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<jats:title>Abstract</jats:title> <jats:p>We present Herschel SPIRE and PACS maps of the Cepheus Flare clouds L1157, L1172, L1228, L1241, and L1251, observed by the Herschel Gould Belt Survey of nearby star-forming molecular clouds. Through modified blackbody fits to the SPIRE and PACS data, we determine typical cloud column densities of (0.5–1.0) × 10<jats:sup>21</jats:sup> cm<jats:sup>−2</jats:sup> and typical cloud temperatures of 14–15 K. Using the <jats:italic>getsources</jats:italic> identification algorithm, we extract 832 dense cores from the SPIRE and PACS data at 160–500 <jats:italic>μ</jats:italic>m. From placement in a mass versus size diagram, we consider 303 to be candidate prestellar cores, and 178 of these to be “robust” prestellar cores. From an independent extraction of sources at 70 <jats:italic>μ</jats:italic>m, we consider 25 of the 832 dense cores to be protostellar. The distribution of background column densities coincident with candidate prestellar cores peaks at (2–4) × 10<jats:sup>21</jats:sup> cm<jats:sup>−2</jats:sup>. About half of the candidate prestellar cores in Cepheus may have formed as a result of the widespread fragmentation expected to occur within filaments of “transcritical” line mass. The lognormal robust prestellar core mass function (CMF) drawn from all five Cepheus clouds peaks at 0.56 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> and has a width of ∼0.5 dex, similar to that of Aquila’s CMF. Indeed, the width of Cepheus’s aggregate CMF is similar to the stellar system initial mass function (IMF). The similarity of CMF widths in different clouds and the system IMF suggests a common, possibly turbulent origin for seeding the fluctuations that evolve into prestellar cores and stars.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Using Magnetospheric Multiscale observations at the Earth’s quasi-parallel bow shock we demonstrate that electrons are heated by two different mechanisms: a quasi-adiabatic heating process during magnetic field compression, characterized by the isotropic temperature relation <jats:inline-formula> <jats:tex-math> <?CDATA $T/B={({T}_{0}/{B}_{0})({B}_{0}/B)}^{\alpha }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>T</mml:mi> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mi>B</mml:mi> <mml:mo>=</mml:mo> <mml:msup> <mml:mrow> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>T</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:msub> <mml:mrow> <mml:mi>B</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi>B</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> </mml:msub> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mi>B</mml:mi> <mml:mo stretchy="false">)</mml:mo> </mml:mrow> <mml:mrow> <mml:mi>α</mml:mi> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabbffaieqn1.gif" xlink:type="simple" /> </jats:inline-formula> with <jats:italic>α</jats:italic> = 2/3 when the electron heating function <jats:inline-formula> <jats:tex-math> <?CDATA $| {\chi }_{e}| \lt 1$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">∣</mml:mo> <mml:msub> <mml:mrow> <mml:mi>χ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">∣</mml:mo> <mml:mo>&lt;</mml:mo> <mml:mn>1</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabbffaieqn2.gif" xlink:type="simple" /> </jats:inline-formula>, and a stochastic heating process when <jats:inline-formula> <jats:tex-math> <?CDATA $| {\chi }_{e}| \gt 1$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo stretchy="false">∣</mml:mo> <mml:msub> <mml:mrow> <mml:mi>χ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>e</mml:mi> </mml:mrow> </mml:msub> <mml:mo stretchy="false">∣</mml:mo> <mml:mo>&gt;</mml:mo> <mml:mn>1</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabbffaieqn3.gif" xlink:type="simple" /> </jats:inline-formula>. Both processes are controlled by the value of the stochastic heating function <jats:inline-formula> <jats:tex-math> <?CDATA ${\chi }_{j}={m}_{j}{q}_{j}^{-1}{B}^{-2}\mathrm{div}({{\boldsymbol{E}}}_{\perp })$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>χ</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>j</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msub> <mml:mrow> <mml:mi>m</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>j</mml:mi> </mml:mrow> </mml:msub> <mml:msubsup> <mml:mrow> <mml:mi>q</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>j</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msubsup> <mml:msup> <mml:mrow> <mml:mi>B</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msup> <mml:mi>div</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:msub> <mml:mrow> <mml:mi mathvariant="bold-italic">E</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>⊥</mml:mo> </mml:mrow> </mml:msub> <mml:mo stretchy="false">)</mml:mo> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabbffaieqn4.gif" xlink:type="simple" /> </jats:inline-formula> for particles with mass <jats:italic>m</jats:italic> <jats:sub> <jats:italic>j</jats:italic> </jats:sub> and charge <jats:italic>q</jats:italic> <jats:sub> <jats:italic>j</jats:italic> </jats:sub> in the electric and magnetic fields <jats:inline-formula> <jats:tex-math> <?CDATA ${\boldsymbol{E}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="bold-italic">E</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabbffaieqn5.gif" xlink:type="simple" /> </jats:inline-formula> and <jats:inline-formula> <jats:tex-math> <?CDATA ${\boldsymbol{B}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="bold-italic">B</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabbffaieqn6.gif" xlink:type="simple" /> </jats:inline-formula>. Test-particle simulations are used to show that the stochastic electron heating and acceleration in the studied shock are accomplished by waves at frequencies (0.4–5) <jats:italic>f</jats:italic> <jats:sub> <jats:italic>ce</jats:italic> </jats:sub> (electron gyrofrequency) for bulk heating, and waves <jats:inline-formula> <jats:tex-math> <?CDATA $f\gt 5\,{f}_{{ce}}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>f</mml:mi> <mml:mo>&gt;</mml:mo> <mml:mn>5</mml:mn> <mml:mspace width="0.25em" /> <mml:msub> <mml:mrow> <mml:mi>f</mml:mi> </mml:mrow> <mml:mrow> <mml:mi mathvariant="italic">ce</mml:mi> </mml:mrow> </mml:msub> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabbffaieqn7.gif" xlink:type="simple" /> </jats:inline-formula> for acceleration of the tail of the distribution function. Stochastic heating can give rise to flat-top electron distribution functions, frequently observed near shocks. It is also shown that obliquely polarized electric fields of electron cyclotron drift and ion acoustic instabilities scatter the electrons into the parallel direction and keep the isotropy of the electron distribution. The results reported in this paper may be relevant to electron heating and acceleration at interplanetary shocks and other astrophysical shocks.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Using Jansky Very Large Array data obtained from high-resolution observations at 5.5 GHz at multiple epochs in 2014 and 2019, we have detected a population of radio variables and transients in the radio-bright zone at the Galactic center. With observations covering a sky area of 180 arcmin<jats:sup>2</jats:sup> at an angular resolution of 0.″4, we report new detections of 110 Galactic center compact radio (GCCR) sources with a size of &lt;1″. The flux densities of GCCR sources exceed 70 <jats:italic>μ</jats:italic>Jy, with at least 10<jats:italic>σ</jats:italic> significance. Among these sources, 82 are variable or transient and 28 are nonvariable. About 10% of them are expected to be extragalactic background sources. We discuss the possible astrophysical nature of the detected sources. As compared to the Galactic disk (GD) population of normal pulsars (NPs) and millisecond pulsars (MSPs), a majority (80%) of the GCCR sources appear to fall within the high flux density tail of the pulsar distribution, as extrapolated from a sample of NPs in the GD. However, MSPs extrapolated from the GD population are too weak to have contributed significantly to the GCCR population that has been detected. We also cross-correlated the GCCR sources with X-ray sources in Chandra X-ray catalogs and found that 42 GCCR sources have candidate X-ray counterparts. Most of the GCCR sources having X-ray counterparts are likely to be associated with unresolved or slightly resolved radio jets launched from X-ray binaries with a compact object, either a black hole or a neutron star.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Stellar engines are hypothesized megastructures that extract energy from the host star, typically with the purpose of generating thrust and accelerating the stellar system. We explore the maximum potential speeds that could be realizable by stellar engines, and determine that speeds up to ∼0.1 <jats:italic>c</jats:italic> might perhaps be attainable under optimal conditions. In contrast, natural astrophysical phenomena in the Milky Way are very unlikely to produce such speeds. Hence, astrometric surveys of hypervelocity stars may be utilized to conduct commensal searches for high-speed stellar engines in the Milky Way. It may be possible to derive bounds on their abundance, but this requires certain assumptions regarding the spatiotemporal distribution of such engines, which are not guaranteed to be valid.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We show that quasar microlensing magnification statistics induced by a population of point microlenses distributed according to a mass spectrum can be very well approximated by that of a single-mass, monochromatic, population. When the spatial resolution (physically defined by the source size) is small compared with the Einstein radius, the mass of the monochromatic population matches the geometric mean (GM) of the mass spectrum. Otherwise, the best-fit mass can be larger. Taking into account the degeneracy with the GM, the interpretation of quasar microlensing observations under the hypothesis of a mixed population of primordial black holes and stars makes the existence of a significant population of intermediate mass black holes (∼100<jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>) unlikely but allows, within a 2<jats:italic>σ</jats:italic> confidence interval, the presence of a large population (≳40% of the total mass) of substellar black holes (∼0.01<jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>).</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Cross-correlations between galaxy weak lensing (WL) and cosmic microwave background (CMB) lensing are powerful tools to probe matter fluctuations at intermediate redshifts and to detect residual systematics in either probe. In this paper, we study the cross-correlation of galaxy WL from the Hyper Suprime-Cam Subaru Strategic Program (HSC) first data release and CMB lensing from the final Planck data release, for HSC source galaxies at 0.3 ≤ <jats:italic>z</jats:italic> ≤ 1.5. HSC is the deepest Stage-III galaxy WL survey, and provides a great opportunity to study the high-redshift universe. It also presents new challenges related to its exceptionally high source density, such as source blending. The cross-correlation signal is measured at a significance level of 3.1<jats:italic>σ</jats:italic>. The amplitude of our best-fit model with respect to the best-fit 2018 Planck cosmology is <jats:italic>A</jats:italic> = 0.81 ± 0.25, consistent with <jats:italic>A</jats:italic> = 1. Our result is also consistent with previous CMB lensing and galaxy WL cross-correlation studies using different surveys. We perform tests with respect to the WL <jats:italic>B</jats:italic>-modes, the point-spread-function, photometric redshift errors, and thermal Sunyaev–Zel’dovich leakage, and find no significant evidence of residual systematics.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The photon spectrum emitted by a transrelativistic pair plasma is calculated in the presence of an ultrastrong magnetic field, and is shown to bear a remarkable resemblance to the rising hard X-ray spectra of quiescent magnetars. This emission is powered by pair annihilation which, in contrast with a weakly magnetized pair plasma, shows an extended low-frequency tail similar to bremsstrahlung. Cross sections for electron–positron annihilation/scattering, two-photon pair creation, and photon-<jats:italic>e</jats:italic> <jats:sup>±</jats:sup> scattering are adopted from our earlier ab initio quantum electrodynamic calculations in the regime <jats:inline-formula> <jats:tex-math> <?CDATA $10{\alpha }_{\mathrm{em}}^{-1}{B}_{{\rm{Q}}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabbe87ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> ≫ <jats:italic>B</jats:italic> ≫ <jats:italic>B</jats:italic> <jats:sub>Q</jats:sub>. Careful attention is given to the <jats:italic>u</jats:italic>-channel scattering resonance. Magnetospheric arcades anchored in zones of intense crustal shear and reaching about twice the magnetar radius are identified as the sites of the persistent hard X-ray emission. We deduce a novel and stable configuration for the magnetospheric circuit, with a high plasma density sustained by ohmic heating and in situ pair creation. Pairs are sourced nonlocally by photon collisions in zones with weak currents, such as the polar cap. Annihilation bremsstrahlung extends to the optical–IR band, where the plasma cutoff is located. The upper magnetar atmosphere experiences strong current-driven growth of ion-acoustic turbulence, which may limit positron diffusion. Coherent optical–IR emission is bounded near the observed flux by induced scattering. This model accommodates the rapid X-ray brightening of an activating magnetar, concentrated thermal hotspots, and the subdominant thermal X-ray emission of some active magnetars. Current injection is ascribed to continuous magnetic braiding, as seen in the global yielding calculations of Thompson, Yang, and Ortiz.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Compact stars containing quark matter may masquerade as neutron stars in the range of measured mass and radius, making it difficult to draw firm conclusions on the phase of matter inside the star. The sensitivity of core <jats:italic>g</jats:italic>-mode oscillations to the presence of a mixed phase may alleviate this difficulty. In hybrid stars that admit quark matter in a mixed phase, the <jats:italic>g</jats:italic>-mode frequency rises sharply due to a marked decrease in the equilibrium sound speed. Resonant excitation of <jats:italic>g</jats:italic>-modes can leave an imprint in the waveform of coalescing binary compact stars. We present analytic and numeric results to assess the sensitivity displayed by <jats:italic>g</jats:italic>-mode oscillations to quark matter in a homogeneous or mixed phase and also compute relevant damping times in quark matter due to viscosity.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate hadronic and leptonic scenarios for the GeV–TeV gamma-ray emission from jets of the microquasar SS 433. The emission region of the TeV photons coincides with the X-ray knots, where electrons are efficiently accelerated. On the other hand, the optical high-density filaments are also located close to the X-ray knots, which may support a hadronic scenario. We calculate multiwavelength photon spectra of the extended jet region by solving the transport equations for the electrons and protons. We find that both hadronic and leptonic models can account for the observational data, including the latest Fermi Large Area Telescope result. The hadronic scenarios predict higher-energy photons than the leptonic scenarios, and future observations such as with the Cherenkov Telescope Array, the Large High-Altitude Air Shower Observatory, and the Southern Wide-field Gamma-ray Observatory may distinguish between these scenarios and unravel the emission mechanism of GeV–TeV gamma rays. Based on our hadronic scenario, the analogy between microquasars and radio galaxies implies that the X-ray knot region of the radio-galaxy jets may accelerate heavy nuclei up to ultrahigh energies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The gravitational pull of a large number of asteroids perturbs a pulsar’s motion to a degree that is detectable through precision timing of millisecond pulsars. The result is a low-frequency, correlated noise process, similar in form to the red timing noise known to affect canonical pulsars, or to the signal expected from a stochastic gravitational-wave background. Motivated by the observed fact that many millisecond pulsars are in binary systems, we describe the ways in which the presence of a binary companion to the pulsar would affect the signal produced by an asteroid belt. The primary effect of the companion is to destabilize the shortest-period orbits, cutting off the high-frequency component of the signal from the asteroid belt. We also discuss the implications of asteroid belts for gravitational-wave search efforts. Compared to the signal from a stochastic gravitational-wave background, asteroid-belt noise has a similar frequency and amplitude, and is similarly independent of radio frequency, but is not correlated between different pulsars, which should allow the two kinds of signal to be distinguished.</jats:p>