adsabs/SciX_UAT_keywords huggingface dataset:
Gaussian Process Modeling Fermi-LAT γ-Ray Blazar Variability: A Sample of Blazars with γ-Ray Quasi-periodicities

Blazar variability may be driven by stochastic processes. On the other hand, quasi-periodic oscillation (QPO) behaviors were recently reported to be detected in the Fermi-LAT data of blazars. However, the significances of these QPO signals given by traditional Fourier-like methods are still questioned. We analyze γ-ray light curves of the QPO blazars with two Gaussian process methods, CARMA and celerite, to examine the appropriateness of Gaussian processes for characterizing γ-ray light curves of blazars and the existence of the reported QPOs. We collect a sample of 27 blazars with possible γ-ray periodicity and generate their ∼11 yr Fermi-LAT light curves. We apply the Gaussian process models to the γ-ray light curves, and build their intrinsic power spectral densities (PSDs). The results show that in general the γ-ray light curves can be characterized by CARMA and celerite models, indicating that γ-ray variabilities of blazars are essentially Gaussian processes. The resulting PSDs are generally the red noise shapes with slopes between -0.6 and -1.7. Possible evidence for the γ-ray QPOs in PKS 0537-441 and PG 1553+113 are found in the Gaussian process modelings.

Keywords: blazars; gamma-rays; time series analysis; period search; gaussian processes regression
A Solar-cycle Study of Coronal Rotation: Large Variations, Rapid Changes, and Implications for Solar-wind Models

Information on the rotation rate of the corona, and its variation over latitude and solar cycle, is valuable for making global connections between the corona and the Sun, for global estimates of reconnection rates and as a basic parameter for solar-wind modeling. Here, we use a time series of tomographical maps gained from coronagraph observations between 2007 and 2020 to directly measure the longitudinal drift of high-density streamers over time. The method reveals abrupt changes in rotation rates, revealing a complex relationship between the coronal rotation and the underlying photosphere. The majority of rates are between -1.°0 to +0.°5 day-1 relative to the standard Carrington rate of 14.°18 day-1, although rates are measured as low as -2.°2 day-1 and as high as 1.°6 day-1. Equatorial rotation rates during the 2008 solar minimum are slightly faster than the Carrington rate, with an abrupt switch to slow rotation in 2009, then a return to faster rates in 2017. Abrupt changes and large variations in rates are seen at all latitudes. Comparison with a magnetic model suggests that periods of equatorial fast rotation are associated with times when a large proportion of the magnetic footpoints of equatorial streamers are near the equator, and we interpret the abrupt changes in terms of the latitudinal distribution of the streamer photospheric footpoints. The coronal rotation rate is a key parameter for solar-wind models, and variations of up to a degree per day or more can lead to large systematic errors over forecasting periods of longer than a few days. The approach described in this paper gives corrected values that can form a part of future forecasting efforts.

Keywords: solar corona; solar atmosphere; solar cycle; solar differential rotation; solar physics; solar rotation; solar wind
Effects of Fully Relativistic Condition on Electron Cyclotron Maser Emission

The electron cyclotron maser (ECM) instability is a very important nonthermal radiation mechanism. It has been developed by proposing various electron distribution functions as well as the relativistic resonance condition, called the semirelativistic correction. Taking account of the relativistic effects of both the velocity distribution of energetic electrons and the resonance condition, called the fully relativistic correction, the present paper investigates the ECM instability driven by a power-law electron distribution with a low-energy cutoff. The results show that (1) both in the semirelativistic and fully relativistic cases, the growth rate and relative frequency bandwidth of ordinary (O) and extraordinary (X) modes show a positive correlation with cutoff energy E c , i.e., the peak frequency decreases with increasing E c ; (2) the peak frequency ratio (H peak/F peak) of the harmonic and fundamental waves is always ~2; (3) compared with the semirelativistic case, the fully relativistic case has a larger growth rate (for both the O and X mode) and a smaller peak frequency (only for the O mode) for energy > 50 keV, and there is almost no difference at lower energy for the two cases; (4) the peak frequency of the X1 mode can be higher than its cutoff frequency in a strongly magnetized plasma, implying that the X1 mode emission may escape more easily for a higher E c and stronger magnetic field. These results can be helpful for us to understand better the physics of radio bursts from the Sun and other objects.

Keywords: astrophysical masers; plasma astrophysics; radio bursts; non-thermal radiation sources; solar radio emission
A High-mass, Young Star-forming Core Escaping from Its Parental Filament

We studied the unique kinematic properties in massive filament G352.63-1.07 at 103 au spatial scale with the dense molecular tracers observed with the Atacama Large Millimeter/submillimeter Array. We find the central massive core M1 (12 M ⊙) being separated from the surrounding filament with a velocity difference of $v-{\overline{v}}_{\mathrm{sys}}=-2\,\mathrm{km}\,{{\rm{s}}}^{-1}$ and a transverse separation within 3″. Meanwhile, as shown in multiple dense-gas tracers, M1 has a spatial extension closely aligned with the main filament and is connected to the filament toward both its ends. M1 thus represents a very beginning state for a massive, young star-forming core escaping from the parental filament, within a timescale of ~4000 yr. Based on its kinetic energy (3.5 × 1044 erg), the core escape is unlikely solely due to the original filament motion or magnetic field but requires more energetic events such as a rapid intense anisotropic collapse. The released energy also seems to noticeably increase the environmental turbulence. This may help the filament to become stabilized again.

Keywords: star formation; young stellar objects; dense interstellar clouds; interstellar filaments; gravitational collapse
Constraints on Strong Phase Transitions in Neutron Stars

We study current bounds on strong first-order phase transitions (PTs) along the equation of state (EOS) of dense strongly interacting matter in neutron stars, under the simplifying assumption that on either side of the PT, the EOS can be approximated by a simple polytropic form. We construct a large ensemble of possible EOSs of this form, anchor them to chiral effective field theory calculations at nuclear density and perturbative Quantum Chromodynamics at high densities, and subject them to astrophysical constraints from high-mass pulsars and gravitational-wave observations. Within this setup, we find that a PT permits neutron-star solutions with larger radii, but only if the transition begins below twice nuclear saturation density. We also identify a large parameter space of allowed PTs currently unexplored by numerical-relativity studies. Additionally, we locate a small region of parameter space allowing twin-star solutions, though we find them to only marginally pass the current astrophysical constraints. Finally, we find that sizeable cores of high-density matter beyond the PT may be located in the centers of some stable neutron stars, primarily those with larger masses.

Keywords: neutron stars; nuclear physics; nuclear astrophysics; neutron star cores; compact objects
Photometric and Spectroscopic Analysis of Four Contact Binaries

We present the photometric and spectroscopic analysis of four W UMa binaries J015829.5+260333 (hereinafter as J0158), J030505.1+293443 (hereinafter as J0305), J102211.7+310022 (hereinafter as J1022), and KW Psc. The VRcIc band photometric observations are carried out with the 1.3 m Devasthal Fast Optical Telescope (DFOT). For low-resolution spectroscopy, we used the 2 m Himalayan Chandra Telescope (HCT) as well as the archival data from the 4 m LAMOST survey. The systems J0158 and J0305 show a period increase rate of 5.26( ± 1.72) × 10-7 days yr-1 and 1.78( ± 1.52) × 10-6 days yr-1, respectively. The period of J1022 is found to be decreasing with a rate of 4.22 ( ± 1.67) × 10-6 days yr-1. The period analysis of KW Psc displays no change in its period. The PHOEBE package is used for the light-curve modeling and basic parameters are evaluated with the help of the GAIA parallax. The asymmetry of light curves is explained with the assumption of cool spots at specific positions on one of the components of the system. On the basis of temperatures, mass ratios, fill-out factors, and periods, the system J1022 is identified as a W-subtype system while the others show some mixed properties. To probe the chromospheric activities in these W UMa binaries, their spectra are compared with the known inactive stars' spectra. The comparison shows emission in Hα, Hβ, and Ca II. To understand the evolutionary status of these systems, the components are plotted in mass-radius and mass-luminosity planes with other well characterized binary systems. The secondary components of all the systems are away from ZAMS, which indicates that the secondary is more evolved than the primary component.

Keywords: contact binary stars; photometry; spectroscopy; eclipsing binary stars; starspots
The Transformation of Centaurs into Jupiter-family Comets

Centaurs are an ephemeral class of objects that can evolve into Jupiter-family comets (or JFCs) due to gravitational perturbations from the giant planets. In this work, we use numerical integration of massless test particles in the six-body problem (the Sun, four giant planets, and a test particle) to study the transformation of Centaurs into JFCs. We find that Centaurs can transform into JFCs via a rapid, continuous drop in perihelion or aphelion distance to a value below 5.2 au or 7 au, respectively, typically within 5 yr from the start of the drop. We call these JFC perihelion drops and JFC aphelion drops, respectively. These drops are correlated with close approaches to Jupiter. For such perihelion and aphelion drops, the maximum possible fractional change in the associated perihelion or aphelion distance increases with decreasing close-approach distance to Jupiter. A perihelion barrier may exist at 6.3 au. If so, then it must be crossed from above in order for a Centaur to transform into a JFC due to a single close approach to Jupiter. Currently, 93 (or 11%) of the known Centaurs have a perihelion distance, q, below 6.3 au. If the inclination of the orbit of the Centaur to the ecliptic plane is above 10.°2, then orbits with q > 6.3 au and 2 < T J < 3 can exist, where T J is the Tisserand parameter with respect to Jupiter. Small bodies in such orbits could be classified as either Centaurs or JFCs.

Keywords: short period comets; comet dynamics; centaur group; comets; small solar system bodies
A Spectroscopic Survey of Superthin Galaxies

We present spectroscopic observations of superthin galaxies. Superthin galaxies have the thinnest stellar disks among disk galaxies. A sample of 138 superthins was observed in visible light with the 3.5 m telescope at Apache Point Observatory in New Mexico to obtain the rotation curves of the ionized gas in the galaxies. The sample represents the largest survey of superthin galaxies so far and provides a database to investigate the kinematic and dynamic properties of this special type of extragalactic objects. Here we present the rotation curves of our sample objects.

Keywords: dark matter; galaxy dynamics; galaxy rotation curves; galaxy kinematics; galaxy spectroscopy; extragalactic astronomy
The DESI PRObabilistic Value-added Bright Galaxy Survey (PROVABGS) Mock Challenge

The PRObabilistic Value-added Bright Galaxy Survey (PROVABGS) catalog will provide measurements of galaxy properties, such as stellar mass (M *), star formation rate (SFR), stellar metallicity (Z), and stellar age (t age), for >10 million galaxies of the Dark Energy Spectroscopic Instrument (DESI) Bright Galaxy Survey. Full posterior distributions of the galaxy properties will be inferred using state-of-the-art Bayesian spectral energy distribution (SED) modeling of DESI spectroscopy and Legacy Surveys photometry. In this work, we present the SED model, the neural emulator for the model, and the Bayesian inference framework of PROVABGS. Furthermore, we apply the PROVABGS SED modeling on realistic synthetic DESI spectra and photometry, constructed using the L-GALAXIES semi-analytic model. We compare the inferred galaxy properties to the true values of the simulation using a hierarchical Bayesian framework to quantify accuracy and precision. Overall, we accurately infer the true M *, SFR, Z, and t age of the simulated galaxies. However, the priors on galaxy properties induced by the SED model have a significant impact on the posteriors, which we characterize in detail. This work also demonstrates that a joint analysis of spectra and photometry significantly improves the constraints on galaxy properties over photometry alone and is necessary to mitigate the impact of the priors. With the methodology presented and validated in this work, PROVABGS will maximize information extracted from DESI observations and extend current galaxy studies to new regimes and unlock cutting-edge probabilistic analyses. https://github.com/changhoonhahn/provabgs/

Keywords: galactic and extragalactic astronomy; galaxies; galaxy spectroscopy; redshift surveys; spectrophotometry; spectral energy distribution; galaxy properties; galaxy physics; galaxy stellar content; galaxy masses; galaxy formation; astrostatistics
The Betelgeuse Project. III. Merger Characteristics

We previously proposed that Betelgeuse might have been spun up by accreting a companion of about 1 M⊙. Here we explore in more detail the possible systematics of such a merger and a larger range of accreted masses. We use the stellar evolutionary code MESA to add angular momentum to a primary star in core helium burning, core carbon burning, or shell carbon burning. Our models provide a reasonable "natural" explanation for why Betelgeuse has a large, but sub-Keplerian equatorial velocity. They eject sufficient mass and angular momentum in rotationally induced mass loss to reproduce the observed ratio of the equatorial velocity to escape velocity of Betelgeuse, ≈0.23, within a factor of 3 nearly independent of the primary mass, the secondary mass, and the epoch at which merger occurs. Our models suggest that merger of a primary of somewhat less than 15 M⊙ with secondaries from 1 to 10 M⊙ during core helium burning or core carbon burning could yield the equatorial rotational velocity of ∼15 km s-1 attributed to Betelgeuse. For accreting models, a wave of angular momentum is halted at the composition boundary at the edge of the helium core. The inner core is thus not affected by the accretion of the companion in these simulations. Accretion has relatively little effect on the production of magnetic fields in the inner core. Our results do not prove, but do not negate, that Betelgeuse might have ingested a companion of several M⊙.

Keywords: asymptotic giant branch stars; post-asymptotic giant branch stars; supernovae; stellar mergers; late stellar evolution
Detection of Energy Cutoffs in Flare-accelerated Electrons

Energy cutoffs in electron distribution define the lower and upper limits on the energy range of energetic electrons accelerated in solar flares. They are crucial parameters for understanding particle acceleration processes and energy budgets. Their signatures have been reported in studies of flattened flare X-ray spectra, i.e., the impulsive emission of nonthermal bremsstrahlung from energetic electrons impacting ambient, thermal plasma. However, these observations have not provided unambiguous constraints on the cutoffs. Moreover, other processes may result in similar spectral features. Even the existence and necessity of cutoffs as physical parameters of energetic electrons have been under debate. Here we report a search for their signatures in flare-accelerated electrons with two approaches, i.e., in both X-ray spectra and solar energetic particle (SEP) events. These represent two different electron populations, but may contain information of the same acceleration process. By studying a special group of late impulsive flares, and a group of selected SEP events, we found evidence of cutoffs revealed in both X-ray spectra and SEP electron distributions. In particular, we found for the first time consistent low- and high-energy cutoffs in both hard X-ray-producing and escaping electrons in two events. We also showed the importance of high-energy cutoff in studies of spectral shapes. These results provide evidence of cutoffs in flare-accelerated energetic electrons and new clues for constraining electron distribution parameters and particle acceleration models.

Keywords: solar x-ray flares; x-ray telescopes; solar x-ray emission; solar flares; solar flare spectra
The Dark Energy Survey Supernova Program: Corrections on Photometry Due to Wavelength-dependent Atmospheric Effects

Wavelength-dependent atmospheric effects impact photometric supernova flux measurements for ground-based observations. We present corrections on supernova flux measurements from the Dark Energy Survey Supernova Program's 5YR sample (DES-SN5YR) for differential chromatic refraction (DCR) and wavelength-dependent seeing, and we show their impact on the cosmological parameters w and Ω m . We use g - i colors of Type Ia supernovae to quantify astrometric offsets caused by DCR and simulate point-spread functions (PSFs) using the GalSIM package to predict the shapes of the PSFs with DCR and wavelength-dependent seeing. We calculate the magnitude corrections and apply them to the magnitudes computed by the DES-SN5YR photometric pipeline. We find that for the DES-SN5YR analysis, not accounting for the astrometric offsets and changes in the PSF shape cause an average bias of +0.2 mmag and -0.3 mmag, respectively, with standard deviations of 0.7 mmag and 2.7 mmag across all DES observing bands (griz) throughout all redshifts. When the DCR and seeing effects are not accounted for, we find that w and Ω m are lower by less than 0.004 ± 0.02 and 0.001 ± 0.01, respectively, with 0.02 and 0.01 being the 1σ statistical uncertainties. Although we find that these biases do not limit the constraints of the DES-SN5YR sample, future surveys with much higher statistics, lower systematics, and especially those that observe in the u band will require these corrections as wavelength-dependent atmospheric effects are larger at shorter wavelengths. We also discuss limitations of our method and how they can be better accounted for in future surveys.

Keywords: type ia supernovae; photometry; atmospheric effects; cosmology
Assessing the Formation of Solid Hydrogen Objects in Starless Molecular Cloud Cores

The properties of the first-discovered interstellar object (ISO), 1I/2017 ('Oumuamua), differ from both solar system asteroids and comets, casting doubt on a protoplanetary disk origin. In this study, we investigate the possibility that it formed with a substantial H2 ice component in the starless core of a giant molecular cloud. While interstellar solid hydrogen has yet to be detected, this constituent would explain a number of the ISO's properties. We consider the relevant processes required to build decameter-sized, solid hydrogen bodies and assess the plausibility of growth in various size regimes. Via an energy balance argument, we find the most severe barrier to formation is the extremely low temperature required for the favorability of molecular hydrogen ice. However, if deposition occurs, we find that the turbulence within starless cores is conducive for growth into kilometer-sized bodies on sufficiently short timescales. Then, we analyze mass loss in the interstellar medium and determine the necessary size for a hydrogen object to survive a journey to the solar system as a function of ISO age. Finally, we discuss the implications if the H2 explanation is correct, and we assess the future prospects of ISO science. If hydrogen ice ISOs do exist, our hypothesized formation pathway would require a small population of porous, 100 μm dust in a starless core region that has cooled to 2.8 K via adiabatic expansion of the surrounding gas and excellent shielding from electromagnetic radiation and cosmic rays.

Keywords: dark interstellar clouds; interstellar clouds; interstellar medium; interstellar objects; dense interstellar clouds
On the Connection between the Repeated X-Ray Quasiperiodic Oscillation and Warm Absorber in the Active Galaxy RE J1034+396

We conduct an in-depth spectral analysis of ∼1 Ms XMM-Newton data of the narrow line Seyfert 1 galaxy RE J1034+396. The long exposure ensures high spectral quality and provides us with a detailed look at the intrinsic absorption and emission features toward this target. Two warm-absorber (WA) components with different ionization states ( $\mathrm{log}(\xi /\mathrm{erg}\,\mathrm{cm}\,{{\rm{s}}}^{-1})\sim 4$ and $\mathrm{log}(\xi /\mathrm{erg}\,\mathrm{cm}\,{{\rm{s}}}^{-1})\sim 2.5\mbox{--}3$ ) are required to explain the intrinsic absorption features in the Reflection Grating Spectrometer spectra. The estimated outflow velocities are around ‑1400 km s‑1 and ‑(100–300) km s‑1 for the high- and low-ionization WA components, respectively. Both absorbers are located beyond the broad-line region and cannot significantly affect the host environment. We analyze the warm absorbers in different flux states. We also examine the 2007 May observation in the low and high phases of quasiperiodic oscillation (QPO). In contrast to previous analyses showing a negative correlation between the high-ionization WA and the QPO phase, we have found no such variation in this WA component. We discover a broad emission bump in the spectral range of ∼12–18 Å, covering the primary features of the high-ionization WA. This emission bump shows a dramatic change in different source states, and its intensity may positively correlate with the QPO phase. The absence of this emission bump in previous work may contribute to the suggested WA–QPO connection.

Keywords: seyfert galaxies; x-ray astronomy; warm ionized medium; high resolution spectroscopy
A Statistical Study of the Plasma and Composition Distribution inside Magnetic Clouds: 1998-2011

A comprehensive analysis of plasma and composition characteristics inside magnetic clouds (MCs) observed by the Advanced Composition Explorer spacecraft from 1998 February to 2011 August is presented. The results show that MCs have specific interior structures, and MCs of different speeds show differences in composition and structure. Compared with the slow MCs, fast MCs have enhanced mean charge states of iron, oxygen, silicon, magnesium, ${{\rm{O}}}^{7+}/{{\rm{O}}}^{6+}$ , ${{\rm{C}}}^{6+}/{{\rm{C}}}^{5+}$ , ${{\rm{C}}}^{6+}/{{\rm{C}}}^{4+}$ , and ${\mathrm{Fe}}^{\geqslant 16+}/{\mathrm{Fe}}_{\mathrm{total}}$ values. For ionic species in fast MCs, a higher atomic number represents a greater enhancement of mean charge state than slow MCs. We also find that both the fast and slow MCs display bimodal structure distribution in the mean iron charge state ( $\langle Q\rangle \mathrm{Fe}$ ), which suggests that the existence of flux rope prior to the eruption is common. Furthermore, the $\langle Q\rangle \mathrm{Fe}$ , ${\mathrm{Fe}}^{\geqslant 16+}/{\mathrm{Fe}}_{\mathrm{total}}$ , and ${{\rm{O}}}^{7+}/{{\rm{O}}}^{6+}$ ratio distribution inside fast MCs have the feature that the posterior peak is higher than the anterior one. This result agrees with the "standard model" for coronal mass ejection/flares, by which magnetic reconnection occurs beneath the flux rope, thereby ionizing the ions of the posterior part of the flux rope sufficiently by high-energy electron collisions or by direct heating in the reconnection region.

Keywords: solar wind; solar coronal mass ejections; interplanetary physics; solar physics; solar storm; solar flares; solar filament eruptions; solar filaments