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<jats:title>Abstract</jats:title> <jats:p>Efficient radiation at second and/or higher harmonics of Ω<jats:sub>ce</jats:sub> has been suggested to circumvent the escaping difficulty of the electron cyclotron maser emission mechanism when it is applied to solar radio bursts, such as spikes. In our earlier study, we developed a three-step numerical scheme to connect the dynamics of energetic electrons within a large-scale coronal loop structure with the microscale kinetic instability energized by the obtained nonthermal velocity distribution and found that direct and efficient harmonic X-mode (X2 for short) emission can be achieved due to the strip-like features of the distribution. That study only considered the radiation from the loop top at a specific time. Here we present the emission properties along the loop at different locations and timings. We found that, in accordance with our earlier results, few to several strip-like features can appear in all cases, and the first two strips play the major role in exciting X2 and Z (i.e., the slow extraordinary mode) that propagate quasi-perpendicularly. For the four sections along the loop, significant excitation of X2 is observed from the upper two sections, and the strongest emission is from the top section. In addition, significant excitation of Z is observed for all loop sections, while there is no significant emission of the fundamental X mode. The study provides new insight into coherent maser emission along the coronal loop structure during solar flares.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We report the results of spectroscopic and photometric observations of the emission-line object IRAS 07080+0605 carried out in 2004–2021. We found that the object is significantly underluminous for its spectroscopic properties (<jats:italic>T</jats:italic> <jats:sub>eff</jats:sub> = 8500 ± 500 K, <jats:inline-formula> <jats:tex-math> <?CDATA $\mathrm{log}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>log</mml:mi> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6de0ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> <jats:italic>g</jats:italic> = 2.0 ± 0.5), if a strong visual attenuation by a factor of ∼43 found through the spectral energy distribution modeling is not taken into account. Visual brightness variations with a stable period of 190 days but a variable amplitude of ∼0.2 mag were found in the ASAS SN data and attributed to variable circumstellar extinction in the dusty disk. We also found that the observed behavior of IRAS 07080+0605 is similar to that of the protoplanetary nebula Red Rectangle. The dusty disk of IRAS 07080+0605 shows the presence of carbonaceous particles (∼10%–20% of the total dust content) and polycyclic aromatic hydrocarbon emission bands. However, IRAS 07080+0605 shows no obvious signs of the refractory element depletion, which is common in post–asymptotic giant branch (AGB) dusty binaries, or of a visual nebula. Absorption-line positions vary with an amplitude of ∼25 km s<jats:sup>−1</jats:sup>, suggesting the presence of a secondary component. Spectroscopic monitoring on a timescale from days to months is needed to search for regular variations. We conclude that IRAS 07080+0605 is most likely a binary system with an A-type component on its way toward the post-AGB evolutionary stage, as binarity is capable of explaining most of the observed features.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Many experiments have confirmed the spectral hardening at a few hundred GV of cosmic-ray (CR) nucleus spectra, and three general different origins have been proposed: the primary source acceleration, the propagation, and the superposition of different kinds of sources. The AMS-02 CR nucleus spectra of He, C, N, O, Ne, Mg, Si, and B (which includes B and its dominating parent species) are collected to study the necessity of employing a break in diffusion coefficient and independent breaks in primary source injection spectra to reproduce the spectral hardening at a few hundred GV. For comparison, three different schemes are introduced to do the global fitting. The fitting results show that both the break in diffusion coefficient and the independent breaks in primary source injection spectra are needed, which correspond to the spatially dependent propagation and the superposition of different kinds of sources, respectively. Consequently, the nucleus spectral hardening in a few hundred GV should have hybrid origins. Moreover, the CR spectral indices of He and Ne show large deviations from other species in the low-rigidity region, which indicates their different CR origins.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present a detailed study of the evolution of the Galactic black hole transient GRS 1716−249 during its 2016–2017 outburst at optical (Las Cumbres Observatory), mid-infrared (Very Large Telescope), near-infrared (Rapid Eye Mount telescope), and ultraviolet (the Neil Gehrels Swift Observatory Ultraviolet/Optical Telescope) wavelengths, along with archival radio and X-ray data. We show that the optical/near-infrared and UV emission of the source mainly originates from a multi-temperature accretion disk, while the mid-infrared and radio emission are dominated by synchrotron emission from a compact jet. The optical/UV flux density is correlated with the X-ray emission when the source is in the hard state, consistent with an X-ray irradiated accretion disk with an additional contribution from the viscous disk during the outburst fade. We find evidence for a weak, but highly variable jet component at mid-infrared wavelengths. We also report the long-term optical light curve of the source and find that the quiescent <jats:inline-formula> <jats:tex-math> <?CDATA ${i}^{{\prime} }$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mrow> <mml:mi>i</mml:mi> </mml:mrow> <mml:mrow> <mml:mo accent="true">′</mml:mo> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6ce1ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>-band magnitude is 21.39 ± 0.15 mag. Furthermore, we discuss how previous estimates of the system parameters of the source are based on various incorrect assumptions, and so are likely to be inaccurate. By comparing our GRS 1716−249 data set to those of other outbursting black hole X-ray binaries, we find that while GRS 1716−249 shows similar X-ray behavior, it is noticeably optically fainter, if the literature distance of 2.4 kpc is adopted. Using several lines of reasoning, we argue that the source distance is further than previously assumed in the literature, likely within 4–17 kpc, with a most likely range of ∼4–8 kpc.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Knowledge of the morphology of nova ejecta is essential for fully understanding the physical processes involved in nova eruptions. We studied the 3D morphology of the expanding ejecta of the extremely slow nova V1280 Sco with a unique light curve. Synthetic line profile spectra were compared to the observed [O <jats:sc>iii</jats:sc>] <jats:italic>λλ</jats:italic>4959, 5007 and [N <jats:sc>ii</jats:sc>] <jats:italic>λ</jats:italic>5755 emission line profiles in order to find the best-fit morphology, inclination angle, and maximum expansion velocity of the ejected shell. We derive the best-fitting expansion velocity, inclination, and squeeze as <jats:inline-formula> <jats:tex-math> <?CDATA ${V}_{\exp }={2100}_{-100}^{+100}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>V</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>exp</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>2100</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>100</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>100</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6c82ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> km s<jats:sup>−1</jats:sup>, <jats:inline-formula> <jats:tex-math> <?CDATA $i={80}_{-3}^{+1}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>i</mml:mi> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>80</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6c82ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> deg, and <jats:inline-formula> <jats:tex-math> <?CDATA ${squ}={1.0}_{-0.1}^{+0.0}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="italic">squ</mml:mi> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>1.0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.1</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.0</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6c82ieqn3.gif" xlink:type="simple" /> </jats:inline-formula> using [O <jats:sc>iii</jats:sc>] line profiles, and <jats:inline-formula> <jats:tex-math> <?CDATA ${V}_{\exp }={1600}_{-100}^{+100}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>V</mml:mi> </mml:mrow> <mml:mrow> <mml:mi>exp</mml:mi> </mml:mrow> </mml:msub> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>1600</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>100</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>100</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6c82ieqn4.gif" xlink:type="simple" /> </jats:inline-formula> km s<jats:sup>−1</jats:sup>, <jats:inline-formula> <jats:tex-math> <?CDATA $i={81}_{-4}^{+2}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>i</mml:mi> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>81</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>4</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6c82ieqn5.gif" xlink:type="simple" /> </jats:inline-formula> deg, and <jats:inline-formula> <jats:tex-math> <?CDATA ${squ}={1.0}_{-0.1}^{+0.0}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="italic">squ</mml:mi> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>1.0</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.1</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.0</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6c82ieqn6.gif" xlink:type="simple" /> </jats:inline-formula> using the [N <jats:sc>ii</jats:sc>] <jats:italic>λ</jats:italic>5755 line profile. A high inclination angle is consistent with the observational results showing multiple absorption lines originating from clumpy gases, which are produced in dense and slow equatorially focused outflows. Based on additional observational features such as optical flares near the maximum light and dust formation on V1280 Sco, a model of internal shock interaction between slow ejecta and fast wind proposed for the <jats:italic>γ</jats:italic>-ray emission detected in other novae seems to be applicable to this extremely slow and peculiar nova. Increasing the sample size of novae whose morphology is studied will be helpful in addressing long-standing mysteries in novae such as the dominant energy source to power the optical light at the maximum, optical flares near the maximum, clumpiness of the ejecta, and dust formation.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The Fermi Gamma-ray Burst Monitor (GBM) triggers on-board in response to ∼40 short gamma-ray bursts (SGRBs) per year; however, their large localization regions have made the search for optical counterparts a challenging endeavour. We have developed and executed an extensive program with the wide field of view of the Zwicky Transient Facility (ZTF) camera, mounted on the Palomar 48 inch Oschin telescope (P48), to perform target-of-opportunity (ToO) observations on 10 Fermi-GBM SGRBs during 2018 and 2020–2021. Bridging the large sky areas with small field-of-view optical telescopes in order to track the evolution of potential candidates, we look for the elusive SGRB afterglows and kilonovae (KNe) associated with these high-energy events. No counterpart has yet been found, even though more than 10 ground-based telescopes, part of the Global Relay of Observatories Watching Transients Happen (GROWTH) network, have taken part in these efforts. The candidate selection procedure and the follow-up strategy have shown that ZTF is an efficient instrument for searching for poorly localized SGRBs, retrieving a reasonable number of candidates to follow up and showing promising capabilities as the community approaches the multi-messenger era. Based on the median limiting magnitude of ZTF, our searches would have been able to retrieve a GW170817-like event up to ∼200 Mpc and SGRB afterglows to <jats:italic>z</jats:italic> = 0.16 or 0.4, depending on the assumed underlying energy model. Future ToOs will expand the horizon to <jats:italic>z</jats:italic> = 0.2 and 0.7, respectively.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The substructures observed in protoplanetary disks may be the signposts of embedded planets carving gaps or creating vortices. The inferred masses of these planets often fall in the Jovian regime despite their low abundance compared to lower-mass planets, partly because previous works often assume that a single substructure (a gap or vortex) is caused by a single planet. In this work, we study the possible imprints of compact systems composed of Neptune-like planets (∼10–30 <jats:italic>M</jats:italic> <jats:sub>⊕</jats:sub>) and show that long-standing vortices are a prevalent outcome when their interplanetary separation (Δ<jats:italic>a</jats:italic>) falls below ∼8 times <jats:italic>H</jats:italic> <jats:sub>p</jats:sub>—the average disk’s scale height at the planet’s locations. In simulations where a single planet is unable to produce long-lived vortices, two-planet systems can preserve them for at least 5000 orbits in two regimes: (i) fully shared density gaps with elongated vortices around the stable Lagrange points <jats:italic>L</jats:italic> <jats:sub>4</jats:sub> and <jats:italic>L</jats:italic> <jats:sub>5</jats:sub> for the most compact planet pairs (Δ<jats:italic>a</jats:italic> ≲ 4.6 <jats:italic>H</jats:italic> <jats:sub>p</jats:sub>), and (ii) partially shared gaps for more widely spaced planets (Δ<jats:italic>a</jats:italic> ∼ 4.6–8 <jats:italic>H</jats:italic> <jats:sub>p</jats:sub>) forming vortices in a density ring between the planets through the Rossby wave instability. The latter case can produce vortices with a wide range of aspect ratios down to ∼3 and can occur for planets captured into the 3:2 (2:1) mean-motion resonances for disks’ aspects ratios of <jats:italic>h</jats:italic> ≳ 0.033 (<jats:italic>h</jats:italic> ≳ 0.057). We suggest that their long lifetimes are sustained by the interaction of spiral density waves launched by the neighboring planets. Overall, our results show that the distinguishing imprint of compact systems with Neptune-mass planets are long-lived vortices <jats:italic>inside</jats:italic> the density gaps, which in turn are shallower than single-planet gaps for a fixed gap width.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We propose that KIC 1573174 is a quadruple-mode <jats:italic>δ</jats:italic> Scuti star with pulsation amplitudes between those of the high-amplitude Delta Scuti star group and average low-amplitude pulsators. The radial modes detected in this star provide a unique opportunity to exploit asteroseismic techniques up to their limits. Detailed frequency analysis is given for the light curve from the Kepler mission. The variation of the light curve is dominated by the strongest mode with a frequency of F0 = 7.3975 day<jats:sup>−1</jats:sup>, as shown by Fourier analysis of long cadence data (Q1–Q17, spanning 1460 days), indicating that the target is a <jats:italic>δ</jats:italic> Scuti star. The other three independent modes with F1 = 9.4397 day<jats:sup>−1</jats:sup>, F2 = 12.1225 day<jats:sup>−1</jats:sup>, and F3 = 14.3577 day<jats:sup>−1</jats:sup>, have ratios of <jats:italic>P</jats:italic> <jats:sub>1</jats:sub>/<jats:italic>P</jats:italic> <jats:sub>0</jats:sub>, <jats:italic>P</jats:italic> <jats:sub>2</jats:sub>/<jats:italic>P</jats:italic> <jats:sub>0</jats:sub>, and <jats:italic>P</jats:italic> <jats:sub>3</jats:sub>/<jats:italic>P</jats:italic> <jats:sub>0</jats:sub> estimated as 0.783, 0.610, and 0.515, which indicate that KIC 1573174 is a quadruple-mode <jats:italic>δ</jats:italic> Scuti star. A different approach has been used to determine the <jats:italic>O</jats:italic> − <jats:italic>C</jats:italic> through the study of phase modulation. The change of period (1/<jats:italic>P</jats:italic>)<jats:italic>dP</jats:italic>/<jats:italic>dt</jats:italic> is obtained resulting in −1.14 × 10<jats:sup>−6</jats:sup> yr<jats:sup>−1</jats:sup> and −4.48 × 10<jats:sup>−6</jats:sup> yr<jats:sup>−1</jats:sup> for F0 and F1 respectively. Based on frequency parameters (i.e., F0, F1, F2, and F3), a series of theoretical models were conducted by employing the stellar evolution code MESA. The ratio of observed <jats:italic>f</jats:italic> <jats:sub>1</jats:sub>/<jats:italic>f</jats:italic> <jats:sub>2</jats:sub> is larger than that of the model, which may be caused by the rotation of the star. We suggest high-resolution spectral observation is highly desired in the future to further constrain models.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the combined Chandra and Swift-BAT spectral analysis of nine low-redshift (<jats:italic>z</jats:italic> ≤ 0.10), candidate heavily obscured active galactic nuclei (AGN) selected from the Swift-BAT 150 month catalog. We located soft (1−10 keV) X-ray counterparts to these BAT sources and joint fit their spectra with physically motivated models. The spectral analysis in the 1−150 keV energy band determined that all sources are obscured, with a line-of-sight column density <jats:italic>N</jats:italic> <jats:sub> <jats:italic>H</jats:italic> </jats:sub> ≥ 10<jats:sup>22</jats:sup> cm<jats:sup>−2</jats:sup> at a 90% confidence level. Four of these sources show significant obscuration with <jats:italic>N</jats:italic> <jats:sub> <jats:italic>H</jats:italic> </jats:sub> ≥ 10<jats:sup>23</jats:sup> cm<jats:sup>−2</jats:sup> and two additional sources are candidate Compton-thick Active Galactic Nuclei (CT-AGNs) with <jats:italic>N</jats:italic> <jats:sub> <jats:italic>H</jats:italic> </jats:sub> ≥ 10<jats:sup>24</jats:sup> cm<jats:sup>−2</jats:sup>. These two sources, 2MASX J02051994–0233055 and IRAS 11058−1131, are the latest addition to the previous 3 CT-AGN candidates found using our strategy for soft X-ray follow-up of BAT sources. Here we present the results of our methodology so far, and analyze the effectiveness of applying different selection criteria to discover CT-AGN in the local Universe. Our selection criteria has an ∼20% success rate of discovering heavily obscured AGN whose CT nature is confirmed by follow-up NuSTAR observations. This is much higher than the ∼5% found in blind surveys.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We present the primary results from the Dragonfly Edge-on Galaxies Survey, an exploration of the stellar halos of twelve nearby (<jats:italic>d</jats:italic> &lt; 25 Mpc) edge-on disk galaxies with the Dragonfly Telephoto Array. The edge-on orientation of these galaxies allows their stellar halos to be explored with minimal obscuration by or confusion with the much brighter disk light. Galaxies in the sample span a range of stellar masses from 10<jats:sup>9.68</jats:sup> to 10<jats:sup>10.88</jats:sup> <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>. We confirm that the wide range of stellar halo mass fractions previously seen for Milky Way–mass galaxies is also found among less massive spiral galaxies. The scatter in stellar halo mass fraction is large, but we do find a significant positive correlation between stellar halo mass fraction and total stellar mass when the former is measured beyond five half-mass radii. Reasonably good agreement is found with predictions from cosmological hydrodynamical simulations, although observed stellar halo fractions appear to be somewhat lower than expected from these simulations.</jats:p>