Sazuna/UAT_keywords huggingface dataset:
TransFit: An Efficient Framework for Transient Light-curve Fitting with Time-dependent Radiative Diffusion. Modeling the light curves (LCs) of luminous astronomical transients, such as supernovae, is crucial for understanding their progenitor physics, particularly with the exponential growth of survey data. However, existing methods face limitations: efficient semianalytical models (e.g., Arnett-like) employ significant physical simplifications (like time-invariant temperature profiles and simplified heating distributions), often compromising accuracy, especially for early-time LCs. Conversely, detailed numerical radiative transfer simulations, while accurate, are computationally prohibitive for large data sets. This paper introduces TransFit, a novel framework that numerically solves a generalized energy conservation equation, explicitly incorporating time-dependent radiative diffusion, continuous radioactive or central engine heating, and ejecta expansion dynamics. The model accurately captures the influence of key ejecta properties and diverse heating source characteristics on LC morphology, including peak luminosity, rise time, and overall shape. Furthermore, TransFit provides self-consistent modeling of the transition from shock-cooling to 56Ni-powered LCs. By combining physical realism with computational speed, TransFit provides a powerful tool for efficiently inverting LCs and extracting detailed physical insights from the vast data sets of current and future transient surveys.

Keywords: Time domain astronomy, Core-collapse supernovae, Supernovae, Radiative transfer
Halo Occupation Distribution of Quasars: Dependence on Luminosity, Redshift, Black Hole Mass and Feedback Modes. We use cosmological hydrodynamic simulations (IllustrisTNG and SIMBA) to explore the redshift, luminosity, and black hole mass dependence of the quasar halo occupation distribution (HOD). In both simulations, we find that the quasar activity is quenched at a characteristic halo mass (∼1013M⊙) scale affecting the nature of its occupation distribution function. We note that the quenching is more pronounced at low redshifts for quasars selected through a luminosity threshold. We show that a very significant bias (a factor of ∼10–50 in the central occupation and ∼10%–70% in the satellite occupation fraction) is introduced in the reconstruction of quasar host halo mass distributions from the observed two-point-correlation function, if the HOD modeling does not account for the quenching effect in the central occupation function. While there is strong suppression of the occupation fraction of central quasars, the satellite occupation still follows a power-law-like behavior. Our results show that the global satellite fraction of quasars increases monotonically from high to low redshifts, with 20%–40% of the quasars being satellite at intermediate redshifts, consistent with previous clustering-based estimates. In addition, our study reveals that while the occupation function of quasars depends on redshift, luminosity, and feedback modes, there is hardly any evolution in the supermassive black hole (SMBH; mass-selected sample) occupation. The SMBH HOD over the entire parameter space is well modeled by a power-law and a step function similar to what has been found for galaxies and low-luminosity active galactic nuclei.

Keywords: Hydrodynamical simulations, Supermassive black holes, Galaxy evolution, Quasars
Study of the IC 443 Region with the HAWC Observatory. Supernova remnants are one potential source class considered a PeVatron (i.e., capable of accelerating cosmic rays above PeV energies). The shock fronts produced after the explosion of the supernova are ideal regions for particle acceleration. IC 443 is a supernova remnant that has been studied extensively at different wavelengths. Using 2966 days of gamma-ray data from the High Altitude Water Cherenkov (HAWC) observatory, we study the emission of IC 443 with the objective of finding signatures of cosmic-ray acceleration at the PeV scale. Using a maximum likelihood method, we find a point source located at (α = 94 .° 42, δ = 22 .° 35) that we associate with IC 443. The measured spectrum is a simple power law with an index of −3.14 ± 0.18, which is consistent with previous TeV observations. Although we cannot confirm that IC 443 is a hadronic PeVatron, we do not find any sign that the spectrum has a cutoff at tens of TeV energies, with the spectrum extending to ∼30 TeV. Furthermore, we also find a new extended component in the region whose emission is described by a simple power law with an index of −2.49 ± 0.08 and which we call HAWC J0615+2213. While we show evidence that this new source might be a new TeV halo, we defer a detailed analysis of this new source to another publication.

Keywords: Supernova remnants, Gamma-rays, High energy astrophysics
MC-BLOS: Automated Software for Determining the Line-of-sight Component of Magnetic Fields Associated with Molecular Clouds. While plane-of-sky magnetic field observations in molecular clouds are now common, observations of their line-of-sight magnetic field remain limited. To address this issue, M. Tahani et al. developed a technique based on Faraday rotation. The technique incorporates an ON–OFF approach to identify the rotation measure induced by the magnetic fields associated with the cloud. The upcoming abundance of observations of Faraday rotation from the Square Kilometre Array and its pathfinders necessitates robustly tested software to automatically obtain line-of-sight magnetic fields of molecular clouds. We developed software, called MC-BLOS (for molecular cloud line-of-sight magnetic field; DOI:10.5281/zenodo.15338512), to carry out the technique in an automated manner. The software's inputs are Faraday rotation of point sources, maps of extinction or column density, results from chemical evolution code, and a parameter file that allows the user to specify the cloud name or other parameters pertaining to the technique. For each cloud, the software invokes a set of predefined initial parameters such as density, temperature, and surrounding boundary, which the user can modify. The software then runs the technique automatically, outputting line-of-sight magnetic field maps and tables (including uncertainties) at the end of the process. MC-BLOS generates diagnostic files for result evaluation and input parameter refinement, allowing for expert judgment in parameter selection. We have tested the software on previously published clouds, and the results are consistent within the reported uncertainty range. This software will facilitate the analysis of forthcoming observations of Faraday rotation, enabling a better understanding of the role of magnetic fields in molecular cloud dynamics and star formation. ∗Software available at https://github.com/MehrnooshTahani/MC-BLOS, DOI: 10.5281/zenodo.15338512.

Keywords: Galaxy magnetic fields, Observational astronomy, Open source software, Molecular clouds, Interstellar magnetic fields, Interstellar medium, Polarimetry
Simultaneous Ion Arrival Times during the Rise Phase of <SUP>3</SUP>He-rich Solar Energetic Particle Events. We have investigated the arrival times of species H–Fe in 3He-rich solar energetic particle (SEP) events to determine if a common acceleration mechanism is responsible for all the ions, assuming that if the particles arrive simultaneously this is evidence of a common mechanism. Compared to other SEP populations, the extremely large enrichment of 3He and much smaller though significant heavy ion enhancements suggest a common origin but without firm observational evidence due to the small size of the events. Using improved instruments close to the Sun on Solar Orbiter, we surveyed the period 2020 April—2025 May for 3He-rich events whose rise phase phases were sufficiently undistorted and intense that the particle arrival times could be measured accurately. We found six events that met the criteria and that appear to be typical impulsive SEP events but with unusually high counting statistics. For C–Fe the mean arrival times of 226–320 keV nucleon‑1 ions are simultaneous to ∼5 minutes, a small fraction of the ion propagation time from the Sun (110–310 minutes depending on heliocentric distance). H and 4He mean arrival times showed a maximum difference of 1.6 minutes. Overall 3He arrival times differ from the others by ∼3 ± 3 minutes. These times are sufficiently close to simultaneity to give evidence for a common acceleration mechanism. This adds a new constraint to models for these events, namely, that the accelerating waves can interact with the broad range of gyrofrequencies associated with the range charge-to-mass ratios for H–Fe.

Keywords: Solar flares, Solar magnetic reconnection, Solar energetic particles, Solar abundances, Solar magnetic fields, Solar particle emission
The Dust Echo Emission of Fast Blue Optical Transients and Application to the Near-infrared Excess of AT 2018cow. A near-infrared (NIR) excess has been discovered in the emission of the representative fast blue optical transient (FBOT) AT 2018cow. It was suggested that this NIR excess could be emitted by the dust surrounding the source and thus could provide a probe into the nature of its progenitor. We develop a model to describe the influence of the FBOT emission on the environmental dust, and as a result, a dust-free evaporation cavity can be formed on a timescale of 1 day. Outside this cavity, the surviving dust grains can have different size distributions at different distances from the source. With such a special dust environment, we fit the multiwavelength light curves of AT 2018cow by taking into account the evolutionary dust echo of the FBOT emission. It is found that the dust temperature can vary with time along with the evolution of the irradiating FBOT emission. Even at a fixed time, the dust temperature can be distributed in a wide range rather than having only a unique value. Furthermore, both the mass of the dust shell and its distance to the FBOT are found to be much larger than those derived with a direct empirical fitting of the NIR spectra but without considering the evolutionary relationship between the spectra.

Keywords: Light curves, Astrophysical dust processes, Infrared astronomy, Carbonaceous grains, Circumstellar dust, Supernovae
Exploring the Nature of Little Red Dots: Constraints on Active Galactic Nucleus and Stellar Contributions from PRIMER MIRI Imaging. JWST has revealed a large population of compact, red objects at z &gt; 4 known as Little Red Dots (LRDs). We analyze the spectral energy distributions (SEDs) of 88 LRDs from the JWST PRIMER survey with complete photometric coverage from 1 to 18 μm using NIRCam and MIRI imaging, representing the most extensive SED analysis on a large LRD sample with long-wavelength MIRI data. We examine SED models in which either galaxy or active galactic nucleus (AGN) emission dominates the rest-frame UV or optical continuum, extracting physical properties to explore each scenario's implications. In the galaxy-only model, we find massive, dusty stellar populations alongside unobscured, low-mass components, hinting at inhomogeneous obscuration. The AGN-only model indicates dusty, luminous AGNs with low hot dust fractions compared to typical quasars. A hybrid AGN and galaxy model suggests low-mass, unobscured galaxies in the UV, with stellar mass estimates spanning ∼2 dex across the different models, underscoring the need for caution in interpreting LRD stellar masses. With MIRI photometry, the galaxy-only model produces stellar masses within cosmological limits, but extremely high stellar mass densities are inferred. The hybrid model infers highly overmassive black holes exceeding those in recently reported high-redshift AGNs, hinting at a partial AGN contribution to the rest-optical continuum or widespread super-Eddington accretion. Our findings highlight the extreme conditions required for both AGN- and galaxy-dominated scenarios in LRDs, supporting a mixed contribution to the red continuum, or novel scenarios to explain the observed emission.

Keywords: Supermassive black holes, Galaxy formation, Active galactic nuclei, High-redshift galaxies
Observing Supernova Neutrino Light Curves with Super-Kamiokande. VI. A Practical Data Analysis Technique Considering Realistic Experimental Backgrounds. Neutrinos from supernovae, especially those emitted during the late phase of core collapse, are essential for understanding the final stages of massive star evolution. We have been dedicated to developing methods for the analysis of neutrinos emitted during the late phase and observed at Super-Kamiokande (SK). Our previous studies have successfully demonstrated the potential of various analysis methods in extracting essential physical properties; however, the lack of background consideration has limited their practical application. In this study, we address this issue by incorporating a realistic treatment of the experimental signal and background events with the on-going SK experiment. We therefore optimize our analysis framework to reflect realistic observational conditions, including both signal and background events. Using this framework we study several long-time supernova models, simulating the late phase neutrino observation in SK and focusing in particular on the identification of the last observed event. We discuss the possibility of model discrimination methods using timing information from this last observed event.

Keywords: Neutron stars, Supernova neutrinos, High energy astrophysics, Core-collapse supernovae, Neutrino astronomy
Enceladus's Limit Cycle. Enceladus exhibits some remarkable phenomena, including water geysers spraying through surface cracks, a global ice shell that is librating atop an ocean, a large luminosity, and rapid outward orbital migration. Here, we model the coupled evolution of Enceladus's orbit and interior structure. We find that Enceladus is driven into a periodic state—a limit cycle. Many of Enceladus's observed phenomena emerge from the model, and the predicted values for the orbital eccentricity, libration amplitude, shell thickness, and luminosity agree with observations. A single limit cycle lasts around 10 million years, and has three distinct stages: (1) freezing, (2) melting, and (3) resonant libration. In our model, Enceladus is currently in the freezing stage, meaning that its ice shell is getting thicker. That pressurizes the ocean, which in turn cracks the shell and pushes water up through the cracks. In this stage, the orbital eccentricity increases, as Saturn pushes Enceladus deeper into resonance with Dione. Once the eccentricity is sufficiently high, tidal heating begins to melt the shell, which is the second stage of the cycle. In the third stage, the shell remains close to 3 km thick. At that thickness, the shell's natural libration frequency is resonant with the orbital frequency. The shell's librations are consequently driven to large amplitude, for millions of years. Most of the tidal heating of Enceladus occurs during this stage, and the observed luminosity is a relic from the last episode of resonant libration, while the present-day heat production is small (∼1 GW).

Keywords: Enceladus
A Search for Chemical Stratification and Magnetic Fields in Eight Field Blue Horizontal-branch Stars<SUP></SUP>. In this article, we present the results of an analysis of chemical abundances and a search for magnetic fields in eight field blue horizontal-branch (BHB) stars: BD +01°0548, HD 74721, HD 86986, HD 87112, HD 93329, HD 109995, HD 161817, and HD 167105. This study is based on high-resolution optical spectra obtained with ESPaDOnS at the Canada─France─Hawaii Telescope. We first calculated the average chemical element abundance, the rotational velocity, and the radial velocity of the stars using the ZEEMAN2 spectrum synthesis code with the PHOENIX model atmospheres. We then studied the abundances of titanium and iron inferred from individual lines in the spectra of each star and their variations with their predicted formation depths τ5000. Similarly to the BHB stars cooler than 11,500 K observed in globular clusters, no clear observational evidence of vertical stratification is detected in the atmosphere of these stars. In the second part of this project, we searched for the presence of a magnetic field in the stars, applying the least-squares deconvolution technique on the Stokes I and V spectra. The measured mean longitudinal magnetic field uncertainties, ranging from 8 to 30 G, effectively rule out the presence of an organized magnetic field in these targets with a strength larger than a few 100 G. *Based on observations obtained at the Canada─France─Hawaii Telescope (CFHT), which is operated by the National Research Council of Canada, the Institut National des Sciences de l'Univers of the Centre National de la Recherche Scientique of France, and the University of Hawaii. The observations at the CFHT were performed with care and respect from the summit of Maunakea, which is a significant cultural and historic site.

Keywords: Horizontal branch stars, Stellar abundances, Stellar magnetic fields, Stellar diffusion, Stellar atmospheres
The Electron Temperature Distribution and the High Ionization Just behind the Shock in the Cygnus Loop. The physical processes behind astrophysical collisionless shocks, such as thermal relaxation and ionization after shock passage, remain poorly understood. To investigate these processes, we analyze the northeastern region of the Cygnus Loop with XMM-Newton. The electron temperature is found to increase toward the interior of the remnant ranging from 0.15 to 0.19 keV energy range within a spatial scale of 6' (or 1.27 pc at a distance of 725 pc) from the shock front. This can be explained well by a modified Sedov solution with radiative cooling. We also show that the ionization timescales determined from our spectroscopy are significantly larger than those estimated based on the electron density of the surrounding materials and the shock velocity. This excess can be qualitatively explained by a mixing of inner multiple plasma components with different ionization states due to turbulence.

Keywords: Supernova remnants, Shocks, Plasma astrophysics, High energy astrophysics
Photospheric Radius Expansion Thermonuclear Burst and X-Ray Reflection from the Neutron Star X-Ray Binary 4U 1702-429. We perform a comprehensive study of thermonuclear bursts from the neutron star low-mass X-ray binary 4U 1702─429 detected with NICER and XMM-Newton. The thermonuclear burst detected with NICER shows clear evidence of a photospheric radius expansion (PRE) event and a distinct feature in the burst profile. The burst profiles demonstrate significant energy dependence, with the hardness ratio varying notably during the PRE phase. The radius of the neutron star photosphere expanded to a maximum of  23.1−3.2+3.8  km while its temperature reached a minimum of ∼1.4 keV. The time-resolved burst spectra can be modeled using the variable persistent emission method, indicating that the soft excess may arise from enhanced mass accretion onto the neutron star, potentially due to the Poynting─Robertson drag. Alternatively, the disk reflection model can be used to explain the soft excess emission during a burst. The time-resolved spectral study is performed for three thermonuclear bursts detected with XMM-Newton. The XMM-Newton time-resolved burst spectra can be modeled using an absorbed blackbody model, without any signatures of the PRE. We conduct a detailed spectral analysis of the 2025 NuSTAR observation of 4U 1702─429, revealing a broad iron line at 6.4 keV and a Compton hump around 20 keV, indicating X-ray reflection features. The disk reflection model relxill provides an inner disk radius of ∼12 Rg and an inclination angle of ∼39°. The magnetic field strength at the pole of the neutron star is estimated to be 5.1 × 108 G, assuming that the accretion disk is truncated at the magnetosphere boundary.

Keywords: Accretion, Low-mass x-ray binary stars, X-ray binary stars, X-ray bursts
On the Singularity Structure of Alfvénic Turbulence. The singularity structure of the electromagnetic field fluctuations in strong Alfvénic turbulence is addressed. Owing to the transverse polarization of the fluctuations, the turbulent cascade is essentially perpendicular to the direction of the guiding magnetic field. A scaling analysis of the local energy transfer rates suggests that the most intense singularities are the sites of inertial dissipation of the energy. The lack of smoothness of the electromagnetic fields can give rise to dissipative processes unrelated to collisional transport phenomena in the magnetized plasma. A log-Poisson cascade model is developed. The random multiplicative cascade process is quantized and acts on the Elsässer field increments. In a multifractal interpretation, the log-Poisson cascade is characterized by three parameters: the most probable singularity strength, the strongest singularity, and its fractal codimension. The resulting probability distribution functions are derived from discrete superpositions of dilated integral scale distributions weighted by scale-dependent Poisson distributions. In addition to the three parameters mentioned above, they depend on the standard deviation of the integral scale fluctuations. The four-parameter family of normal log-Poisson mixture distributions is sensitive to the strongest singularities responsible for inertial dissipation of the electromagnetic energy in collisionless space plasma environments.

Keywords: Interplanetary turbulence, Magnetohydrodynamics, Solar wind
Frequency-dependent Evolution of Propagating Intensity Disturbances in Polar Plumes. Quasiperiodic disturbances in EUV emission intensity, propagating along polar plumes in the solar corona, are frequently observed. Analysis of these propagating disturbances in the 171 Å bandpass of the Solar Dynamics Observatory/Atmospheric Imaging Assembly reveals that the wave spectrum evolves with height. Near the footpoints, the dominant spectral peak corresponds to oscillation periods of 12–15 minutes. As the disturbances propagate upward, the shorter-period spectral component diminishes, while a longer-period component of 20–30 minutes becomes dominant. Theoretical modeling of coronal slow magnetoacoustic waves effectively reproduces this spectral evolution. The model incorporates field-aligned thermal conduction and the back reaction of wave-induced perturbations on local thermal equilibrium. Coronal slow waves, driven by a broadband source with a peak at a shorter period, show a decrease in shorter-period spectral power with height, while the 20–30 minute spectral power increases due to thermal overstability. Analysis of the dispersion relations reveals that, given the chosen model parameters, the most rapidly growing spectral component corresponds to a 22.5 minute period, which aligns well with the observational findings.

Keywords: Solar coronal waves