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<jats:title>Abstract</jats:title> <jats:p>Constraining Jupiter’s internal structure is crucial for understanding its formation and evolution history. Recent interior models of Jupiter that fit Juno’s measured gravitational field suggest an inhomogeneous interior and potentially the existence of a diluted core. These models, however, strongly depend on the model assumptions and the equations of state used. A complementary modeling approach is to use empirical structural models. These can later be used to reveal new insights into the planetary interior and be compared to standard models. Here we present empirical structural models of Jupiter where the density profile is constructed by piecewise-polytropic equations. With these models we investigate the relation between the normalized moment of inertia (MoI) and the gravitational moments <jats:italic>J</jats:italic> <jats:sub>2</jats:sub> and <jats:italic>J</jats:italic> <jats:sub>4</jats:sub>. Given that only the first few gravitational moments of Jupiter are measured with high precision, we show that an accurate and independent measurement of the MoI value could be used to further constrain Jupiter’s interior. An independent measurement of the MoI with an accuracy better than ∼0.1% could constrain Jupiter’s core region and density discontinuities in its envelope. We find that models with a density discontinuity at ∼1 Mbar, as would produce a presumed hydrogen–helium separation, correspond to a fuzzy core in Jupiter. We next test the appropriateness of using polytropes, by comparing them with empirical models based on polynomials. We conclude that both representations result in similar density profiles and ranges of values for quantities like core mass and MoI.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present version 10 of the CHIANTI package. In this release, we provide updated atomic models for several helium-like ions and for all the ions of the beryllium, carbon, and magnesium isoelectronic sequences that are abundant in astrophysical plasmas. We include rates from large-scale atomic structure and scattering calculations that are in many cases a significant improvement over the previous version, especially for the Be-like sequence, which has useful line diagnostics to measure the electron density and temperature. We have also added new ions and updated several of them with new atomic rates and line identifications. Also, we have added several improvements to the IDL software, to speed up the calculations and to estimate the suppression of dielectronic recombination.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We investigate the use of approximate Bayesian neural networks (BNNs) in modeling hundreds of time delay gravitational lenses for Hubble constant (<jats:italic>H</jats:italic> <jats:sub>0</jats:sub>) determination. Our BNN was trained on synthetic Hubble Space Telescope quality images of strongly lensed active galactic nuclei with lens galaxy light included. The BNN can accurately characterize the posterior probability density functions (PDFs) of model parameters governing the elliptical power-law mass profile in an external shear field. We then propagate the BNN-inferred posterior PDFs into an ensemble <jats:italic>H</jats:italic> <jats:sub>0</jats:sub> inference, using simulated time delay measurements from a plausible dedicated monitoring campaign. Assuming well-measured time delays and a reasonable set of priors on the environment of the lens, we achieve a median precision of 9.3% per lens in the inferred <jats:italic>H</jats:italic> <jats:sub>0</jats:sub>. A simple combination of a set of 200 test lenses results in a precision of 0.5 km s<jats:sup>−1</jats:sup> Mpc<jats:sup>−1</jats:sup> (0.7%), with no detectable bias in this <jats:italic>H</jats:italic> <jats:sub>0</jats:sub> recovery test. The computation time for the entire pipeline—including the generation of the training set, BNN training and <jats:italic>H</jats:italic> <jats:sub>0</jats:sub> inference—translates to 9 minutes per lens on average for 200 lenses and converges to 6 minutes per lens as the sample size is increased. Being fully automated and efficient, our pipeline is a promising tool for exploring ensemble-level systematics in lens modeling for <jats:italic>H</jats:italic> <jats:sub>0</jats:sub> inference.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the first results of a systematic investigation to characterize blazar variability power spectral densities (PSDs) at optical frequencies using densely sampled (5–15 minutes of integration time), high photometric accuracy (≲0.2%–0.5%) <jats:italic>R</jats:italic>-band intranight light curves, covering timescales ranging from several hours to ∼15 minutes. Our sample consists of 14 optically bright blazars—nine BL Lacertae objects and five flat-spectrum radio quasars (FSRQs)—which have shown statistically significant variability during 29 monitoring sessions. We model the intranight PSDs as simple power laws and derive the best-fit slope along with the uncertainty using the “power spectral response” method. Our main results are as follows: (1) in 19 out of 29 monitoring sessions, the intranight PSDs show an acceptable fit to simple power laws at a rejection confidence ≤90%; (2) for these 19 instances, the PSD slopes show a wide range of 1.4 to 4.0, consistent with the statistical characters of red-noise (slope ∼ 2) and black-noise (slope ≥ 3) stochastic processes; (3) the average PSD slopes for the BL Lac objects and FSRQs are indistinguishable from one another; and (4) the normalization of intranight PSDs for individual blazar sources monitored on more than one occasion turns out to be consistent with one another with a few exceptions. The average PSD slope, 2.9 ± 0.3 (1<jats:italic>σ</jats:italic> uncertainty), is steeper than that of red noise–type variability found on longer timescales (many decades to days), indicative of a cutoff in the variability spectrum on timescales around a few days at the synchrotron frequencies of the emission spectrum.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present an analysis of the formation and eruption of a filament and fast coronal mass ejection associated with a flare that occurred in active region 11429 using observations in the ultraviolet, extreme ultraviolet, X-ray, and radio wavelength bands. Precursor activity began as an interaction between two filaments, F1 and F2, that are identified as having twisted magnetic flux ropes (MFRs). Transient brightenings in all wavelengths are observed as a result of this interaction, likely the result of magnetic reconnection between the two filaments. This interaction results in a reconfiguration of the two filaments into a long overlying filament and a shorter low-lying filament. The upper filament subsequently undergoes a partial confined eruption. Plasma flows originating near the east footpoint of F1 lead to an extension of the upper filament into the filament channel to the west, resulting in a new active region filament (ARF). This new filament begins a slow rise and expansion. During its slowly rising phase, the MFR in which the filament is embedded becomes visible, with both the filament and flux rope rising and expanding simultaneously. The twist of the magnetic rope is determined as four turns. The erupting configuration changes from a twisted arch shape to a reversed <jats:italic>γ</jats:italic> shape within ∼75 s at the beginning of the fast-rise phase, representing a transformation from twist to writhe. The observations provide a clear example of filament formation via the tether-cutting reconnection of two nearby filaments. A helical kink instability may be the trigger of the ARF eruption.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The composition of giant planets is imprinted by their migration history and the compositional structure of their hosting disks. Studies in recent literature have investigated how the abundances of C and O can constrain the formation pathways of giant planets forming within few tens of au from a star. New ALMA observations, however, suggest planet-forming regions possibly extending to hundreds of au. We explore the implications of these wider formation environments through <jats:italic>n</jats:italic>-body simulations of growing and migrating giant planets embedded in planetesimal disks, coupled with a compositional model of the protoplanetary disk where volatiles are inherited from the molecular cloud and refractories are calibrated against extrasolar and Solar System data. We find that the C/O ratio provides limited insight on the formation pathways of giant planets that undergo large-scale migration. This limitation can be overcome, however, thanks to nitrogen and sulfur. Jointly using the C/N, N/O, and C/O ratios breaks any degeneracy in the formation and migration tracks of giant planets. The use of elemental ratios normalized to the respective stellar ratios supplies additional information on the nature of giant planets, thanks to the relative volatility of O, C, and N in disks. When the planetary metallicity is dominated by the accretion of solids C/N* &gt; C/O* &gt; N/O* (* denoting this normalized scale), otherwise N/O* &gt; C/O* &gt; C/N*. The S/N ratio provides an additional independent probe into the metallicity of giant planets and their accretion of solids.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Power-law size distributions are the hallmarks of nonlinear energy dissipation processes governed by self-organized criticality (SOC). Here we analyze 75 data sets of stellar flare size distributions, mostly obtained from the Extreme-Ultraviolet Explorer and the Kepler mission. We aim to answer the following questions for size distributions of stellar flares. (i) What are the values and uncertainties of power-law slopes? (ii) Do power-law slopes vary with time? (iii) Do power-law slopes depend on the stellar spectral type? (iv) Are they compatible with solar flares? (v) Are they consistent with SOC models? We find that the observed size distributions of stellar flare fluences (or energies) exhibit power-law slopes of <jats:italic>α</jats:italic> <jats:sub> <jats:italic>E</jats:italic> </jats:sub> = 2.09 ± 0.24 for optical data sets observed with Kepler. The observed power-law slopes do not show much time variability and do not depend on the stellar spectral type (M, K, G, F, A, giants). In solar flares, we find that background subtraction lowers the uncorrected value of <jats:italic>α</jats:italic> <jats:sub> <jats:italic>E</jats:italic> </jats:sub> = 2.20 ± 0.22 to <jats:italic>α</jats:italic> <jats:sub> <jats:italic>E</jats:italic> </jats:sub> = 1.57 ± 0.19. Furthermore, most of the stellar flares are temporally not resolved in low-cadence (30 minutes) Kepler data, which causes an additional bias. Taking these two biases into account, the stellar flare data sets are consistent with the theoretical prediction <jats:inline-formula> <jats:tex-math> <?CDATA $N(x)\propto {x}^{-{\alpha }_{x}}$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabdec7ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> of SOC models, i.e., <jats:italic>α</jats:italic> <jats:sub> <jats:italic>E</jats:italic> </jats:sub> = 1.5. Thus, accurate power-law fits require automated detection of the inertial range and background subtraction, which can be modeled with the generalized Pareto distribution, finite-system size effects, and extreme event outliers.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>GRS 1915+105 is a stellar-mass black hole that is well known for exhibiting at least 12 distinct classes of X-ray variability and correlated multi-wavelength behavior. Despite such extraordinary variability, GRS 1915+105 remained one of the brightest sources in the X-ray sky. However, in early 2019, the source became much fainter, apparently entering a new accretion state. Here, we report the results of an extensive, year-long monitoring campaign of GRS 1915+105 with the Neil Gehrels Swift Observatory. During this interval, the flux of GRS 1915+105 gradually diminished; the observed count rate eventually dropped by two orders of magnitude. Simple but robust spectral fits to these monitoring observations show that this new state results from the combination of a dramatic and persistent increase in internal obscuration, and a reduced mass accretion rate. The internal obscuration is the dominant effect, with a median value of <jats:italic>N</jats:italic> <jats:sub> <jats:italic>H</jats:italic> </jats:sub> = 7 × 10<jats:sup>23</jats:sup> cm<jats:sup>−2</jats:sup>. In a number of observations, the source appears to be Compton-thick. We suggest that this state should be identified as the “obscured state,” and discuss the implications of this new (or rarely observed) accretion mode for black holes across the mass scale.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present our photometric and spectroscopic observations of the peculiar transient AT2018cow. The multiband photometry covers from peak to ∼70 days, and the spectroscopy ranges from 5 to ∼50 days. The rapid rise (<jats:italic>t</jats:italic> <jats:sub>r</jats:sub> ≲ 2.9 days), high luminosity (<jats:italic>M</jats:italic> <jats:sub> <jats:italic>V</jats:italic>,peak</jats:sub> ∼ −20.8 mag), and fast decline after peak make AT2018cow stand out from any other optical transients, whereas we find that its light curves show a high resemblance to those of Type Ibn supernovae. Moreover, the spectral energy distribution remains at a high temperature of ∼14,000 K at <jats:italic>t</jats:italic> &gt; 15 days after discovery. The spectra are featureless in the first 10 days, while some broad emission lines due to H, He, C, and O emerge later, with velocity declining from ∼14,000 to ∼3000 km s<jats:sup>−1</jats:sup> at the end of our observations. Narrow and weak He <jats:sc>I</jats:sc> emission lines emerge in the spectra at <jats:italic>t</jats:italic> &gt; 20 days after discovery. These emission lines are reminiscent of the features seen in interacting supernovae like the Type Ibn and IIn subclasses. We fit the bolometric light curves with a model of circumstellar interaction and radioactive decay of <jats:sup>56</jats:sup>Ni and find a good fit with ejecta mass <jats:italic>M</jats:italic> <jats:sub>ej</jats:sub> ∼ 3.16 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, circumstellar medium (CSM) mass <jats:italic>M</jats:italic> <jats:sub>CSM</jats:sub> ∼ 0.04 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>, and ejected <jats:sup>56</jats:sup>Ni mass <jats:inline-formula> <jats:tex-math> <?CDATA ${M}_{{}^{56}\mathrm{Ni}}\sim 0.23$?> </jats:tex-math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjabdebaieqn1.gif" xlink:type="simple" /> </jats:inline-formula> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. The CSM shell might be formed in an eruptive mass ejection of the progenitor star. Furthermore, the host environment of AT2018cow implies a connection of AT2018cow with massive stars. Combining observational properties and the light-curve fitting results, we conclude that AT2018cow might be a peculiar interacting supernova that originated from a massive star.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Energetic particles spectra at interplanetary shocks often exhibit a power law within a narrow momentum range softening at higher energy. We introduce a transport equation accounting for particle acceleration and escape with diffusion contributed by self-generated turbulence close to the shock and by preexisting turbulence far upstream. The upstream particle intensity steepens within one diffusion length from the shock as compared with diffusive shock acceleration rollover. The momentum spectrum, controlled by macroscopic parameters such as shock compression, speed, far-upstream diffusion coefficient, and escape time at the shock, can be reduced to a log-parabola and also to a broken power law. In the case of upstream uniform diffusion coefficient, the largely used power-law/exponential cutoff solution is retrieved.</jats:p>