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<jats:title>Abstract</jats:title> <jats:p>The interplanetary magnetic field carried out from the Sun by the solar wind displays fluctuations over a wide range of scales. While at large scales, say at frequencies lower than 0.1–1 Hz, fluctuations display the universal character of fully developed turbulence with a well-defined Kolmogorov-like inertial range, the physical and dynamical properties of the small-scale regime as well as their connection with the large-scale ones are still a debated topic. In this work we investigate the near-Sun magnetic field fluctuations at subproton scales by analyzing the Markov property of fluctuations and recovering basic information about the nature of the energy transfer across different scales. By evaluating the Kramers–Moyal coefficients we find that fluctuations in the subproton range are well described as a Markovian process with Probability Density Functions (PDFs) modeled via a Fokker–Planck (FP) equation. Furthermore, we show that the shape of the PDFs is globally scale-invariant and similar to the one recovered for the stationary solution of the FP equation at different scales. The relevance of our results on the Markovian character of subproton scale fluctuations is also discussed in connection with the occurrence of turbulence in this domain.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present general relativistic magnetohydrodynamical simulations of equal-mass spinning black hole binary mergers embedded in a magnetized gas cloud. We focus on the effect of the spin orientation relative to the orbital angular momentum on the flow dynamics, mass accretion rate, and Poynting luminosity. We find that, across the inspiral, the gas accreting onto the individual black holes concentrates into disklike overdensities whose angular momenta are oriented toward the spin axes and that persist until merger. We identify quasiperiodic modulations occurring in the mass accretion rate at the level of ∼1%–20%, evolving in parallel with the gravitational-wave chirp. The similarity between the accretion rate time series and the gravitational strain is a consequence of the interplay between strong, dynamical gravitational fields and magnetic fields in the vicinity of the inspiraling black holes. This result suggests that quasiperiodicity in the premerger accretion rate of massive binaries is not exclusive of environments in which the black holes are embedded in a circumbinary accretion disk and could provide an additional useful signature of electromagnetic emission concurrent to low-frequency gravitational-wave detection.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The elemental composition of the Sun’s hot atmosphere, the corona, shows a distinctive pattern that is different from the underlying surface or photosphere. Elements that are easy to ionize in the chromosphere are enhanced in abundance in the corona compared to their photospheric values. A similar pattern of behavior is often observed in the slow-speed (&lt;500 km s<jats:sup>−1</jats:sup>) solar wind and in solar-like stellar coronae, while a reversed effect is seen in M dwarfs. Studies of the inverse effect have been hampered in the past because only unresolved (point-source) spectroscopic data were available for these stellar targets. Here we report the discovery of several inverse events observed in situ in the slow solar wind using particle-counting techniques. These very rare events all occur during periods of high solar activity that mimic conditions more widespread on M dwarfs. The detections allow a new way of connecting the slow wind to its solar source and are broadly consistent with theoretical models of abundance variations due to chromospheric fast-mode waves with amplitudes of 8–10 km s<jats:sup>−1</jats:sup>, sufficient to accelerate the solar wind. The results imply that M-dwarf winds are dominated by plasma depleted in easily ionized elements and lend credence to previous spectroscopic measurements.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>This work reports on the interaction between a fast forward shock and an interplanetary coronal-mass-ejection-like structure (ICMELS) as observed by in situ observations of radially aligned spacecraft. Around 2011 March 22, the Venus EXpress (VEX) and Solar TErrestrial RElations Observatory-A (STEREO-A) were nearly at the same longitude, providing us with an excellent opportunity to study the formation and evolution of the complex structures. The shock and ICMELS investigated in this paper are isolated near Venus, but when they approach STEREO-A, the shock nearly approaches the front edge of the ICMELS and forms a shock–ICMELS complex structure. The maximal magnetic field in the ICMELS increased 2.3 times due to shock compression, according to the observation. The recovery model, which restores the shocked portion of the shock–ICMELS to its uncompressed condition, likewise confirms this improvement. The interaction with the ICMELS, on the other hand, weakens shock 2. The magnetic compression ratio falls from 2.4 at Venus to 2.0 at STEREO-A. This research enables us to have a better physical knowledge of the impacts of the interaction between a shock and an ICME (or ICMELS), which will aid future space weather predictions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The recent discovery of a new population of ultrahigh-energy gamma-ray sources with spectra extending beyond 100 TeV revealed the presence of Galactic PeVatrons—cosmic-ray factories accelerating particles to PeV energies. These sources, except for the one associated with the Crab Nebula, are not yet identified. With an extension of 1° or more, most of them contain several potential counterparts, including supernova remnants, young stellar clusters, and pulsar wind nebulae (PWNe), which can perform as PeVatrons and thus power the surrounding diffuse ultrahigh-energy gamma-ray structures. In the case of PWNe, gamma-rays are produced by electrons, accelerated at the pulsar wind termination shock, through the inverse Compton scattering of 2.7 K cosmic microwave background (CMB)radiation. The high conversion efficiency of pulsar rotational power to relativistic electrons, combined with the short cooling timescales, allow gamma-ray luminosities up to the level of <jats:inline-formula> <jats:tex-math> <?CDATA ${L}_{\gamma }\sim 0.1\dot{E}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>L</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>γ</mml:mi> </mml:mrow> </mml:msub> <mml:mo>∼</mml:mo> <mml:mn>0.1</mml:mn> <mml:mover accent="true"> <mml:mrow> <mml:mi>E</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="apjlac66cfieqn1.gif" xlink:type="simple" /> </jats:inline-formula>. The pulsar spin-down luminosity, <jats:inline-formula> <jats:tex-math> <?CDATA $\dot{E}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>E</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="apjlac66cfieqn2.gif" xlink:type="simple" /> </jats:inline-formula>, also determines the absolute maximum energy of individual photons: <jats:inline-formula> <jats:tex-math> <?CDATA ${E}_{\gamma ,max}\approx 0.9{\dot{E}}_{36}^{0.65}\,\,{\rm{PeV}}$?> </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>γ</mml:mi> <mml:mo>,</mml:mo> <mml:mo form="prefix" movablelimits="true">max</mml:mo> </mml:mrow> </mml:msub> <mml:mo>≈</mml:mo> <mml:mn>0.9</mml:mn> <mml:msubsup> <mml:mrow> <mml:mover accent="true"> <mml:mi>E</mml:mi> <mml:mo>̇</mml:mo> </mml:mover> </mml:mrow> <mml:mrow> <mml:mn>36</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>0.65</mml:mn> </mml:mrow> </mml:msubsup> <mml:mspace width="0.25em" /> <mml:mspace width="0.25em" /> <mml:mrow> <mml:mi mathvariant="normal">PeV</mml:mi> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac66cfieqn3.gif" xlink:type="simple" /> </jats:inline-formula>. This fundamental constraint dominates over the condition set by synchrotron energy losses of electrons for young PWNe with typical magnetic field of ≈100 <jats:italic>μ</jats:italic>G with <jats:inline-formula> <jats:tex-math> <?CDATA $\dot{E}\lesssim {10}^{37}\ \mathrm{erg}\,{{\rm{s}}}^{-1}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mrow> <mml:mi>E</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̇</mml:mo> </mml:mrow> </mml:mover> <mml:mo>≲</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>37</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.33em" /> <mml:mi>erg</mml:mi> <mml:mspace width="0.25em" /> <mml:msup> <mml:mrow> <mml:mi mathvariant="normal">s</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlac66cfieqn4.gif" xlink:type="simple" /> </jats:inline-formula>. We discuss the implications of <jats:italic>E<jats:sub>γ</jats:sub> </jats:italic> <jats:sub>,max</jats:sub> by comparing it with the highest-energy photons reported by LHAASO from a dozen of ultrahigh-energy sources. Whenever a PWN origin of the emission is possible, we use the LHAASO measurements to set upper limits on the nebular magnetic field.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report an Atacama Large Millimeter/submillimeter Array 0.88 mm (Band 7) continuum detection of the accretion disk around SR 12 c, an ∼11 <jats:italic>M</jats:italic> <jats:sub>Jup</jats:sub> planetary-mass companion (PMC) orbiting its host binary at 980 au. This is the first submillimeter detection of a circumplanetary disk around a wide PMC. The disk has a flux density of 127 ± 14 <jats:italic>μ</jats:italic>Jy and is not resolved by the ∼0.″1 beam, so the dust disk radius is likely less than 5 au and can be much smaller if the dust continuum is optically thick. If, however, the dust emission is optically thin, then the SR 12 c disk has a comparable dust mass to the circumplanetary disk around PDS 70 c but is about five times lower than that of the ∼12 <jats:italic>M</jats:italic> <jats:sub>Jup</jats:sub> free-floating OTS 44. This suggests that disks around bound and unbound planetary-mass objects can span a wide range of masses. The gas mass estimated with an accretion rate of 10<jats:sup>−11</jats:sup> <jats:italic>M</jats:italic> <jats:sub>☉</jats:sub> yr<jats:sup>−1</jats:sup> implies a gas-to-dust ratio higher than 100. If cloud absorption is not significant, a nondetection of <jats:sup>12</jats:sup>CO(3–2) implies a compact gas disk around SR 12 c. Future sensitive observations may detect more PMC disks at 0.88 mm flux densities of ≲100 <jats:italic>μ</jats:italic>Jy.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We hereby report the discovery of ATLAS17jrp as an extraordinary tidal disruption event (TDE) in the star-forming galaxy SDSS J162034.99+240726.5 in our recent sample of mid-infrared outbursts in nearby galaxies. Its optical/UV light curves rise to a peak luminosity of ∼1.06 × 10<jats:sup>44</jats:sup> erg s<jats:sup>−1</jats:sup> in about a month and then decay as <jats:italic>t</jats:italic> <jats:sup>−5/3</jats:sup> with a roughly constant temperature around 19,000 K, and the optical spectra show a blue continuum and very broad Balmer lines with FWHM ∼ 15,000 km s<jats:sup>−1</jats:sup>, which gradually narrowed to 1400 km s<jats:sup>−1</jats:sup> within 4 yr, all agreeing well with other optical TDEs. A delayed and rapidly rising X-ray flare with a peak luminosity of ∼1.27 × 10<jats:sup>43</jats:sup> erg s<jats:sup>−1</jats:sup> was detected ∼170 days after the optical peak. The high MIR luminosity of ATLAS17jrp (∼2 × 10<jats:sup>43</jats:sup> erg s<jats:sup>−1</jats:sup>) has revealed a distinctive dusty environment with a covering factor as high as ∼0.2, which is comparable to that of a torus in active galactic nuclei but at least one order of magnitude higher than normal optical TDEs. Therefore, ATLAS17jrp turns out to be one of the rare unambiguous TDEs found in star-forming galaxies, and its high dust-covering factor implies that dust extinction could play an important role in the absence of optical TDEs in star-forming galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Large-scale extreme-ultraviolet (EUV) waves are frequently observed as an accompanying phenomenon of flares and coronal mass ejections (CMEs). Previous studies mainly focused on EUV waves with single wave fronts that are generally thought to be driven by the lateral expansion of CMEs. Using high spatiotemporal resolution multi-angle imaging observations taken by the Solar Dynamics Observatory and the Solar Terrestrial Relations Observatory, we present the observation of a broad quasiperiodic fast-propagating (QFP) wave train composed of multiple wave fronts along the solar surface during the rising phase of a GOES M3.5 flare on 2011 February 24. The wave train transmitted through a lunate coronal hole (CH) with a speed of ∼840 ± 67 km s<jats:sup>−1</jats:sup>, and the wave fronts showed an intriguing refraction effect when they passed through the boundaries of the CH. Due to the lunate shape of the CH, the transmitted wave fronts from the north and south arms of the CH started to approach each other and finally collided, leading to a significant intensity enhancement at the collision site. This enhancement might hint at the occurrence of interference between the two transmitted wave trains. The estimated magnetosonic Mach number of the wave train is about 1.13, which indicates that the observed wave train was a weak shock. Period analysis reveals that the period of the wave train was ∼90 s, in good agreement with that of the accompanying flare. Based on our analysis results, we conclude that the broad QFP wave train was a large-amplitude fast-mode magnetosonic wave or a weak shock driven by some nonlinear energy release processes in the accompanying flare.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The ideal exoplanets to search for life are those within a star’s habitable zone. However, even within the habitable zone, planets can still develop uninhabitable climate states. Sustaining a temperate climate over geologic (∼gigayear) timescales requires a planet to contain sufficient internal energy to power a planetary-scale carbon cycle. A major component of a rocky planet’s energy budget is the heat produced by the decay of radioactive elements, especially <jats:sup>40</jats:sup>K, <jats:sup>232</jats:sup>Th, <jats:sup>235</jats:sup>U, and <jats:sup>238</jats:sup>U. As the planet ages and these elements decay, this radiogenic energy source dwindles. Here we estimate the probability distribution of the amount of these heat-producing elements that enter into rocky exoplanets through Galactic history by combining the system-to-system variation seen in stellar abundance data with the results from Galactic chemical evolution models. From this, we perform Monte Carlo thermal evolution models that maximize the mantle cooling rate, thus allowing us to create a pessimistic estimate of lifetime a rocky, stagnant-lid exoplanet can support a global carbon cycle through Galactic history. We apply this framework to a sample of 17 likely rocky exoplanets with measured ages, seven of which we predict are likely to be actively degassing today, despite our pessimistic assumptions. For the remaining planets, including those orbiting TRAPPIST-1, we cannot confidently assume that they currently contain sufficient internal heat to support mantle degassing at a rate sufficient to sustain a global carbon cycle or temperate climate without additional tidal heating or undergoing plate tectonics.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Microflares, one of the small-scale solar activities, are believed to be caused by magnetic reconnection. Nevertheless, their three-dimensional (3D) magnetic structures, thermodynamic structures, and physical links to reconnection are unclear. In this Letter, based on a high-resolution 3D radiative magnetohydrodynamic simulation of the quiet Sun spanning from the upper convection zone to the corona, we investigate the 3D magnetic and thermodynamic structures of three homologous microflares. It is found that they originate from localized hot plasma embedded in the chromospheric environment at the height of 2–10 Mm above the photosphere and last for 3–10 minutes with released magnetic energy in the range of 10<jats:sup>27</jats:sup>–10<jats:sup>28</jats:sup> erg. The heated plasma is almost cospatial with the regions where the heating rate per particle is maximal. The 3D velocity field reveals a pair of converging flows with velocities of tens of km s<jats:sup>−1</jats:sup> moving toward and outflows with velocities of about 100 km s<jats:sup>−1</jats:sup> moving away from the hot plasma. These features support magnetic reconnection playing a critical role in heating the localized chromospheric plasma to coronal temperature, giving rise to the observed microflares. The magnetic topology analysis further discloses that the reconnection region is located near quasi-separators where both current density and squashing factors are maximal although the specific topology may vary from a tether-cutting to fan-spine-like structure.</jats:p>