we call Pontus. All of these mergers, together, comprise 62 objects (≈25% of our sample). We discuss their members, orbital properties, and metallicity distributions. We find that the three most-metal-poor streams of our galaxy—“C-19” ([Fe/H] = −3.4 dex), “Sylgr” ([Fe/H] = −2.9 dex), and “Phoenix” ([Fe/H] = −2.7 dex)—are associated with LMS-1/Wukong, showing it to be the most-metal-poor merger. The global dynamical atlas of Milky Way mergers that we present here provides a present-day reference for galaxy formation models.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Current neutrino detectors will observe hundreds to thousands of neutrinos from Galactic supernovae, and future detectors will increase this yield by an order of magnitude or more. With such a data set comes the potential for a huge increase in our understanding of the explosions of massive stars, nuclear physics under extreme conditions, and the properties of the neutrino. However, there is currently a large gap between supernova simulations and the corresponding signals in neutrino detectors, which will make any comparison between theory and observation very difficult. SNEWPY is an open-source software package that bridges this gap. The SNEWPY code can interface with supernova simulation data to generate from the model either a time series of neutrino spectral fluences at Earth, or the total time-integrated spectral fluence. Data from several hundred simulations of core-collapse, thermonuclear, and pair-instability supernovae is included in the package. This output may then be used by an event generator such as sntools or an event rate calculator such as the SuperNova Observatories with General Long Baseline Experiment Simulator (SNOwGLoBES). Additional routines in the SNEWPY package automate the processing of the generated data through the SNOwGLoBES software and collate its output into the observable channels of each detector. In this paper we describe the contents of the package, the physics behind SNEWPY, the organization of the code, and provide examples of how to make use of its capabilities.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Sagittarius A* (Sgr A*), the Galactic Center supermassive black hole (SMBH), is one of the best targets in which to resolve the innermost region of an SMBH with very long baseline interferometry (VLBI). In this study, we have carried out observations toward Sgr A* at 1.349 cm (22.223 GHz) and 6.950 mm (43.135 GHz) with the East Asian VLBI Network, as a part of the multiwavelength campaign of the Event Horizon Telescope (EHT) in 2017 April. To mitigate scattering effects, the physically motivated scattering kernel model from Psaltis et al. (2018) and the scattering parameters from Johnson et al. (2018) have been applied. As a result, a single, symmetric Gaussian model well describes the intrinsic structure of Sgr A* at both wavelengths. From closure amplitudes, the major-axis sizes are ∼704 ± 102 <jats:italic>μ</jats:italic>as (axial ratio ∼<jats:inline-formula> <jats:tex-math> <?CDATA ${1.19}_{-0.19}^{+0.24}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mn>1.19</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.19</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.24</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac4165ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>) and ∼300 ± 25 <jats:italic>μ</jats:italic>as (axial ratio ∼1.28 ± 0.2) at 1.349 cm and 6.95 mm, respectively. Together with a quasi-simultaneous observation at 3.5 mm (86 GHz) by Issaoun et al. (2019), we show that the intrinsic size scales with observing wavelength as a power law, with an index ∼1.2 ± 0.2. Our results also provide estimates of the size and compact flux density at 1.3 mm, which can be incorporated into the analysis of the EHT observations. In terms of the origin of radio emission, we have compared the intrinsic structures with the accretion flow scenario, especially the radiatively inefficient accretion flow based on the Keplerian shell model. With this, we show that a nonthermal electron population is necessary to reproduce the source sizes.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Since its launch, the Alpha Magnetic Spectrometer–02 (AMS-02) has delivered outstanding quality measurements of the spectra of cosmic-ray (CR) species (<jats:inline-formula> <jats:tex-math> <?CDATA $\bar{p}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>p</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>¯</mml:mo> </mml:mrow> </mml:mover> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac313dieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, <jats:italic>e</jats:italic> <jats:sup>±</jats:sup>) and nuclei (H–O, Ne, Mg, Si, Fe), which resulted in a number of breakthroughs. The most recent AMS-02 result is the measurement of the spectrum of CR fluorine up to ∼2 TV. Given its very low solar system abundance, fluorine in CRs is thought to be mostly secondary, produced in fragmentations of heavier species, predominantly Ne, Mg, and Si. Similar to the best-measured secondary-to-primary boron to carbon nuclei ratio that is widely used to study the origin and propagation of CR species, the precise fluorine data would allow the origin of Si-group nuclei to be studied independently. Meanwhile, the secondary origin of CR fluorine has never been tested in a wide energy range due to the lack of accurate CR data. In this paper, we use the first ever precise measurements of the fluorine spectrum by AMS-02 together with ACE-CRIS and Voyager 1 data to actually test this paradigm. Our detailed modeling shows an excess below 10 GV in the fluorine spectrum that may hint at a primary fluorine component. We also provide an updated local interstellar spectrum (LIS) of fluorine in the rigidity range from a few MV to ∼2 TV. Our calculations employ the self-consistent <jats:sc>GalProp</jats:sc>–<jats:sc>HelMod</jats:sc> framework that has proved to be a reliable tool in deriving the LIS of CR <jats:inline-formula> <jats:tex-math> <?CDATA $\bar{p}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>p</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>¯</mml:mo> </mml:mrow> </mml:mover> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac313dieqn2.gif" xlink:type="simple" /> </jats:inline-formula> and <jats:italic>e</jats:italic> <jats:sup>−</jats:sup>, and nuclei <jats:italic>Z</jats:italic> ≤ 28.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate the interaction of turbulence with shock waves by performing 2D hybrid kinetic simulations. We inject force-free magnetic fields upstream that are unstable to the tearing-mode instability. The magnetic fields evolve into turbulence and interact with a shock wave whose sonic Mach number is 2.4. Turbulence properties, the total and normalized residual energy and the normalized cross helicity, change across the shock wave. While the energy of velocity and magnetic fluctuations is mostly distributed equally upstream, the velocity fluctuations are amplified dominantly downstream of the shock wave. The amplitude of turbulence spectra for magnetic, velocity, and density fluctuations are also increased at the shock wave while their spectral index remains unchanged. We compare our results with the Zank et al. model of turbulence transmission across a shock, and find that it provides a reasonable explanation for the spectral change across the shock wave. We find that particles are efficiently accelerated at the shock front, and a power-law spectrum forms downstream. This can be explained by diffusive shock acceleration, in which particles gain energy by being scattered upstream and downstream of a shock wave. The trajectory of an accelerated particle suggests that upstream turbulence plays a role scattering of particles.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We advance theoretical methods for studying propagation effects in fast radio burst (FRB) spectra. We derive their autocorrelation function in the model with diffractive lensing and strong Kolmogorov-type scintillations and analytically obtain the spectra lensed on different plasma density profiles. With these tools, we reanalyze the highest frequency 4–8 GHz data of Gajjar et al. for the repeating FRB 20121102A (FRB 121102). In the data, we discover, first, a remarkable spectral structure of almost equidistant peaks separated by 95 ± 16 MHz. We suggest that it can originate from diffractive lensing of the FRB signals on a compact gravitating object of mass 10<jats:sup>−4</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> or on a plasma underdensity near the source. Second, the spectra include erratic interstellar, presumably Milky Way scintillations. We extract their decorrelation bandwidth 3.3 ± 0.6 MHz at reference frequency 6 GHz. The third feature is a GHz-scale pattern that, as we find, linearly drifts with time and presumably represents a wideband propagation effect, e.g., GHz-scale scintillations. Fourth, many spectra are dominated by a narrow peak at 7.1 GHz. We suggest that it can be caused by propagation through a plasma lens, e.g., in the host galaxy. Fifth, separating the propagation effects, we give strong arguments that the intrinsic progenitor spectrum has a narrow GHz bandwidth and variable central frequency. This confirms expectations from the previous observations. We discuss alternative interpretations of the above spectral features.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The discovery of the sources of ultrahigh-energy photons in our Galaxy by the High-Altitude Water Cherenkov Gamma-ray Observatory and the Large High Altitude Air Shower Observatory (LHAASO) has revolutionized the field of gamma-ray astronomy in the last few years. These emissions are sometimes found in the vicinity of powerful pulsars or supernova remnants (SNRs) associated with giant molecular clouds (GMCs). Inverse Compton emission by shock-accelerated electrons emitted by pulsars and proton–proton interactions of shock-accelerated protons emitted by SNRs with cold protons in molecular clouds are often identified as the causes of these emissions. In this paper we have selected two ultrahigh-energy photon sources, LHAASO J2108+5157 and LHAASO J0341+5258, which are associated with GMCs, but no powerful pulsar or SNR has been detected in their vicinity. We have proposed a scenario where shock-accelerated electrons and protons are injected in the local environment of these sources from past explosions, which happened thousands of years ago. We show that the observed ultrahigh-energy photon flux can be explained with the secondary gamma rays produced by the time-evolved relativistic electron and proton spectra.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the structural and chemical investigation of nine presolar silicate grains from the CH3/CB<jats:sub>b</jats:sub>3 chondrite Isheyevo and CR2 chondrite Northwest Africa (NWA) 801. Five of these grains belong to group 1, likely condensed in low- to intermediate-mass asymptotic giant branch (AGB) stars, super-AGB stars, or core-collapse supernovae, while the remaining four grains belong to group 4 and have a supernova origin. The advanced transmission electron microscopy and associated electron spectroscopy analyses show a diverse range of chemical and structural compositions for presolar silicates. Two GEMS (glass with embedded metal and sulfide)-like silicates, each from different groups, condensed under nonequilibrium conditions in stellar outflows. Two nonstoichiometric silicates from group 1 have dissimilar formation and alteration histories. An amorphous silicate from group 1 with olivine-like [(Mg,Fe)<jats:sub>2</jats:sub>SiO<jats:sub>4</jats:sub>] composition likely formed as a crystalline olivine that subsequently amorphized in the interstellar medium. An oldhamite (CaS) grain within a stoichiometric enstatite (MgSiO<jats:sub>3</jats:sub>) from group 1 probably formed by heterogeneous condensation in circumstellar outflows. Of the two crystalline grains from group 4, one is an antigorite [(Mg,Fe)<jats:sub>3</jats:sub>Si<jats:sub>2</jats:sub>O<jats:sub>5</jats:sub>(OH)<jats:sub>4</jats:sub>], while the other is a nontronite [Na,Fe<jats:sub>2</jats:sub>(Si,Al)<jats:sub>4</jats:sub>O<jats:sub>10</jats:sub>(OH)<jats:sub>2</jats:sub>.nH<jats:sub>2</jats:sub>O], both formed as a crystalline forsterite and later altered to have hydrated silicate composition. A group-4 silicate has a chemical composition similar to a low Ca-pyroxene [(Ca,Mg)(Si,Al)<jats:sub>2</jats:sub>O<jats:sub>6</jats:sub>]. Our data imply that presolar grains from different groups can have a similar range of grain-formation conditions.</jats:p>