adsabs/SciX_UAT_keywords huggingface dataset:
Compositional Mapping of Europa Using MCMC Modeling of Near-IR VLT/SPHERE and Galileo/NIMS Observations

We present maps of surface composition of Europa's anti-Jovian hemisphere acquired using high spatial resolution IFU multispectral data from the SPHERE instrument on the Very Large Telescope (0.95-1.65 μm) and the NIMS instrument on the Galileo orbiter (0.7-5.2 μm). Spectral modeling was performed using a Markov Chain Monte Carlo method to estimate endmember abundances and to quantify their associated uncertainties. Modeling results support the leading-trailing hemisphere difference in hydrated sulfuric acid abundances caused by exogenic plasma bombardment. Water-ice grains are found to be in the 100 μm-1 mm range, with larger grains present on the trailing hemisphere, consistent with radiation-driven sputtering destroying smaller grains. Modeling best estimates suggest a mixture of sulfate and chlorinated salts, although uncertainties derived from the MCMC modeling suggest that it is difficult to confidently detect individual salt abundances with low spectral resolution spectra from SPHERE and NIMS. The high spatial resolution offered by SPHERE allows the small-scale spatial distribution (<150 km) of potential species to be mapped, including ground-based detection of lineae and impact features. This could be used in combination with other higher spectral resolution observations to confirm the presence of these species.

Keywords: europa; near infrared astronomy; very large telescope
Jitter Radiation as an Alternative Mechanism for the Nonthermal X-Ray Emission of Cassiopeia A

Synchrotron radiation from relativistic electrons is usually invoked as responsible for the nonthermal emission observed in supernova remnants. Diffusive shock acceleration is the most popular mechanism to explain the process of particles acceleration and within its framework a crucial role is played by the turbulent magnetic field. However, the standard models commonly used to fit X-ray synchrotron emission do not take into account the effects of turbulence in the shape of the resulting photon spectra. An alternative mechanism that properly includes such effects is the jitter radiation, which provides for an additional power law beyond the classical synchrotron cutoff. We fitted a jitter spectral model to Chandra, NuSTAR, SWIFT/BAT, and INTEGRAL/ISGRI spectra of Cassiopeia A (Cas A) and found that it describes the X-ray soft-to-hard range better than any of the standard cutoff models. The jitter radiation allows us to measure the index of the magnetic turbulence spectrum ν B and the minimum scale of the turbulence ${\lambda }_{\min }$ across several regions of Cas A, with best-fit values ν B ~ 2 - 2.4 and ${\lambda }_{\min }\lesssim 100$ km.

Keywords: high-energy cosmic radiation; galactic cosmic rays; x-ray astronomy; supernova remnants; particle astrophysics; shocks; interstellar synchrotron emission; x-ray observatories
Deep H I Mapping of Stephan's Quintet and Its Neighborhood

We carried out deep mapping observations of the atomic hydrogen (H I) 21 cm line emission in a field centered on the famous galaxy group Stephan's Quintet (SQ), using the Five-hundred-meter Aperture Spherical Telescope (FAST) equipped with a 19-beam receiver. The final data cube reaches an H I column density sensitivity of 5σ = 2.1 × 1017 cm-2 per 20 km s-1 channel with an angular resolution of 4.'0. The discovery of a large diffuse feature of the H I emission in the outskirts of the intragroup medium of SQ was reported in a previous paper (Xu et al.). Here we present a new study of the total H I emission of SQ and the detection of several neighboring galaxies, exploiting the high sensitivity and the large sky coverage of the FAST observations. A total H I mass of M H I = 3.48 ± 0.35 × 1010 M ☉ is found for SQ, which is significantly higher than previous measurements in the literature. This indicates that, contrary to earlier claims, SQ is not H I deficient. The excessive H I gas is mainly found in the velocity ranges of 6200-6400 km s-1 and 6800-7000 km s-1, which were undetected in previous observations that are less sensitive than ours. Our results suggest that the "missing H I" in compact groups may be hidden in the low-density diffuse neutral gas instead of in the ionized gas.

Keywords: hickson compact group; galaxy groups; h i line emission
Prompt Detection of Fast Optical Bursts with the Vera C. Rubin Observatory

The transient optical sky has remained largely unexplored on very short timescales. While there have been some experiments searching for optical transients from minutes to years, none have had the capability to distinguish millisecond fast optical bursts (FOBs). Such very fast transients could be the optical counterparts of fast radio bursts, the prompt emission from γ-ray bursts, or other previously unknown phenomena. Here, we investigate a novel approach to the serendipitous detection of FOBs, which relies on searching for anomalous spatial images. In particular, due to their short duration, the seeing-distorted images of FOBs should look characteristically different than those of steady sources in a standard optical exposure of finite duration. We apply this idea to simulated observations with the Vera C. Rubin Observatory, produced by tracing individual photons through a turbulent atmosphere, and down through the optics and camera of the Rubin telescope. We compare these simulated images to steady-source star simulations in 15 s integrations, the nominal Rubin exposure time. We report the classification accuracy results of a neural network classifier for distinguishing FOBs from steady sources. From this classifier, we derive constraints in duration-intensity parameter space for unambiguously identifying FOBs in Rubin observations. We conclude with estimates of the total number of detections of FOB counterparts to FRBs expected during the 10 yr Rubin Legacy Survey of Space and Time.

Keywords: optical bursts; burst astrophysics; radio transient sources; high energy astrophysics; transient sources
A Radio Galaxy Gravitational Lens in the COSMOS-Web Survey

COSMOS 5914+1219 is a radio galaxy that is gravitationally lensing a background star-forming galaxy. We use a total of eight Hubble Space Telescope and JWST images to model the radio source host galaxy as a bulge plus disk system and fit the photometry from the optical through mid-infrared. We find best-fitting photometric redshifts of ≈1.65 for the radio galaxy and ≈4 for the lensed galaxy. We confirm a high stellar mass for the lens of 3.3 ± 0.2 × 1011 M ⊙ compared to a mass enclosed by the Einstein Ring of 1.6 ± 0.1 × 1012 M ⊙ and a star formation rate (SFR) of 340 ± 150 M ⊙ yr‑1. For the lensed galaxy, we estimate a stellar mass of 9.9 ± 1.7 M ⊙/μ and a SFR of 150 ± 55 M ⊙/μ, where μ is the amount of magnification via lensing.

Keywords: gravitational lensing; radio active galactic nuclei
S-type Stars Discovered in Medium-resolution Spectra of LAMOST DR9

In this paper, we report on 606 S-type stars identified from Data Release 9 of the LAMOST medium-resolution spectroscopic (MRS) survey; 539 of them are reported for the first time. The discovery of these stars is a three-step process, i.e., selecting with ZrO-band indices greater than 0.25, excluding non-S-type stars with the iterative Support Vector Machine method, and finally retaining stars with absolute bolometric magnitude larger than -7.1. The 606 stars are consistent with the distribution of known S-type stars in the color-magnitude diagram. We estimated the C/Os using the [C/Fe] and [O/Fe] provided by APOGEE and the MARCS model for S-type stars, respectively, and the results of the two methods show that the C/Os of all stars are larger than 0.5. Both the locations on the color-magnitude diagram and C/Os further verify the nature of our S-type sample. Investigating the effect of TiO and atmospheric parameters on ZrO with the sample, we found that log g has a more significant impact on ZrO than T eff and [Fe/H], and both TiO and log g may negatively correlate with ZrO. According to the criterion of Tian et al., a total of 238 binary candidates were found by the zero-point-calibrated radial velocities from the officially released catalog of LAMOST MRS and the catalog of Zhang et al. A catalog of these 606 S-type stars is available from the following link: doi.org/10.12149/101097.

Keywords: s stars
Accelerating Early Massive Galaxy Formation with Primordial Black Holes

Recent observations with JWST have identified several bright galaxy candidates at z ≳ 10, some of which appear unusually massive (up to ~1011 M ⊙). Such early formation of massive galaxies is difficult to reconcile with standard ΛCDM predictions, demanding a very high star formation efficiency (SFE), possibly even in excess of the cosmic baryon mass budget in collapsed structures. With an idealized analysis based on linear perturbation theory and the Press-Schechter formalism, we show that the observed massive galaxy candidates can be explained with lower SFE than required in ΛCDM if structure formation is accelerated/seeded by massive (≳109 M ⊙) primordial black holes (PBHs) that make a up a small fraction (~10-6-10-3) of dark matter, considering existing empirical constraints on PBH parameters. We also discuss the potential observational signatures of PBH cosmologies in the JWST era. More work needs to be done to fully evaluate the viability of such PBH models to explain observations of the high-z Universe.

Keywords: galaxy abundances; dark matter; primordial black holes
Extreme Eccentricities of Triple Systems: Analytic Results

Triple stars and compact objects are ubiquitously observed in nature. Their long-term evolution is complex; in particular, the von Zeipel-Lidov-Kozai (ZLK) mechanism can potentially lead to highly eccentric encounters of the inner binary. Such encounters can lead to a plethora of interacting binary phenomena, as well as stellar and compact-object mergers. Here we find implicit analytical formulae for the maximal eccentricity, ${e}_{\max }$ , of the inner binary undergoing ZLK oscillations, where both the test-particle limit (parameterized by the inner-to-outer angular momentum ratio η) and the double-averaging approximation (parameterized by the period ratio, ϵ SA) are relaxed, for circular outer orbits. We recover known results in both limiting cases (either η or ϵ SA → 0) and verify the validity of our model using numerical simulations. We test our results with two accurate numerical N-body codes, REBOUND for Newtonian dynamics and TSUNAMI for general-relativistic dynamics, and find excellent correspondence. We discuss the implications of our results for stellar triples and both stellar and supermassive triple black hole mergers.

Keywords: close binary stars; multiple stars; supermassive black holes; stellar dynamics; stellar mass black holes; galaxy mergers; compact objects
X-Ray Polarization of the Eastern Lobe of SS 433

How astrophysical systems translate the kinetic energy of bulk motion into the acceleration of particles to very high energies is a pressing question. SS 433 is a microquasar that emits TeV γ-rays indicating the presence of high-energy particles. A region of hard X-ray emission in the eastern lobe of SS 433 was recently identified as an acceleration site. We observed this region with the Imaging X-ray Polarimetry Explorer and measured a polarization degree in the range 38%-77%. The high polarization degree indicates the magnetic field has a well-ordered component if the X-rays are due to synchrotron emission. The polarization angle is in the range -12° to +10° (east of north), which indicates that the magnetic field is parallel to the jet. Magnetic fields parallel to the bulk flow have also been found in supernova remnants and the jets of powerful radio galaxies. This may be caused by interaction of the flow with the ambient medium.

Keywords: high mass x-ray binary stars; jets; high energy astrophysics; supernova remnants; astrophysical black holes
Comparing the Locations of Supernovae to CO (2-1) Emission in Their Host Galaxies

We measure the molecular gas environment near recent (<100 yr old) supernovae (SNe) using ~1″ or ≤150 pc resolution CO (2-1) maps from the PHANGS-Atacama Large Millimeter/submillimeter Array (ALMA) survey of nearby star-forming galaxies. This is arguably the first such study to approach the scales of individual massive molecular clouds (M mol ≳ 105.3 M ⊙). Using the Open Supernova Catalog, we identify 63 SNe within the PHANGS-ALMA footprint. We detect CO (2-1) emission near ~60% of the sample at 150 pc resolution, compared to ~35% of map pixels with CO (2-1) emission, and up to ~95% of the SNe at 1 kpc resolution, compared to ~80% of map pixels with CO (2-1) emission. We expect the ~60% of SNe within the same 150 pc beam, as a giant molecular cloud will likely interact with these clouds in the future, consistent with the observation of widespread SN-molecular gas interaction in the Milky Way, while the other ~40% of SNe without strong CO (2-1) detections will deposit their energy in the diffuse interstellar medium, perhaps helping drive large-scale turbulence or galactic outflows. Broken down by type, we detect CO (2-1) emission at the sites of ~85% of our 9 stripped-envelope SNe (SESNe), ~40% of our 34 Type II SNe, and ~35% of our 13 Type Ia SNe, indicating that SESNe are most closely associated with the brightest CO (2-1) emitting regions in our sample. Our results confirm that SN explosions are not restricted to only the densest gas, and instead exert feedback across a wide range of molecular gas densities.

Keywords: supernovae; type ii supernovae; type ia supernovae; type ib supernovae; type ic supernovae; molecular gas; interstellar medium; stellar feedback; galaxy evolution
A Relook at the Black Hole Binary Candidate J1328+2752 with VLBI

We present multiband follow-up observations of the supermassive binary black hole (BBH) candidate and misaligned double–double radio galaxy, J1328+2752. To investigate its parsec-scale structure, we have carried out observations with the Very Long Baseline Array (VLBA) and the European Very Long Baseline Interferometry (VLBI) Network. Additionally, we have obtained optical spectroscopic observations with the 3.6 m Devasthal Optical Telescope. Within 3.5 yr of our previous VLBI observations, the central parsec-scale radio structure of J1328+2752 has changed from a double component to a single central component and its flux density has increased by a factor of 3 in the 5 GHz VLBA observations. The new radio component is largely unresolved at 3, 5, and 8 GHz. The multifrequency radio data shows a convex-shaped spectrum for this unresolved component. The turnover frequency is at ∼3 GHz. While the total intensity image does not reveal any details, a super-resolved VLBA 5 and 8 GHz spectral index image does indicate the presence of two components at a separation of ∼4.2 pc with spectral indices ‑0.5 ± 0.3 and ‑0.9 ± 0.3. We have not observed a simultaneous change in the optical line profiles or intensities over the past few years. The radio structure, the variation of the flux density, and spectral shape can potentially be consistent both with the signature of a young radio source or a BBH at the center of J1328+2752.

Keywords: radio galaxies; very long baseline interferometry; active galactic nuclei; supermassive black holes; spectral line identification
Testing High-energy Emission Models for Blazars with X-Ray Polarimetry

Both leptonic and hadronic emission processes may contribute to blazar jet emission; which dominates in blazars' high-energy emission component remains an open question. Some intermediate synchrotron peaked blazars transition from their low- to high-energy emission components in the X-ray band making them excellent laboratories to probe both components simultaneously, and good targets for the newly launched Imaging X-ray Polarimetry Explorer (IXPE). We characterize the spectral energy distributions for three such blazars, CGRaBS J0211+1051, TXS 0506+056, and S5 0716+714, predicting their X-ray polarization behavior by fitting a multizone polarized leptonic jet model. We find that a significant detection of electron synchrotron dominated polarization is possible with a 300 ks observation for S5 0716+714 and CGRaBS J0211+1051 in their flaring states, while even 500 ks observations are unlikely to measure synchrotron self-Compton (SSC) polarization. Importantly, nonleptonic emission processes like proton synchrotron are marginally detectable for our brightest intermediate synchrotron peaked blazar (ISP), S5 0716+714, during a flaring state. Improved IXPE data reduction methods or next-generation telescopes like eXTP are needed to confidently measure SSC polarization.

Keywords: x-ray active galactic nuclei; x-ray telescopes; relativistic jets; galaxy jets; polarimetry; polarimeters; bl lacertae objects
An Extreme-precision Radial-velocity Pipeline: First Radial Velocities from EXPRES

The EXtreme-PREcision Spectrograph (EXPRES) is an environmentally stabilized, fiber-fed, R = 137,500, optical spectrograph. It was recently commissioned at the 4.3 m Lowell Discovery Telescope near Flagstaff, Arizona. The spectrograph was designed with a target radial-velocity (RV) precision of 30 cm s-1. In addition to instrumental innovations, the EXPRES pipeline, presented here, is the first on-sky, optical, fiber-fed spectrograph to employ many novel techniques -- including an "extended flat" fiber used for wavelength-dependent quantum efficiency characterization of the CCD, a flat-relative optimal extraction algorithm, chromatic barycentric corrections, chromatic calibration offsets, and an ultra-precise laser frequency comb for wavelength calibration. We describe the reduction, calibration, and RV analysis pipeline used for EXPRES and present an example of our current sub-meter-per-second RV measurement precision, which reaches a formal, single-measurement error of 0.3 m s-1 for an observation with a per-pixel signal-to-noise ratio of 250. These velocities yield an orbital solution on the known exoplanet host 51 Peg that matches literature values with a residual rms of 0.895 m s-1.

Keywords: high resolution spectroscopy; radial velocity; astronomy data analysis; observational astronomy
X-Ray Pulsar XTE J1858+034: Discovery of the Cyclotron Line and the Revised Optical Identification

We present the results of a detailed investigation of the poorly studied X-ray pulsar (XRP) XTE J1858+034 based on the data obtained with the NuSTAR observatory during the outburst of the source in 2019. The spectral analysis resulted in the discovery of a cyclotron absorption feature in the source spectrum at ∼48 keV in both the pulse phase-averaged and resolved spectra. Accurate X-ray localization of the source using the NuSTAR and Chandra observatories allowed us to accurately determine the position of the X-ray source and identify the optical companion of the pulsar. The analysis of the counterpart properties suggested that the system is likely a symbiotic binary hosting an XRP and a late-type companion star of the K-M classes rather than a Be X-ray binary as previously suggested.

Keywords: accretion; stellar accretion disks; magnetic fields; binary pulsars; neutron stars; high mass x-ray binary stars; x-ray binary stars
Magnetic Field Measurements of Low-mass Stars from High-resolution Near-infrared IGRINS Spectra

We present average magnetic field measurements derived from high-resolution near-infrared IGRINS spectra of a carefully selected sample of 28 M dwarfs. All 28 have reported magnetic field strengths in the literature. The main goal of this work is to investigate the accuracy, precision, and limitations of magnetic field measurements from IGRINS spectra. This investigation is critical to validating the robustness of our methods before we apply them to over 500 IGRINS-observed M dwarfs in the next paper of the series. We used the Zeeman broadening and Zeeman intensification methods to measure average magnetic fields. Our measurements are all consistent with the previous measurements to within ±1 kG, with an average offset of -0.17 kG for the broadening method and +0.19 kG for the intensification method. We find that the detection limit of IGRINS is ~0.9 kG with the Zeeman broadening method, in accordance with the instrumental broadening limit of the spectrograph. With the Zeeman intensification method, we are able to detect down to ~0.7 kG with a signal-to-noise ratio of 150 or greater. We find an advantage of using the intensification method over the broadening method, which is the ability to reliably measure the magnetic field strengths of stars that are cooler than 3100 K where the spectrum becomes dominated by molecular lines. Therefore, the intensification method is crucial to study stellar magnetism of late-M and brown dwarfs.

Keywords: m dwarf stars; late-type dwarf stars; stellar astronomy; low mass stars
A New Method to Model Magnetic Cloud-driven Forbush Decreases: The 2016 August 2 Event

Interplanetary coronal mass ejections (ICMEs), generally containing magnetic clouds (MCs), are associated with galactic-cosmic ray (GCR) intensity depressions known as Forbush decreases (FDs). An ICME was observed at L1 between 2016 August 2 at 14:00 UT and August 3 at 03:00 UT. The MC region was identified and its magnetic configuration was retrieved by using the Grad-Shafranov (GS) reconstruction. A weak FD in the GCR count-rate was observed on 2016 August 2 by a particle detector on board the European Space Agency LISA Pathfinder mission. The spacecraft orbited around L1 and the particle detector allowed us to monitor the GCR intensity at energies above 70 MeV n-1. A 9% decrease in the cosmic-ray intensity was observed during the ICME passage. The first structure of the ICME caused a 6.4% sharp decrease, while the MC produced a 2.6% decrease. A suited full-orbit test-particle simulation was performed on the MC configuration obtained through the GS reconstruction. The FD amplitude and time profile obtained through the simulation show an excellent agreement with observations. The test-particle simulation allows us to derive the energy dependence of the MC-driven FD providing an estimate of the amplitude at different rigidities, here compared with several neutron monitor observations. This work points out the importance of the large-scale MC configuration in the interaction between GCRs and ICMEs and suggests that particle drifts have a primary role in modulating the GCR intensity within the MC under study and possibly in at least all slowly expanding ICMEs lacking a shock/sheath region.

Keywords: forbush effect; galactic cosmic rays; cosmic ray detectors; solar coronal mass ejections; ejecta; interplanetary physics
Gamma-Ray Bursts as Distance Indicators by a Statistical Learning Approach

Gamma-ray bursts (GRBs) can be probes of the early Universe, but currently, only 26% of GRBs observed by the Neil Gehrels Swift Observatory have known redshifts (z) due to observational limitations. To address this, we estimated the GRB redshift (distance) via a supervised statistical learning model that uses optical afterglow observed by Swift and ground-based telescopes. The inferred redshifts are strongly correlated (a Pearson coefficient of 0.93) with the observed redshifts, thus proving the reliability of this method. The inferred and observed redshifts allow us to estimate the number of GRBs occurring at a given redshift (GRB rate) to be 8.47–9 yr‑1 Gpc‑1 for 1.9 < z < 2.3. Since GRBs come from the collapse of massive stars, we compared this rate with the star formation rate, highlighting a discrepancy of a factor of 3 at z < 1.

Keywords: stellar phenomena