Sazuna/UAT_keywords huggingface dataset:
Irradiated Ocean Planets Bridge Super-Earth and Sub-Neptune Populations. Small planets (∼1-3.9 ${R}_{\oplus }$ ) constitute more than half of the inventory of the 4000-plus exoplanets discovered so far. Smaller planets are sufficiently dense to be rocky, but those with radii larger than ∼1.6 ${R}_{\oplus }$ are thought to display in many cases hydrogen/helium gaseous envelopes up to ∼30% of the planetary mass. These low-mass planets are highly irradiated and the question of their origin, evolution, and possible links remains open. Here we show that close-in ocean planets affected by the greenhouse effect display hydrospheres in supercritical state, which generate inflated atmospheres without invoking the presence of large hydrogen/helium gaseous envelopes. We present a new set of mass-radius relationships for ocean planets with different compositions and different equilibrium temperatures, which are found to be well adapted to low-density sub-Neptune planets. Our model suggests that super-Earths and water-rich sub-Neptunes could belong to the same family of planets, I.e., hydrogen/helium-free planets, with differences between their interiors simply resulting from the variation in the water content.

Keywords: Planetary theory, Hydrosphere, Exoplanets, Exoplanet astronomy, Exoplanet structure, Planetary interior
On the Gamma-Ray Emission of W44 and Its Surroundings. We present the analysis of 9.7 yr Fermi-LAT data of the middle-aged supernova remnant W44 and the massive molecular gas complex that surrounds it. We derived a high-quality spectral energy distribution of gamma-radiation of the shell over three decades. The very hard spectrum below 1 GeV supports the earlier claims regarding the hadronic origin of radiation. We also confirm the presence of two extended γ-ray structures located at two opposite edges of the remnant along its major axis. Based on the high-resolution gas maps, we demonstrate that the gamma-ray structures are caused by the enhanced cosmic-ray density rather than the gradient of the gas distribution. We argue that the revealed cosmic-ray "clouds" suggest an anisotropic character of the escape of high-energy particles from the shell along the magnetic field of the remnant.

Keywords: Molecular clouds, Galactic cosmic rays, Supernova remnants, Non-thermal radiation sources, Interstellar medium, Gamma-ray astronomy, Cosmic rays
Atmospheric Escape From TOI-700 d: Venus versus Earth Analogs. The recent discovery of an Earth-sized planet (TOI-700 d) in the habitable zone of an early-type M-dwarf by the Transiting Exoplanet Survey Satellite constitutes an important advance. In this Letter, we assess the feasibility of this planet to retain an atmosphere—one of the chief ingredients for surface habitability—over long timescales by employing state-of-the-art magnetohydrodynamic models to simulate the stellar wind and the associated rates of atmospheric escape. We take two major factors into consideration, namely, the planetary atmospheric composition and magnetic field. In all cases, we determine that the atmospheric ion escape rates are potentially a few orders of magnitude higher than the inner solar system planets, but TOI-700 d is nevertheless capable of retaining a 1 bar atmosphere over gigayear timescales for certain regions of the parameter space. The simulations show that the unmagnetized TOI-700 d with a 1 bar Earth-like atmosphere could be stripped away rather quickly (&lt;1 gigayear), while the unmagnetized TOI-700 d with a 1 bar CO2-dominated atmosphere could persist for many billions of years; we find that the magnetized Earth-like case falls in between these two scenarios. We also discuss the prospects for detecting radio emission of the planet (thereby constraining its magnetic field) and discerning the presence of an atmosphere.

Keywords: Stellar winds, Astrobiology, Magnetic fields, Habitable planets, Exoplanet atmospheres, Magnetohydrodynamical simulations
Evidence for an Ancient Sea Level on Mars. Mars shares many similarities and characteristics to Earth including various geological features and planetary structure. The remarkable bimodal distribution of elevations in both planets is one of the most striking global features suggesting similar geodynamic processes of crustal differentiation on Earth and Mars. There also exists much evidence, based on geographic features resembling ancient shorelines, for the existence of an ancient Martian ocean in the northern hemisphere that covers nearly one-third of the planet's surface. However, the interpretation of some features as ancient shorelines has been thoroughly challenged, which left the existence of a primordial Martian ocean controversial. Moreover, if oceans were formerly present on Mars, there is still significant ambiguity about the volume of water with the estimations ranging over 4 orders of magnitude. Here we map the Martian sea level problem onto a percolation model that provides strong evidence that the longest isoheight line on Mars that separates the northern and southern hemispheres acts as a critical level height with divergent correlation length and plays the same role as the present mean sea level does on Earth. Our results unravel remarkable similarities between Mars and Earth, posing a testable hypothesis about the level of the ancient ocean on Mars that can be answered experimentally by the future investigations and spacecraft exploration.

Keywords: Mars
Effects of Stellar Feedback on Stellar and Gas Kinematics of Star-forming Galaxies at 0.6 &lt; z &lt; 1.0. Recent zoom-in cosmological simulations have shown that stellar feedback can flatten the inner density profile of the dark matter halo in low-mass galaxies. A correlation between the stellar/gas velocity dispersion (σstar, σgas) and the specific star formation rate (sSFR) is predicted as an observational test of the role of stellar feedback in re-shaping the dark matter density profile. In this work we test the validity of this prediction by studying a sample of star-forming galaxies at 0.6 &lt; z &lt; 1.0 from the LEGA-C survey, which provides high signal-to-noise measurements of stellar and gas kinematics. We find that a weak but significant correlation between σstar (and σgas) and sSFR indeed exists for galaxies in the lowest mass bin (M* ∼ 1010 M☉). This correlation, albeit with a ∼35% scatter, holds for different tracers of star formation, and becomes stronger with redshift. This result generally agrees with the picture that at higher redshifts star formation rate was generally higher, and galaxies at M* ≲ 1010 M☉ have not yet settled into a disk. As a consequence, they have shallower gravitational potentials more easily perturbed by stellar feedback. The observed correlation between σstar (and σgas) and sSFR supports the scenario predicted by cosmological simulations, in which feedback-driven outflows cause fluctuations in the gravitation potential that flatten the density profiles of low-mass galaxies.

Keywords: Galaxy dark matter halos, Galaxy dynamics, Galaxy kinematics, Galaxy evolution, Spectroscopy, Photometry
Compact Radio Emission from Nearby Galaxies with Mid-infrared Nuclear Outbursts. We present 5.5 GHz observations with the Very Large Array of a sample of nearby galaxies with energetic nuclear outbursts at mid-infrared (MIR) bands. These observations reach a uniform depth down to a median rms of ∼10 μJy, representing one of the most sensitive searches for radio emission associated with nuclear transients. We detect radio emission in 12 out of 16 galaxies at a level of &gt;5σ, corresponding to a detection rate of 75%. Such a high detection is remarkably different from previous similar searches in stellar tidal disruption events. The radio emission is compact and not resolved for the majority of sources on scales of ≲0"5 (&lt;0.9 kpc at z &lt; 0.1). We find that the possibility of the star formation contributing to the radio emission is low, but an active galactic nucleus (AGN) origin remains a plausible scenario, especially for sources that show evidence of AGN activity in their optical spectra. If the detections could represent radio emission associated with a nuclear transient phenomenon such as a jet or outflow, we could use the blast wave model by analogy with the gamma-ray burst afterglows to describe the evolution of radio light curves. In this context, the observations are consistent with a decelerating jet with an energy of ∼1051-52 erg viewed at 30°-60° off-axis at later times, suggesting that powerful jets may be ubiquitous among MIR-burst galaxies. Future continuous monitoring observations will be crucial to decipher the origin of radio emission through detections of potential flux and spectral evolution. Our results highlight the importance of radio observations to constrain the nature of nuclear MIR outbursts in galaxies.

Keywords: Radio jets, Surveys, Tidal disruption, Active galaxies, Dust continuum emission, Radio continuum emission
Evidence for a Past Martian Ring from the Orbital Inclination of Deimos. We numerically explore the possibility that the large orbital inclination of the Martian satellite Deimos originated in an orbital resonance with an ancient inner satellite of Mars more massive than Phobos. We find that Deimos's inclination can be reliably generated by outward evolution of a Martian satellite that is about 20 times more massive than Phobos through the 3:1 mean-motion resonance with Deimos at 3.3 Mars radii. This outward migration, in the opposite direction from tidal evolution within the synchronous radius, requires interaction with a past massive ring of Mars. Our results therefore strongly support the cyclic Martian ring-satellite hypothesis of Hesselbrock &amp; Minton. Our findings, combined with the model of Hesselbrock &amp; Minton, suggest that the age of the surface of Deimos is about 3.5-4 Gyr, and require Phobos to be significantly younger.

Keywords: Celestial mechanics, Martian satellites, Orbital resonances, N-body simulations
HAWC J2227+610 and Its Association with G106.3+2.7, a New Potential Galactic PeVatron. We present the detection of very-high-energy gamma-ray emission above 100 TeV from HAWC J2227+610 with the High-Altitude Water Cherenov Gamma-Ray Observatory (HAWC) observatory. Combining our observations with previously published results by the Very Energetic Radiation Imaging Telescope Array System (VERTIAS), we interpret the gamma-ray emission from HAWC J2227+610 as emission from protons with a lower limit in their cutoff energy of 800 TeV. The most likely source of the protons is the associated supernova remnant G106.3+2.7, making it a good candidate for a Galactic PeVatron. However, a purely leptonic origin of the observed emission cannot be excluded at this time.

Keywords: Gamma-ray observatories, Gamma-ray sources, Supernova remnants, Cosmic ray sources, Gamma-ray astronomy, Gamma-rays
A Very Young Radio-loud Magnetar. The magnetar Swift J1818.0-1607 was discovered in 2020 March when Swift detected a 9 ms hard X-ray burst and a long-lived outburst. Prompt X-ray observations revealed a spin period of 1.36 s, soon confirmed by the discovery of radio pulsations. We report here on the analysis of the Swift burst and follow-up X-ray and radio observations. The burst average luminosity was Lburst ∼ 2 × 1039 erg s-1 (at 4.8 kpc). Simultaneous observations with XMM-Newton and NuSTAR three days after the burst provided a source spectrum well fit by an absorbed blackbody ( ${N}_{{\rm{H}}}$ = (1.13 ± 0.03) × 1023 cm-2 and kT = 1.16 ± 0.03 keV) plus a power law (Γ = 0.0 ± 1.3) in the 1-20 keV band, with a luminosity of ∼8 × 1034 erg s-1, dominated by the blackbody emission. From our timing analysis, we derive a dipolar magnetic field B ∼ 7 × 1014 G, spin-down luminosity ${\dot{E}}_{\mathrm{rot}}\sim 1.4\times {10}^{36}$ erg s-1, and characteristic age of 240 yr, the shortest currently known. Archival observations led to an upper limit on the quiescent luminosity &lt;5.5 × 1033 erg s-1, lower than the value expected from magnetar cooling models at the source characteristic age. A 1 hr radio observation with the Sardinia Radio Telescope taken about 1 week after the X-ray burst detected a number of strong and short radio pulses at 1.5 GHz, in addition to regular pulsed emission; they were emitted at an average rate 0.9 min-1 and accounted for ∼50% of the total pulsed radio fluence. We conclude that Swift J1818.0-1607 is a peculiar magnetar belonging to the small, diverse group of young neutron stars with properties straddling those of rotationally and magnetically powered pulsars. Future observations will make a better estimation of the age possible by measuring the spin-down rate in quiescence.

Keywords: Neutron stars, Transient sources, Magnetars, X-ray bursts, Radio pulsars
Particle Acceleration in Kink-unstable Jets. Magnetized jets in gamma-ray bursts and active galactic nuclei are thought to be efficient accelerators of particles; however, the process responsible for the acceleration is still a matter of active debate. In this work, we study the kink instability in non-rotating force-free jets using first-principle particle-in-cell simulations. We obtain similar overall evolution of the instability as found in magnetohydrodynamics simulations. The instability first generates large-scale current sheets, which at later times break up into small-scale turbulence. Reconnection in these sheets proceeds in the strong guide field regime, which results in a formation of steep power laws in the particle spectra. Later evolution shows heating of the plasma, which is driven by small-amplitude turbulence induced by the kink instability. These two processes energize particles due to a combination of ideal and non-ideal electric fields.

Keywords: Jets, High energy astrophysics, Plasma jets, Plasma physics, Plasma astrophysics
Shouts and Murmurs: Combining Individual Gravitational-wave Sources with the Stochastic Background to Measure the History of Binary Black Hole Mergers. One of the goals of gravitational-wave astronomy is to quantify the evolution of the compact binary merger rate with redshift. The redshift distribution of black hole mergers would offer considerable information about their evolutionary history, including their progenitor formation rate, the dependence of black hole formation on stellar metallicity, and the time delay distribution between formation and merger. Efforts to measure the binary redshift distribution are currently limited, however, by the detection range of existing instruments, which can individually resolve compact binary merger events only out to $z\lesssim 1$ . We present a novel strategy with which to measure the redshift distribution of binary black hole mergers well beyond the detection range of current instruments. By synthesizing direct detections of individually resolved mergers with indirect searches for the stochastic gravitational-wave background due to unresolved distant sources, we can glean information about the peak redshift, zp, at which the binary black hole merger rate attains its maximum, even when this redshift is beyond the detection horizon. Using data from Advanced LIGO and Virgo's first and second observing runs, we employ this strategy to place joint constraints on zp and the slope α with which the binary merger rate increases at low redshifts, ruling out merger rates that grow faster than $\alpha \gtrsim 7$ and peak beyond ${z}_{p}\gtrsim 1.5$ . Looking ahead, we project that approximately one year of observation with design-sensitivity Advanced LIGO will further break remaining degeneracies, enabling a direct measurement of the peak redshift of the binary black hole merger history.

Keywords: Black holes, Compact binary stars, Gravitational wave sources, Gravitational waves, LIGO
A Serendipitous Discovery of GeV Gamma-Ray Emission from Supernova 2004dj in a Survey of Nearby Star-forming Galaxies with Fermi-LAT. The interaction between a supernova ejecta and the circumstellar medium drives a strong shock wave that accelerates particles (I.e., electrons and protons). The radio and X-ray emission observed after the supernova explosion can be interpreted as synchrotron emission from accelerated electrons. The accelerated protons are expected to produce GeV-TeV gamma-ray emission via proton-proton collisions, but the flux is usually low since only a small fraction of the supernova kinetic energy is converted into the shock energy at the very early time. The low gamma-ray flux of the nearest supernova explosion, SN 1987A, agrees with this picture. Here we report a serendipitous discovery of a fading GeV gamma-ray source in spatial coincidence with one of the nearest and brightest supernova—SN 2004dj from our gamma-ray survey of nearby star-forming galaxies with Fermi-LAT. The total gamma-ray energy released by SN 2004dj is about 6 × 1047 erg. We interpret this gamma-ray emission arising from the supernova ejecta interacting with a surrounding high-density shell, which decelerates the ejecta and converts ∼1% of the SN kinetic energy to relativistic protons.

Keywords: Gamma-ray sources, Type II supernovae, Non-thermal radiation sources
Large-scale Turbulent Driving Regulates Star Formation in High-redshift Gas-rich Galaxies. The question of what regulates star formation is a longstanding issue. To investigate this issue, we run simulations of a kiloparsec cube section of a galaxy with three kinds of stellar feedback: the formation of H II regions, the explosion of supernovae, and ultraviolet heating. We show that stellar feedback is sufficient to reduce the averaged star formation rate (SFR) to the level of the Schmidt-Kennicutt law in Milky Way-like galaxies but not in high-redshift gas-rich galaxies, suggesting that another type of support should be added. We investigate whether an external driving of the turbulence such as the one created by the large galactic scales could diminish the SFR at the observed level. Assuming that the Toomre parameter is close to 1 as suggested by the observations, we infer a typical turbulent forcing that we argue should be applied parallel to the plane of the galactic disk. When this forcing is applied in our simulations, the SFR within our simulations closely follows the Schmidt-Kennicutt relation. We found that the velocity dispersion is strongly anisotropic with the velocity dispersion alongside the galactic plane being up to 10 times larger than the perpendicular velocity.

Keywords: Galaxy physics, Galaxy dynamics, Star formation, Interstellar medium, Radiative transfer simulations, Magnetohydrodynamical simulations
Signatures of Helium Continuum in Cool Flare Loops Observed by SDO/AIA. We present an analysis of off-limb cool flare loops observed by the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) during the gradual phase of SOL2017-09-10T16:06 X8.2-class flare. In the extreme-ultraviolet (EUV) channels starting from the 335 Å one, cool loops appear as dark structures against the bright loop arcade. These dark structures were precisely coaligned (spatially and temporally) with loops observed by Swedish Solar Telescope (SST) in emission lines of hydrogen and ionized calcium. A recently published semi-empirical model of cool loops based on SST observations serves to predict the level of hydrogen and helium recombination continua. The continua were synthesized using an approximate non-LTE (I.e., departures from local thermodynamic equilibrium) approach and theoretical spectra were then transformed to AIA signals. Comparison with signals detected inside the dark loops shows that only in AIA 211 Å channel the computed level of recombination continua is consistent with observations for some models, while in all other channels that are more distant from the continua edges the synthetic continuum is far too low. In analogy with on-disk observations of flares we interpret the surplus emission as due to numerous EUV lines emitted from hot but faint loops in front of the cool ones. Finally we briefly comment on failure of the standard absorption model when used for analysis of the dark-loop brightness.

Keywords: Solar flares, Solar extreme ultraviolet emission, Solar coronal loops, Solar flare spectra, Radiative transfer
Two Major Constraints on the Inner Radii of Accretion Disks. The Stefan-Boltzmann law yields a fundamental constraint on the geometry of inner accretion disks in black hole X-ray binaries. It follows from considering the irradiating flux and the effective temperature of the inner parts of the disk, which implies that a strong quasi-thermal component with the average energy higher than that of a blackbody at the effective temperature has to be present whenever relativistic Fe K fluorescence and reflection features are observed. The apparent absence of such quasi-thermal component with the color temperature of ∼1 keV in high-luminosity hard states is not compatible with a strongly irradiated disk extending close to the innermost stable circular orbit. Instead, the disk should be either truncated at a relatively large radius or irradiated by a corona at a large height, which would reduce the effective temperature and bring it to an agreement with the data. We also study constraints on disk/corona models following from comparing the disk densities fitted in literature using variable-density reflection codes with those calculated by us from the ionization parameter, the luminosity, and the disk inner radius. We find that the fitted densities are much higher/lower in the hard/soft state of binaries, implying significant problems with the used assumptions and methods.

Keywords: Accretion, X-ray binary stars, Non-thermal radiation sources
Spectropolarimetric Properties of Swift J1818.0-1607: A 1.4 s Radio Magnetar. The soft-gamma repeater Swift J1818.0-1607 is only the fifth magnetar found to exhibit pulsed radio emission. Using the Ultra-Wideband Low receiver system of the Parkes radio telescope, we conducted a 3 hr observation of Swift J1818.0-1607. Folding the data at a rotation period of P = 1.363 s, we obtained wideband polarization profiles and flux density measurements covering radio frequencies between 704 and 4032 MHz. After measuring, and then correcting for the pulsar's rotation measure of 1442.0 ± 0.2 rad m-2, we find the radio profile is between 80% and 100% linearly polarized across the wide observing band, with a small amount of depolarization at low frequencies that we ascribe to scatter broadening. We also measure a steep spectral index of $\alpha =-{2.26}_{-0.03}^{+0.02}$ across our large frequency range, a significant deviation from the flat or inverted spectra often associated with radio-loud magnetars. The steep spectrum and temporal rise in flux density bears some resemblance to the behavior of the magnetar-like, rotation-powered pulsar PSR J1119-6127. This leads us to speculate that Swift J1818.0-1607 may represent an additional link between rotation-powered pulsars and magnetars.

Keywords: Neutron stars, Magnetars, Radio pulsars, Pulsars