Sazuna/UAT_keywords huggingface dataset:
On the Intermittency of Hot Plasma Loops in the Solar Corona. A recent analysis has suggested that the heating of plasma loops in the solar corona depends not just on the Poynting flux but also on processes yet to be identified. This discovery reflects and refines earlier questions such as, Why and how are entire hydromagnetic structures only intermittently loaded with bright coronal plasma? The present work scrutinizes more chromospheric and coronal data, with the aim of finding reproducible observational constraints on coronal heating mechanisms. Six independent scans of chromospheric active-region magnetic fields are investigated and correlated to overlying hot plasma loops. For the first time, the footpoints of over 30 bright plasma loops are thus related to scalar proxies for the Poynting fluxes measured from the upper chromosphere. Although imperfect, the proxies all indicate a general lack of correlation between footpoint Poynting flux and loop brightness. Our findings consolidate the claim that unobserved physical processes are at work, which govern the heating of long-lived coronal loops.

Keywords: Solar active region magnetic fields, Solar coronal heating, Active sun, Solar chromosphere
Refinement of Global Coronal and Interplanetary Magnetic Field Extrapolations Constrained by Remote-sensing and In Situ Observations at the Solar Minimum. Solar magnetic fields are closely related to various physical phenomena on the Sun, which can be extrapolated with different models from photospheric magnetograms. However, the open flux problem (OFP), the underestimation of the magnetic field derived from the extrapolated model, is still unsolved. To minimize the impact of the OFP, we propose three evaluation parameters to quantitatively evaluate magnetic field models and determine the optimal free parameters in the models by constraining the coronal magnetic fields and the interplanetary magnetic fields (IMFs) with real observations. Although the OFP still exists, we find that magnetic field lines traced from the coronal models effectively capture the intricate topological configurations observed in the corona, including streamers and plumes. The OFP is lessened by using the Helioseismic and Magnetic Imager synoptic map instead of the Global Oscillation Network Group daily synoptic maps, and the potential field source surface + potential field current sheet (PFSS+PFCS) model instead of the current sheet source surface (CSSS) model. For Carrington Rotation 2231 at the solar minimum, we suggest that the optimal parameters for the PFSS+PFCS model are R ss = 2.2–2.5 R ☉ and R scs = 10.5–14.0 R ☉, as well as for the CSSS model, are R cs = 2.0–2.4 R ☉, R ss = 11.0–14.7 R ☉, and a = 1.0 R ☉. Despite the IMFs at 1 au being consistent with the measurements by artificially increasing the polar magnetic fields, the IMFs near the Sun are still underestimated. The OFP might be advanced by improving the accuracy of both the weak magnetic fields and polar magnetic fields, especially considering magnetic activities arising from interplanetary physical processes.

Keywords: Solar photosphere, Solar wind, Interplanetary magnetic fields, Solar magnetic fields, Solar corona
Magnetic Spectra Comparison for Kappa-distributed Whistler Electron Fluctuations. In the inner heliosphere, space measurements have revealed that plasma is well described by the kappa distributions, which are characterized by the value of the κ parameter. This parameter indicates how far plasma is from the ideal Maxwell–Boltzmann equilibrium distribution and gives the distribution a typical high-energy power-law tail. In these quasi-equilibrium conditions, the plasma spontaneously emits electromagnetic fluctuations. When suprathermal electrons are involved, these spontaneous emissions get enhanced, and the kappa distributions improve the description of the related nonthermal effects by taking into account the contribution of these high-energy electrons. Nevertheless, the kappa distributions describe different scenarios in which the velocity distribution may obey a power-law decay. Here, we present a systematic and quantitative comparison of kappa-distributed magnetized plasma through a comparison of magnetic spectra for electron cyclotron whistler mode fluctuations. Our results show that for a kappa distribution with a thermal speed equal to the one obtained in thermal equilibrium, the magnetic field fluctuations exhibit higher energy levels that scale with increasing values of β and decreasing values of κ, even though the same thermal speed is considered for all studied cases. Conversely, for a kappa distribution with a kappa-dependent thermal speed, the magnetic field fluctuations tend to exhibit less total energy with lower kappa values, even when compared to the Maxwellian distribution equilibrium results in the same range of parameters.

Keywords: Interplanetary turbulence, Space plasmas, Solar wind, Plasma astrophysics
Establishment and Application of an Interplanetary Disturbance Index Based on the Solar Wind–Magnetosphere Energy Coupling Function and the Spectral Whitening Method. We develop a preliminary interplanetary disturbance index (J  sW ) by applying the spectral whitening method to an energy coupling function with solar wind measurements during the years 1998–2014 as the input, which can be used as an indicator of perturbations in the near-Earth solar wind. The correlation and temporal variation between J  sW  and the geomagnetic disturbance index (J  pG ) constructed from the same method have been analyzed in detail for 167 geomagnetic storms with the minimum D st index less than or equal to ‑50 nT. The time delay between J  sW  and J  pG  is clearly observable and varies for different events, according to which J  sW  is shifted backward with respect to J  pG . We obtain a fairly good negative correlation between the shifted J  sW  and the J  pG  indices for the majority of events, and the significance level for 88% of the events (i.e., 147 events) does not exceed 0.05. A statistical analysis of the shifted J  sW  and the J  pG  indices for 147 selected events reveals that larger values of J  sW  and smaller magnitudes of J  pG  are commonly accompanied by enhanced southward magnetic fields, which implies that more solar wind energy is entering the magnetosphere and thus causing strong geomagnetic storms. Furthermore, a linear fit of the two indices suggests that the evolution of J  pG  can be predicted about 2 hr in advance based on J  sW , indicating that J  sW  can provide early warnings of possible disturbances in the geomagnetic fields, which is crucial for space weather monitoring and operational forecasting.

Keywords: Solar-terrestrial interactions, Space weather, Solar wind, Interplanetary magnetic fields
Extracting the True Cosmic-ray Relative Intensity Sky Map from Normalized Relative Intensity Data Measured by Air Shower Experiments. We use data from the Tibet AS γ experiment for 4 teraelectronvolt (TeV) cosmic rays as an example to perform a nonlinear interstellar distribution model regression according to the way the observed anisotropy is typically presented, from which we extract normalization factors that allow us to obtain a true relative intensity sky map from the measurements. By using various test statistics, we show that the nonlinear fit significantly outperforms the direct linear fit in its ability to model cosmic-ray anisotropy. The procedure also allows us to produce normalization constants that can trace minute latitudinal variations of experimental response to cosmic-ray intensity. Applying the correction of the latitudinal response function to the Tibet ASγ data, we generate a sky map of true relative intensity. As a result, we observe that the measured and corrected sky maps show significant differences in intensity and angular spectral power. Our full anisotropy sky map of true relative intensity contradicts the assumption that the latitudinal variation in longitudinally averaged flux is negligible. The result further confirms that TeV cosmic-ray anisotropy is dominated by a dipole (ℓ = 1) aligned with the interstellar magnetic field's direction. Our results also confirm the existence of much weaker middle-scale interstellar anisotropy between ℓ = 2 and ℓ = 13.

Keywords: Galactic cosmic rays, Computational methods, Heliosphere
Klein–Nishina Corrections to the Spectra and Light Curves of Gamma-Ray Burst Afterglows. Multiwavelength modeling of the synchrotron radiation from relativistic transients such as gamma-ray burst (GRB) afterglows is a powerful means of exploring the physics of relativistic shocks and of deriving properties of the explosion, such as the kinetic energy of the associated relativistic outflows. Capturing the location and evolution of the synchrotron cooling break is critical to break parameter degeneracies associated with such modeling. However, the shape of the spectrum above the cooling break, as well as the location and evolution of the break itself can be significantly altered by synchrotron self-Compton (SSC) cooling. We present an observer's guide to applying SSC cooling with and without Klein–Nishina (KN) corrections to GRB afterglow modeling. We provide a publicly available Python code to calculate the Compton Y-parameter as a function of electron Lorentz factor, from which we compute changes to the electron distribution, along with KN-corrected afterglow spectra and light curves. In this framework, the canonical synchrotron spectral shapes split into multiple subregimes. We summarize each new spectral shape and describe its observational significance. We discuss how KN corrections can account for harder spectra and shallower decline rates observed in some GRB X-ray afterglows. Our overall aim is to provide an easy application of SSC+KN corrections into analytical multiwavelength modeling frameworks for relativistic transients.

Keywords: Astronomical models, Astronomy data modeling, Gamma-ray bursts, Theoretical models, High energy astrophysics
First Detection of CO Isotopologues in a High-redshift Main-sequence Galaxy: Evidence of a Top-heavy Stellar Initial Mass Function. Recent observations and theories have presented a strong challenge to the universality of the stellar initial mass function (IMF) in extreme environments. A notable example has been found for starburst conditions, where evidence favors a top-heavy IMF, i.e., there is a bias toward massive stars compared to the IMF that is responsible for the stellar mass function and elemental abundances observed in the Milky Way. Local starburst galaxies have star formation rates similar to those in high-redshift main-sequence galaxies, which appear to dominate the stellar mass budget at early epochs. However, the IMF of high-redshift main-sequence galaxies is yet to be probed. Since 13CO and C18O isotopologues are sensitive to the IMF, we have observed these lines toward four strongly lensed high-redshift main-sequence galaxies using the Atacama Large Millimeter/submillimeter Array. Of our four targets, SDSS J0901+1814, at z ≍ 2.26, is seen clearly in 13CO and C18O, the first detection of CO isotopologues in the high-redshift main-sequence galaxy population. The observed 13C/18O ratio, 2.4 ± 0.8, is significantly lower than that of local main-sequence galaxies. We estimate the isotope ratio, oxygen abundance, and stellar mass using a series of chemical evolution models with varying star formation histories and IMFs. All models favor an IMF that is more top-heavy than that of the Milky Way. Thus, as with starburst galaxies, main-sequence galaxies in the high-redshift Universe have a greater fraction of massive stars than a Milky Way IMF would imply.

Keywords: Radio spectroscopy, Isotopic abundances, Initial mass function, High-redshift galaxies
The Empirical and Radiative Transfer Hybrid (EaRTH) Disk Model: Merging Analyses of Protoplanetary Dust Disk Mineralogy and Structure. Our understanding of how exoplanets form and evolve relies on analyses of both the mineralogy of protoplanetary disks and their detailed structures; however, these key complementary aspects of disks are usually studied separately. We present initial results from a hybrid model that combines the empirical characterization of the mineralogy of a disk, as determined from its mid-infrared spectral features, with the MCFOST radiative transfer disk model, a combination we call the Empirical and Radiative Transfer Hybrid (EaRTH) Disk Model. With the results of the mineralogy detection serving as input to the radiative transfer model, we generate mid-infrared spectral energy distributions (SEDs) that reflect both the mineralogical and structural parameters of the corresponding disk. Initial fits of the SED output by the resulting integrated model of Spitzer Space Telescope mid-infrared spectra of the protoplanetary disk orbiting the nearby T Tauri star MP Mus demonstrate the potential advantages of this approach by revealing details like the dominance of micron-sized olivine and micron-sized forsterite in this dusty disk. The simultaneous insight into disk composition and structure provided by the EaRTH Disk methodology should be directly applicable to the interpretation of mid-infrared spectra of protoplanetary disks that will be produced by the James Webb Space Telescope.

Keywords: Circumstellar dust, Dust composition, Young stellar objects, Protoplanetary disks
Identification of Hot Gas around Low-mass Protostars. The low carbon content of Earth and primitive meteorites compared to the Sun and interstellar grains suggests that carbon-rich grains were destroyed in the inner few astronomical units of the young solar system. A promising mechanism to selectively destroy carbonaceous grains is thermal sublimation within the soot line at ≳300 K. To address whether such hot conditions are common among low-mass protostars, we observe CH3CN transitions at 1, 2, and 3 mm with the NOrthern Extended Millimeter Array toward seven low-mass and one intermediate-mass protostar (L bol ∼ 2–300L ⊙), as CH3CN is an excellent temperature tracer. We find &gt;300 K gas toward all sources, indicating that hot gas may be prevalent. Moreover, the excitation temperature for CH3OH obtained with the same observations is always lower (∼135–250 K), suggesting that CH3CN and CH3OH have a different spatial distribution. A comparison of the column densities at 1 and 3 mm shows a stronger increase at 3 mm for CH3CN than for CH3OH. Since the dust opacity is lower at longer wavelengths, this indicates that CH3CN is enhanced in the hot gas compared to CH3OH. If this CH3CN enhancement is the result of carbon-grain sublimation, these results suggest that Earth's initial formation conditions may not be rare.

Keywords: Protostars, Astrochemistry
A Radio Flare in the Long-lived Afterglow of the Distant Short GRB 210726A: Energy Injection or a Reverse Shock from Shell Collisions?. We present the discovery of the radio afterglow of the short gamma-ray burst (GRB) 210726A, localized to a galaxy at a photometric redshift of z ∼ 2.4. While radio observations commenced ≲1 day after the burst, no radio emission was detected until ∼11 days. The radio afterglow subsequently brightened by a factor of ∼3 in the span of a week, followed by a rapid decay (a "radio flare"). We find that a forward shock afterglow model cannot self-consistently describe the multiwavelength X-ray and radio data, and underpredicts the flux of the radio flare by a factor of ≍5. We find that the addition of substantial energy injection, which increases the isotropic kinetic energy of the burst by a factor of ≍4, or a reverse shock from a shell collision are viable solutions to match the broadband behavior. At z ∼ 2.4, GRB 210726A is among the highest-redshift short GRBs discovered to date, as well as the most luminous in radio and X-rays. Combining and comparing all previous radio afterglow observations of short GRBs, we find that the majority of published radio searches conclude by ≲10 days after the burst, potentially missing these late-rising, luminous radio afterglows.

Keywords: Gamma-ray bursts, Radio astronomy, Time domain astronomy, High energy astrophysics
Solar Coronal Heating by Kinetic Alfvén Waves. The utilization of the Cairns distribution serves as a vital tool for characterizing the nonthermal attributes commonly observed in space plasmas. In these intricate plasma environments, extensive measurements have been conducted to monitor the fluctuations inherent in the perturbed electromagnetic (EM) field and the associated Poynting flux, specifically concerning kinetic Alfvén waves (KAWs). Traditionally, these fluctuations have been attributed to gyroradius correction terms within the framework of Maxwellian distributed plasmas. However, our study introduces an innovative perspective grounded in kinetic theory coupled with the Cairns distribution, adept at encapsulating the nonthermal nuances characterized by the index parameter Λ. Within the domain of the solar corona, our investigation centers on the perturbed EM field ratios and the Poynting flux of KAWs, with a foundation in the Cairns distribution function. It is noteworthy that the perpendicular components, although deemed less significant due to the dominance of k ⊥ over k ∥, remain unquantified regarding their relative insignificance. Similarly, the exploration of the imaginary part of the normalized EM field ratio has been a relatively understudied domain. Furthermore, we delve into the nuanced assessment of the power rate I  x /I  z  characterizing the perpendicular and parallel normalized Poynting fluxes (S  x  and S  z ). Intriguingly, we discern that large values of Λ, compared to their Maxwellian counterparts, manifest advantageous attributes, particularly concerning the energization of the plasma over extended distances along the ambient magnetic field lines. The analytical insights gleaned from this study find practical application in understanding phenomena within the solar atmosphere, particularly shedding light on the significant role played by nonthermal particles in the observed heating processes.

Keywords: Solar coronal heating
Multiwavelength Modeling for the Shallow Decay Phase of Gamma-Ray Burst Afterglows. We simulate the emission in the shallow decay phase of gamma-ray burst afterglows using a time-dependent code. We test four models: the energy injection model, evolving the injection efficiency of nonthermal electrons, evolving the amplification of the magnetic field, and the wind model with a relatively low bulk Lorentz factor. All of the four models can reproduce the typical X-ray afterglow lightcurve. The spectral shape depends on not only the parameter values at the time corresponding to the observer time but also the past evolution of the parameters. The model differences appear in the evolution of the broadband spectrum, especially in the inverse Compton component. Future gamma-ray observations with imaging atmospheric Cherenkov telescopes such as the Cherenkov Telescope Array will reveal the mechanism of the shallow decay phase.

Keywords: Shocks, Gamma-ray bursts
Galaxy Ages with Redshift z = 2–4: Stellar Population Synthesis for Candidates in FourStar Galaxy Evolution Survey. Observations of large amounts of massive galaxies with relatively old populations found at high redshifts are challenging galaxy formation scenarios within the standard cosmology. Precise determinations of the average age of these galaxies would be useful for the discussion of this problem. Here we carry out a better constraint of the age of 200 V-shaped spectral energy distribution (SED) nonactive galactic nucleus galaxies at redshifts 2 &lt; z &lt; 4 of the catalog of the FourStar Galaxy Evolution Survey, identified by the V shape in their SED with a Lyman and a Balmer break. The SED fitting includes a main stellar population in addition to a residual younger population and extinction. The galaxies are younger at a higher redshift on average. However, for the galaxies with z &gt; 2.5, we do not see a significant evolution of their average age, with all average ages of the galaxies mostly remaining between 1 and 2 Gyr. Our research finds that most massive galaxies (∼1010 M ⊙) are older (typically &gt; ∼1 Gyr old) and formed earlier than less massive galaxies in our sample.

Keywords: Galaxy ages, Observational cosmology, High-redshift galaxies
The Galaxy–Galaxy Strong Lensing Cross Section and the Internal Distribution of Matter in ΛCDM Substructure. Strong gravitational lensing offers a powerful probe of the detailed distribution of matter in lenses, while magnifying and bringing faint background sources into view. Observed strong lensing by massive galaxy clusters, which are often in complex dynamical states, has also been used to map their dark matter (DM) substructures on smaller scales. Deep high-resolution imaging has revealed the presence of strong lensing events associated with these substructures, namely galaxy-scale sub-halos. However, an inventory of these observed galaxy–galaxy strong lensing (GGSL) events is noted to be discrepant with state-of-the-art ΛCDM simulations. Cluster sub-halos appear to be over-concentrated compared to their simulated counterparts yielding an order-of-magnitude higher value of GGSL. In this paper, we explore the possibility of resolving this observed discrepancy by redistributing the mass within observed cluster sub-halos in ways that are consistent within the ΛCDM paradigm of structure formation. Lensing mass reconstructions from data provide constraints on the mass enclosed within apertures and are agnostic to the detailed mass profile within them. Therefore, as the detailed density profile within cluster sub-halos currently remains unconstrained by data, we are afforded the freedom to redistribute the enclosed mass. We investigate if rearranging the mass to a more centrally concentrated density profile helps alleviate the GGSL discrepancy. We report that refitting cluster sub-halos to the ubiquitous ΛCDM-motivated Navarro–Frenk–White profile, and further modifying them to include significant baryonic components, does not resolve this tension. A resolution to this persisting GGSL discrepancy may require more careful exploration of alternative DM models.

Keywords: Cosmology, Galaxy dark matter halos, Strong gravitational lensing, Galaxy clusters
Cosmic-Ray Transport in the Presence of a Fisk-type Heliospheric Magnetic Field: Investigating the Influence of Drift. Drifts due to the gradients in, and curvatures of, the heliospheric magnetic field (HMF) play a significant role in the transport of galactic cosmic rays (GCRs) in the heliosphere. Although this has been well studied for the Parker HMF, the influence of Fisk-type fields, with their unique geometry, has hitherto received less attention. Here, drift velocity profiles computed for a Schwadron–Parker hybrid field are compared with those for a purely Parkerian field. Furthermore, the influence of this field on GCR modulation, as computed with a 3D, ab initio, modulation model, is investigated. Globally, the differences between the computed intensities are small. Nevertheless, local measures, such as azimuthal variations in the GCR intensities, show a significant influence of the Schwadron–Parker hybrid field on GCR transport.

Keywords: Galactic cosmic rays, Interplanetary turbulence, Heliosphere