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<jats:title>Abstract</jats:title> <jats:p>We present the first statistical analysis of complexity changes affecting the magnetic structure of interplanetary coronal mass ejections (ICMEs), with the aim of answering the questions: How frequently do ICMEs undergo magnetic complexity changes during propagation? What are the causes of such changes? Do the in situ properties of ICMEs differ depending on whether they exhibit complexity changes? We consider multispacecraft observations of 31 ICMEs by MESSENGER, Venus Express, ACE, and STEREO between 2008 and 2014 while radially aligned. By analyzing their magnetic properties at the inner and outer spacecraft, we identify complexity changes that manifest as fundamental alterations or significant reorientations of the ICME. Plasma and suprathermal electron data at 1 au, and simulations of the solar wind enable us to reconstruct the propagation scenario for each event, and to identify critical factors controlling their evolution. Results show that ∼65% of ICMEs change their complexity between Mercury and 1 au and that interaction with multiple large-scale solar wind structures is the driver of these changes. Furthermore, 71% of ICMEs observed at large radial (&gt;0.4 au) but small longitudinal (&lt;15°) separations exhibit complexity changes, indicating that propagation over large distances strongly affects ICMEs. Results also suggest that ICMEs may be magnetically coherent over angular scales of at least 15°, supporting earlier theoretical and observational estimates. This work presents statistical evidence that magnetic complexity changes are consequences of ICME interactions with large-scale solar wind structures, rather than intrinsic to ICME evolution, and that such changes are only partly identifiable from in situ measurements at 1 au.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We examine Solar Dynamics Observatory (SDO)/EUV Variability Experiment (EVE) data to better understand solar flare irradiance, and how that irradiance may vary for large events. We measure scaling laws relating Geostationary Orbital Environmental Satellites (GOES) flare classes to irradiance in 21 lines measured with SDO/EVE, formed across a wide range of temperatures, and find that this scaling depends on the line-formation temperature. We extrapolate these irradiance values to large events, exceeding X10. In order to create full spectra, however, we need a physical model of the irradiance. We present the first results of a new physical model of solar flare irradiance, NRLFLARE, that sums together a series of flare loops to calculate the spectral irradiance ranging from the X-rays through the far-UV (≈0 to 1250 Å), constrained only by GOES/X-ray Sensors observations. We test this model against SDO/EVE data. The model spectra and time evolution compares well in high-temperature emission, but cooler lines show large discrepancies. We speculate that the discrepancies are likely due to both a nonuniform cross-section of the flaring loops as well as opacity effects. We then show that allowing the cross-sectional area to vary with height significantly improves agreement with observations, and is therefore a crucial parameter needed to accurately model the intensity of spectral lines, particularly in the transition region from <jats:inline-formula> <jats:tex-math> <?CDATA $4.7\lesssim \mathrm{log}T\lesssim 6$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>4.7</mml:mn> <mml:mo>≲</mml:mo> <mml:mi>log</mml:mi> <mml:mi>T</mml:mi> <mml:mo>≲</mml:mo> <mml:mn>6</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac4784ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Rich and poor galaxy clusters have the same measured halo metallicity, 0.35–0.4 <jats:italic>Z</jats:italic> <jats:sub>⊙</jats:sub>, even though they are an order of magnitude apart in stellar fraction, <jats:italic>M</jats:italic> <jats:sub>*</jats:sub>/<jats:italic>M</jats:italic> <jats:sub>gas</jats:sub>. The measured intracluster medium (ICM) metallicity in high-mass clusters cannot be explained by the visible stellar population as stars typically make up 3%–20% of the total baryon mass. The independence of metallicity of <jats:italic>M</jats:italic> <jats:sub>*</jats:sub>/<jats:italic>M</jats:italic> <jats:sub>gas</jats:sub> suggests an external and universal source of metals such as an early enrichment population (EEP). Galaxy cluster RX J1416.4+2315, classified as a fossil system, has a stellar fraction of <jats:italic>M</jats:italic> <jats:sub>*</jats:sub>/<jats:italic>M</jats:italic> <jats:sub>gas</jats:sub> = 0.054 ± 0.018, and here we improve the halo metallicity determination using archival Chandra and XMM-Newton observations. We determine the ICM metallicity of RXJ1416 to be 0.303 ± 0.053 <jats:italic>Z</jats:italic> <jats:sub>⊙</jats:sub> within 0.3 &lt; <jats:italic>R</jats:italic>/<jats:italic>R</jats:italic> <jats:sub>500</jats:sub> &lt; 1, excluding the central galaxy. We combine this measurement with other clusters with a wider range of <jats:italic>M</jats:italic> <jats:sub>*</jats:sub>/<jats:italic>M</jats:italic> <jats:sub>gas</jats:sub>, resulting in the fit of <jats:italic>Z</jats:italic> <jats:sub>tot</jats:sub> = (0.36 ± 0.01) + (0.10 ± 0.17)(<jats:italic>M</jats:italic> <jats:sub>*</jats:sub>/<jats:italic>M</jats:italic> <jats:sub>gas</jats:sub>). This fit is largely independent of <jats:italic>M</jats:italic> <jats:sub>*</jats:sub>/<jats:italic>M</jats:italic> <jats:sub>gas</jats:sub> and shows that for a low <jats:italic>M</jats:italic> <jats:sub>*</jats:sub>/<jats:italic>M</jats:italic> <jats:sub>gas</jats:sub> system, the observed stellar population can make only 10%–20% of the total metals. We quantify the Fe contribution of the EEP further by adopting a standard Fe yield for visible stellar populations, and find that <jats:italic>Z</jats:italic> <jats:sub>EEP</jats:sub> = (0.36 ± 0.01) − − (0.96 ± 0.17)(<jats:italic>M</jats:italic> <jats:sub>*</jats:sub>/<jats:italic>M</jats:italic> <jats:sub>gas</jats:sub>). To account for the observed Fe mass, a supernova (SN) rate of 10 ± 5 SNe yr<jats:sup>−1</jats:sup> (Type Ia) and 40 ± 19 SNe yr<jats:sup>−1</jats:sup> (core collapse) is required over the redshift range 3 &lt; <jats:italic>z</jats:italic> &lt; 10 for a single galaxy cluster with mass ∼3 × 10<jats:sup>14</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub> at <jats:italic>z</jats:italic> = 0. These SNe might be visible in observations of high-redshift clusters and protoclusters with the James Webb Space Telescope.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Coherent curvature radiation as the radiation mechanism for fast radio bursts (FRBs) has been discussed since FRBs were discovered. We study the spectral and polarization properties of repeating FRBs within the framework of coherent curvature radiation by charged bunches in the magnetosphere of a highly magnetized neutron star. The spectra can be generally characterized by multisegmented broken power laws, and evolve as bunches move and the line of sight sweeps. Emitted waves are highly linear polarized and polarization angles are flat across the burst envelopes, if the line of sight is confined to the beam within an angle of 1/<jats:italic>γ</jats:italic>, while a circular polarization fraction becomes strong for off-beam cases. The spectro-temporal pulse-to-pulse properties can be a natural consequence due to the magnetospheric geometry. We investigate the relationship between drift rate, central frequency, and temporal duration. The radius-to-frequency mapping is derived and simulated within the assumptions of both dipolar and quadrupolar magnetic configurations. The geometric results show that FRBs are emitted in field lines more curved than open field lines for a dipolar geometry. This suggests that there are most likely existing multipolar magnetic configurations in the emission region.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>DR21(OH) ridge, the central part of a high-mass star- and cluster-forming hub-filament system, is resolved spatially and kinematically into three nearly parallel fibers (f1, f2, and f3) with a roughly north–south orientation, using the observations of molecular transitions of H<jats:sup>13</jats:sup>CO<jats:sup>+</jats:sup> (1 − 0), N<jats:sub>2</jats:sub>H<jats:sup>+</jats:sup> (1 − 0), and NH<jats:sub>2</jats:sub>D (1<jats:sub>1,1</jats:sub> − 1<jats:sub>0,1</jats:sub>) with the Combined Array for Research in Millimeter Astronomy. These fibers are all mildly supersonic (<jats:italic>σ</jats:italic> velocity dispersions about 2 times the sound speed), having lengths around 2 pc and widths about 0.1 pc, and they entangle and conjoin in the south where the most active high-mass star formation takes place. They all have line masses 1–2 orders of magnitude higher than their low-mass counterparts and are gravitationally unstable both radially and axially. However, only f1 exhibits high-mass star formation all the way along the fiber, yet f2 and f3 show no signs of significant star formation in their northern parts. A large velocity gradient increasing from north to south is seen in f3, and can be well reproduced with a model of freefall motion toward the most massive and active dense core in the region, which corroborates the global collapse of the ridge and suggests that the disruptive effects of the tidal forces may explain the inefficiency of star formation in f2 and f3. On larger scales, some of the lower-density, peripheral filaments are likely to be the outer extensions of the fibers, and provide hints on the origin of the ridge.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We utilize mid-infrared multiepoch data from the Wide-field Infrared Survey Explorer over a ∼10 yr period in the W1 (3.4 <jats:italic>μ</jats:italic>m) and W2 (4.6 <jats:italic>μ</jats:italic>m) bands to investigate the structure of dusty torus in low-redshift (0.15 &lt; <jats:italic>z</jats:italic> ≤ 0.4) active galactic nuclei (AGNs). We calculate a Spearman correlation coefficient (<jats:italic>r</jats:italic> <jats:sub>12</jats:sub>) between the W1 magnitude and W1 − W2 color based on the light curve in individual objects. Interestingly, <jats:italic>r</jats:italic> <jats:sub>12</jats:sub> spans a broad range from −1 to 1 and is detected to be correlated with mean W1 − W2 color and AGN bolometric luminosity, in the sense that objects with a blue W1 − W2 color and low AGN luminosity tend to become redder (bluer) with increasing (decreasing) W1 brightness in the light curve (i.e., <jats:italic>r</jats:italic> <jats:sub>12</jats:sub> &lt; 0), although the correlation of <jats:italic>r</jats:italic> <jats:sub>12</jats:sub> with the bolometric luminosity is relatively weak. The fit for the spectral energy distribution reveals a significant contribution from the host galaxy in the W1 and W2 bands. However, the dependencies of <jats:italic>r</jats:italic> <jats:sub>12</jats:sub> on the W1 − W2 color and AGN luminosity still persist even after careful elimination of the host light contribution. We propose that this result can be explained if the covering factor of the hot dust component decreases as the AGN luminosity increases.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Using the observations from the Solar Dynamics Observatory, we study an eruption of a hot-channel flux rope (FR) near the solar limb on 2015 February 9. The pre-eruptive structure is visible mainly in EUV 131 Å images, with two highly sheared loop structures. They undergo a slow rising motion and then reconnect to form an eruptive hot channel, as in the tether-cutting reconnection model. The J-shaped flare ribbons trace the footpoint of the FR that is identified as the hot channel. Initially, the hot channel is observed to rise slowly at 40 km s<jats:sup>−1</jats:sup>, followed by an exponential rise from 22:55 UT at a coronal height of 87 ± 2 Mm. Following the onset of the eruption at 23:00 UT, the flare reconnection then adds to the acceleration process of the coronal mass ejection (CME) within 3 <jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub>. Later on, the CME continues to accelerate at 8 m s<jats:sup>−2</jats:sup> during its propagation period. Further, the eruption also launched type II radio bursts, which were followed by type III and type IVm radio bursts. The start and end times of the type IVm burst correspond to the CME’s core height of 1.5 and 6.1 <jats:italic>R</jats:italic> <jats:sub>⊙</jats:sub>, respectively. Also, the spectral index is negative, suggesting that nonthermal electrons are trapped in the closed loop structure. Accompanied by this type IVm burst, this event is unique in the sense that the flare ribbons are very clearly observed together with the erupting hot channel, which strongly suggests that the hooked parts of the J-shaped flare ribbons outline the boundary of the erupting FR.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Large-scale astronomical surveys have the potential to capture data on large numbers of strongly gravitationally lensed supernovae (LSNe). To facilitate timely analysis and spectroscopic follow-up before the supernova fades, an LSN needs to be identified soon after it begins. To quickly identify LSNe in optical survey data sets, we designed ZipperNet, a multibranch deep neural network that combines convolutional layers (traditionally used for images) with long short-term memory layers (traditionally used for time series). We tested ZipperNet on the task of classifying objects from four categories—no lens, galaxy-galaxy lens, lensed Type-Ia supernova, lensed core-collapse supernova—within high-fidelity simulations of three cosmic survey data sets: the Dark Energy Survey, Rubin Observatory’s Legacy Survey of Space and Time (LSST), and a Dark Energy Spectroscopic Instrument (DESI) imaging survey. Among our results, we find that for the LSST-like data set, ZipperNet classifies LSNe with a receiver operating characteristic area under the curve of 0.97, predicts the spectroscopic type of the lensed supernovae with 79% accuracy, and demonstrates similarly high performance for LSNe 1–2 epochs after first detection. We anticipate that a model like ZipperNet, which simultaneously incorporates spatial and temporal information, can play a significant role in the rapid identification of lensed transient systems in cosmic survey experiments.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The arrival directions of TeV-PeV cosmic rays are remarkably uniform due to the isotropization of their directions by scattering on turbulent magnetic fields. Small anisotropies can exist in standard diffusion models, however, only on the largest angular scales. Yet, high-statistics observatories like IceCube and High-Altitude Water Cherenkov Observatory have found significant deviations from isotropy down to small angular scales. Here, we explain the formation of small-scale anisotropies by considering pairs of cosmic rays that get correlated by their transport through the same realization of the turbulent magnetic field. We argue that the formation of small-scale anisotropies is the reflection of the particular realization of the turbulent magnetic field experienced by cosmic rays on timescales intermediate between the early, ballistic regime and the late, diffusive regime. We approach this problem in two different ways: First, we run test particle simulations in synthetic turbulence, covering for the first time the TV rigidities of observations with realistic turbulence parameters. Second, we extend the recently introduced mixing matrix approach and determine the steady-state angular power spectrum. Throughout, we adopt magneto-static, slab-like turbulence. We find excellent agreement between the predicted angular power spectra in both approaches over a large range of rigidities. In the future, measurements of small-scale anisotropies will be valuable in constraining the nature of the turbulent magnetic field in our Galactic neighborhood.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We demonstrate the use of an eigenbasis that is derived from principal component analysis (PCA) applied on an ensemble of random-noise images that have a “red” power spectrum; i.e., a spectrum that decreases smoothly from large to small spatial scales. The pattern of the resulting eigenbasis allows for the reconstruction of images with a broad range of image morphologies. In particular, we show that this general eigenbasis can be used to efficiently reconstruct images that resemble possible astronomical sources for interferometric observations, even though the images in the original ensemble used to generate the PCA basis are significantly different from the astronomical images. We further show that the efficiency and fidelity of the image reconstructions depends only weakly on the particular parameters of the red-noise power spectrum used to generate the ensemble of images.</jats:p>