adsabs/SciX_UAT_keywords huggingface dataset:
A Month of Monitoring the New Magnetar Swift J1555.2-5402 during an X-Ray Outburst

The soft gamma-ray repeater Swift J1555.2-5402 was discovered by means of a short burst detected with Swift BAT on 2021 June 3. Then, 1.6 hr after the burst, the Neutron star Interior Composition Explorer (NICER) started daily monitoring of this target for a month. The absorbed 2-10 keV flux stayed nearly constant at around 4 × 10-11 erg s-1 cm-2 during the monitoring, showing only a slight gradual decline. An absorbed blackbody with a temperature of 1.1 keV approximates the soft X-ray spectrum. A 3.86 s periodicity is detected, and the period derivative is measured to be 3.05(7) × 10-11 s s-1. The soft X-ray pulse shows a single sinusoidal shape with an rms pulsed fraction that increases as a function of energy from 15% at 1.5 keV to 39% at 7 keV. The equatorial surface magnetic field, characteristic age, and spin-down luminosity are derived under the dipole field approximation to be 3.5 × 1014 G, 2.0 kyr, and 2.1 × 1034 erg s-1, respectively. We detect 5 and 45 bursts with Swift/BAT and NICER, respectively. Based on these properties, this new source is classified as a magnetar. A hard X-ray power-law component that extends up to at least 40 keV is detected with the Nuclear Spectroscopic Telescope Array (NuSTAR). The 10-60 keV flux is ~9 × 10-12 erg s-1 cm-2 with a photon index of ~1.2. The pulsed fraction has a sharp cutoff at around 10 keV with an upper limit (≲10%) in the hard-tail band. No radio pulsations are detected during the DSN or VERA observations. The 7σ upper limits of the flux density are 0.043 and 0.026 mJy at the S and X bands, respectively.

Keywords: magnetars; magnetic fields; neutron stars; pulsars; soft gamma-ray repeaters; x-ray transient sources
Spatial Variations in the Altitude of the CH4 Homopause at Jupiter's Mid-to-high Latitudes, as Constrained from IRTF-TEXES Spectra

We present an analysis of IRTF-TEXES spectra of Jupiter's mid-to-high latitudes in order to test the hypothesis that the CH4 homopause altitude is higher in Jupiter's auroral regions compared to elsewhere on the planet. A family of photochemical models, based on Moses & Poppe (2017), were computed with a range of CH4 homopause altitudes. Adopting each model in turn, the observed TEXES spectra of H2 S(1), CH4, and CH3 emission measured on 2019 April 16 and August 20 were inverted, the vertical temperature profile was allowed to vary, and the quality of the fit to the spectra was used to discriminate between models. At latitudes equatorward of Jupiter's main auroral ovals (>62°S, <54°N, planetocentric), the observations were adequately fit assuming a homopause altitude lower than ∼360 km (above 1 bar). At 62°N, inside the main auroral oval, we derived a CH4 homopause altitude of ${461}_{-39}^{+147}$ km, whereas outside the main oval at the same latitude, a 1σ upper limit of 370 km was derived. Our interpretation is that a portion of energy from the magnetosphere is deposited as heat within the main oval, which drives vertical winds and/or higher rates of turbulence and transports CH4 and its photochemical by-products to higher altitudes. Inside the northern main auroral oval, a factor of ∼3 increase in CH3 abundance was also required to fit the spectra. This could be due to uncertainties in the photochemical modeling or an additional source of CH3 production in Jupiter's auroral regions.

Keywords: atmospheric circulation; aeronomy; jupiter; infrared astronomy; planetary atmospheres; planetary magnetospheres; planetary polar regions; high resolution spectroscopy
Connecting the Gravity Field, Moment of Inertia, and Core Properties in Jupiter through Empirical Structural Models

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 J2 and J4. 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.

Keywords: planetary interior; planetary structure; planetary cores
Discriminating Accretion States via Rotational Symmetry in Simulated Polarimetric Images of M87

In 2017 April, the Event Horizon Telescope observed the shadow of the supermassive black hole at the core of the elliptical galaxy Messier 87. While the original image was constructed from measurements of the total intensity, full polarimetric data were also collected, and linear polarimetric images are expected in the near future. We propose a modal image decomposition of the linear polarization field into basis functions with varying azimuthal dependence of the electric vector position angle. We apply this decomposition to images of ray traced general relativistic magnetohydrodynamics simulations of the Messier 87 accretion disk. For simulated images that are physically consistent with previous observations, the magnitude of the coefficient associated with rotational symmetry, β2, is a useful discriminator between accretion states. We find that at 20 μas resolution, $| {\beta }_{2}| $ is greater than 0.2 only for models of disks with horizon-scale magnetic pressures large enough to disrupt steady accretion. We also find that images with a more radially directed electric vector position angle correspond to models with higher black hole spin. Our analysis demonstrates the utility of the proposed decomposition as a diagnostic framework to improve constraints on theoretical models.

Keywords: accretion; black holes; magnetic fields; radiative transfer; very long baseline interferometry
The Chandra Deep Wide-field Survey: A New Chandra Legacy Survey in the Boötes Field. I. X-Ray Point Source Catalog, Number Counts, and Multiwavelength Counterparts

We present a new, ambitious survey performed with the Chandra X-ray Observatory of the 9.3 deg2 Boötes field of the NOAO Deep Wide-Field Survey. The wide field probes a statistically representative volume of the universe at high redshift. The Chandra Deep Wide-field Survey exploits the excellent sensitivity and angular resolution of Chandra over a wide area, combining 281 observations spanning 15 yr, for a total exposure time of 3.4 Ms, and detects 6891 X-ray point sources down to limiting fluxes of 4.7 × 10-16, 1.5 × 10-16, and 9 ×10-16 erg cm-2 s-1 in the 0.5-7, 0.5-2, and 2-7 keV bands, respectively. The robustness and reliability of the detection strategy are validated through extensive, state-of-the-art simulations of the whole field. Accurate number counts, in good agreement with previous X-ray surveys, are derived thanks to the uniquely large number of point sources detected, which resolve 65.0% ± 12.8% of the cosmic X-ray background between 0.5 and 2 keV and 81.0% ± 11.5% between 2 and 7 keV. Exploiting the wealth of multiwavelength data available on the field, we assign redshifts to ∼94% of the X-ray sources, estimate their obscuration, and derive absorption-corrected luminosities. We provide an electronic catalog containing all of the relevant quantities needed for future investigations.

Keywords: catalogs; x-ray active galactic nuclei; x-ray astronomy; active galactic nuclei; agn host galaxies
Measuring the Temperature of Starspots from Multi-filter Photometry

Using simultaneous multi-filter observations during the transit of an exoplanet around a K dwarf star, we determine the temperature of a starspot through modeling the radius and position with wavelength-dependent spot contrasts. We model the spot using the starspot modeling program STarSPot (STSP), which uses the transiting companion as a knife-edge probe of the stellar surface. The contrast of the spot, i.e., the ratio of the integrated flux of a darker spot region to the star's photosphere, is calculated for a range of filters and spot temperatures. We demonstrate this technique using simulated data of HAT-P-11, a K dwarf (T eff = 4780 K) with well-modeled starspot properties for which we obtained simultaneous multi-filter transits using Las Cumbres Observatory's MuSCAT3 instrument on the 2m telescope at Haleakala Observatory, which allows for simultaneous, multi-filter, diffuser-assisted high-precision photometry. We determine the average (i.e., a combination of penumbra and umbra) spot temperature for HAT-P-11's spot complexes is 4500 K ± 100 K using this technique. We also find for our set of filters that comparing the SDSS ${g}^{{\prime} }$ and ${i}^{{\prime} }$ filters maximizes the signal difference caused by a large spot in the transit. Thus, this technique allows for the determination of the average spot temperature using only one spot occultation in transit and can provide simultaneous information on the spot temperature and spot properties.

Keywords: starspots; stellar activity; multi-color photometry
Libration- and Precession-driven Dissipation in the Fluid Cores of the TRAPPIST-1 Planets

The seven planets orbiting TRAPPIST-1 have sizes and masses similar to Earth and mean densities that suggest that their interior structures are comprised of a fluid iron core and rocky mantle. Here we use idealized analytical models to compute estimates of the viscous dissipation in the fluid cores of the TRAPPIST-1 planets induced by mantle libration and precession. The dissipation induced by the libration at orbital periods is largest for TRAPPIST-1b, of the order of 600 MW, and decreases with orbital distance, to values of 5-500 W for TRAPPIST-1h, depending on its triaxial shape. Extrapolating these results to the larger libration amplitudes expected at longer periods, dissipation may perhaps be as high as 1 TW in TRAPPIST-1b. Orbital precession induces a misalignment between the spin axes of the fluid core and mantle of a planet, the amplitude of which depends on the resonant amplification of its free precession and free core nutation. Assuming Cassini states, we show that the dissipation from this misalignment can reach a few TW for planets e and f. Our dissipation estimates are lower bounds, as we neglect ohmic dissipation, which may dominate if the fluid cores of the TRAPPIST-1 planets sustain magnetic fields. Our results suggest that dissipation induced by precession can be of the same order as tidal dissipation for the outermost planets, may perhaps be sufficient to supply the power to a generate a magnetic field in their liquid cores, and likely played an important role in the evolution of the TRAPPIST-1 system.

Keywords: extrasolar rocky planets; libration; planetary interior; planetary cores; exoplanet dynamics
Solar Eruptions Triggered by Flux Emergence below or near a Coronal Flux Rope

Observations have shown a clear association of filament/prominence eruptions with the emergence of magnetic flux in or near filament channels. Magnetohydrodynamic (MHD) simulations have been employed to systematically study the conditions under which such eruptions occur. These simulations to date have modeled filament channels as 2D flux ropes or 3D uniformly sheared arcades. Here we present MHD simulations of flux emergence into a more realistic configuration consisting of a bipolar active region containing a line-tied 3D flux rope. We use the coronal flux-rope model of Titov et al. as the initial condition and drive our simulations by imposing boundary conditions extracted from a flux emergence simulation by Leake et al. We identify three mechanisms that determine the evolution of the system: (i) reconnection displacing footpoints of field lines overlying the coronal flux rope, (ii) changes of the ambient field due to the intrusion of new flux at the boundary, and (iii) interaction of the (axial) electric currents in the preexisting and newly emerging flux systems. The relative contributions and effects of these mechanisms depend on the properties of the preexisting and emerging flux systems. Here we focus on the location and orientation of the emerging flux relative to the coronal flux rope. Varying these parameters, we investigate under which conditions an eruption of the latter is triggered.

Keywords: solar physics; solar magnetic fields; solar magnetic flux emergence; solar coronal mass ejections
Nova-produced Common Envelope: Source of the Nonsolar Abundances and an Additional Frictional Angular Momentum Loss in Cataclysmic Variables

A substantial fraction of cataclysmic variables (CVs) reveal nonsolar abundances. A comprehensive list of CVs that includes those that have been examined for these abundances is given. Three possible sources of these nonsolar abundances on the secondary are accretion during the red giant common envelope phase, an evolved main-sequence secondary, and nova-processed material. Use of the secondary's cross section just on the escaping nova material to change the abundances of its convective region has been the killing objection for considering nova-processed material. The key element, ignored in other studies, is that a thermonuclear runaway on a white dwarf causes a strong propagating shock wave that not only ejects material but also produces a large amount of nonejected material that forms a common envelope. This nova-produced common envelope contains a large amount of nonsolar material. We demonstrate that the secondary has the capacity and time to reaccrete enough of this material to acquire a significant nonsolar convective region. This same envelope interacting with the binary will produce a frictional angular momentum loss, which can be the consequential angular momentum loss needed for the average CV white dwarf mass, the white dwarf mass accretion rates, the period minimum, the orbital period distribution, and the space density of CV problems. This interaction will decrease the orbital period, which can cause the recently observed sudden period decreases across nova eruptions. A simple, rapid evolutionary model of the secondary that includes the swept-up nova-produced material and the increasing convective region is developed and applied to individual CVs.

Keywords: binary stars; cataclysmic variable stars; classical novae
Magnetic Cloud and Sheath in the Ground-level Enhancement Event of 2000 July 14. II. Effects on the Forbush Decrease

Forbush decreases (Fds) in galactic cosmic ray intensity are related to interplanetary coronal mass ejections (ICMEs). The parallel diffusion of particles is reduced because the magnetic turbulence level in the sheath region bounded by the ICME's leading edge and shock is high. In the sheath and magnetic cloud (MC) energetic particles would feel an enhanced magnetic focusing effect caused by the strong inhomogeneity of the background magnetic field. Therefore, particles would be partially blocked in the sheath-MC structure. Here, we study two-step Fds by considering the magnetic turbulence and background magnetic field in the sheath-MC structure with diffusion coefficients calculated using theoretical models, to reproduce the Fd associated with the ground-level enhancement event on 2000 July 14 by solving the focused transport equation. The sheath and MC are set to spherical caps that are portions of spherical shells with enhanced background magnetic field. The magnetic turbulence levels in the sheath and MC are set to higher and lower than those in ambient solar wind, respectively. In general, the simulation result conforms to the main characteristics of the Fd observation, such as the pre-increase precursor, amplitude, total recovery time, and two-step decrease of the flux at the arrival of the sheath and MC. It is suggested that the sheath plays an important role in the amplitude of the Fd while the MC contributes to the formation of the second-step decrease and prolonged recovery time. It is also inferred that both magnetic turbulence and background magnetic field in the sheath-MC structure are important for reproducing the observed two-step Fd.

Keywords: forbush effect; galactic cosmic rays; solar coronal mass ejections; space weather
Constraining Annihilating Dark Matter by the Radio Continuum Spectrum of the Large Magellanic Cloud

Recent radio observations have obtained stringent constraints for annihilating dark matter. In this article, we use the radio continuum spectral data of the Large Magellanic Cloud to analyze the dark matter annihilation signals. We have discovered a slightly positive signal of dark matter annihilation with a 1.5σ statistical significance. The overall best-fit dark matter mass is m DM ≈ 90 GeV, annihilating via the $b\bar{b}$ channel. We have also constrained the 3σ lower limits of dark matter mass with the standard thermal dark matter annihilation cross section for the e + e -, μ + μ -, τ + τ -, and $b\bar{b}$ channels.

Keywords: cold dark matter; dwarf galaxies; particle astrophysics
Diffusive Shock Acceleration at Oblique High Mach Number Shocks

The current paradigm of cosmic-ray (CR) origin states that the greater part of galactic CRs is produced by supernova remnants. The interaction of supernova ejecta with the interstellar medium after a supernova's explosions results in shocks responsible for CR acceleration via diffusive shock acceleration (DSA). We use particle-in-cell (PIC) simulations and a combined PIC-magnetohydrodynamic (PIC-MHD) technique to investigate whether DSA can occur in oblique high Mach number shocks. Using the PIC method, we follow the formation of the shock and determine the fraction of the particles that gets involved in DSA. With this result, we use PIC-MHD simulations to model the large-scale structure of the plasma and the magnetic field surrounding the shock and find out whether or not the reflected particles can generate upstream turbulence and trigger DSA. We find that the feasibility of this process in oblique shocks depends strongly on the Alfvénic Mach number, and the DSA process is more likely to be triggered at high Mach number shocks.

Keywords: shocks; supernova remnants; plasma astrophysics; interstellar medium
Gravity and Rotation Drag the Magnetic Field in High-mass Star Formation

The formation of hot stars out of the cold interstellar medium lies at the heart of astrophysical research. Understanding the importance of magnetic fields during star formation remains a major challenge. With the advent of the Atacama Large Millimeter Array, the potential to study magnetic fields by polarization observations has tremendously progressed. However, the major question remains how much magnetic fields shape the star formation process or whether gravity is largely dominating. Here, we show that for the high-mass star-forming region G327.3 the magnetic field morphology appears to be dominantly shaped by the gravitational contraction of the central massive gas core where the star formation proceeds. We find that in the outer parts of the region, the magnetic field is directed toward the gravitational center of the region. Filamentary structures feeding the central core exhibit U-shaped magnetic field morphologies directed toward the gravitational center as well, again showing the gravitational drag toward the center. The inner part then shows rotational signatures, potentially associated with an embedded disk, and there the magnetic field morphology appears to be rotationally dominated. Hence, our results demonstrate that for this region gravity and rotation are dominating the dynamics and shaping the magnetic field morphology.

Keywords: star formation; interstellar magnetic fields; interstellar medium; collapsing clouds; dynamical evolution; interstellar dynamics
Exploring the Chemical Evolution of Nitrogen and Oxygen in Local Star-forming Galaxies

We utilize a sample of 45 local star-forming galaxies (z < 0.18) from the COS Legacy Archive Spectroscopic SurveY (CLASSY) to analyze the N/O versus O/H relationship. Nitrogen and oxygen are ejected into the interstellar medium at different timescales by intermediate-mass and massive stars. Therefore, the N/O abundance ratio with respect to the gas-phase metallicity (O/H) is a powerful tool to improve our interpretation on galaxy formation and evolution. In order to analyze such a relation, we derive the the electron density and temperature for the whole sample, allowing for accurate determinations of N/O and the metallicity. We compare our results with an additional sample of dwarf star-forming galaxies and extragalactic H II regions. We also analyze the N/O ratio with the stellar mass and star formation rate.

Keywords: dwarf galaxies; galaxy chemical evolution; emission line galaxies; galaxy spectroscopy
High-resolution Spectra and Biosignatures of Earth-like Planets Transiting White Dwarfs

With the first observations of debris disks as well as proposed planets around white dwarfs (WDs), the question of how rocky planets around such stellar remnants can be characterized and probed for signs of life becomes tangible. WDs are similar in size to Earth and have relatively stable environments for billions of years after initial cooling, making them intriguing targets for exoplanet searches and terrestrial planet atmospheric characterization. Their small size and the resulting large planet transit signal allows observations with next-generation telescopes to probe the atmosphere of such rocky planets, if they exist. We model high-resolution transmission spectra for planets orbiting WDs as they cool from 6000 to 4000 K, for (I) planets receiving equivalent irradiation to modern Earth, and (II) planets orbiting at the distance around a cooling WD that allows for the longest continuous time in the habitable zone. All high-resolution transmission spectra are publicly available online and can be used as a tool to prepare and interpret upcoming observations with the James Webb Space Telescope, the Extremely Large Telescopes, as well as mission concepts like Origins, HabEx, and LUVOIR.

Keywords: white dwarf stars; habitable zone; habitable planets; stellar evolution; exoplanet atmospheres; astrobiology; biosignatures; transmission spectroscopy; extrasolar rocky planets
The Extinction and Distance of the MBM Molecular Clouds at High Galactic Latitude

Based on the accurate color excess {E}_{{{\rm{G}}}_{\mathrm{BP}},{{\rm{G}}}_{\mathrm{RP}}}$ of more than 4 million stars and the {E}_{\mathrm{NUV},{{\rm{G}}}_{\mathrm{BP}}}$ of more than 1 million stars from Sun et al., the distance and extinction of the molecular clouds (MCs) in the Magnani-Blitz-Mundy catalog at ∣b∣ > 20° are studied in combination with the distance measurement of Gaia/EDR3. The distance, as well as the color excess, is determined for 66 MCs. The color excess ratio {E}_{{\rm{N}}{\rm{U}}{\rm{V}},{{\rm{G}}}_{{\rm{B}}{\rm{P}}}}/{E}_{{{\rm{G}}}_{{\rm{B}}{\rm{P}}},{{\rm{G}}}_{{\rm{R}}{\rm{P}}}}$ is derived for 39 of them, which is obviously larger and implies more small particles at smaller extinction. In addition, the scale height of the dust disk is found to be about 100 pc and becomes large at the anticenter direction due to the disk flaring.

Keywords: interstellar dust; ultraviolet extinction; high latitude field; molecular clouds