adsabs/SciX_UAT_keywords huggingface dataset:
Microphysics of Diffusive Shock Acceleration: Impact on the Spectrum of Accelerated Particles

Diffusive shock acceleration at collisionless shocks remains the most likely process for accelerating particles in a variety of astrophysical sources. While the standard prediction for strong shocks is that the spectrum of accelerated particles is universal, f(p) ∝ p -4, numerous phenomena affect this simple conclusion. In general, the nonlinear dynamical reaction of accelerated particles leads to a concave spectrum, steeper than p -4 at momenta below a few tens of GeV c -1 and harder than the standard prediction at high energies. However, the nonlinear effects become important in the presence of magnetic field amplification, which in turn leads to higher values of the maximum momentum p max. It was recently discovered that the self-generated perturbations that enhance particle scattering, when advected downstream, move in the same direction as the background plasma, so that the effective compression factor at the shock decreases and the spectrum becomes steeper. We investigate the implications of the excitation of the non-resonant streaming instability on these spectral deformations, the dependence of the spectral steepening on the shock velocity, and the role played by the injection momentum.

Keywords: supernova remnants; galactic cosmic rays
Artificial Broadcasts as Galactic Populations. II. Comparing Individualist and Collective Bounds on Broadcast Populations in Single Galaxies

The search for extraterrestrial intelligence includes efforts to constrain populations of artificial broadcasts in other galaxies. Previous efforts use individualist methods, searching for single broadcasts with high signal-to-noise ratio. These would be detected as observables with extreme values. This approach is limited to very bright broadcasts and also is subject to confusion, where a large number of broadcasts blend together to form a noise continuum. The mean value of the total emission provides an additional collective bound: the luminosity of the transmitters is no higher than the galaxy's observed luminosity. Using the framework developed in Paper I, I evaluate how confusion affects individualist searches. I then compare individualist and collective approaches for radio broadcasts from the Milky Way, M31, and three Virgo Cluster elliptical galaxies. For current observations, confusion blurs narrowband radio broadcasts together in the Virgo ellipticals when there is one broadcast per gigahertz per 1000 stars. The collective bound implies fewer than $\sim {10}^{6}{(\bar{{\ell }}/{10}^{13}\ {\rm{W}})}^{-1}$ L-band broadcasts per star per gigahertz in the Milky Way wideband and is about 10 and 400 times stronger in M31 and M59, respectively. Applying the collective bound to the far-infrared–radio correlation yields constraints on radio broadcast populations in star-forming galaxies throughout the Universe. The collective bound allows us to rule out large regions of broadcast population parameter space even for distant galaxies. It also imposes constraints on gamma-ray, neutrino, and gravitational-wave broadcasts in the nearest galaxies.

Keywords: search for extraterrestrial intelligence; technosignatures; galaxy luminosities; astronomical techniques; radio astronomy; spatial point processes
A Meteor Spectroscopic Survey in the Nullarbor

We report the start of science operations of a meteor spectroscopic survey in the Nullarbor region, Western Australia. The observation program consists of well-proven observatories developed as part of the All-Sky Meteor Orbit System (AMOS) project. These comprise high-sensitivity all-sky imaging units, as well as spectroscopic instruments observing brighter meteors. They are co-located with Desert Fireball Network (DFN) instruments, which themselves provide high-resolution astrometry for fireballs. There are two goals for this program. One is to keep a constant watch on meteor activity by always having one AMOS sub-network in the dark. The second is to provide spectroscopic coverage for recovered meteorites by the DFN, establishing essential calibration points between meteoritic samples and fireball spectra.

Keywords: fireballs; spectroscopy; meteorites
The CAMELS Multifield Data Set: Learning the Universe's Fundamental Parameters with Artificial Intelligence

We present the Cosmology and Astrophysics with Machine Learning Simulations (CAMELS) Multifield Data set (CMD), a collection of hundreds of thousands of 2D maps and 3D grids containing many different properties of cosmic gas, dark matter, and stars from more than 2000 distinct simulated universes at several cosmic times. The 2D maps and 3D grids represent cosmic regions that span ~100 million light-years and have been generated from thousands of state-of-the-art hydrodynamic and gravity-only N-body simulations from the CAMELS project. Designed to train machine-learning models, CMD is the largest data set of its kind containing more than 70 TB of data. In this paper we describe CMD in detail and outline a few of its applications. We focus our attention on one such task, parameter inference, formulating the problems we face as a challenge to the community. We release all data and provide further technical details at https://camels-multifield-dataset.readthedocs.io.

Keywords: cosmological parameters from large-scale structure; magnetohydrodynamical simulations; astrostatistics; n-body simulations
A Mystery in Chamaeleon: Serendipitous Discovery of a Galactic Symbiotic Nova

We present the serendipitous discovery of a low optical-luminosity nova occurring in a D-type symbiotic binary star system in the Milky Way. We lay out the extensive archival data alongside new follow-up observations related to the stellar object CN Cha in the constellation of Chamaeleon. The object had long period (250 days), high amplitude (3 mag) optical variability in its recent past, preceding an increase in optical brightness by 8 magnitudes and a persistence at this brightness for about 3 yr, followed by a period of 1.4 mag yr-1 dimming. The object's current optical luminosity seems to be dominated by Hα emission, which also exhibits blueshifted absorption (a P-Cygni-like profile). After consideration of a number of theories to explain these myriad observations, we determine that CN Cha is most likely a symbiotic (an evolved-star-white-dwarf binary) system that has undergone a long-duration, low optical brightness, nova, placing it squarely in the class of so-called "slow novae," of which there are only a few known examples. The duration of the optical plateau in CN Cha would make it the shortest timescale plateau of any known slow symbiotic novae.

Keywords: novae; symbiotic binary stars; interacting binary stars
TOI-811b and TOI-852b: New Transiting Brown Dwarfs with Similar Masses and Very Different Radii and Ages from the TESS Mission

We report the discovery of two transiting brown dwarfs (BDs), TOI-811b and TOI-852b, from NASA's Transiting Exoplanet Survey Satellite mission. These two transiting BDs have similar masses but very different radii and ages. Their host stars have similar masses, effective temperatures, and metallicities. The younger and larger transiting BD is TOI-811b at a mass of Mb = 59.9 ± 13.0MJ and radius of Rb = 1.26 ± 0.06RJ, and it orbits its host star in a period of P = 25.16551 ± 0.00004 days. We derive the host star's age of ${93}_{-29}^{+61}$ Myr from an application of gyrochronology. The youth of this system, rather than external heating from its host star, is why this BD's radius is relatively large. This constraint on the youth of TOI-811b allows us to test substellar mass-radius evolutionary models at young ages where the radius of BDs changes rapidly. TOI-852b has a similar mass at Mb = 53.7 ± 1.4MJ but is much older (4 or 8 Gyr, based on bimodal isochrone results of the host star) and is also smaller with a radius of Rb = 0.83 ± 0.04RJ. TOI-852b's orbital period is P = 4.94561 ± 0.00008 days. TOI-852b joins the likes of other old transiting BDs that trace out the oldest substellar mass-radius evolutionary models where contraction of the BD's radius slows and approaches a constant value. Both host stars have a mass of M⋆ = 1.32M⊙ ± 0.05 and differ in their radii, Teff, and [Fe/H], with TOI-811 having R⋆ = 1.27 ± 0.09R⊙, Teff = 6107 ± 77 K, and [Fe/H] = + 0.40 ± 0.09 and TOI-852 having R⋆ = 1.71 ± 0.04R⊙, Teff = 5768 ± 84 K, and [Fe/H] = + 0.33 ± 0.09. We take this opportunity to examine how TOI-811b and TOI-852b serve as test points for young and old substellar isochrones, respectively.

Keywords: brown dwarfs; radial velocity; transit photometry; spectroscopy; photometry; substellar companion stars
Ionized and Atomic Interstellar Medium in the z = 6.003 Quasar SDSS J2310+1855

Observing the interstellar medium (ISM) in the z ≳ 6 quasar host galaxies is essential for understanding the coevolution between supermassive black holes and their hosts. To probe the gas physical conditions and search for imprints of active galactic nuclei (AGNs) on the ISM, we report ALMA observations of the [N II]122 μm and [O I]146 μm lines and the underlying continuum from the z = 6.003 quasar SDSS J231038.88+185519.7. Together with previous [C II]158 μm and [O III]88 μm observations, we use the ratios of these fine-structure lines to probe the ISM properties. Similar to other high-z systems, this object exhibits a [C II]158 μm/[O I]146 μm ratio comparable to the lowest values found in local (ultra)luminous infrared galaxies, suggesting a "warmer" and "denser" gas component compared to typical local systems. The [O III]88 μm/[O I]146 μm ratio is lower than that of other local and high-z systems, indicating a smaller ionized gas fraction in this quasar. The [O III]88 μm/[N II]122 μm ratio is comparable to that of local systems and suggests a metallicity of Z/Z⊙ = 1.5-2.1. Based on the [N II]122 μm detection, we estimate that 17% of the [C II]158 μm emission is associated with ionized gas. The [N II]122 μm line shows a "flux deficit" comparable to local systems. The [O I]146 μm line, with an [O I]146 μm/FIR ratio >2× than expected from the local relation, indicates no [O I]146 μm deficit. The low [C II]158 μm/[O I]146 μm ratio, together with the high [O I]146 μm/FIR ratio in J2310+1855, reveals that the warm and dense gas is likely a result of AGN heating of the ISM.

Keywords: interstellar medium; quasars; active galactic nuclei; high-redshift galaxies; early universe; submillimeter astronomy; dust continuum emission
Radioactive Planet Formation

Young stellar objects are observed to have large X-ray fluxes and are thought to produce commensurate luminosities in energetic particles (cosmic rays). This particle radiation, in turn, can synthesize short-lived radioactive nuclei through spallation. With a focus on 26Al, this paper estimates the expected abundances of radioactive nuclei produced by spallation during the epoch of planet formation. In this model, cosmic rays are accelerated near the inner truncation radii of circumstellar disks, rX ≈ 0.1 au, where intense magnetic activity takes place. For planets forming in this region, radioactive abundances can be enhanced over the values inferred for the early solar system (from meteoritic measurements) by factors of ~10-20. These short-lived radioactive nuclei influence the process of planet formation and the properties of planets in several ways. The minimum size required for planetesimals to become fully molten decreases with increasing levels of radioactive enrichment, and such melting leads to loss of volatile components, including water. Planets produced with an enhanced radioactive inventory have significant internal luminosity, which can be comparable to that provided by the host star; this additional heating affects both atmospheric mass loss and chemical composition. Finally, the habitable zone of red dwarf stars is coincident with the magnetic reconnection region, so that planets forming at those locations will experience maximum exposure to particle radiation and subsequent depletion of volatiles.

Keywords: exoplanet astronomy; exoplanet formation; exoplanet evolution; exoplanet structure; nucleosynthesis; cosmic ray nucleosynthesis
Evidence of a Massive Stellar Disruption in the X-Ray Spectrum of ASASSN-14li

The proximity and duration of the tidal disruption event ASASSN-14li led to the discovery of narrow, blueshifted absorption lines in X-rays and UV. The gas seen in X-ray absorption is consistent with bound material close to the apocenter of elliptical orbital paths, or with a disk wind similar to those seen in Seyfert-1 active galactic nuclei. We present a new analysis of the deepest high-resolution XMM-Newton and Chandra spectra of ASASSN-14li. Driven by the relative strengths of He-like and H-like charge states, the data require [N/C] ≥ 2.4, in qualitative agreement with UV spectral results. Flows of the kind seen in the X-ray spectrum of ASASSN-14li were not clearly predicted in simulations of TDEs; this left open the possibility that the observed absorption might be tied to gas released in prior active galactic nucleus (AGN) activity. However, the abundance pattern revealed in this analysis points to a single star rather than a standard AGN accretion flow comprised of myriad gas contributions. The simplest explanation of the data is likely that a moderately massive star (M ≳ 3 M ⊙) with significant CNO processing was disrupted. An alternative explanation is that a lower mass star was disrupted that had previously been stripped of its envelope. We discuss the strengths and limitations of our analysis and these interpretations.

Keywords: black hole physics; high energy astrophysics
A Possible Gamma-Ray Enhancement Event in Tycho's Supernova Remnant

We report a possible γ-ray enhancement event detected from Tycho's supernova remnant (SNR), the outcome of a type Ia supernova explosion that occurred in the year 1572. The event lasted for 1.5 yr and showed a factor of 3.6 flux increase mainly in the energy range of 4-100 GeV, while notably accompanied with two 478 GeV photons. Several young SNRs (including Tycho's SNR) were previously found to show peculiar X-ray structures with flux variations in one- or several-year timescales, such an event at γ-ray energies is for the first time seen. The year-long timescale of the event suggests a synchrotron radiation process, but the hard γ-ray emission requires extreme conditions of either ultrahigh energies for the electrons up to ~10 PeV (well above the cosmic-ray knee energy) or high inhomogeneity of the magnetic field in the SNR. This event in Tycho's SNR is likely analogous to the γ-ray flares observed in the Crab Nebula, the comparably short timescales of them both requiring a synchrotron process, and similar magnetohydrodynamic processes such as magnetic reconnection would be at work as well in the SNR to accelerate particles to ultrarelativistic energies. The event, if confirmed, helps reveal the more complicated side of the physical processes that can occur in young SNRs.

Keywords: high energy astrophysics; supernova remnants; gamma-rays
Beyond Gaussian Noise: A Generalized Approach to Likelihood Analysis with Non-Gaussian Noise

Likelihood analysis is typically limited to normally distributed noise due to the difficulty of determining the probability density function of complex, high-dimensional, non-Gaussian, and anisotropic noise. This is a major limitation for precision measurements in many domains of science, including astrophysics, for example, for the analysis of the cosmic microwave background, gravitational waves, gravitational lensing, and exoplanets. This work presents Score-based LIkelihood Characterization, a framework that resolves this issue by building a data-driven noise model using a set of noise realizations from observations. We show that the approach produces unbiased and precise likelihoods even in the presence of highly non-Gaussian correlated and spatially varying noise. We use diffusion generative models to estimate the gradient of the probability density of noise with respect to data elements. In combination with the Jacobian of the physical model of the signal, we use Langevin sampling to produce independent samples from the unbiased likelihood. We demonstrate the effectiveness of the method using real data from the Hubble Space Telescope and James Webb Space Telescope.

Keywords: james webb space telescope; hubble space telescope; non-gaussianity; astronomy image processing; observational astronomy; bayesian statistics; ccd observation; cosmic rays; posterior distribution; neural networks; astronomy data analysis; computational methods
Nonparametric Inference of the Population of Compact Binaries from Gravitational-wave Observations Using Binned Gaussian Processes

The observation of gravitational waves from multiple compact binary coalescences by the LIGO-Virgo-KAGRA detector networks has enabled us to infer the underlying distribution of compact binaries across a wide range of masses, spins, and redshifts. In light of the new features found in the mass spectrum of binary black holes and the uncertainty regarding binary formation models, nonparametric population inference has become increasingly popular. In this work, we develop a data-driven clustering framework that can identify features in the component mass distribution of compact binaries simultaneously with those in the corresponding redshift distribution, from gravitational-wave data in the presence of significant measurement uncertainties, while making very few assumptions about the functional form of these distributions. Our generalized model is capable of inferring correlations among various population properties, such as the redshift evolution of the shape of the mass distribution itself, in contrast to most existing nonparametric inference schemes. We test our model on simulated data and demonstrate the accuracy with which it can reconstruct the underlying distributions of component masses and redshifts. We also reanalyze public LIGO-Virgo-KAGRA data from events in GWTC-3 using our model and compare our results with those from some alternative parametric and nonparametric population inference approaches. Finally, we investigate the potential presence of correlations between mass and redshift in the population of binary black holes in GWTC-3 (those observed by the LIGO-Virgo-KAGRA detector network in their first three observing runs), without making any assumptions about the specific nature of these correlations.

Keywords: gravitational waves; gravitational wave astronomy; black holes; compact objects; high energy astrophysics
Top-of-the-atmosphere and Vertical Cloud Structure of a Fast-rotating Late T Dwarf

Only a handful of late T brown dwarfs have been monitored for spectrophotometric variability, leaving incomplete the study of the atmospheric cloud structures of the coldest brown dwarfs, which share temperatures with some cold, directly imaged exoplanets. 2MASS J00501994-332240 is a T7.0 rapidly rotating, field brown dwarf that showed low-level photometric variability in data obtained with the Spitzer Space Telescope. We monitored 2MASS J00501994-332240 during ~2.6 hr with MOSFIRE, installed at the Keck I telescope, with the aim of constraining its near-infrared spectrophotometric variability. We measured fluctuations with a peak-to-peak amplitude of 1.48% ± 0.75% in the J-band photometric light curve, an amplitude of 0.62% ± 0.18% in the J-band spectrophotometric light curve, an amplitude of 1.26% ± 0.93% in the H-band light curve, and an amplitude of 5.33% ± 2.02% in the CH4 - H2O band light curve. Nevertheless, the Bayesian information criterion does not detect significant variability in any of the light curves. Thus, given the detection limitations due to the MOSFIRE sensitivity, we can only claim tentative low-level variability for 2M0050-3322 in the best-case scenario. The amplitudes of the peak-to-peak fluctuations measured for 2MASS J00501994-332240 agree with the variability amplitude predictions of general circulation models for a T7.0 brown dwarf for an edge-on object. Radiative transfer models predict that the Na2S and KCl clouds condense at pressures lower than that traced by the CH4-H2O band, which might explain the higher peak-to-peak fluctuations measured for this light curve. Finally, we provide a visual recreation of the map provided by general circulation models and the vertical structure of 2MASS J00501994-332240 provided by radiative transfer models.

Keywords: t dwarfs; atmospheric variability
Fantastic Fits with fantasy of Active Galactic Nuclei Spectra: Exploring the Fe II Emission near the Hα Line

In this study, a refined approach for multicomponent fitting of active galactic nuclei (AGNs) spectra is presented utilizing the newly developed Python code Fully Automated pythoN Tool for AGN Spectra analYsis (fantasy). AGN spectra are modeled by simultaneously considering the underlying broken power-law continuum, predefined emission line lists, and an Fe II model, which is here extended to cover the wavelength range 3700-11000 Å. The Fe II model, founded solely on atomic data, effectively describes the extensive emission of the complex iron ion in the vicinity of the Hγ and Hβ lines, as well as near the Hα line, which was previously rarely studied. The proposed spectral fitting approach is tested on a sample of high-quality AGN spectra from the Sloan Digital Sky Survey Data Release 17. The results indicate that when Fe II emission is present near Hβ, it is also detected redward from Hα, potentially contaminating the broad Hα line wings and thus affecting the measurements of its flux and width. The production of Fe II emission is found to be strongly correlated with Eddington luminosity and appears to be controlled by a similar mechanism as the hydrogen Balmer lines. The study highlights the benefits of fitting type 1 AGN spectra with the fantasy code, pointing that it may be used as a robust tool for analyzing a large number of AGN spectra in the coming spectral surveys.

Keywords: active galactic nuclei; quasars; atomic data; spectral line lists
The Giant Metrewave Radio Telescope Cold-HI AT z ≈ 1 Survey

We describe the design, data analysis, and basic results of the Giant Metrewave Radio Telescope Cold-HI AT z ≈ 1 (GMRT-CATz1) survey, a 510 hr upgraded GMRT HI 21 cm emission survey of galaxies at z = 0.74-1.45 in the DEEP2 survey fields. The GMRT-CAT z1 survey is aimed at characterizing HI in galaxies during and just after the epoch of peak star formation activity in the universe, a key epoch in galaxy evolution. We obtained high-quality HI 21 cm spectra for 11,419 blue star-forming galaxies at z = 0.74-1.45, in seven pointings on the DEEP2 subfields. We detect the stacked HI 21 cm emission signal of the 11,419 star-forming galaxies, which have an average stellar mass of M * ≈ 1010 M ⊙, at 7.1σ statistical significance, obtaining an average HI mass of <M H I > = (13.7 ± 1.9) × 109 M ⊙. This is significantly higher than the average HI mass of <M H I > = (3.96 ± 0.17) × 109 M ⊙ in star-forming galaxies at z ≈ 0 with an identical stellar-mass distribution. We stack the rest-frame 1.4 GHz continuum emission of our 11,419 galaxies to infer an average star formation rate (SFR) of 8.07 ± 0.82 M ⊙ yr-1. Combining our average HI mass and average SFR estimates yields an HI depletion timescale of 1.70 ± 0.29 Gyr, for star-forming galaxies at z ≈ 1, ≈3 times lower than that of local galaxies. We thus find that, although main-sequence galaxies at z ≈ 1 have a high HI mass, their short HI depletion timescale is likely to cause quenching of their star formation activity in the absence of rapid gas accretion from the circumgalactic medium.

Keywords: galaxy evolution; radio spectroscopy; neutral hydrogen clouds; high-redshift galaxies