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<jats:title>Abstract</jats:title> <jats:p>Brown dwarfs exhibit patchy or spatially varying banded cloud structures that are inferred through photometric and spectroscopic variability modeling techniques. However, these methods are insensitive to rotationally invariant structures, such as the bands seen in Jupiter. Here, we present <jats:italic>H</jats:italic>-band Very Large Telescope/NaCo linear polarization measurements of the nearby Luhman 16 L/T transition binary, which suggest that Luhman 16A exhibits constant longitudinal cloud bands. The instrument was operated in pupil tracking mode, allowing us to unambiguously distinguish between a small astrophysical polarization and the ∼2% instrumental linear polarization. We measure the degree and angle of linear polarization of Luhman 16A and B to be <jats:italic>p</jats:italic> <jats:sub> <jats:italic>A</jats:italic> </jats:sub> = 0.031%  ± 0.004% and <jats:italic>ψ</jats:italic> <jats:sub> <jats:italic>A</jats:italic> </jats:sub> = −32° ± 4°, and <jats:italic>p</jats:italic> <jats:sub> <jats:italic>B</jats:italic> </jats:sub> = 0.010%  ± 0.004% and <jats:inline-formula> <jats:tex-math> <?CDATA ${\psi }_{B}={73}_{-11}^{+13\circ} $?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab6ef2ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, respectively. Using known physical parameters of the system, we demonstrate that an oblate homogeneous atmosphere cannot account for the polarization measured in Luhman 16A, but could be responsible for that of the B component. Through a nonexhaustive search of banded cloud morphologies, we demonstrate a two-banded scenario that can achieve a degree of linear polarization of <jats:italic>p</jats:italic> = 0.03% and conclude that the measured polarization of the A component must be predominantly due to cloud banding. For Luhman 16B, either oblateness or cloud banding could be the dominant source of the measured polarization. The misaligned polarization angles of the two binary components tentatively suggest spin–orbit misalignment. These measurements provide new evidence for the prevalence of cloud banding in brown dwarfs while at the same time demonstrating a new method—complementary to photometric and spectroscopic variability methods—for characterizing the cloud morphologies of substellar objects without signs of variability.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Ultra-long-duration gamma-ray burst GRB 111209A was found to be associated with a very luminous supernovae (SNe) SN 2011kl. The physics of GRB 111209A/SN 2011kl has been extensively studied in the literature, but such research has not yet settled down. By investigating in detail the characteristics of the X-ray light curve of GRB 111209A, coupled with the temporal and spectral features observed in SN 2011kl, we argue that a short-lived supramassive magnetar could be responsible for the initial shallow X-ray emission. Then the electromagnetic extraction of spin energy from a black hole (BH) results in the steeply declining X-ray flux when the magnetar collapses into a BH. A fraction of the envelope materials falls back and activates the accretion onto the newborn BH, which produces the X-ray rebrightening bump at late times. During this process, a centrifugally driven baryon-rich quasi-isotropic Blandford &amp; Payne outflow from the revived accretion disk deposits its kinetic energy on the SN ejecta, which powers luminous SN 2011kl. Finally, we place a limitation on the magnetar’s physical parameters based on the observations.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A constructive approach is developed to build the solar flare complex network by utilizing a visibility graph condition alongside the Abe–Suzuki method. Solar flare information such as position, start time, and peak flux is used for this purpose. The obtained characteristics of the topological features (such as the characteristic path length, power-law behavior of the probability distribution function of degrees, and the clustering coefficient) demonstrate the scale-free and small-world properties of the solar flare modified network. To explain the complexity of the constructed network, Omori’s law as well as the universal scaling features are investigated. Furthermore, a nonextensive modification of the Gutenberg–Richter law is examined for the solar flare modified network using a q-stretched exponential model. Establishing a two-dimensional map for the configuration of 118 energetic main flares observed between 2006 and 2016, it is found that the main flares are located within the regions consisting of hubs (high-connectivity regions) of the network. A fractal dimension of the solar flare network of about 0.79 is also obtained.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate the initiation and early evolution of 12 solar eruptions, including six active-region hot channel and six quiescent filament eruptions, which were well observed by the Solar Dynamics Observatory, as well as by the Solar Terrestrial Relations Observatory for the latter. The sample includes one failed eruption and 11 coronal mass ejections, with velocities ranging from 493 to 2140 km s<jats:sup>−1</jats:sup>. A detailed analysis of the eruption kinematics yields the following main results. (1) The early evolution of all events consists of a slow-rise phase followed by a main-acceleration phase, the height–time profiles of which differ markedly and can be best fit, respectively, by a linear and an exponential function. This indicates that different physical processes dominate in these phases, which is at variance with models that involve a single process. (2) The kinematic evolution of the eruptions tends to be synchronized with the flare light curve in both phases. The synchronization is often but not always close. A delayed onset of the impulsive flare phase is found in the majority of the filament eruptions (five out of six). This delay and its trend to be larger for slower eruptions favor ideal MHD instability models. (3) The average decay index at the onset heights of the main acceleration is close to the threshold of the torus instability for both groups of events (although, it is based on a tentative coronal field model for the hot channels), suggesting that this instability initiates and possibly drives the main acceleration.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The mirror structures identified by the depressed or enhanced magnetic field associated with the enhanced or depressed plasma density are widely observed in the solar system plasma. These structures are generated by the mirror instability as a result of sufficiently large temperature anisotropy of <jats:italic>T</jats:italic> <jats:sub>⊥</jats:sub> &gt; <jats:italic>T</jats:italic> <jats:sub>∥</jats:sub>. Here, <jats:italic>T</jats:italic> <jats:sub>⊥</jats:sub> and <jats:italic>T</jats:italic> <jats:sub>∥</jats:sub> are, respectively, to be the temperatures perpendicular and parallel to the magnetic field and <jats:italic>β</jats:italic> = <jats:italic>p</jats:italic>/(<jats:italic>B</jats:italic> <jats:sup>2</jats:sup>/2<jats:italic>μ</jats:italic> <jats:sub>0</jats:sub>). Two important observed characteristics are the uneven density-magnetic field compressibility, defined as <jats:inline-formula> <jats:tex-math> <?CDATA ${C}_{\rho ,B}=(\delta \rho /\rho )/(\delta B/B)$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab8476ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, among the various mirror events, and the anticorrelation between the temperatures and magnetic field. This study first shows two mirror structures observed in the magnetosheath with distinct <jats:italic>β</jats:italic> and <jats:inline-formula> <jats:tex-math> <?CDATA ${C}_{\rho ,B}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab8476ieqn2.gif" xlink:type="simple" /> </jats:inline-formula>. Specifically, <jats:italic>β</jats:italic> ∼ 6.67, <jats:inline-formula> <jats:tex-math> <?CDATA ${C}_{\rho ,B}\sim -0.23$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab8476ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> and <jats:italic>β</jats:italic> ∼ 1.44, <jats:inline-formula> <jats:tex-math> <?CDATA ${C}_{\rho ,B}\sim -0.67$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab8476ieqn4.gif" xlink:type="simple" /> </jats:inline-formula>. The linear kinetic theory is adopted to derive the phase relations for the mirror instability which show an inverse relation between <jats:inline-formula> <jats:tex-math> <?CDATA ${C}_{\rho ,B}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab8476ieqn5.gif" xlink:type="simple" /> </jats:inline-formula> and <jats:inline-formula> <jats:tex-math> <?CDATA ${C}_{{T}_{\perp },B}=(\delta {T}_{\perp }/{T}_{\perp })/(\delta B/B)$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab8476ieqn6.gif" xlink:type="simple" /> </jats:inline-formula>, which are negative for various parameter values, and <jats:italic>β</jats:italic>. While the correlation <jats:inline-formula> <jats:tex-math> <?CDATA ${C}_{{T}_{\parallel },B}=(\delta {T}_{\parallel }/{T}_{\parallel })/(\delta B/B)$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab8476ieqn7.gif" xlink:type="simple" /> </jats:inline-formula> may be negative or positive for the mirror unstable and stable parameter regimes, respectively. The theoretical analyses are consistent with the observational results that <jats:italic>δT</jats:italic> <jats:sub>⊥</jats:sub> <jats:italic>δB</jats:italic> &lt; 0 for both events and <jats:italic>δT</jats:italic> <jats:sub>∥</jats:sub> <jats:italic>δB</jats:italic> &lt; 0 is more pronounced for the high <jats:italic>β</jats:italic> case. The statistical analysis results are summarized by the relationships between <jats:inline-formula> <jats:tex-math> <?CDATA ${C}_{\rho ,B}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab8476ieqn8.gif" xlink:type="simple" /> </jats:inline-formula>, <jats:inline-formula> <jats:tex-math> <?CDATA ${C}_{{T}_{\perp },B}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab8476ieqn9.gif" xlink:type="simple" /> </jats:inline-formula>, <jats:inline-formula> <jats:tex-math> <?CDATA ${C}_{{T}_{\parallel },B}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjab8476ieqn10.gif" xlink:type="simple" /> </jats:inline-formula>, and <jats:italic>β</jats:italic> for six mirror wave events that show high agreements between the observations and theory.</jats:p>