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<jats:title>Abstract</jats:title> <jats:p>We present the results of a spectral-line survey of the W51e1/e2 star-forming region at 68–88 GHz. 79 molecules and their isotopologues were detected, from simple diatomic or triatomic molecules, such as SO, SiO, and CCH, to complex organic compounds, such as CH<jats:sub>3</jats:sub>OCH<jats:sub>3</jats:sub> or CH<jats:sub>3</jats:sub>COCH<jats:sub>3</jats:sub>. A number of lines that are absent from the Lovas list of molecular lines observed in space were detected, and most of these were identified. A significant number of the detected molecules are typical for hot cores. These include the neutral molecules HCOOCH<jats:sub>3</jats:sub>, CH<jats:sub>3</jats:sub>CH<jats:sub>2</jats:sub>OH, and CH<jats:sub>3</jats:sub>COCH<jats:sub>3</jats:sub>, which are currently believed to exist in the gas phase only in hot cores and shock-heated gas. In addition, vibrationally excited C<jats:sub>4</jats:sub>H and HC<jats:sub>3</jats:sub>N lines with upper-level energies of several hundred Kelvins were found. Such lines can arise only in hot gas with temperatures on the order of 100 K or higher. Apart from neutral molecules, various molecular ions were also detected. Some of these (HC<jats:sup>18</jats:sup>O<jats:sup>+</jats:sup>, H<jats:sup>13</jats:sup>CO<jats:sup>+</jats:sup>, and HCS<jats:sup>+</jats:sup>) usually exist in molecular clouds with high visual extinctions. Potential formation pathways of complex organic molecules and hydrocarbons, along with nitriles, are considered. These formation routes are first discussed in the context of laboratory experiments elucidating the synthesis of organic molecules in interstellar ices in cold molecular clouds, followed by sublimation into the gas phase in the hot core stage. Thereafter, we discuss the predominant formation of hydrocarbons and their nitriles in the gas phase through bimolecular neutral–neutral reactions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The water snowline in circumstellar disks is a crucial component in planet formation, but direct observational constraints on its location remain sparse owing to the difficulty of observing water in both young embedded and mature protoplanetary disks. Chemical imaging provides an alternative route to locate the snowline, and HCO<jats:sup>+</jats:sup> isotopologues have been shown to be good tracers in protostellar envelopes and Herbig disks. Here we present ∼0.″5 resolution (∼35 au radius) Atacama Large Millimeter/submillimeter Array (ALMA) observations of HCO<jats:sup>+</jats:sup> <jats:italic>J</jats:italic> = 4 − 3 and H<jats:sup>13</jats:sup>CO<jats:sup>+</jats:sup> <jats:italic>J</jats:italic> = 3 − 2 toward the young (Class 0/I) disk L1527 IRS. Using a source-specific physical model with the midplane snowline at 3.4 au and a small chemical network, we are able to reproduce the HCO<jats:sup>+</jats:sup> and H<jats:sup>13</jats:sup>CO<jats:sup>+</jats:sup> emission, but for HCO<jats:sup>+</jats:sup> only when the cosmic-ray ionization rate is lowered to 10<jats:sup>−18</jats:sup> s<jats:sup>−1</jats:sup>. Even though the observations are not sensitive to the expected HCO<jats:sup>+</jats:sup> abundance drop across the snowline, the reduction in HCO<jats:sup>+</jats:sup> above the snow surface and the global temperature structure allow us to constrain a snowline location between 1.8 and 4.1 au. Deep observations are required to eliminate the envelope contribution to the emission and to derive more stringent constraints on the snowline location. Locating the snowline in young disks directly with observations of H<jats:sub>2</jats:sub>O isotopologues may therefore still be an alternative option. With a direct snowline measurement, HCO<jats:sup>+</jats:sup> will be able to provide constraints on the ionization rate.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Here we present a detailed study of the broadband noise in the power density spectra of the black hole X-ray binary MAXI J1820+070 during the hard state of its 2018 outburst, using Hard X-ray Modulation Telescope observations. The broadband noise shows two main humps, which might separately correspond to variability from a variable disk and two Comptonization regions. We fitted the two humps with multiple Lorentzian functions and studied the energy-dependent properties of each component up to 90–150 keV and their evolution with spectral changes. The lowest-frequency component is considered as the subharmonic of the quasiperiodic oscillation component and shows a different energy dependence compared with other broadband noise components. We found that although the fractional rms of all the broadband noise components mainly decreases with the energy, their rms spectra are different in shape. Above ∼20–30 keV, the characteristic frequencies of these components increase sharply with the energy, meaning that the high-energy component is more variable on short timescales. Our results suggest that the hot inner flow in MAXI J1820+070 is likely to be inhomogeneous. We propose a geometry with a truncated accretion disk and two Comptonization regions.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>In this study, we present a compressible test-field method (CTFM) for computing <jats:italic>α-</jats:italic>effect and turbulent magnetic diffusivity tensors, as well as those relevant for the mean ponderomotive force and mass source, applied to the full MHD equations. We describe the theoretical background of the method and compare it to the quasi-kinematic test-field method and to the previously studied variant working in simplified MHD (SMHD). We present several test cases using velocity and magnetic fields of the Roberts geometry and also compare with the imposed-field method. We show that, for moderate imposed-field strengths, the nonlinear CTFM (nCTFM) gives results in agreement with the imposed-field method. A comparison of different flavors of the nCTFM in the shear dynamo case also yields agreement up to equipartition field strengths. Some deviations between the CTFM and SMHD variants exist. As a relevant physical application, we study nonhelically forced shear flows, which exhibit large-scale dynamo action, and present a reanalysis of low-Reynolds-number, moderate shear systems, where we previously ignored the pressure gradient in the momentum equation and found no coherent shear-current effect. Another key difference is that in the earlier study we used magnetic forcing to mimic small-scale dynamo action, while here it is self-consistently driven by purely kinetic forcing. The kinematic CTFM with general validity forms the core of our analysis. We still find no coherent shear-current effect, but do recover strong large-scale dynamo action that, according to our analysis, is driven by incoherent effects.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The origin of life on Earth involves the early appearance of an information-containing molecule such as RNA. The basic building blocks of RNA could have been delivered by carbon-rich meteorites or produced in situ by processes beginning with the synthesis of hydrogen cyanide (HCN) in the early Earth’s atmosphere. Here, we construct a robust physical and nonequilibrium chemical model of the early Earth’s atmosphere. The atmosphere is supplied with hydrogen from impact degassing of meteorites, water evaporated from the oceans, carbon dioxide from volcanoes, and methane from undersea hydrothermal vents, and in it lightning and external UV-driven chemistry produce HCN. This allows us to calculate the rain-out of HCN into warm little ponds (WLPs). We then use a comprehensive numerical model of sources and sinks to compute the resulting abundances of nucleobases, ribose, and nucleotide precursors such as 2-aminooxazole resulting from aqueous and UV-driven chemistry within them. We find that 4.4 billion years ago the limit of adenine concentrations in ponds for habitable surfaces is 0.05 <jats:italic>μ</jats:italic>M in the absence of seepage. Meteorite delivery of adenine to WLPs can provide boosts in concentration by 2–3 orders of magnitude, but these boosts deplete within months by UV photodissociation, seepage, and hydrolysis. The early evolution of the atmosphere is dominated by the decrease in hydrogen due to falling impact rates and atmospheric escape, and the rise of oxygenated species such as OH from H<jats:sub>2</jats:sub>O photolysis. The source of HCN is predominantly from UV radiation rather than lightning. Our work points to an early origin of RNA on Earth within ∼200 Myr of the Moon-forming impact.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The cosmic formation rate of long gamma-ray bursts (LGRBs) encodes the evolution, across cosmic times, of the properties of their progenitors and of their environment. The LGRB formation rate and the luminosity function, with its redshift evolution, are derived by reproducing the largest sets of observations collected over the last four decades, namely the observer-frame prompt emission properties of the GRB samples detected by the Fermi and Compton Gamma Ray Observatory satellites and the redshift, luminosity, and energy distributions of the flux-limited, redshift-complete samples of GRBs detected by Swift. The model that best reproduces all these constraints consists of a GRB formation rate increasing with redshift ∝(1 + <jats:italic>z</jats:italic>)<jats:sup>3.2</jats:sup>, i.e., steeper than the star formation rate, up to <jats:italic>z</jats:italic> ∼ 3, followed by a decrease ∝(1 + <jats:italic>z</jats:italic>)<jats:sup>−3</jats:sup>. On top of this, our model also predicts a moderate evolution of the characteristic luminosity function break ∝(1 + <jats:italic>z</jats:italic>)<jats:sup>0.6</jats:sup>. Models with only luminosity or rate evolution are excluded at &gt;5<jats:italic>σ</jats:italic> significance. The cosmic rate evolution of LGRBs is interpreted as their preference for occurring in environments with metallicity <jats:inline-formula> <jats:tex-math> <?CDATA $12+\mathrm{log}({\rm{O}}/{\rm{H}})\lt 8.6$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mn>12</mml:mn> <mml:mo>+</mml:mo> <mml:mi>log</mml:mi> <mml:mo stretchy="false">(</mml:mo> <mml:mi mathvariant="normal">O</mml:mi> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mi mathvariant="normal">H</mml:mi> <mml:mo stretchy="false">)</mml:mo> <mml:mo>&lt;</mml:mo> <mml:mn>8.6</mml:mn> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6e43ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, consistent with theoretical models and host galaxy observations. The LGRB rate at <jats:italic>z</jats:italic> = 0, accounting for their collimation, is <jats:inline-formula> <jats:tex-math> <?CDATA ${\rho }_{0}\,=\,{79}_{-33}^{+57}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msub> <mml:mrow> <mml:mi>ρ</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0</mml:mn> </mml:mrow> </mml:msub> <mml:mspace width="0.10em" /> <mml:mo>=</mml:mo> <mml:mspace width="0.10em" /> <mml:msubsup> <mml:mrow> <mml:mn>79</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>33</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>57</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6e43ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> Gpc<jats:sup>−3</jats:sup> yr<jats:sup>−1</jats:sup> (68% confidence interval). This corresponds to ∼1% of broad-line Type Ibc supernovae producing a successful jet in the local universe. This fraction increases up to ∼7% at <jats:italic>z</jats:italic> ≥ 3. Finally, we estimate that at least ≈0.2−0.7 yr<jats:sup>−1</jats:sup> of the Swift- and Fermi-detected bursts at <jats:italic>z</jats:italic> &lt; 0.5 are jets observed slightly off-axis.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>We compare the X-ray profiles and fluxes of the Crab pulsar before and after the glitches in 2017 and 2019, using the data collected by the Insight-HXMT, NICER, and Fermi/GBM, to test whether there is any evidence for magnetosphere rearrangement after glitch. For the 2017 glitch, the profiles from Insight-HXMT (27–200 keV) and NICER (0.5–10 keV) remain unchanged within rms 0.47% and 0.28%, respectively, while the pulsed fluxes measured by these two detectors remain stable with 1<jats:italic>σ</jats:italic> uncertainty of 0.07% and 0.011%. Considering that the persistent offset of the spin-down rate post-glitch is 0.13% and the X-ray luminosity of the Crab pulsar is proportional to <jats:inline-formula> <jats:tex-math> <?CDATA ${\dot{E}}^{1.6\pm 0.3}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msup> <mml:mrow> <mml:mover accent="true"> <mml:mrow> <mml:mi>E</mml:mi> </mml:mrow> <mml:mrow> <mml:mo>̇</mml:mo> </mml:mrow> </mml:mover> </mml:mrow> <mml:mrow> <mml:mn>1.6</mml:mn> <mml:mo>±</mml:mo> <mml:mn>0.3</mml:mn> </mml:mrow> </mml:msup> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjac6d53ieqn1.gif" xlink:type="simple" /> </jats:inline-formula>, we find that the X-ray flux does not increase proportionally to the spin-down power at a significance of about 2.8<jats:italic>σ</jats:italic> by fitting the flux measurements with a Heaviside function, and thus the additional torque constantly braking the pulsar spin post-glitch is unlikely due to a global magnetosphere variation. For the 2019 glitch, after which a possible soft X-ray polarization variation was detected, the profiles remain unchanged within rms 2.02%, 0.35%, 0.90%, and 0.47% in 10–200, 0.5–10, 3–4.5, and 27–200 keV, respectively, suggesting that the geometry of the X-ray emitting region after the glitch is similar to the pre-glitch one. Therefore the possible polarization variation during the 2019 glitch is unlikely a consequence of the overall magnetosphere changes. The invariance of the pulse profiles is also verified by Kolmogorov–Smirnov tests and that of pulsed fluxes by Z-tests.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The mass-loss rates from single massive stars are high enough to form radio photospheres at large distances from the stellar surface, where the wind is optically thick to (thermal) free–free opacity. Here we calculate the far-infrared, millimeter, and radio band spectral energy distributions (SEDs) that can result from the combination of free–free processes and synchrotron emission, to explore the conditions for nonthermal SEDs. Simplifying assumptions are adopted in terms of scaling relations for the magnetic field strength and the spatial distribution of relativistic electrons. The wind is assumed to be spherically symmetric, and we consider the effect of Razin suppression on the synchrotron emission. Under these conditions, long-wavelength SEDs with synchrotron emission can be either more steep or more shallow than the canonical asymptotic power-law SED from a nonmagnetic wind. When nonthermal emission is present, the resultant SED shape is generally not a power law; however, the variation in the slope can change slowly with wavelength. Consequently, over a limited range of wavelengths, the SED can masquerade as approximately a power law. While most observed nonthermal long-wavelength spectra are associated with binarity, synchrotron emission can have only a mild influence on single-star SEDs, requiring finer levels of wavelength sampling for the detection of the effect.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>The results of the recently published spectroscopically complete survey of dusty star-forming galaxies detected by the South Pole Telescope over 2500 deg<jats:sup>2</jats:sup> proved to be challenging for galaxy formation models that generally underpredict the observed abundance of high-<jats:italic>z</jats:italic> galaxies. In this paper we interpret these results in the light of a physically grounded model for the evolution of spheroidal galaxies. The model accurately reproduces the measured redshift distribution of galaxies without any adjustment of the parameters. The data do not support the indications of an excess of <jats:italic>z</jats:italic> &gt; 4 dusty galaxies reported by some analyses of Herschel surveys.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Massive contact binaries contain two early-type stars that have filled their respective critical Roche lobes and share a common envelope. Their formation and evolution are still unknown. Searching for massive binaries in special evolutionary stages is required to solve this problem. Many massive binaries in the Andromeda galaxy (M31) have been found out and they provide an ideal laboratory to explore the formation of massive contact binaries and to test evolutionary models in massive binaries. By analyzing the light curves of two massive binaries containing twin components, M31V J00452011+4145037 (hereafter J004520) and M31V J00450522+4138462 (hereafter J004505), observed by Vilardell et al., we found that J004520 is a semidetached binary with a mass ratio of 0.924 and a lobe-filling secondary, while J004505 is a deep-contact binary with a mass ratio of 0.974 and a fill-out factor of 88%. Both of them evolved from originally detached binaries via case A mass transfer and are at a critical evolutionary state with the shortest possible period and the highest possible mass ratio (<jats:italic>q</jats:italic> = 1). The evolution of J004520 has passed the critical state and cannot evolve into a contact binary, while J004505 is just close to the key state. The asymmetric light curve of J004505 is explained by the presence of a hot spot on the less-massive component caused by mass transfer from the more-massive one; the same conclusion can be obtained from the <jats:italic>O</jats:italic> − <jats:italic>C</jats:italic> curve. These results support the conclusion that massive contact binaries are formed from mass transfer between the two components and only some systems can evolve into the contact stage.</jats:p>