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<jats:title>Abstract</jats:title> <jats:p>The globular cluster 47 Tucanae (47 Tuc) is one of the most massive star clusters in the Milky Way and is exceptionally rich in exotic stellar populations. For several decades it has been a favorite target of observers, and yet it is computationally very challenging to model because of its large number of stars (<jats:italic>N</jats:italic> ≳ 10<jats:sup>6</jats:sup>) and high density. Here we present detailed and self-consistent 47 Tuc models computed with the <jats:monospace>Cluster Monte Carlo</jats:monospace> code (<jats:monospace>CMC</jats:monospace>). The models include all relevant dynamical interactions coupled to stellar and binary evolution, and reproduce various observations, including the surface brightness and velocity dispersion profiles, pulsar accelerations, and numbers of compact objects. We show that the present properties of 47 Tuc are best reproduced by adopting an initial stellar mass function that is both bottom-heavy and top-light relative to standard assumptions (as in, e.g., Kroupa 2001), and an initial Elson profile (Elson et al. 1987) that is overfilling the cluster’s tidal radius. We include new prescriptions in <jats:monospace>CMC</jats:monospace> for the formation of binaries through giant star collisions and tidal captures, and we show that these mechanisms play a crucial role in the formation of neutron star binaries and millisecond pulsars in 47 Tuc; our best-fit model contains ∼50 millisecond pulsars, 70% of which are formed through giant collisions and tidal captures. Our models also suggest that 47 Tuc presently contains up to ∼200 stellar-mass black holes, ∼5 binary black holes, ∼15 low-mass X-ray binaries, and ∼300 cataclysmic variables.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a detailed study of the Planck-selected binary galaxy cluster PLCK G165.7+67.0 (G165; <jats:italic>z</jats:italic> = 0.348). A multiband photometric catalog is generated incorporating new imaging from the Large Binocular Telescope/Large Binocular Camera and Spitzer/IRAC to existing imaging. To cope with the different image characteristics, robust methods are applied in the extraction of the matched-aperture photometry. Photometric redshifts are estimated for 143 galaxies in the 4 arcmin<jats:sup>2</jats:sup> field of overlap covered by these data. We confirm that strong-lensing effects yield 30 images of 11 background galaxies, of which we contribute new photometric redshift estimates for three image multiplicities. These constraints enable the construction of a revised lens model with a total mass of <jats:italic>M</jats:italic> <jats:sub>600 kpc</jats:sub> = (2.36 ± 0.23) × 10<jats:sup>14</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. In parallel, new spectroscopy using MMT/Binospec and archival data contributes thirteen galaxies that meet our velocity and transverse radius criteria for cluster membership. The two cluster components have a pair-wise velocity of ≲100 km s<jats:sup>−1</jats:sup>, favoring an orientation in the plane of the sky with a transverse velocity of 100–1700 km s<jats:sup>−1</jats:sup>. At the same time, the brightest cluster galaxy (BCG) is offset in velocity from the systemic mean value, suggesting dynamical disturbance. New LOFAR and Very Large Array data uncover head-tail radio galaxies in the BCG and a large red galaxy in the northeast component. From the orientation and alignment of the four radio trails, we infer that the two cluster components have already traversed each other, and are now exiting the cluster.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate the properties, composition, and dynamics of dust formation and growth for a diverse set of core-collapse supernovae (CCSNe), with 15, 20, and 25 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> progenitor masses, explosion energies ranging from 0.5 to 120 foe, and varied engine type. These explosions are evolved with a 1D Lagrangian hydrodynamics code out to a minimum of 1157 days to model the ejecta as it expands and cools. A multigrain dust nucleation and growth model is applied to these results. We find that higher explosion energies lead to an earlier onset of dust formation, smaller grain sizes, and larger silicate abundances. Further, we see that nuclear burning during the explosion leads to enhanced formation of silicate dust. Finally, we build composite models from our suite to predict the efficiency of CCSN dust production as a function of metallicity.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Thermal electrons cannot directly participate in the process of diffusive acceleration at electron–ion shocks because their Larmor radii are smaller than the shock transition width: this is the well-known electron injection problem of diffusive shock acceleration. Instead, an efficient pre-acceleration process must exist that scatters electrons off of electromagnetic fluctuations on scales much shorter than the ion gyroradius. The recently found intermediate-scale instability provides a natural way to produce such fluctuations in parallel shocks. The instability drives comoving (with the upstream plasma) ion–cyclotron waves at the shock front and only operates when the drift speed is smaller than half of the electron Alfvén speed. Here we perform particle-in-cell simulations with the SHARP code to study the impact of this instability on electron acceleration at parallel nonrelativistic, electron–ion shocks. To this end, we compare a shock simulation in which the intermediate-scale instability is expected to grow to simulations where it is suppressed. In particular, the simulation with an Alfvénic Mach number large enough to quench the intermediate instability shows a great reduction (by two orders of magnitude) of the electron acceleration efficiency. Moreover, the simulation with a reduced ion-to-electron mass ratio (where the intermediate instability is also suppressed) not only artificially precludes electron acceleration but also results in erroneous electron and ion heating in the downstream and shock transition regions. This finding opens up a promising route for a plasma physical understanding of diffusive shock acceleration of electrons, which necessarily requires realistic mass ratios in simulations of collisionless electron–ion shocks.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The atmospheric structure of WASP-12b has been hotly contested for years, with disagreements on the presence of a thermal inversion as well as the carbon-to-oxygen ratio, C/O, due to retrieved abundances of H<jats:sub>2</jats:sub>O, CO<jats:sub>2</jats:sub>, and other included species such as HCN and C<jats:sub>2</jats:sub>H<jats:sub>2</jats:sub>. Previously, these difficult-to-diagnose discrepancies have been attributed to model differences; assumptions in these models were thought to drive retrievals toward different answers. Here, we show that some of these differences are independent of model assumptions and are instead due to subtle differences in the inputs, such as the eclipse depths and line-list databases. We replicate previously published retrievals and find that the retrieved results are data driven and are mostly unaffected by the addition of species such as HCN and C<jats:sub>2</jats:sub>H<jats:sub>2</jats:sub>. We also propose a new physically motivated model that takes into consideration the formation of H<jats:sup>−</jats:sup> via the thermal dissociation of H<jats:sub>2</jats:sub>O and H<jats:sub>2</jats:sub> at the temperatures reached in the dayside atmosphere of WASP-12b, but the data’s current resolution does not support its inclusion in the atmospheric model. This study raises the concern that other exoplanet retrievals may be similarly sensitive to slight changes in the input data.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Spectral hardening has been identified in solar flare hard X-ray observations for several decades and remains a puzzle. We examine spectral hardening under the diffusive shock acceleration mechanism using numerical simulations. The hardening is related to the finite width of the shock and is controlled by the shock Péclet number. We implement two different types of Monte Carlo simulations. The first is based on the backward stochastic differential equation method, where the Parker transport equation is solved by casting it to a set of stochastic different equations, and by following the trajectories of individual quasiparticles. In the second approach, we follow real particles and particles are assumed to move freely between scatterings from magnetic turbulence in the plasma. The scattering is modeled as either large-angle hard-sphere elastic collision, or small-angle pitch-angle scattering. We show that the results from these two approaches agree well with each other and agree with analytical results. We also use a Pan-spectrum form to fit the resulting spectra.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The repeating fast radio burst FRB 20190520B is localized to a galaxy at <jats:italic>z</jats:italic> = 0.241, much closer than expected given its dispersion measure DM = 1205 ± 4 pc cm<jats:sup>−3</jats:sup>. Here we assess implications of the large DM and scattering observed from FRB 20190520B for the host galaxy’s plasma properties. A sample of 75 bursts detected with the Five-hundred-meter Aperture Spherical radio Telescope shows scattering on two scales: a mean temporal delay <jats:italic>τ</jats:italic>(1.41 GHz) = 10.9 ± 1.5 ms, which is attributed to the host galaxy, and a mean scintillation bandwidth Δ<jats:italic>ν</jats:italic> <jats:sub>d</jats:sub>(1.41 GHz) = 0.21 ± 0.01 MHz, which is attributed to the Milky Way. Balmer line measurements for the host imply an H<jats:italic>α</jats:italic> emission measure (galaxy frame) EM<jats:sub>s</jats:sub> = 620 pc cm<jats:sup>−6</jats:sup> × (<jats:italic>T</jats:italic>/10<jats:sup>4</jats:sup> K)<jats:sup>0.9</jats:sup>, implying DM<jats:sub>H<jats:italic>α</jats:italic> </jats:sub> of order the value inferred from the FRB DM budget, <jats:inline-formula> <jats:tex-math> <?CDATA ${\mathrm{DM}}_{{\rm{h}}}={1121}_{-138}^{+89}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>DM</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="normal">h</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>1121</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>138</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>89</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6504ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> pc cm<jats:sup>−3</jats:sup> for plasma temperatures greater than the typical value 10<jats:sup>4</jats:sup> K. Combining <jats:italic>τ</jats:italic> and DM<jats:sub>h</jats:sub> yields a nominal constraint on the scattering amplification from the host galaxy <jats:inline-formula> <jats:tex-math> <?CDATA $\widetilde{F}G\,=\,{1.5}_{-0.3}^{+0.8}{({\mathrm{pc}}^{2}\,\mathrm{km})}^{-1/3}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>F</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="true">˜</mml:mo> </mml:mrow> </mml:mover> <mml:mi>G</mml:mi> <mml:mspace width="0.50em" /> <mml:mo>=</mml:mo> <mml:mspace width="0.50em" /> <mml:msubsup> <mml:mrow> <mml:mn>1.5</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.8</mml:mn> </mml:mrow> </mml:msubsup> <mml:msup> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:msup> <mml:mrow> <mml:mi>pc</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em" /> <mml:mi>km</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6504ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>, where <jats:inline-formula> <jats:tex-math> <?CDATA $\widetilde{F}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>F</mml:mi> </mml:mrow> <mml:mrow> <mml:mo stretchy="true">˜</mml:mo> </mml:mrow> </mml:mover> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6504ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> describes turbulent density fluctuations and <jats:italic>G</jats:italic> represents the geometric leverage to scattering that depends on the location of the scattering material. For a two-screen scattering geometry where <jats:italic>τ</jats:italic> arises from the host galaxy and Δ<jats:italic>ν</jats:italic> <jats:sub>d</jats:sub> from the Milky Way, the implied distance between the FRB source and dominant scattering material is ≲100 pc. The host galaxy scattering and DM contributions support a novel technique for estimating FRB redshifts using the <jats:italic>τ</jats:italic>–DM relation, and are consistent with previous findings that scattering of localized FRBs is largely dominated by plasma within host galaxies and the Milky Way.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present an analytic model for clustered supernovae (SNe) feedback in galaxy disks, incorporating the dynamical evolution of superbubbles formed from spatially overlapping SNe remnants. We propose two realistic outcomes for the evolution of superbubbles in galactic disks: (1) the expansion velocity of the shock front falls below the turbulent velocity dispersion of the interstellar medium in the galaxy disk, whereupon the superbubble stalls and fragments, depositing its momentum entirely within the galaxy disk; or (2) the superbubble grows in size to reach the gas scale height, breaking out of the galaxy disk and driving galactic outflows/fountains. In either case, we find that superbubble breakup/breakout almost always occurs before the last Type II SN (≲40 Myr) in the recently formed star cluster, assuming a standard high-end initial mass function slope, and scalings between stellar lifetimes and masses. The threshold between these two cases implies a break in the effective strength of feedback in driving turbulence within galaxies, and a resulting change in the scalings of, for example, star formation rates with gas surface density (the Kennicutt–Schmidt relation) and the star formation efficiency in galaxy disks.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A sample of 14 FRBs with measured redshifts and scattering times is used to assess contributions to dispersion and scattering from the intergalactic medium (IGM), galaxy halos, and the disks of host galaxies. The IGM and galaxy halos contribute significantly to dispersion measures (DMs) but evidently not to scattering, which is then dominated by host galaxies. This enables the usage of scattering times for estimating DM contributions from host galaxies and also for a combined scattering–dispersion redshift estimator. Redshift estimation is calibrated using the scattering of Galactic pulsars after taking into account different scattering geometries for Galactic and intergalactic lines of sight. The DM-only estimator has a bias of ∼0.1 and rms error of ∼0.15 in the redshift estimate for an assumed ad hoc value of 50 pc cm<jats:sup>−3</jats:sup> for the host galaxy’s DM contribution. The combined redshift estimator shows less bias by a factor of 4 to 10 and a 20%–40% smaller rms error. We find that values for the baryonic fraction of the ionized IGM <jats:italic>f</jats:italic> <jats:sub>igm</jats:sub> ≃ 0.85 ± 0.05 optimize redshift estimation using dispersion and scattering. Our study suggests that 2 of the 14 candidate galaxy associations (FRB 20190523A and FRB 20190611B) should be reconsidered.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the results of X-ray (Chandra X-ray Observatory (CXO)) and radio (ATCA) observations of the pulsar wind nebula (PWN) powered by the young pulsar PSR J1016–5857, which we dub “the Goose” PWN. In both bands, the images reveal a tail-like PWN morphology that can be attributed to the pulsar’s motion. By comparing archival and new CXO observations, we measure the pulsar’s proper motion <jats:italic>μ</jats:italic> = 28.8 ± 7.3 mas yr<jats:sup>−1</jats:sup>, yielding a projected pulsar velocity <jats:italic>v</jats:italic> ≈ 440 ± 110 km s<jats:sup>−1</jats:sup> (at <jats:italic>d</jats:italic> = 3.2 kpc); its direction is consistent with the PWN shape. Radio emission from the PWN is polarized, with the magnetic field oriented along the pulsar tail. The radio tail connects to a larger radio structure (not seen in X-rays), which we interpret as a relic PWN (also known as a plerion). The spectral analysis of the CXO data shows that the PWN spectrum softens from Γ = 1.7 to Γ ≈ 2.3–2.5 with increasing distance from the pulsar. The softening can be attributed to the rapid synchrotron burn-off, which would explain the lack of X-ray emission from the older relic PWN. In addition to nonthermal PWN emission, we detected thermal emission from a hot plasma, which we attribute to the host supernova remnant. The radio PWN morphology and the proper motion of the pulsar suggest that the reverse shock passed through the pulsar’s vicinity and pushed the PWN to one side.</jats:p>