adsabs/SciX_UAT_keywords huggingface dataset:
Temporal and Spatial Characteristics of Hard X-Ray Sources in a Flare Model with a Vertical Current Sheet

We analyzed changes in the height of the coronal hard X-ray (HXR) source for flares SOL2013-05-13T01:50 and SOL2013-05-13T15:51. Analysis of the Reuven Ramaty High Energy Solar Spectroscopic Imager data revealed the downward motion of the HXR source and the separation of the sources by energy and height. In the early stages of the flares, a negative correlation was found between the HXR source area in the corona and HXR flux. For the SOL2013-05-13T15:51 event, an increasing trend in the time delay spectra at the footpoints was obtained. For both events, the spectra of the time delays in the coronal HXR source showed a decreasing trend with energy in certain flare phases. To interpret the observed phenomena, we considered a flare model of collapsing traps and calculated the distribution functions of accelerated electrons along the magnetic loop using a nonstationary relativistic kinetic equation. This approach considers betatron and Fermi first-order acceleration mechanisms. The increasing trend of the time delay spectra at the footpoints was explained by the high mirror ratio in the magnetic loop and betatron acceleration mechanism. The observed features in the spatial and temporal behavior of the HXR sources, such as the negative correlation between the HXR source area and HXR flux, can be interpreted by the collapsing trap model.

Keywords: active solar corona; solar flares; solar activity; solar active regions; solar active region magnetic fields; solar energetic particles; solar x-ray emission; solar extreme ultraviolet emission
Lithium in Turnoff Stars in the Globular Cluster M5: A Quest for Primordial Lithium

The light element lithium is formed by nucleosynthesis during the Big Bang. Its abundance can help to define the parameters of the early Universe. To find this primordial value, it is necessary to determine Li abundances in the oldest stars because it is readily destroyed by nuclear reactions in stellar interiors. We have made high-resolution (~45,000) spectroscopic observations of five identical unevolved turnoff stars in the 13 Gyr old globular cluster M5. In our analysis we find a range in Li abundance of a factor of 2; the spread is 5 times the individual error. The comparison of these results with those for turnoff stars from five other globular clusters reveals a similarly large range in Li. Lithium in M5 and the other clusters all have stars above the field star Li plateau, but none are as high as the predictions for primordial Li. The maximum values for Li are the same in all six clusters. Multiple generations of stars are found in many globular clusters; those later generations are expected to have formed from Li-depleted gas. Such second- and later-generation stars would have no Li. However, only one of the six clusters has a few unevolved stars with upper limits on the Li abundance.

Keywords: stellar abundances; stellar atmospheres; stellar astronomy; stellar interiors
Dark Matter Cosmology with Varying Viscosity: A Possible Resolution to the S 8 Tension

We study varying forms of viscous dark matter (DM) and try to address the intriguing tensions of the standard model of cosmology with recent cosmological data, including the Hubble and S 8 tensions. We note that by assuming the DM viscosity depends on the Hubble parameter, DM density, or both, one can improve the statistics. Although the models tend to aggravate the Hubble tension a bit, they tend to reduce the S 8 tension, even in comparison with the constant viscosity case. Since similar-to-viscosity massive neutrinos suppress the power spectrum of matter on small length scales, considering them along with the viscous DM, we find that the neutrino mass range is tightened.

Keywords: dark matter; sigma8; cosmological parameters from large-scale structure; observational cosmology
Local Starburst Conditions and Formation of GRB 980425/SN 1998bw within a Collisional Ring

We present the first spatially resolved study of molecular gas in the vicinity of a gamma-ray burst (GRB), using CO(2-1) emission-line observations with the Atacama Large Millimetre Array at ∼50 pc scales. The host galaxy of GRB 980425 contains a ring of high column density H I gas, which is likely to have formed due to a collision between the GRB host and its companion galaxy, within which the GRB is located. We detect 11 molecular gas clumps in the galaxy, 7 of which are within the gas ring. The clump closest to the GRB position is at a projected separation of ∼280 pc. Although it is plausible that the GRB progenitor was ejected from clusters formed in this clump, we argue that the in situ formation of the GRB progenitor is the most likely scenario. We measure the molecular gas masses of the clumps and find them to be sufficient for forming massive star clusters. The molecular gas depletion times of the clumps show a variation of ∼2 dex, comparable with the large variation in depletion times found in starburst galaxies in the nearby universe. This demonstrates the presence of starburst modes of star formation on local scales in the galaxy, even while the galaxy as a whole cannot be categorized as a starburst based on its global properties. Our findings suggest that the progenitor of GRB 9802425 was originated in a young massive star cluster formed in the starburst mode of star formation.

Keywords: interacting galaxies; galaxy collisions; starburst galaxies; galaxy dynamics; interstellar medium; molecular clouds; young massive clusters; massive stars; gamma-ray bursts; supernovae
First Constraints on Helium +He3 Evolution in z = 3-4 Using the 8.67 GHz Hyperfine Transition

We present the first constraints on the cross-correlation power spectrum of the He II (+He3) signal strength using the redshifted 8.67 GHz hyperfine transition between z = 2.9 and 4.1 and with interferometric data obtained from the public archive of the Australia Telescope Compact Array (ATCA). 210 hr of observations of the primary calibrator source B1934-638 were extracted from data obtained with the telescope from 2014-2021, and coherently combined in a power spectrum pipeline to measure the He II power across a range of spatial scales, and at three redshifts that span the period of helium reionization. Our best limit places the fluctuation of the brightness temperature to be less than 557 μK on spatial scales of 30' at z = 2.91, and less than 755 μK on scales of 30' at z = 4.14 (2σ noise limited). We measure a temperature of 489 μK at z = 2.91. ATCA's few antennas and persistent remaining radio frequency interference in the data prevent deeper integrations improving the results. This work is a proof of principle to demonstrate how this type of experiment can be undertaken to reach the 0.01-1 μK level expected for the helium signal at z ~ 4.

Keywords: cosmology; reionization; astronomical instrumentation; radio interferometers
External Inverse-Compton Emission Associated with Extended and Plateau Emission of Short Gamma-Ray Bursts: Application to GRB 160821B

The recent detection of TeV photons from two gamma-ray bursts (GRBs), GRB 190114C and GRB 180720B, has opened a new window for multimessenger and multiwavelength astrophysics of high-energy transients. We study the origin of very high energy (VHE) γ-rays from the short GRB 160821B, for which the MAGIC Collaboration reported a ∼3σ statistical significance. Short GRBs are often accompanied by extended and plateau emission, which is attributed to internal dissipation resulting from activities of a long-lasting central engine, and Murase et al. (2018) recently suggested the external inverse-Compton (EIC) scenario for VHE counterparts of short GRBs and neutron star mergers. Applying this scenario to GRB 160821B, we show that the EIC flux can reach ∼10-12 erg cm-2 s-1 within a time period of ∼103-104 s, which is consistent with the MAGIC observations. EIC γ-rays expected during the extended and plateau emission will be detectable with greater significance by future detectors such as the Cerenkov Telescope Array. The resulting light curve has a distinguishable feature, where the VHE emission is predicted to reach the peak around the end of the seed photon emission.

Keywords: gamma-ray bursts; gamma-ray sources; gamma-ray astronomy; high energy astrophysics; relativistic jets; gravitational wave astronomy; non-thermal radiation sources
Investigating Cosmic Discordance

We show that a combined analysis of cosmic microwave background anisotropy power spectra obtained by the Planck satellite and luminosity distance data simultaneously excludes a flat universe and a cosmological constant at 99% confidence level. These results hold separately when combining Planck with three different data sets: the two determinations of the Hubble constant from Riess et al. and Freedman et al., and the Pantheon catalog of high-redshift Type Ia supernovae. We conclude that either the Lambda cold dark matter model needs to be replaced by a different paradigm, or else there are significant but still undetected systematics. Our result calls for new observations and stimulates the investigation of alternative theoretical models and solutions.

Keywords: cosmological models; closed universe; early universe; dark energy; hubble constant; cosmic microwave background radiation; cosmic background radiation
A Statistical Search for a Uniform Trigger Threshold in Solar Flares from Individual Active Regions

Solar flares result from the sudden release of energy deposited by subphotospheric motions into the magnetic field of the corona. The deposited energy accumulates secularly between events. One may interpret the observed event statistics as resulting from a state-dependent Poisson process in which the instantaneous flare rate is a function of the stress in the system and a flare becomes certain as the stress approaches a threshold set by the microphysics of the flare trigger. If the system is driven fast, and if the threshold is static and uniform globally, a cross-correlation is predicted between the size of a flare and the forward waiting time to the next flare. This cross-correlation is broadly absent from the Geostationary Operational Environmental Satellite (GOES) soft X-ray flare database. One also predicts higher cross-correlations in active regions where the shapes of the waiting time and size distributions match. Again, there is no evidence for such an association in the GOES data. The data imply at least one of the following: (i) the threshold at which a flare is triggered varies in time; (ii) the rate at which energy is driven into active regions varies in time; (iii) historical flare catalogs are incomplete; or (iv) the description of solar flares as resulting from a buildup and release of energy, once a threshold is reached, is incomplete.

Keywords: astrostatistics; solar flares
Simulated Climate of TRAPPIST-1e Using MPAS-A and Comparisons with Other GCMs

Dayside convection is one of the most important contributors to a tidally locked planet's climate. Considering the long-standing challenge of simulating convections, we employ a convection-resolving model known as the Model for Prediction across Scales—Atmosphere and perform a series of simulations with spatial resolution ranging from 960 to 10 km. With TRAPPIST-1e, a potentially habitable exoplanet, as the target, we aim to draw a comparative analysis against the results from the TRAPPIST-1 Habitable Atmosphere Intercomparison project. Regarding the overall climate states, our simulations reaffirm the findings of the previous general circulation model (GCM). Both the extensive substellar cloud cluster and the intricate cloud street feature are successfully reproduced. The influence of varying grid resolution exhibits a remarkably marginal impact across our resolution spectrum, albeit with a slightly heightened sensitivity observed at the nightside. Major differences center around the cloud-related variables, including cloud phase (liquid and ice), amount, and height, in both the grid resolution assessments and GCM intercomparison scenarios. Furthermore, we explore the repercussions on the phase curve and transit spectrum.

Keywords: exoplanet atmospheres; atmospheric clouds; planetary climates; habitable planets; atmospheric circulation
Chemical Complexity of Phosphorous-bearing Species in Various Regions of the Interstellar Medium

Phosphorus-related species are not known to be as omnipresent in space as hydrogen, carbon, nitrogen, oxygen, and sulfur-bearing species. Astronomers spotted very few P-bearing molecules in the interstellar medium and circumstellar envelopes. Limited discovery of the P-bearing species imposes severe constraints in modeling the P-chemistry. In this paper, we carry out extensive chemical models to follow the fate of P-bearing species in diffuse clouds, photon-dominated or photodissociation regions (PDRs), and hot cores/corinos. We notice a curious correlation between the abundances of PO and PN and atomic nitrogen. Since N atoms are more abundant in diffuse clouds and PDRs than in the hot core/corino region, PO/PN reflects <1 in diffuse clouds, ≪1 in PDRs, and >1 in the late warm-up evolutionary stage of the hot core/corino regions. During the end of the post-warm-up stage, we obtain PO/PN > 1 for hot core and <1 for its low-mass analog. We employ a radiative transfer model to investigate the transitions of some of the P-bearing species in diffuse cloud and hot core regions and estimate the line profiles. Our study estimates the required integration time to observe these transitions with ground-based and space-based telescopes. We also carry out quantum chemical computation of the infrared features of PH3, along with various impurities. We notice that SO2 overlaps with the PH3 bending-scissoring modes around ~1000-1100 cm-1. We also find that the presence of CO2 can strongly influence the intensity of the stretching modes around ~2400 cm-1 of PH3.

Keywords: astrochemistry; abundance ratios; chemical abundances; interstellar molecules; molecular clouds
Energetic Electron Observations by Parker Solar Probe/IS⊙IS during the First Widespread SEP Event of Solar Cycle 25 on 2020 November 29

At the end of 2020 November, two coronal mass ejections (CMEs) erupted from the Sun and propagated through the interplanetary medium in the direction of Parker Solar Probe while the spacecraft was located at ~0.81 au. The passage of these interplanetary CMEs (ICMEs) starting on November 29 (DOY 334) produced the largest enhancement of energetic ions and electrons observed by the Integrated Science Investigation of the Sun (IS⊙IS) energetic particle instrument suite on board Parker Solar Probe during the mission's first eight orbits. This was also the first spatially widespread solar energetic particle event observed in solar cycle 25. We investigate several key characteristics of the energetic electron event including the time profile and anisotropy distribution of near-relativistic electrons as measured by IS⊙IS's low-energy Energetic Particle Instrument (EPI-Lo) and compare these observations with contextual data from the Parker Solar Probe Fields Experiment magnetometer. These are the first electron anisotropy measurements from IS⊙IS/EPI-Lo, demonstrating that the instrument can successfully produce these measurements. We find that the electron count rate peaks at the time of the shock driven by the faster of the two ICMEs, implying that the shock parameters of this ICME are conducive to the acceleration of electrons. Additionally, the angular distribution of the electrons during the passage of the magnetic clouds associated with the ICMEs shows significant anisotropy, with electrons moving primarily parallel and antiparallel to the local magnetic field as well as bidirectionally, providing an indication of the ICME's magnetic topology and connectivity to the Sun or magnetic structures in the inner heliosphere.

Keywords: solar flares; solar activity; solar coronal mass ejection shocks; interplanetary shocks; solar energetic particles; solar particle emission
Proton Synchrotron Origin of the Very-high-energy Emission of GRB 190114C

We consider here a proton-synchrotron model to explain the MAGIC observation of GRB 190114C afterglow in the energy band of 0.2-1 TeV, while the X-ray spectra are explained by electron-synchrotron emission. Given the uncertainty of the particle acceleration process, we consider several variations of the model, and show that they all match the data very well. We find that the values of the uncertain model parameters are reasonable: isotropic explosion energy ~1054.5 erg, ambient density ~10-100 cm-3, and the fraction of electrons/protons accelerated to a high-energy power law is of a few percent. All these values are directly derived from the observed teraelectronvolt and X-ray fluxes. The model also requires that protons be accelerated to observed energies as high as a few 1020 eV. Further, assuming that the jet break takes place after 106 s gives the beaming-corrected energy of the burst to be ≈1053 erg, which is one to two orders of magnitude higher than usually inferred, because of the small fraction of electrons accelerated. Our modeling is consistent with both late time data at all bands, from optical to X-rays, and with numerical models of particle acceleration. Our results thus demonstrate the relevance of proton-synchrotron emission to the high-energy observations of gamma-ray bursts during their afterglow phase.

Keywords: gamma-ray bursts; interstellar synchrotron emission
Correlations of Dark Matter, Gas, and Stellar Profiles in Dark Matter Halos

Halos of similar mass and redshift exhibit a large degree of variability in their differential properties, such as dark matter, hot gas, and stellar mass density profiles. This variability is an indicator of diversity in the formation history of these dark matter halos that is reflected in the coupling of scatters about the mean relations. In this work, we show that the strength of this coupling depends on the scale at which halo profiles are measured. By analyzing the outputs of the IllustrisTNG hydrodynamical cosmological simulations, we report the radial- and mass-dependent couplings between the dark matter, hot gas, and stellar mass radial density profiles utilizing the population diversity in dark matter halos. We find that for the same mass halos, the scatters in the density of baryons and dark matter are strongly coupled at large scales (r > R 200), but the coupling between gas and dark matter density profiles fades near the core of halos (r < 0.3R 200). We then show that the correlation between halo profile and integrated quantities induces a radius-dependent additive bias in the profile observables of halos when halos are selected on properties other than their mass. We discuss the impact of this effect on cluster abundance and cross-correlation cosmology with multiwavelength cosmological surveys.

Keywords: galaxy dark matter halos; galaxy clusters; galactic and extragalactic astronomy; cold dark matter; circumgalactic medium; galaxy structure
Physics of Eclipsing Binaries. IV. The Impact of Interstellar Extinction on the Light Curves of Eclipsing Binaries

Traditionally, the effects of interstellar extinction on binary star light curves have been treated as a uniform reduction in the observed brightness of the system that is independent of the orbital phase. However, unless the orbital plane of the system coincides with the plane of the sky, or if the two stars are completely identical and present with minimal mutual irradiation and tidal/rotational distortions, then this is unlikely to be an accurate representation of the effect of interstellar extinction. Here, we present an updated treatment of interstellar extinction as incorporated in the PHOEBE 2.2 release (publicly available from http://phoebe-project.org) and assess the importance of using such an approach in the modeling of different types of binary systems. We also present the incorporation of PHOENIX model atmospheres into the PHOEBE 2.2 release, providing increased fidelity on computed observables down to lower temperatures than previously available. The importance of these new code developments is then highlighted via an extincted toy model of the eclipsing white-dwarf-subdwarf binary SDSS J235524.29+044855.7, demonstrating that, in the age of the Rubin Observatory Legacy Survey of Space and Time as well as complementary space-based photometric missions, a proper accounting for extinction and as well as the use of realistic model atmospheres will be essential in deriving accurate binary parameters.

Keywords: eclipsing binary stars; binary stars; extinction
Where Did the Amaterasu Particle Come From?

The Telescope Array Collaboration recently reported the detection of a cosmic-ray particle, "Amaterasu," with an extremely high energy of 2.4 × 1020 eV. Here we investigate its probable charge and the locus of its production. Interpreted as a primary iron nucleus or slightly stripped fragment, the event fits well within the existing paradigm for UHECR composition and spectrum. Using the most up-to-date modeling of the Galactic magnetic field strength and structure, and taking into account uncertainties, we identify the likely volume from which it originated. We estimate a localization uncertainty on the source direction of 6.6% of 4π or 2726 deg2. The uncertainty of magnetic deflections and the experimental energy uncertainties contribute about equally to the localization uncertainty. The maximum source distance is 8–50 Mpc, with the range reflecting the uncertainty on the energy assignment. We provide sky maps showing the localization region of the event and superimpose the location of galaxies of different types. There are no candidate sources among powerful radio galaxies. An origin in active galactic nuclei or star-forming galaxies is unlikely but cannot be completely ruled out without a more precise energy determination. The most straightforward option is that Amaterasu was created in a transient event in an otherwise undistinguished galaxy.

Keywords: cosmic rays; ultra-high-energy cosmic radiation; milky way magnetic fields; cosmic ray astronomy
Searching for TeV Dark Matter in Irregular Dwarf Galaxies with HAWC Observatory

We present the results of dark matter (DM) searches in a sample of 31 dwarf irregular (dIrr) galaxies within the field of view of the HAWC Observatory. dIrr galaxies are DM-dominated objects in which astrophysical gamma-ray emission is estimated to be negligible with respect to the secondary gamma-ray flux expected by annihilation or decay of weakly interacting massive particles (WIMPs). While we do not see any statistically significant DM signal in dIrr galaxies, we present the exclusion limits (95% C.L.) for annihilation cross section and decay lifetime for WIMP candidates with masses between 1 and 100 TeV. Exclusion limits from dIrr galaxies are relevant and complementary to benchmark dwarf Spheroidal (dSph) galaxies. In fact, dIrr galaxies are targets kinematically different from benchmark dSph, preserving the footprints of different evolution histories. We compare the limits from dIrr galaxies to those from ultrafaint and classical dSph galaxies previously observed with HAWC. We find that the constraints are comparable to the limits from classical dSph galaxies and ~2 orders of magnitude weaker than the ultrafaint dSph limits.

Keywords: dark matter; cold dark matter; galaxies; dwarf irregular galaxies; particle astrophysics; gamma-rays