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<jats:title>Abstract</jats:title> <jats:p>Coronal mass ejections (CMEs) are energetic eruptions of organized magnetic structures from the Sun. Therefore, the reconnection of the magnetic field during ejection can excite periodic speed oscillations of CMEs. A previous study showed that speed oscillations are frequently associated with CME propagation. The Solar and Heliospheric Observatory mission’s white-light coronagraphs have observed about 30,000 CMEs from 1996 January to the end of 2019 December. This period of time covers two solar cycles (23 and 24). In the present study, the basic attributes of speed oscillations during this period of time were analyzed. We showed that the oscillation parameters (period and amplitude) significantly depend not only on the phase of a given solar cycle but also on the intensity of individual cycles as well. This reveals that the basic attributes of speed oscillation are closely related to the physical conditions prevailing inside the CMEs as well as in the interplanetary medium in which they propagate. Using this approximation, we estimated that, on average, the CME internal magnetic field varies from 18 up to 25 mG between minimum and maximum solar activity. The obtained results show that a detailed analysis of speed oscillations can be a very efficient tool for studying not only the physical properties of the ejections themselves but also the condition of the interplanetary medium in which they expand. This creates completely new perspectives for studying the physical parameters of CMEs shortly after their eruption in the Sun’s environment (space seismology).</jats:p>

<jats:title>Abstract</jats:title> <jats:p>For the first ∼3 yrs after the binary neutron star merger event GW 170817, the radio and X-ray radiation has been dominated by emission from a structured relativistic off-axis jet propagating into a low-density medium with <jats:italic>n</jats:italic> &lt; 0.01 cm<jats:sup>−3</jats:sup>. We report on observational evidence for an excess of X-ray emission at <jats:italic>δt</jats:italic> &gt; 900 days after the merger. With <jats:italic>L</jats:italic> <jats:sub> <jats:italic>x</jats:italic> </jats:sub> ≈ 5 × 10<jats:sup>38</jats:sup> erg s<jats:sup>−1</jats:sup> at 1234 days, the recently detected X-ray emission represents a ≥3.2<jats:italic>σ</jats:italic> (Gaussian equivalent) deviation from the universal post-jet-break model that best fits the multiwavelength afterglow at earlier times. In the context of <jats:monospace>JetFit</jats:monospace> afterglow models, current data represent a departure with statistical significance ≥3.1<jats:italic>σ</jats:italic>, depending on the fireball collimation, with the most realistic models showing excesses at the level of ≥3.7<jats:italic>σ</jats:italic>. A lack of detectable 3 GHz radio emission suggests a harder broadband spectrum than the jet afterglow. These properties are consistent with the emergence of a new emission component such as synchrotron radiation from a mildly relativistic shock generated by the expanding merger ejecta, i.e., a kilonova afterglow. In this context, we present a set of ab initio numerical relativity binary neutron star (BNS) merger simulations that show that an X-ray excess supports the presence of a high-velocity tail in the merger ejecta, and argues against the prompt collapse of the merger remnant into a black hole. Radiation from accretion processes on the compact-object remnant represents a viable alternative. Neither a kilonova afterglow nor accretion-powered emission have been observed before, as detections of BNS mergers at this phase of evolution are unprecedented.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Gravitational wave (GW) emissions from extreme-mass-ratio inspirals (EMRIs) are promising sources for low-frequency GW detectors. They result from a compact object, such as a stellar-mass black hole (BH), captured by a supermassive BH (SMBH). Several physical processes have been proposed to form EMRIs. In particular, weak two-body interactions over a long timescale (i.e., relaxation processes) have been proposed as a likely mechanism to drive the BH orbit to high eccentricity. Consequently, it is captured by the SMBH and becomes an EMRI. Here we demonstrate that EMRIs are naturally formed in SMBH binaries. Gravitational perturbations from an SMBH companion, known as the eccentric Kozai–Lidov (EKL) mechanism, combined with relaxation processes, yield a significantly more enhanced rate than any of these processes operating alone. Because EKL is sensitive to the orbital configuration, two-body relaxation can alter the orbital parameters, rendering the system in a more EKL-favorable regime. As SMBH binaries are expected to be prevalent in the universe, this process predicts a substantially high EMRI rate.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Tidal disruption events (TDEs) are valuable probes of the demographics of supermassive black holes as well as the dynamics and population of stars in the centers of galaxies. In this Letter, we focus on studying how debris disk formation and circularization processes can impact the possibility of observing prompt flares in TDEs. First, we investigate how the efficiency of disk formation is determined by the key parameters, namely, the black hole mass <jats:italic>M</jats:italic> <jats:sub>BH</jats:sub>, the stellar mass <jats:italic>m</jats:italic> <jats:sub>⋆</jats:sub>, and the orbital penetration parameter <jats:italic>β</jats:italic> that quantifies how close the disrupted star would orbit around the black hole. Then we calculate the intrinsic differential TDE rate as a function of these three parameters. Combining these two results, we find that the rates of TDEs with prompt disk formation are significantly suppressed around lighter black holes, which provides a plausible explanation for why the observed TDE host black hole mass distribution peaks between 10<jats:sup>6</jats:sup> and 10<jats:sup>7</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. Therefore, the consideration of disk formation efficiency is crucial for recovering the intrinsic black hole demographics from TDEs. Furthermore, we find that the efficiency of the disk formation process also impacts the distributions of both stellar orbital penetration parameter and stellar mass observed in TDEs.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Forty-four years of Wilcox Solar Observatory, 14 years of Michelson Doppler Imager on the Solar and Heliospheric Observatory, and 11 years of Helioseismic and Magnetic Imager on the Solar Dynamics Observatory magnetic field data have been studied to determine the east–west inclination—the toroidal component—of the magnetic field. Maps of the zonal averaged inclination show that each toroidal field cycle begins at around the same time at high latitudes in the northern and southern hemispheres, and ends at the equator. Observation of these maps also shows that each instance of a dominant toroidal field direction starts at high latitudes near sunspot maximum and is still visible near the equator well past the minimum of its cycle, indicating that the toroidal field cycle spans approximately two sunspot cycles. The length of the extended activity cycle is measured to be approximately 16.8 yr.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the analysis of archival XMM-Newton European Photon Imaging Camera (EPIC) X-ray observations of the symbiotic star R Aquarii. We used the Extended Source Analysis Software package to disclose diffuse soft X-ray emission extending up to 2.′2 (≈0.27 pc) from this binary system. The depth of these XMM-Newton EPIC observations reveals in unprecedented detail the spatial distribution of this diffuse emission, with a bipolar morphology spatially correlated with the optical nebula. The extended X-ray emission shares the same dominant soft X-ray-emitting temperature as the clumps in the jet-like feature resolved by Chandra in the vicinity of the binary system. The harder component in the jet might suggest that the gas cools down; however, the possible presence of nonthermal emission produced by the presence of a magnetic field collimating the mass ejection cannot be discarded. We propose that the ongoing precessing jet creates bipolar cavities filled with X-ray-emitting hot gas that feeds the more extended X-ray bubble as they get disrupted. These EPIC observations demonstrate that the jet feedback mechanism produced by an accreting disk around an evolved, low-mass star can blow hot bubbles, similar to those produced by jets arising from the nuclei of active galaxies.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Very long baseline interferometric (VLBI) localizations of repeating fast radio bursts (FRBs) have demonstrated a diversity of local environments: from nearby star-forming regions to globular clusters. Here we report the VLBI localization of FRB 20201124A using an ad hoc array of dishes that also participate in the European VLBI Network (EVN). In our campaign, we detected 18 bursts from FRB 20201124A at two separate epochs. By combining the visibilities from both epochs, we were able to localize FRB 20201124A with a 1<jats:italic>σ</jats:italic> uncertainty of 2.7 mas. We use the relatively large burst sample to investigate astrometric accuracy and find that for ≳20 baselines (≳7 dishes) we can robustly reach milliarcsecond precision even using single-burst data sets. Subarcsecond precision is still possible for single bursts, even when only ∼6 baselines (four dishes) are available. In such cases, the limited <jats:italic>uv</jats:italic> coverage for individual bursts results in very high side-lobe levels. Thus, in addition to the peak position from the dirty map, we also explore smoothing the structure in the dirty map by fitting Gaussian functions to the fringe pattern in order to constrain individual burst positions, which we find to be more reliable. Our VLBI work places FRB 20201124A 710 ± 30 mas (1<jats:italic>σ</jats:italic> uncertainty) from the optical center of the host galaxy, consistent with originating from within the recently discovered extended radio structure associated with star formation in the host galaxy. Future high-resolution optical observations, e.g., with Hubble Space Telescope, can determine the proximity of FRB 20201124A’s position to nearby knots of star formation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>A sample of 60,410 bona fide optical quasars with astrometric proper motions in Gaia Early Data Release 3 and spectroscopic redshifts above 0.5 in an oval 8400 square degree area of the sky is constructed. Using orthogonal Zernike functions of polar coordinates, the proper motion fields are fitted in a weighted least-squares adjustment of the entire sample and of six equal bins of sorted redshifts. The overall fit with 37 Zernike functions reveals a statistically significant pattern, which is likely to be of instrumental origin. The main feature of this pattern is a chain of peaks and dips mostly in the R.A. component with an amplitude of 25 <jats:italic>μ</jats:italic>as yr<jats:sup>−1</jats:sup>. This field is subtracted from each of the six analogous fits for quasars grouped by redshifts covering the range 0.5 through 7.03, with median values of 0.72, 1.00, 1.25, 1.52, 1.83, 2.34. The resulting residual patterns are noisier, with formal uncertainties up to 8 <jats:italic>μ</jats:italic>as yr<jats:sup>−1</jats:sup> in the central part of the area. We detect a single high-confidence Zernike term for the R.A. proper motion components of quasars with redshifts around 1.52 representing a general gradient of 30 <jats:italic>μ</jats:italic>as yr<jats:sup>−1</jats:sup> over 150° on the sky. We do not find any small- or medium-scale systemic variations of the residual proper motion field as functions of redshift above the 2.5<jats:italic>σ</jats:italic> significance level.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a near-infrared transmission spectrum of the long-period (<jats:italic>P</jats:italic> = 542 days), temperate (<jats:italic>T</jats:italic> <jats:sub>eq</jats:sub> = 294 K) giant planet HIP 41378 f obtained with the Wide-Field Camera 3 instrument aboard the Hubble Space Telescope (HST). With a measured mass of 12 ± 3 <jats:italic>M</jats:italic> <jats:sub>⊕</jats:sub> and a radius of 9.2 ± 0.1 <jats:italic>R</jats:italic> <jats:sub>⊕</jats:sub>, HIP 41378 f has an extremely low bulk density (0.09 ± 0.02 g cm<jats:sup>−3</jats:sup>). We measure the transit depth with a median precision of 84 ppm in 30 spectrophotometric channels with uniformly sized widths of 0.018 <jats:italic>μ</jats:italic>m. Within this level of precision, the spectrum shows no evidence of absorption from gaseous molecular features between 1.1 and 1.7 <jats:italic>μ</jats:italic>m. Comparing the observed transmission spectrum to a suite of 1D radiative-convective-thermochemical-equilibrium forward models, we rule out clear, low-metallicity atmospheres and find that the data prefer high-metallicity atmospheres or models with an additional opacity source, such as high-altitude hazes and/or circumplanetary rings. We explore the ringed scenario for HIP 41378 f further by jointly fitting the K2 and HST light curves to constrain the properties of putative rings. We also assess the possibility of distinguishing between hazy, ringed, and high-metallicity scenarios at longer wavelengths with the James Webb Space Telescope. HIP 41378 f provides a rare opportunity to probe the atmospheric composition of a cool giant planet spanning the gap in temperature, orbital separation, and stellar irradiation between the solar system giants, directly imaged planets, and the highly irradiated hot Jupiters traditionally studied via transit spectroscopy.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Using the JVLA, we explored the Galactic center (GC) with a resolution of 0.″05 at 33.0 and 44.6 GHz. We detected 64 hypercompact radio sources (HCRs) in the central parsec. The dense group of HCRs can be divided into three spectral types: 38 steep-spectrum (<jats:italic>α</jats:italic> ≤ −0.5) sources, 10 flat-spectrum (−0.5 &lt; <jats:italic>α</jats:italic> ≤ 0.2) sources, and 17 inverted-spectrum sources having <jats:italic>α</jats:italic> &gt; 0.2, assuming <jats:italic>S</jats:italic> ∝ <jats:italic>ν</jats:italic> <jats:sup> <jats:italic>α</jats:italic> </jats:sup>. The steep-spectrum HCRs are likely to represent a population of massive stellar remnants associated with nonthermal compact radio sources powered by neutron stars and stellar black holes. The surface-density distribution of the HCRs as a function of radial distance (<jats:italic>R</jats:italic>) from Sgr A* can be described as a steep power law Σ(<jats:italic>R</jats:italic>) ∝ <jats:italic>R</jats:italic> <jats:sup>−Γ</jats:sup>, with Γ = 1.6 ± 0.2, along with the presence of a localized order-of-magnitude enhancement in the range 0.1–0.3 pc. The steeper profile of the HCRs relative to that of the central cluster might result from the concentration of massive stellar remnants by mass segregation at the GC. The GC magnetar SGR J1745−2900 belongs to the inverted-spectrum subsample. We find two spectral components present in the averaged radio spectrum of SGR J1745−2900, separated at <jats:italic>ν</jats:italic> ∼ 30 GHz. The centimeter component is fitted to a power law with <jats:italic>α</jats:italic> <jats:sub>cm</jats:sub> = −1.5 ± 0.6. The enhanced millimeter component shows a rising spectrum <jats:italic>α</jats:italic> <jats:sub>mm</jats:sub> = 1.1 ± 0.2. Based on the ALMA observations at 225 GHz, we find that the GC magnetar is highly variable on a day-to-day timescale, showing variations up to a factor of 6. Further JVLA and ALMA observations of the variability, spectrum, and polarization of the HCRs are critical for determining whether they are associated with stellar remnants.</jats:p>