adsabs/SciX_UAT_keywords huggingface dataset:
Microlensing Optical Depth and Event Rate in the OGLE-IV Galactic Plane Fields

Searches for gravitational microlensing events are traditionally concentrated on the central regions of the Galactic bulge but many microlensing events are expected to occur in the Galactic plane, far from the Galactic Center. Owing to the difficulty in conducting high-cadence observations of the Galactic plane over its vast area, which are necessary for the detection of microlensing events, their global properties were hitherto unknown. Here, we present results of the first comprehensive search for microlensing events in the Galactic plane. We searched an area of almost 3000 square degrees along the Galactic plane ( $| b| \lt 7^\circ $ , 0° < l < 50°, 190° < l < 360°) observed by the Optical Gravitational Lensing Experiment (OGLE) during 2013-2019 and detected 630 events. We demonstrate that the mean Einstein timescales of Galactic plane microlensing events are on average three times longer than those of Galactic bulge events, with little dependence on the Galactic longitude. We also measure the microlensing optical depth and event rate as a function of Galactic longitude and demonstrate that they exponentially decrease with the angular distance from the Galactic Center (with the characteristic angular scale length of 32°). The average optical depth decreases from 0.5 × 10-6 at l = 10° to 1.5 × 10-8 in the Galactic anticenter. We also find that the optical depth in the longitude range 240° < l < 330° is asymmetric about the Galactic equator, which we interpret as a signature of the Galactic warp.

Keywords: gravitational microlensing; microlensing optical depth; microlensing event rate; milky way disk; milky way galaxy
Toward More Accurate Synthetic Reflection Spectra: Improving the Calculations of Returning Radiation

We present a new model to calculate reflection spectra of thin accretion disks in Kerr spacetimes. Our model includes the effect of returning radiation, which is the radiation that is emitted by the disk and returns to the disk because of the strong light bending near a black hole. The major improvement with respect to the existing models is that it calculates the reflection spectrum at every point on the disk by using the actual spectrum of the incident radiation. Assuming a lamppost coronal geometry, we simulate simultaneous observations of NICER and NuSTAR of bright Galactic black holes and we fit the simulated data with the latest version of relxill (modified to read the table of reflionx, which is the nonrelativistic reflection model used in our calculations). We find that relxill with returning radiation cannot fit well the simulated data when the black hole spin parameter is very high and the coronal height and disk's ionization parameter are low, and some parameters can be significantly overestimated or underestimated. We can find better fits and recover the correct input parameters as the value of the black hole spin parameter decreases and the value of the coronal height increases.

Keywords: astrophysical black holes; x-ray astronomy; accretion
Atmosphere Origins for Exoplanet Sub-Neptunes

Planets with 2 R⊕ < R < 3 R⊕ and orbital period <100 days are abundant; these sub-Neptune exoplanets are not well understood. For example, Kepler sub-Neptunes are likely to have deep magma oceans in contact with their atmospheres, but little is known about the effect of the magma on the atmosphere. Here we study this effect using a basic model, assuming that volatiles equilibrate with magma at T ∼ 3000 K. For our Fe-Mg-Si-O-H model system, we find that chemical reactions between the magma and the atmosphere and dissolution of volatiles into the magma are both important. Thus, magma matters. For H, most moles go into the magma, so the mass target for both H2 accretion and H2 loss models is weightier than is usually assumed. The known span of magma oxidation states can produce sub-Neptunes that have identical radius but with total volatile masses varying by 20-fold. Thus, planet radius is a proxy for atmospheric composition but not for total volatile content. This redox diversity degeneracy can be broken by measurements of atmosphere mean molecular weight. We emphasize H2 supply by nebula gas, but also consider solid-derived H2O. We find that adding H2O to Fe probably cannot make enough H2 to explain sub-Neptune radii because >103 km thick outgassed atmospheres have high mean molecular weight. The hypothesis of magma-atmosphere equilibration links observables such as atmosphere H2O/H2 ratio to magma FeO content and planet formation processes. Our model's accuracy is limited by the lack of experiments (lab and/or numerical) that are specific to sub-Neptunes; we advocate for such experiments.

Keywords: extrasolar rocky planets; exoplanet atmospheres; exoplanet evolution; exoplanet formation
Understanding the Capability of Future Direct-imaging Observations to Quantify Atmospheric Chemical Effects of Stellar Proton Events

Models developed for Earth are often applied in exoplanet contexts. Validation in extraterrestrial settings can provide an important test of model realism and increase our confidence in model predictions. NASA's upcoming space-based IROUV telescope will provide unprecedented opportunities to perform such tests. Here, we use the Planetary Spectrum Generator to simulate IROUV reflected-light spectroscopic observations of flare-driven photochemical changes produced by the Whole Atmosphere Community Climate Model, part of the Community Earth System Model framework. We find that NO2 is the most observable gas to target, and integrating the signal for two days following the flare and comparing to a baseline of preflare data would achieve the highest signal-to-noise ratio. The NO2 response is much larger for K-star tidally locked planets than G-star rapidly rotating planets and does not depend strongly on O2 level. The NO2 response should be observable for planets within 3-4 pc independent of the phase angle since the amount of reflected light is larger at smaller phases, but the NO2 concentration is low near the substellar point. This work outlines a methodology for validating and ground-truthing atmospheric chemistry models developed for Earth that could be useful for the numerical exploration of exoplanets.

Keywords: exoplanet atmospheres; exoplanet atmospheric composition; direct imaging; radiative transfer simulations; radiative transfer
Observational Study of Recurrent Jets Confined by Active Region Loops

With high spatial and temporal resolution data from the Solar Dynamics Observatory and the New Vacuum Solar Telescope (NVST), we present observations of recurrent jets confined by coronal loops that occurred in the active region NOAA 11726 from 02:00 to 12:00 UT on 2013 April 21. Three jets are clearly observed by the NVST in Hα line. These recurrent jets originate from the emerging bipolar magnetic region at the north of the active region. Half of them are related to the magnetic flux emergence, and the others are associated with the magnetic flux cancellation. Their velocities range from 80.6 ± 1.3 km s-1 to 433.6 ± 20.1 km s-1. Though they eject from the same source region, their shapes, sizes, and eruptive trajectories are not exactly the same. Most of them consist of cool (dark) and hot (bright) components. The differential emission measure distributions of the recurrent jets suggest that they are multithermal structures. The rotation directions of the recurrent jets are not consistent. Eight of them have a counterclockwise rotation, and the others have a clockwise rotation. The 12 recurrent jets are classified as blowout (accounting for 33%) and standard (accounting for 67%) jets. The velocity and density range of the blowout jets are slightly wider than those of the standard jets. The blowout jets have lower temperatures than the standard jets. These observational results suggest that the recurrent jets are probably triggered by recurrent magnetic reconnection between the emerging bipolar magnetic region and its overlying large-scale active region loops.

Keywords: solar magnetic reconnection; solar coronal transients; solar magnetic fields
Low- and High-energy Neutrinos from SN 2023ixf in M101

Supernova (SN) 2023ixf in M101 is the closest SN explosion observed in the last decade. Therefore, it is a suitable test bed to study the role of jets in powering the SN ejecta. With this aim, we explored the idea that high-energy neutrinos could be produced during the interaction between the jets and the intense radiation field produced in the SN explosion and eventually be observed by the IceCube neutrino telescope. The lack of detection of such neutrinos has significantly constrained both the fraction of stellar collapses that produce jets and/or the theoretical models for neutrino production. Finally, we investigated the possibility of detecting low-energy neutrinos from SN 2023ixf with the Super- and Hyper-Kamiokande experiments, obtaining, in both cases, subthreshold estimates.

Keywords: supernova neutrinos; jets
Determining the Origin of Very-high-energy Gamma Rays from Galactic Sources by Future Neutrino Observations

Recently, the Large High Altitude Air Shower Observatory (LHAASO) identified 12 gamma-ray sources emitting gamma rays with energies above 100 TeV, making them potential PeV cosmic-ray accelerators (PeVatrons). Neutrino observations are crucial in determining whether the gamma-ray radiation process is of hadronic or leptonic origin. In this paper, we study three detected sources, LHAASO J1908+0621, LHAASO J2018+3651, and LHAASO J2032+4102, which are also the most promising Galactic high-energy neutrino candidate sources with the lowest pretrial p-value based on the stacking searches testing for excess neutrino emission by the IceCube Neutrino Observatory. We study the lepto-hadronic scenario for the observed multiband spectra of these LHAASO sources considering the possible counterpart source of the LHAASO sources. The very-high-energy gamma rays are entirely attributed to the hadronic contribution; therefore, the most optimistic neutrino flux can be derived. Then, we evaluate the statistical significance (p-value) as a function of the observation time of IceCube and the next-generation IceCube-Gen2 neutrino observatory, respectively. Our results tend to disfavor that all gamma rays above 100 GeV from LHAASO J1908+0621 are of purely hadronic origin based on current IceCube observations, but the purely hadronic origin of gamma rays above 100 TeV is still possible. By IceCube-Gen2, the origin of gamma rays above 100 TeV from LHAASO J1908+0621 can be further determined at a 5σ significance level within a running time of ∼3 yr. For LHAASO J2018+3651 and LHAASO J2032+4102, the required running time of IceCube-Gen2 is ∼10 yr (3σ) and ∼10 yr (5σ), respectively. Future observations by the next-generation neutrino telescope will be crucial to understanding the particle acceleration and radiation processes inside the sources.

Keywords: high energy astrophysics; neutrino astronomy; supernova remnants; pulsar wind nebulae; gamma-rays
Vibrational, Rotational, and Electronic Spectroscopy for Possible Interstellar Detection of AlNH2 and HAlNH

We obtained accurate vibrational frequencies, rotational constants, and vertical transition energy for AlNH2(X1A1) and HAlNH(X1A') isomers using ab initio calculations at various levels of theory. These two isomers are potential candidates for astronomical observation. AlNH2 and HAlNH are thermodynamically stable, with Al-NH2 and HAl-NH bond dissociation energies predicted to be 4.39 and 3.60 eV, respectively. The two isomers are characterized by sizable dipole moments of 1.211 and 3.64 D, respectively. The anharmonic frequencies and spectroscopic constants reported for the two isomers should facilitate their experimental differentiation. In addition, we evaluated the evolution of the low-lying electronic states along the stretching coordinates, as well as the absorption cross sections. AlNH2 absorbs strongly around 287, 249, and 200 nm, whereas the HAlNH absorption is centered around 370 and 233 nm.

Keywords: astrochemistry; circumstellar envelopes; interstellar medium; computational methods
Polarimetry as a Tool for Observing Orographic Gravity Waves on Venus

Planet-wide stationary gravity waves have been observed with the thermal camera on the Akatsuki spacecraft. These waves have been attributed to the underlying surface topography and have successfully been reproduced using the Institut Pierre Simon Laplace (IPSL) Venus Mesoscale Model (VMM). Here, we use numerical radiative transfer computations of the total and polarized fluxes of the sunlight that is reflected by Venus under the conditions of these gravity waves to show that the waves could also be observed in polarimetric observations. To model the waves, we use the density perturbations computed by the IPSL VMM. We show the computed wave signatures in the polarization for nadir-viewing geometries observed by a spacecraft in orbit around Venus and as they could be observed using an Earth-based telescope. We find that the strength of the signatures of the atmospheric density waves in the degree of polarization of the reflected sunlight depends not only on the density variations themselves, but also on the wavelength and the cloud top altitude. Observations of such wave signatures on the dayside of the planet would give insight into the occurrence of the waves and possibly into the conditions that govern their onset and development. The computed change in degree of polarization due to these atmospheric density waves is about 1000 ppm at a wavelength of 300 nm. This signal is large enough for an accurate polarimeter to detect.

Keywords: venus; polarimetry; radiative transfer; planetary atmospheres
Observations of the Disk/Jet Coupling of MAXI J1820+070 during Its Descent to Quiescence

Black hole X-ray binaries in the quiescent state (Eddington ratios typically ≲10-5) display softer X-ray spectra (photon indices Γ ∼ 2) compared to higher-luminosity black hole X-ray binaries in the hard state (Γ ∼ 1.7). However, the cause of this softening and its implications for the underlying accretion flow are still uncertain. Here, we present quasi-simultaneous X-ray and radio spectral monitoring of the black hole X-ray binary MAXI J1820+070 during the decay of its 2018 outburst and of a subsequent reflare in 2019, providing an opportunity to monitor a black hole X-ray binary as it actively transitions into quiescence. We probe 1-10 keV X-ray luminosities as low as LX ∼ 4 × 1032 erg s-1, equivalent to Eddington fractions of ∼4 × 10-7. During its decay toward quiescence, the X-ray spectrum of MAXI J1820+070 softens from Γ ∼ 1.7 to Γ ∼ 2, with the softening taking ∼30 days and completing at LX ≈ 1034 erg s-1 (≈10-5 LEdd). While the X-ray spectrum softens, the radio spectrum generally remains flat or inverted throughout the decay. We also find that MAXI J1820+070 follows a radio (LR)-X-ray luminosity correlation of the form LR ∝ LX0.52±0.07, making it the fourth black hole system to follow the so-called "standard track" unbroken over several (in this case, four) decades in LX. Comparing the radio/X-ray spectral evolution(s) with the LR-LX plane, we find that the X-ray softening is consistent with X-rays produced by Comptonization processes in a radiatively inefficient accretion flow. We generally disfavor X-ray emission originating solely from within the jet, with the possible exception of X-rays produced via synchrotron self-Compton processes.

Keywords: black holes; accretion; low-mass x-ray binary stars; x-ray transient sources
Host Star Metallicity of Directly Imaged Wide-orbit Planets: Implications for Planet Formation

Directly imaged planets (DIPs) are self-luminous companions of pre-main-sequence and young main-sequence stars. They reside in wider orbits (∼tens to thousands of astronomical units) and generally are more massive compared to the close-in (≲10 au) planets. Determining the host star properties of these outstretched planetary systems is important to understand and discern various planet formation and evolution scenarios. We present the stellar parameters and metallicity ([Fe/H]) for a subsample of 18 stars known to host planets discovered by the direct imaging technique. We retrieved the high-resolution spectra for these stars from public archives and used the synthetic spectral fitting technique and Bayesian analysis to determine the stellar properties in a uniform and consistent way. For eight sources, the metallicities are reported for the first time, while the results are consistent with the previous estimates for the other sources. Our analysis shows that metallicities of stars hosting DIPs are close to solar with a mean [Fe/H] = -0.04 ± 0.27 dex. The large scatter in metallicity suggests that a metal-rich environment may not be necessary to form massive planets at large orbital distances. We also find that the planet mass-host star metallicity relation for the directly imaged massive planets in wide orbits is very similar to that found for the well-studied population of short-period (≲1 yr) super-Jupiters and brown dwarfs around main-sequence stars.

Keywords: direct imaging; spectroscopy; bayesian statistics; markov chain monte carlo; planet formation; extrasolar gaseous giant planets
The Splashback Mass Function in the Presence of Massive Neutrinos

We present a complementary methodology to constrain the total neutrino mass, ∑m ν , based on the diffusion coefficient of the splashback mass function of dark matter halos. Analyzing the snapshot data from the Massive Neutrino Simulations, we numerically obtain the number densities of distinct halos identified via the SPARTA code as a function of their splashback masses at various redshifts for two different cases of ∑m ν = 0.0 and 0.1 eV. Then, we fit the numerical results to the recently developed analytic formula characterized by the diffusion coefficient that quantifies the degree of ambiguity in the identification of the splashback boundaries. Our analysis confirms that the analytic formula works excellently even in the presence of neutrinos and that the decrement of its diffusion coefficient with redshift is well described by a linear fit, B(z - z c ), in the redshift range of 0.2 ≤ z ≤ 2. It turns out that the massive neutrino case yields a significantly lower value of B and a substantially higher value of z c than the massless neutrino case, which indicates that the higher the masses that neutrinos have, the more severely the splashback boundaries become disturbed by the surroundings. Given our result, we conclude that the total neutrino mass can in principle be constrained by measuring how rapidly the diffusion coefficient of the splashback mass function diminishes with redshifts at z ≥ 0.2. We also discuss the anomalous behavior of the diffusion coefficient found at lower redshifts for both of the ∑m ν cases, and ascribe it to the fundamental limitation of the SPARTA code at z ≤ 0.13.

Keywords: large-scale structure of the universe
Inferring Small Neutron Star Spins with Neutron Star–Black Hole Mergers

The precise measurement of neutron star (NS) spins can provide important insight into the formation and evolution of compact binaries containing NSs. While traditional methods of NS spin measurement rely on pulsar observations, gravitational-wave detections offer a complementary avenue. However, determining component spins with gravitational waves is hindered by the small dimensionless spins of the NSs and the degeneracy in the mass and spin parameters. This degeneracy can be addressed by the inclusion of higher-order modes in the waveform, which are important for systems with unequal masses. This study shows the suitability of NS–black hole mergers, which are naturally mass-asymmetric, for precise NS spin measurements. We explore the effects of the black hole masses and spins, higher-mode content, inclination angles, and detector sensitivity on the measurement of NS spin. We find that networks with next-generation observatories like the Cosmic Explorer and the Einstein Telescope can distinguish NS dimensionless spin of 0.04 (0.1) from zero at 1σ confidence for events within ∼350 (∼1000) Mpc. Networks with A+ and A♯ detectors achieve similar distinction within ∼30 (∼70) Mpc and ∼50 (∼110) Mpc, respectively.

Keywords: gravitational waves; neutron stars; compact objects; pulsars; black holes; astrophysical black holes
Predicting Solar Flares Using CNN and LSTM on Two Solar Cycles of Active Region Data

We consider the flare prediction problem that distinguishes flare-imminent active regions that produce an M- or X-class flare in the succeeding 24 hr, from quiet active regions that do not produce any flares within ±24 hr. Using line-of-sight magnetograms and parameters of active regions in two data products covering Solar Cycles 23 and 24, we train and evaluate two deep learning algorithms-a convolutional neural network (CNN) and a long short-term memory (LSTM)-and their stacking ensembles. The decisions of CNN are explained using visual attribution methods. We have the following three main findings. (1) LSTM trained on data from two solar cycles achieves significantly higher true skill scores (TSSs) than that trained on data from a single solar cycle with a confidence level of at least 0.95. (2) On data from Solar Cycle 23, a stacking ensemble that combines predictions from LSTM and CNN using the TSS criterion achieves a significantly higher TSS than the "select-best" strategy with a confidence level of at least 0.95. (3) A visual attribution method called "integrated gradients" is able to attribute the CNN's predictions of flares to the emerging magnetic flux in the active region. It also reveals a limitation of CNNs as flare prediction methods using line-of-sight magnetograms: it treats the polarity artifact of line-of-sight magnetograms as positive evidence of flares.

Keywords: solar flares; neural networks; solar active region magnetic fields; astronomy data analysis; classification
The Hydrogen-poor Superluminous Supernovae from the Zwicky Transient Facility Phase I Survey. I. Light Curves and Measurements

During the Zwicky Transient Facility (ZTF) Phase I operations, 78 hydrogen-poor superluminous supernovae (SLSNe-I) were discovered in less than 3 yr, constituting the largest sample from a single survey. This paper (Paper I) presents the data, including the optical/UV light curves and classification spectra, while Paper II in this series will focus on the detailed analysis of the light curves and modeling. Our photometry is primarily taken by ZTF in the g, r, and i bands, and with additional data from other ground-based facilities and Swift. The events of our sample cover a redshift range of z = 0.06 - 0.67, with a median and 1σ error (16% and 84% percentiles) of ${z}_{\mathrm{med}}={0.265}_{-0.135}^{+0.143}$ . The peak luminosity covers -22.8 mag ≤ M g,peak ≤ -19.8 mag, with a median value of $-{21.48}_{-0.61}^{+1.13}$ mag. The light curves evolve slowly with a mean rest-frame rise time of t rise = 41.9 ± 17.8 days. The luminosity and timescale distributions suggest that low-luminosity SLSNe-I with a peak luminosity ~-20 mag or extremely fast-rising events (<10 days) exist, but are rare. We confirm previous findings that slowly rising SLSNe-I also tend to fade slowly. The rest-frame color and temperature evolution show large scatters, suggesting that the SLSN-I population may have diverse spectral energy distributions. The peak rest-frame color shows a moderate correlation with the peak absolute magnitude, i.e., brighter SLSNe-I tend to have bluer colors. With optical and UV photometry, we construct the bolometric luminosity and derive a bolometric correction relation that is generally applicable for converting g, r-band photometry to the bolometric luminosity for SLSNe-I.

Keywords: supernovae