adsabs/SciX_UAT_keywords huggingface dataset:
Limits on Precursor and Afterglow Radio Emission from a Fast Radio Burst in a Star-forming Galaxy

We present a new fast radio burst (FRB) at 920 MHz discovered during commensal observations conducted with the Australian Square Kilometre Array Pathfinder (ASKAP) as part of the Commensal Real-time ASKAP Fast Transients (CRAFT) survey. FRB 191001 was detected at a dispersion measure (DM) of 506.92(4) pc cm-3 and its measured fluence of 143(15) Jy ms is the highest of the bursts localized to host galaxies by ASKAP to date. The subarcsecond localization of the FRB provided by ASKAP reveals that the burst originated in the outskirts of a highly star-forming spiral in a galaxy pair at redshift z = 0.2340(1). Radio observations show no evidence for a compact persistent radio source associated with the FRB 191001 above a flux density of 15 μJy. However, we detect diffuse synchrotron radio emission from the disk of the host galaxy that we ascribe to ongoing star formation. FRB 191001 was also detected as an image-plane transient in a single 10 s snapshot with a flux density of 19.3 mJy in the low-time-resolution visibilities obtained simultaneously with CRAFT data. The commensal observation facilitated a search for repeating and slowly varying radio emissions 8 hr before and 1 hr after the burst. We found no variable radio emission on timescales ranging from 1 ms to 1.4 hr. We report our upper limits and briefly review FRB progenitor theories in the literature that predict radio afterglows. Our data are still only weakly constraining of any afterglows at the redshift of the FRB. Future commensal observations of more nearby and bright FRBs will potentially provide stronger constraints.

Keywords: radio continuum emission; interferometers; polarimetry; starburst galaxies
Evaluating Atmospheric and Surface Drivers for O2 Variations at Gale Crater as Observed by MSL SAM

We explore and evaluate various processes that could drive the variations in the volume mixing ratio (VMR) of atmospheric O2 observed by the quadrupole mass spectrometer (QMS) of the Sample Analysis at Mars (SAM) instrument suite on the Mars Science Laboratory (MSL) Curiosity rover. First reported by Trainer et al. (2019), these ∼20% variations in the O2 VMR on a seasonal timescale over Mars Years 31–34, in excess of circulation and transport effects driven by the seasonal condensation and sublimation of CO2 at the poles, are significantly shorter than the modeled O2 photochemical lifetime. While there remains significant uncertainty about the various processes we investigated (atmospheric photochemistry, surface oxychlorines and H2O2, dissolution from brines, and airborne dust), the most plausible driver is surface oxychlorines, exchanging O2 with the atmosphere through decomposition by solar ultraviolet and regeneration via O3. A decrease in O3 from increased atmospheric H2O would reduce the removal rate of O2 from the atmosphere to form oxychlorines at the surface. This is consistent with the tentative observation that increases in O2 are associated with increases in water vapor. A lack of correlation with the local surface geology along Curiosity's traverse within Gale crater, the nonuniqueness of the relevant processes to Gale crater, and the short mixing timescales of the atmosphere all suggest that the O2 variations are a regional, or even global, phenomenon. Nonetheless, further laboratory experiments and modeling are required to accurately scale the laboratory-measured rates to Martian conditions and to fully elucidate the driving mechanisms.

Keywords: mars; atmospheric composition; surface composition; surface processes; atmospheric variability
Thermal Oxidation Reaction between NH3 and O3: Low-temperature Formation of an {\mathrm{NH}}_{4}(+) -bearing Salt

NH3 has long been predicted to be an important component of outer solar system bodies, yet detection of this compound suggests a low abundance or absence on many objects where it would be expected. Here, we demonstrate that a thermally driven oxidation reaction between ammonia (NH3) and ozone (O3) in a H2O + NH3 + O3 mixture may contribute to the low abundance of NH3 on some of these objects, as this reaction efficiently occurs at temperatures as low as 70 K. We determined the overall activation energy for this reaction to be 17 ± 2 kJ mol‑1, which is consistent with other chemical systems that react at cryogenic temperatures. The loss of these two compounds coincides with the formation of ${\mathrm{NH}}_{4}^{+}$ and ${\mathrm{NO}}_{3}^{-}$ at low temperatures, both of which are observable with infrared spectroscopy. Warming our H2O + NH3 + O3 mixtures through sublimation, we find a number of higher-temperature phases, such as ammonia hemihydrate, nitric acid, and ammonium nitrate (NH4NO3). The most stable of these is NH4NO3, which remains on the substrate until temperatures near 270 K. The salt product within this sample contains near-infrared spectral features between 2.0 and 2.22 μm, which is a spectral region of interest for several outer solar system objects, including the Uranian satellites Miranda, Ariel and Umbriel, and Pluto's satellite Charon.

Keywords: astrochemistry; laboratory astrophysics; natural satellites (solar system); surface ices
A Coronal Mass Ejection Impacting Parker Solar Probe at 14 Solar Radii

The relationship between CME properties in the corona and their interplanetary counterparts is not well understood. Until recently, a wide spatial gap existed between the two regions, which prevented us from disentangling the spatial and temporal evolution of CMEs. NASA's Parker Solar Probe (PSP) has imaged multiple CMEs since its launch in 2018, but these events either intercepted the spacecraft far from the corona or completely missed it. Here we describe one of the first CMEs observed simultaneously by remote sensing and in situ instruments, and compare the corresponding measured properties, such as orientation, cross section diameter, density, and speed. The CME encounter occurred on 2022 June 2, while PSP was around 14 solar radii from the Sun center. We reconstruct the CME with forward modeling and determine its morphology and kinematics. The reconstruction suggests that PSP misses the CME apex but encounters its flank. The encounter time matches the period when the PSP in situ measurements indicate the passage of a CME. We also reconstruct the flux rope diameter and orientation using the in situ magnetic field measurements. The results are consistent with the CME reconstruction from imaging data. The close agreement between remote sensing and in situ analyses suggests that discrepancies found in past studies are more likely associated with the CME temporal evolution. We also find that the magnetic field of the CME flank extrapolated to 1 au is well below the average solar wind background and likely indistinguishable from it. This point could explain past events where the CMEs' interplanetary counterparts were not identified.

Keywords: solar corona; solar coronal transients; solar wind; interplanetary magnetic fields; space plasmas; solar coronal mass ejections; interplanetary medium
X-Ray, Near-ultraviolet, and Optical Flares Produced by Colliding Magnetospheres in the Young High-eccentricity Binary DQ Tau

DQ Tau is a unique young high-eccentricity binary system that exhibits regular magnetic reconnection flares and pulsed accretion near periastron. We conducted NuSTAR, Swift, and Chandra observations during the 2022 July 30 periastron to characterize X-ray, near-ultraviolet (NUV), and optical flaring emissions. Our findings confirm the presence of X-ray superflares accompanied by substantial NUV and optical flares, consistent with previous discoveries of periastron flares in 2010 and 2021. These observations, supported by new evidence, strongly establish the magnetosphere collision mechanism as the primary driver of magnetic energy release during DQ Tau's periastron flares. The energetics of the observed X-ray superflares remain consistent across the three periastra, indicating recurring energy sources during each passage, surpassing the capabilities of single stars. The observed flaring across multiple bands supports the Adams et al. model for magnetosphere interaction in eccentric binaries. Evidence from modeling and past and current observations suggests that both the millimeter/X-ray periastron flares and, tentatively, the magnetic-reconnection-related components of the optical/NUV emissions conform to the classical solar/stellar nonthermal thick-target model, except for the distinctive magnetic energy source. However, our NuSTAR observations suffered from high background levels, hindering the detection of anticipated nonthermal hard X-rays. Furthermore, we report the serendipitous discovery of X-ray superflares occurring away from periastron, potentially associated with interacting magnetospheres. The current study is part of a broader multiwavelength campaign, which plans to investigate the influence of DQ Tau's stellar radiation on gas-phase ion chemistry within its circumbinary disk.

Keywords: pre-main sequence stars; spectroscopic binary stars; x-ray stars; stellar magnetic fields; optical flares; ultraviolet transient sources; stellar x-ray flares; solar x-ray flares; solar flares; stellar flares; protoplanetary disks
The Inner Disk of RY Tau: Evidence of Stellar Occultation by the Disk Atmosphere at the Sublimation Rim from K-band Continuum Interferometry

We present models of the inner region of the circumstellar disk of RY Tau that aim to explain our near-infrared (K-band: 2.1 μm) interferometric observations, while remaining consistent with the optical to near-infrared portions of the spectral energy distribution. Our submilliarcsecond-resolution CHARA Array observations are supplemented with shorter baseline, archival data from PTI, KI, and VLTI/GRAVITY and modeled using an axisymmetric Monte Carlo radiative transfer code. The K-band visibilities are well fit by models incorporating a central star illuminating a disk with an inner edge shaped by dust sublimation at 0.210 ± 0.005 au, assuming a viewing geometry adopted from millimeter interferometry (65° inclined with a disk major axis position angle of 23°). This sublimation radius is consistent with that expected of silicate grains with a maximum size of 0.36-0.40 μm contributing to the opacity, and is an order of magnitude further from the star than the theoretical magnetospheric truncation radius. The visibilities on the longest baselines probed by CHARA indicate that we lack a clear line of sight to the stellar photosphere. Instead, our analysis shows that the central star is occulted by the disk surface layers close to the sublimation rim. While we do not see direct evidence of temporal variability in our multiepoch CHARA observations, we suggest the aperiodic photometric variability of RY Tau is likely related temporal and/or azimuthal variations in the structure of the disk surface layers.

Keywords: young stellar objects; optical interferometry; herbig ae/be stars; t tauri stars; near infrared astronomy; star formation; circumstellar disks; radiative transfer; infrared excess
Standing Kink Waves in Sigmoid Solar Coronal Loops: Implications for Coronal Seismology

Using full three-dimensional magnetohydrodynamic numerical simulations, we study the effects of magnetic field sigmoidity or helicity on the properties of the fundamental kink oscillation of solar coronal loops. Our model consists of a single denser coronal loop, embedded in a plasma with dipolar force-free magnetic field with a constant α-parameter. For the loop with no sigmoidity, we find that the numerically determined oscillation period of the fundamental kink mode matches the theoretical period calculated using WKB theory. In contrast, with increasing sigmoidity of the loop, the actual period is increasingly smaller than the one estimated by WKB theory. Translated through coronal seismology, increasing sigmoidity results in magnetic field estimates that are increasingly shifting toward higher values, and even surpassing the average value for the highest α value considered. Nevertheless, the estimated range of the coronal magnetic field value lies within the minimal/maximal limits, proving the robustness coronal seismology. We propose that the discrepancy in the estimations of the absolute value of the force-free magnetic field could be exploited seismologically to determine the free energy of coronal loops, if averages of the internal magnetic field and density can be reliably estimated by other methods.

Keywords: magnetohydrodynamics; solar coronal seismology; magnetohydrodynamical simulations
The Spectral Energy Distributions and Bolometric Luminosities of Local AGN: Study of the Complete 12 μm AGN Sample

We measure the bolometric luminosity of a complete and unbiased 12 μm-selected sample of active galactic nuclei (AGN) in the local Universe. For each galaxy, we used a 10-band radio-to-X-ray spectral energy distribution (SED) to isolate the genuine AGN continuum in each band, including subarcsecond measurements where available, and correcting those contaminated by the host galaxy. We derive the median SED of Seyfert type 1 AGN, Seyferts with hidden broad lines (HBLs), Seyferts of type 2, and LINER nuclei in our sample. The median Seyfert 1 SED shows the characteristic blue bump feature in the UV, but nevertheless, the largest contribution to the bolometric luminosity comes from the IR and X-ray continua. The median SEDs of both HBL and type 2 AGN are affected by starlight contamination in the optical/UV. The median SED of HBL AGN is consistent with that of Seyfert 1s, when an extinction of A V ∼ 1.2 mag is applied. The comprehensive SEDs allowed us to measure accurate bolometric luminosities and derive robust bolometric corrections for the different tracers. The 12 μm and K-band nuclear luminosities have good linear correlations with the bolometric luminosity, similar to those in the X-rays. We derive bolometric corrections for either continuum bands (K band, 12 μm, 2–10 keV, and 14–195 keV) or narrow emission lines (mid-IR high-ionization lines of [O IV] and [Ne V] and optical [O III] 5007 Å) as well as for combinations of IR continuum and line emission. A combination of continuum plus line emission accurately predicts the bolometric luminosity up to quasar luminosities (∼1046 erg s‑1).

Keywords: active galactic nuclei; agn host galaxies; seyfert galaxies; infrared photometry; infrared spectroscopy; ultraviolet photometry; x-ray active galactic nuclei
Terminator Double Layer Explorer (TerDLE): Examining the Near-Moon Lunar Wake

As the solar wind flows by the Moon, an antisunward-directed low-density wake forms as the plasma expands to fill in the trailing void in the plasma flow. Analytical modeling and modern plasma simulations suggest that plasma quasi-neutrality could possibly be broken close to the terminator obstruction as solar wind electrons expand into the wake ahead of the ions, leading to the formation of a standing (time-stationary) double layer. The objective of the Terminator Double Layer Explorer is to extend the fundamental understanding of the plasma expansion into the trailing near-vacuum wake region by (1) identifying any plasma expansion density anomalies at low altitudes near the terminator wake initiation region, (2) assessing the highly variable solar wind's effect on the low-altitude wake region, and (3) determining if plasma neutrality is maintained or lost during passages through the low-altitude expansion region. The mission concept uses a propulsion-driven CubeSat with ion spectrometer and plasma wave system in elliptical orbit about the Moon with periselene near the terminator. Over the course of the mission, the periselene decreases, placing the CubeSat ever closer to the terminator wake initiation location and the possible nonneutral region.

Keywords: lunar science; plasma physics; space plasmas
Correlating High-energy IceCube Neutrinos with 5BZCAT Blazars and RFC Sources

We investigate the possibility that blazars in the Roma-BZCAT Multifrequency Catalogue of Blazars (5BZCAT) are sources of the high-energy astrophysical neutrinos detected by the IceCube Neutrino Observatory, as recently suggested by Buson et al. Although we can reproduce their ~4.5σ result, which applies to 7 yr of neutrino data in the southern sky, we find no significant correlation with 5BZCAT sources when extending the search to the northern sky, where IceCube is most sensitive to astrophysical signals. To further test this scenario, we use a larger sample consisting of 10 yr of neutrino data recently released by the IceCube Collaboration, this time finding no significant correlation in neither the southern nor the northern sky. These results suggest that the strong correlation reported by Buson et al. using 5BZCAT could be due to a statistical fluctuation and possibly the spatial and flux nonuniformities in the blazar sample. We perform some additional correlation tests using the more uniform, flux-limited, and blazar-dominated Radio Fundamental Catalogue and find a ~3.2σ equivalent p-value when correlating it with the 7 yr southern neutrino sky. However, this correlation disappears completely when extending the analysis to the northern sky and when analyzing 10 yr of all-sky neutrino data. Our findings support a scenario where the contribution of the whole blazar class to the IceCube signal is relevant but not dominant, in agreement with most previous studies.

Keywords: neutrino astronomy; blazars; high energy astrophysics; neutrino telescopes; active galactic nuclei; cosmic ray astronomy; radio source catalogs
Elemental Abundances in M31: A Comparative Analysis of Alpha and Iron Element Abundances in the the Outer Disk, Giant Stellar Stream, and Inner Halo of M31

We measured [Fe/H] and [α/Fe] using spectral synthesis of low-resolution stellar spectroscopy for 70 individual red-giant-branch stars across four fields spanning the outer disk, Giant Stellar Stream (GSS), and inner halo of M31. Fields at M31-centric projected distances of 23 kpc in the halo, 12 kpc in the halo, 22 kpc in the GSS, and 26 kpc in the outer disk are α-enhanced, with $\langle $ [α/Fe] $\rangle $ = 0.43, 0.50, 0.41, and 0.58, respectively. The 23 and 12 kpc halo fields are relatively metal-poor, with $\langle $ [Fe/H] $\rangle $ = -1.54 and -1.30, whereas the 22 kpc GSS and 26 kpc outer disk fields are relatively metal-rich with $\langle $ [Fe/H] $\rangle $ = -0.84 and -0.92, respectively. For fields with substructure, we separated the stellar populations into kinematically hot stellar halo components and kinematically cold components. We did not find any evidence of a radial [α/Fe] gradient along the high surface brightness core of the GSS between ∼17 and 22 kpc. However, we found tentative suggestions of a negative radial [α/Fe] gradient in the stellar halo, which may indicate that different progenitor(s) or formation mechanisms contributed to the build up of the inner versus outer halo. Additionally, the [α/Fe] distribution of the metal-rich ([Fe/H] > -1.5), smooth inner stellar halo (rproj ≲ 26 kpc) is inconsistent with having formed from the disruption of a progenitor(s) similar to present-day M31 satellite galaxies. The 26 kpc outer disk is most likely associated with the extended disk of M31, where its high α-enhancement provides support for an episode of rapid star formation in M31's disk possibly induced by a major merger.

Keywords: andromeda galaxy; stellar abundances; galaxy stellar halos; local group; galaxy stellar disks; galaxy formation
The Influence of Metallicity on the Leavitt Law from Geometrical Distances of Milky Way and Magellanic Cloud Cepheids

The Cepheid period-luminosity (PL) relation is the key tool for measuring astronomical distances and for establishing the extragalactic distance scale. In particular, the local value of the Hubble constant (H0) strongly depends on Cepheid distance measurements. The recent Gaia Data Releases and other parallax measurements from the Hubble Space Telescope (HST) already enabled us to improve the accuracy of the slope (α) and intercept (β) of the PL relation. However, the dependence of this law on metallicity is still largely debated. In this paper, we combine three samples of Cepheids in the Milky Way (MW), the Large Magellanic Cloud (LMC), and the Small Magellanic Cloud (SMC) in order to derive the metallicity term (hereafter γ) of the PL relation. The recent publication of extremely precise LMC and SMC distances based on late-type detached eclipsing binary systems provides a solid anchor for the Magellanic Clouds. In the MW, we adopt Cepheid parallaxes from the early third Gaia Data Release. We derive the metallicity effect in V, I, J, H, KS, WVI, and WJK. In the KS band we report a metallicity effect of -0.221 ± 0.051 mag dex-1, the negative sign meaning that more metal-rich Cepheids are intrinsically brighter than their more metal-poor counterparts of the same pulsation period.

Keywords: cepheid distance; parallax; metallicity; magellanic clouds; milky way galaxy
Shocks and Photoionization of the Inner 650 au Jet of the Interacting Binary Star R Aquarii from Multiwavelength Hubble Space Telescope Observations

Astrophysical jets are present in a range of environments, including young stellar objects, X-ray binaries, and active galactic nuclei, but their formation is still not fully understood. As one of the nearest symbiotic binary stars, R Aquarii (D ~ 220 pc) offers a unique opportunity to study the inner region within ~600 au of the jet source, which is particularly crucial to our understanding of nonrelativistic jet formation and origin. We present high-angular resolution UV and optical imaging from the Hubble Space Telescope in six emission-line regions of the inner jet. Using these observations to obtain a range of representative line ratios for our system and kinematic data derived from a comparison with previous studies, we model the shocked gas in order to determine the relative roles of shock heating and photoionization in the R Aquarii system. We find that our shock models suggest that a nonzero magnetic field is needed to describe the measured line ratios. We also find that the Mg II λλ2795,2802 intensities are overpredicted by our models for most of the jet regions, perhaps because of depletion onto grains or to opacity in these resonance lines.

Keywords: stellar winds; symbiotic binary stars; stellar jets; shocks; mira variable stars; interacting binary stars
Radio Counterpart Candidates to Unassociated 4FGL-DR2 Sources

For the duration of the Fermi Gamma-Ray Space Telescope's mission, approximately one-third of the point sources detected have been noted as "unassociated," meaning that they seem to have no known counterpart at any other wavelength/frequency. This mysterious part of the gamma-ray sky is perhaps one of the largest unknowns in current astronomical pursuits and as such has been probed extensively by various techniques at various frequencies. Radio frequencies have been perhaps one of the most fruitful, producing a large fraction of the identified and associated active galactic nuclei and pulsars noted in each update of the point-source catalogs. Here we present a catalog of 7432 radio counterpart candidates for unassociated gamma-ray fields in the Second Data Release of the Fourth Fermi Point Source Catalog (4FGL-DR2). A description of the catalog and source types is provided followed by a discussion that demonstrates how the results of this work will aid new associations and identifications. As part of this work, we also present a first catalog derived from "quicklook" images of the Very Large Array Sky Survey.

Keywords: high energy astrophysics; surveys; radio source catalogs; spectral index; radio astronomy; active galaxies; gamma-ray astronomy; radio continuum emission