Sazuna/UAT_keywords huggingface dataset:
Probing X-Ray Timing and Spectral Variability in the Blazar PKS 2155–304 over a Decade of XMM-Newton Observations. Blazars, a class of active galactic nuclei (AGN) powered by supermassive black holes, are known for their remarkable variability across multiple timescales and wavelengths. Despite significant advancements in our understanding of AGN central engines, thanks to both ground- and space-based telescopes, the details of the mechanisms driving this variability remain elusive. The primary objective of this study is to constrain the X-ray variability properties of the TeV blazar PKS 2155–304. We conducted a comprehensive X-ray spectral and timing analysis, focusing on both long-term and intraday variability (IDV), using data from 22 epochs of XMM-Newton observations collected over 15 yr (2000–2014). For the timing analysis, we estimated the fractional variability, variability amplitude, minimum variability timescales, flux distribution, and power spectral density. In the spectral analysis, we fitted the X-ray spectra using power-law, log-parabola, and broken power-law models to determine the best-fitting parameters. We observed moderate IDV in the majority of the light curves (LCs). Seven out of the 22 observations showed a clear bimodal flux distribution, indicating the presence of two distinct flux states. Our analysis revealed a variable power spectral slope. Most hardness ratio plots did not show significant variation with flux, except for two observations, where the hardness ratio changed considerably with flux. The fitted X-ray spectra favored the broken power-law model for the majority of observations, indicating a break in the spectral profiles. The findings of this work shed light on the IDV of blazars, providing insights into the nonthermal jet processes that drive the observed flux variations.

Keywords: Supermassive black holes, BL Lacertae objects, Blazars, Relativistic jets, X-ray point sources, Active galactic nuclei, Non-thermal radiation sources
Powerful Explosions from the Collapse of Rotating Supermassive Stars. We perform new general relativistic hydrodynamics simulations for collapses of rotating supermassive star cores with an approximate nuclear burning up to carbon and a detailed equation of state. For all the models we investigate, the energy generation by nuclear burning plays only a minor role, leading to the formation of a black hole without a nuclear-powered explosion. For rotating models, however, the stellar explosion associated with shock heating is driven from a torus, which forms after the black hole formation. The explosion energy is up to 10‑4 of the mass energy of the supermassive star cores (∼1055–1056 erg). We find that, even if we increase the rotational angular momentum of the progenitor, the ejecta mass saturates at ∼1% of the total mass of the initial stellar core. The average ejecta velocity also saturates at ≈20% of the speed of light. As a result, the ejecta kinetic energy is approximately proportional to the initial mass of the supermassive star core for the rapidly rotating case. We also perform viscous hydrodynamics simulations to explore the evolution of the remnant torus. Although the viscous heating drives an outflow from the torus, we find that its effect is subdominant in terms of the kinetic energy because of the small velocity (≈0.07c) of the ejecta component.

Keywords: Supermassive black holes, Massive stars, Gravitational collapse
Unusual X-Ray Oxygen Line Ratios of SN 1987A Arising from the Absorption of Galactic Hot Interstellar Medium. Recent high-resolution X-ray spectroscopic studies have revealed unusual oxygen line ratios, such as the high O VII forbidden-to-resonance ratio, in several supernova remnants. While the physical origin is still under debate, for most of them it has been suggested that this phenomenon arises from either charge exchange (CX) or resonant scattering (RS). In this work, we report the high O VII G-ratio (≳1) and high O VIII Lyβ/Lyα ratio (≳0.2) found in multiepoch XMM-Newton Reflection Grating Spectrometer observations of SN 1987A. The line ratios cannot be fully explained by nonequilibrium ionization effects, CX, or RS. We suggest the absorption of foreground hot gas as the most likely origin, which plays the major role in modifying line fluxes and line ratios. Based on this scenario, we introduced two Gaussian absorption components at the O VII resonance line and the O VIII Lyα line and constrained the optical depth of the two lines as τO VII ∼ 0.6 and τO VIII ∼ 0.2. We estimated the temperature as kTe ∼ 0.15 keV and the oxygen column density as NO ∼0.5 × 1016 cm‑2 for the absorbing gas, which is consistent with the hot interstellar medium in the Galactic halo. Neglecting this absorption component may lead to an underestimation of the O abundance. We revised the O abundance of SN 1987A, which is increased by ∼20% compared with previous results. The N/O ratio by number of atoms is revised to be ∼1.2.

Keywords: X-ray astronomy, Supernova remnants, Interstellar medium
On the Magnetic and Thermodynamic Properties of Dark Fibrils in the Chromosphere. Fibrillar structures are ubiquitous in the solar chromosphere. An accurate determination of their properties requires the use of advanced high-resolution observations, which are now becoming broadly available from different observatories. We exploit the capabilities of multi-atom, multiline spectropolarimetric inversions using the Stockholm Inversion Code. Non–local thermodynamic equilibrium inversions of a fibril-rich area are performed using spectropolarimetric observations on the Ca II 854.2 nm line obtained with the CRISP imaging spectropolarimeter and spectroscopic observations on the Ca II H line obtained with the CHROMospheric Imaging Spectrometer at the Swedish 1 m Solar Telescope. Additionally, co-observations on the Mg II h and k lines obtained with the Interface Region Imaging Spectrograph are used in the inversions to better constrain the thermodynamic properties of the fibrils. The incorporation of multiple atomic species and spectral lines proves to better constrain the properties of the plasma constituting the fibrils. In particular, the tracing of a large number of fibrils allowed for the study of the variation of the temperature and magnetic field along their projected length over the field of view. The results provide a view of fibrils possessing hot footpoints of about 5900 K. The temperature drop away from the footpoints is on average 250 K, with a larger drop of around 500 K for the longer fibrils. The magnetic field is also reported to be larger at the footpoints, being almost twice as large as the minimum value reported at the middle point of the fibrils.

Keywords: Solar atmosphere, Solar chromosphere, Spectropolarimetry, Radiative transfer
A Second Radio Flare from the Tidal Disruption Event AT2020vwl: A Delayed Outflow Ejection?. We present the discovery of a second radio flare from the tidal disruption event (TDE) AT2020vwl via long-term monitoring radio observations. Late-time radio flares from TDEs are being discovered more commonly, with many TDEs showing radio emission thousands of days after the stellar disruption, but the mechanism that powers these late-time flares is uncertain. Here, we present radio spectral observations of the first and second radio flares observed from the TDE AT2020vwl. Through detailed radio spectral monitoring, we find evidence for two distinct outflow ejection episodes or a period of renewed energy injection into the preexisting outflow. We deduce that the second radio flare is powered by an outflow that is initially slower than the first flare but carries more energy and shows tentative indication of accelerating over time. Through modelling the long-term optical and UV emission from the TDE as arising from an accretion disk, we infer that the second radio outflow launch or energy injection episode occurred approximately at the time of the peak accretion rate. The fast decay of the second flare precludes environmental changes as an explanation, while the velocity of the outflow is at all times too low to be explained by an off-axis relativistic jet. Future observations that search for any link between the accretion disk properties and late-time radio flares from TDEs will aid understanding of what powers the radio outflows in TDEs and confirm if multiple outflow ejections or energy injection episodes are common.

Keywords: Black hole physics, Tidal disruption, High energy astrophysics, Radio transient sources
On Gamma Rays as Predictors of Ultra-high-energy Cosmic-Ray Flux in Active Galactic Nuclei. Active galactic nuclei (AGN) are among the main candidates for ultra-high-energy cosmic-ray (UHECR) sources. However, while some theoretical and phenomenological works favor AGNs as the main sources, recent works have shown that using the very-high-energy γ-ray flux as a proxy for the UHECR flux leads to a bad agreement with data. In this context, the energy spectrum and composition data are hardly fitted. At the same time, the arrival directions map is badly described and a spurious dipole direction is produced. In this work, we propose a possible solution to these contradictions. Using the observed γ-ray flux as a proxy may carry the implicit assumption of beamed UHECR emission and, consequently, its beam will remain collimated up to its detection on Earth. We show that assuming an isotropic UHECR emission and correcting the γ-ray emission proxy by Doppler boosting can overcome the problem. The combined fit of the spectrum and composition is improved, with a change of reduced χ2 from 4.6 to 3.1. In particular, the tension between the observed and modeled dipole directions can be reduced from 5.9 (2.1)σ away from the data to 3.5 (1.1)σ for E &gt; 8 EeV (E &gt; 32 EeV). We also show that this effect is particularly important when including AGNs of different classes in the same analysis, such as radio galaxies and blazars.

Keywords: Cosmic ray sources, Active galactic nuclei, Gamma-rays, Ultra-high-energy cosmic radiation
Disrupted Wide Binaries as Dynamical Probes of Galactic Structure. Many of the stars in the Galaxy are members of binary systems, the widest of which can eventually become disrupted due to a combination of kicks from passing objects and the Galactic tidal field. If the Galactic disk were purely axisymmetric, the stars from a disrupted binary system would slowly drift apart on nearly identical orbits. We study how the existence of nonaxisymmetric structures, such as a rigidly rotating bar, can greatly alter this picture. In particular, we show how the orbital dynamics near the resonances sourced by these nonaxisymmetric perturbations create local fluctuations in the distribution of disrupted binary separations. We simulate the evolution of wide binary systems embedded in a gravitational potential with a rotating galactic bar, and show how features and fluctuations in the distribution of disrupted binaries can be used to locate bar resonances and constrain the bar's pattern speed and amplitude.

Keywords: Wide binary stars, Galaxy structure, Orbital resonances, Galactic bar
Multiwavelength Observations of a Jet Launch in Real Time from the Post-changing-look Active Galaxy 1ES 1927+654. We present results from a high-cadence multiwavelength observational campaign of the enigmatic changing-look active galactic nucleus 1ES 1927+654 from 2022 May to 2024 April, coincident with an unprecedented radio flare (an increase in flux by a factor of ∼60 over a few months) and the emergence of a spatially resolved jet at 0.1–0.3 pc scales. Companion work has also detected a recurrent quasi-periodic oscillation (QPO) in the 2–10 keV band with an increasing frequency (1–2 mHz) over the same period. During this time, the soft X-rays (0.3–2 keV) monotonically increased by a factor of ∼8, while the UV emission remained nearly steady with &lt;30% variation and the 2–10 keV flux showed variation by a factor ≲2. The weak variation of the 2–10 keV X-ray emission and the stability of the UV emission suggest that the magnetic energy density and accretion rate are relatively unchanged and that the jet could be launched owing to a reconfiguration of the magnetic field (toroidal to poloidal) close to the black hole. Advecting poloidal flux onto the event horizon would trigger the Blandford–Znajek mechanism, leading to the onset of the jet. The concurrent softening of the coronal slope (from Γ = 2.70 ± 0.04 to Γ = 3.27 ± 0.04), the appearance of a QPO, and the low coronal temperature ( ) during the radio outburst suggest that the poloidal field reconfiguration can significantly impact coronal properties and thus influence jet dynamics. These extraordinary findings in real time are crucial for coronal and jet plasma studies, particularly as our results are independent of coronal geometry.

Keywords: Supermassive black holes, Active galaxies
Tracking X-Ray Variability in Next-generation EHT Low-luminosity Active Galactic Nucleus Targets. We present a 5 month NICER X-ray monitoring campaign for two low-luminosity active galactic nuclei (LLAGNs)—NGC 4594 and IC 1459—with complementary Swift and NuSTAR observations. Utilizing an absorbed power-law and thermal source model combined with NICER's SCORPEON background model, we demonstrate the effectiveness of joint source–background modeling for constraining emission from faint, background-dominated targets. Both sources are dominated by nuclear power-law emission with photon indices Γ ∼ 1.5–2, with NGC 4594 being slightly harder than IC 1459. The thermal contribution in both sources is fainter, but constant, with kT ∼ 0.5 keV (∼5 × 106 K). The power-law flux and Γ are strongly anticorrelated in both sources, as has been seen for other LLAGNs with radiatively inefficient accretion flows. NGC 4594 is the brighter source and exhibits significant aperiodic variability. Its variability timescale with an upper limit of 5–7 days indicates emission originating from ≲100 rg, at the scale of the inner accretion flow. A spectral break found at ∼6 keV, while tentative, could arise from synchrotron/inverse Compton emission. This high-cadence LLAGN X-ray monitoring campaign underlines the importance of multiwavelength variability studies for a sample of LLAGNs to truly understand their accretion and outflow physics.

Keywords: LINER galaxies, Active galaxies, X-ray active galactic nuclei
A Detailed Look at a Trio of Changing-look Quasars: Spectral Energy Distributions and the Dust Extinction Test. Changing-look quasars (CLQs) exhibit dramatic variability in broad emission-line fluxes on short timescales. This behavior is challenging to many models of the quasar broad-line region, due in large part to the short transition times between high and low states. In order to constrain the cause of the dramatic variability, we obtained contemporaneous Hubble Space Telescope ultraviolet and Hobby Eberly Telescope optical spectra of three CLQs caught in their low state. We use these spectra, along with archival spectra taken during both the high and low states, to investigate potential scenarios for the change in state. Our data strongly disfavor a variable dust obscuration scenario for these three CLQs, and instead suggest that the observed transformation reflects a change in the intrinsic luminosity of the central engine. We also find that the low-state spectral energy distributions of all three quasars are reminiscent of those of low-luminosity active galactic nuclei, which suggests that the transition may result from a change in accretion flow structure caused by a reduced Eddington ratio. *Based on observations obtained with the Hobby–Eberly Telescope (HET), which is a joint project of the University of Texas at Austin, the Pennsylvania State University, Ludwig-Maximillians- Universitaet Muenchen, and Georg-August Universitaet Goettingen. The HET is named in honor of its principal benefactors, William P. Hobby and Robert E. Eberly. †Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. These observations are associated with program GO-14799.

Keywords: Accretion, Supermassive black holes, Active galactic nuclei, Quasars
B-fields and Dust in Interstellar Filaments Using Dust Polarization (BALLAD-POL). III. Grain Alignment and Disruption Mechanisms in G34.43+0.24 Using Polarization Observations from JCMT/POL-2. Polarization of starlight and thermal dust emission due to aligned non-spherical grains helps us to trace magnetic field (B-field) morphology in molecular clouds and to study grain alignment mechanisms. In this work, we study grain alignment and disruption mechanisms in a filamentary infrared dark cloud G34.43+0.24 using thermal dust polarization observations from JCMT/POL-2 at 850 μm. We study three regions: the North harboring the MM3 core, the Center harboring the MM1 and MM2 cores, and the South harboring no core. We find the decrease in polarization fraction P with increasing total intensity and gas column density, known as polarization hole. To disentangle the effect of magnetic field tangling on the polarization hole, we estimate the polarization angle dispersion function. We find depolarizations in the North and Center regions are due to a decrease in the net alignment efficiency of grains, but in the South region, the effect of magnetic field tangling is significant to cause depolarization. To test whether the radiative torque (RAT) mechanism can reproduce the observational data, we calculate minimum alignment and disruption sizes of grains using RAT theory, and our study finds that the RAT alignment (RAT-A) mechanism can explain the depolarizations in the North and Center regions where the B-field tangling effect is less important, except for core regions. We find hints of RAT disruption (RAT-D) in the core regions of MM3 in the North, and MM1 and MM2 in the Center. We also find that the high P value of around 8%–20% in the outer regions of the filament can potentially be explained by the magnetically enhanced RAT alignment mechanism.

Keywords: Interstellar dust, Interstellar magnetic fields, Star forming regions, Interstellar filaments
Dormancy and Reawakening over Years: Eight New Recurrent Changing-look AGNs. We report the discovery of eight new recurrent changing-look (CL) active galactic nuclei (AGNs), consisting of seven rebrightening turn-off AGNs and one fading turn-on AGN. These systems are valuable for placing constraints on the duration of dim and bright states, which may be linked to the AGN duty cycle or disk instability. Long-term analysis of optical light curves reveals that many objects in our sample exhibit a prolonged plateau during the dim states lasting 5─7 yr, with a gradual turn-on/off process. We observe no significant difference between the turn-on and turn-off timescales, and this timescale is broadly consistent with the propagation timescale for the heating/cooling front. Comparison between the optical and infrared variations supports the idea that these transitions are driven by changes in accretion disk emission rather than dust obscuration. Our discovery significantly increases the previously identified recurrent CL AGN sample, demonstrating that some AGNs can enter dormancy and reawaken on timescales of a few years, which provides useful information for understanding episodic AGN accretion.

Keywords: Active galactic nuclei, Quasars
A New Spectral Library for Modeling the Surfaces of Hot, Rocky Exoplanets. JWST's MIRI LRS provides the first opportunity to spectroscopically characterize the surface compositions of close-in terrestrial exoplanets. Models for the bare-rock spectra of these planets often utilize a spectral library from R. Hu et al., which is based on room-temperature reflectance measurements of materials that represent archetypes of rocky planet surfaces. Here we present an expanded library that includes hemispherical reflectance measurements for a greater variety of compositions, varying textures (solid slab, coarsely crushed, and fine powder), as well as high-temperature (500–800 K) emissivity measurements for select samples. We incorporate this new library into version 6.3 of the open-source retrieval package PLATON and use it to show that planetary surfaces with similar compositions can have widely varying albedos and surface temperatures. We additionally demonstrate that changing the texture of a material can significantly alter its albedo, making albedo a poor proxy for surface composition. We identify key spectral features—the 5.6 μm olivine feature, the transparency feature, the Si-O stretching feature, and the Christiansen feature—that indicate silicate abundance and surface texture. We quantify the number of JWST observations needed to detect these features in the spectrum of the most favorable super-Earth target, LHS 3844 b, and revisit the interpretation of its Spitzer photometry. Lastly, we show that temperature-dependent changes in spectral features are likely undetectable at the precision of current exoplanet observations. Our results illustrate the importance of spectroscopically resolved thermal emission measurements, as distinct from surface albedo constraints, for characterizing the surface compositions of hot, rocky exoplanets.

Keywords: Extrasolar rocky planets, Exoplanets, Super Earths, Exoplanet surface composition, Exoplanet surfaces, Exoplanet surface characteristics
Search for Neutrino Emission from Hard X-Ray AGN with IceCube. Active galactic nuclei (AGN) are promising candidate sources of high-energy astrophysical neutrinos, since they provide environments rich in matter and photon targets where cosmic-ray interactions may lead to the production of gamma rays and neutrinos. We searched for high-energy neutrino emission from AGN using the Swift-BAT Spectroscopic Survey catalog of hard X-ray sources and 12 yr of IceCube muon track data. First, upon performing a stacked search, no significant emission was found. Second, we searched for neutrinos from a list of 43 candidate sources and found an excess from the direction of two sources, the Seyfert galaxies NGC 1068 and NGC 4151. We observed NGC 1068 at flux   =   TeV‑1 cm‑2 s‑1 normalized at 1 TeV, with a power-law spectral index γ = 3.10 , consistent with previous IceCube results. The observation of a neutrino excess from the direction of NGC 4151 is at a posttrial significance of 2.9σ. If interpreted as an astrophysical signal, the excess observed from NGC 4151 corresponds to a flux   =   TeV‑1 cm‑2 s‑1 normalized at 1 TeV and γ = 2.83 .

Keywords: Seyfert galaxies, Neutrino astronomy, Active galaxies, High energy astrophysics