SLB Digital’s Post

📃Scientific paper: The Physical Properties of Changing-look Blazars Abstract: Changing-look active galactic nuclei (AGNs) are a special class of AGNs that change their spectral type from type 1 to type 2 or vice versa. In recent years, a number of changing-look blazars (CLBs) were also reported, which transition between flat-spectrum radio quasars and BL Lacs. The physical properties of CLBs are still unclear. Using the $mclust$ R package for Gaussian Mixture Modeling, we performed a clustering analysis for a sample of 105 CLBs selected from the literature. Three kinds of analysis found that CLBs lie in between the parameter distributions of FSRQs and BL Lacs: (i) univariate analysis; (ii) bivariate analysis; and (iii) multivariate analysis, carried out with a dimension reduction approach of the physical properties of the three types of blazars. Our results suggest that CLBs belong to a transition type between FSRQs and BL Lacs, which may be regulated by the change of accretion process and may be similar to other changing-look AGNs. ;Comment: Published in ApJ. 8 pages, 3 figures, 1 table Continued on ES/IODE ➡️ https://etcse.fr/WhT ------- If you find this interesting, feel free to follow, comment and share. We need your help to enhance our visibility, so that our platform continues to serve you.

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📃Scientific paper: Dramatic Drop in the X-Ray Polarization of Swift J1727.8$-$1613 in the Soft Spectral State Abstract: Black-hole X-ray binaries exhibit different spectral and timing properties in different accretion states. The X-ray outburst of a recently discovered and extraordinarily bright source, Swift$\~$J1727.8$-$1613, has enabled the first investigation of how the X-ray polarization properties of a source evolve with spectral state. The 2$-$8 keV polarization degree was previously measured by the Imaging X-ray Polarimetry Explorer \(IXPE\) to be $\approx$ 4% in the hard and hard intermediate states. Here we present new IXPE results taken in the soft state, with the X-ray flux dominated by the thermal accretion-disk emission. We find that the polarization degree has dropped dramatically to $\lesssim$ 1%. This result indicates that the measured X-ray polarization is largely sensitive to the accretion state and the polarization fraction is significantly higher in the hard state when the X-ray emission is dominated by up-scattered radiation in the X-ray corona. The combined polarization measurements in the soft and hard states disfavor a very high or low inclination of the system. ;Comment: 10 pages, 6 figures, submitted to ApJL Continued on ES/IODE ➡️ https://etcse.fr/EeL ------- If you find this interesting, feel free to follow, comment and share. We need your help to enhance our visibility, so that our platform continues to serve you.

📃Scientific paper: Minutes-duration Optical Flares with Supernova Luminosities Abstract: In recent years, certain luminous extragalactic optical transients have been observed to last only a few days. Their short observed duration implies a different powering mechanism from the most common luminous extragalactic transients (supernovae) whose timescale is weeks. Some short-duration transients, most notably AT2018cow, display blue optical colours and bright radio and X-ray emission. Several AT2018cow-like transients have shown hints of a long-lived embedded energy source, such as X-ray variability, prolonged ultraviolet emission, a tentative X-ray quasiperiodic oscillation, and large energies coupled to fast (but subrelativistic) radio-emitting ejecta. Here we report observations of minutes-duration optical flares in the aftermath of an AT2018cow-like transient, AT2022tsd (the "Tasmanian Devil"). The flares occur over a period of months, are highly energetic, and are likely nonthermal, implying that they arise from a near-relativistic outflow or jet. Our observations confirm that in some AT2018cow-like transients the embedded energy source is a compact object, either a magnetar or an accreting black hole. ;Comment: 79 pages, 3 figures (main text) + 7 figures (extended data) + 2 figures (supplementary information). Published online in Nature on 15 November 2023 Continued on ES/IODE ➡️ https://etcse.fr/Efcu ------- If you find this interesting, feel free to follow, comment and share. We need your help to enhance our visibility, so that our platform continues to serve you.

📃Scientific paper: LoVoCCS -- II. Weak Lensing Mass Distributions, Red-Sequence Galaxy Distributions, and Their Alignment with the Brightest Cluster Galaxy in 58 Nearby X-ray-Luminous Galaxy Clusters Abstract: The Local Volume Complete Cluster Survey \(LoVoCCS\) is an on-going program to observe nearly a hundred low-redshift X-ray-luminous galaxy clusters \(redshifts $0.03\<z\<0.12$ and X-ray luminosities in the 0.1-2.4 keV band $L\_\{X500c\}\>10^\{44\}$ erg/s\) with the Dark Energy Camera \(DECam\), capturing data in $u,g,r,i,z$ bands with a $5\sigma$ point source depth of approximately 25-26th AB magnitudes. Here, we map the aperture masses in 58 galaxy cluster fields using weak gravitational lensing. These clusters span a variety of dynamical states, from nearly relaxed to merging systems, and approximately half of them have not been subject to detailed weak lensing analysis before. In each cluster field, we analyze the alignment between the 2D mass distribution described by the aperture mass map, the 2D red-sequence \(RS\) galaxy distribution, and the brightest cluster galaxy \(BCG\). We find that the orientations of the BCG and the RS distribution are strongly aligned throughout the interiors of the clusters: the median misalignment angle is 19 deg within 2 Mpc. We also observe the alignment between the orientations of the RS distribution and the overall cluster mass distribution \(by a median difference of 32 deg within 1 Mpc\), although this is constrained by galaxy shape noise and the limitations of our cluster sample size. These types of alignment suggest long-term dynamical evolution within the clusters over cosmic timescales. ;Comment: 40 pages, 16 figures, 5 tables. Submitted to ... Continued on ES/IODE ➡️ https://etcse.fr/1xW ------- If you find this interesting, feel free to follow, comment and share. We need your help to enhance our visibility, so that our platform continues to serve you.

📃Scientific paper: High-resolution observations of two pores with the integral field unit (IFU) of the GREGOR Infrared Spectrograph (GRIS) Abstract: The goal is to compare the intricate details of the magnetic and flow fields around two solar pores, where one is part of an active region and the other is an isolated pore, with a secondary goal of demonstrating the scientific capabilities of the GRIS IFU. Two pores were observed with the HiFI and the GRIS IFU at the GREGOR solar telescope on 29 May and 6 June 2019. The GRIS IFU mosaics provide spectropolarimetric data for inversions of the Ca I 1083.9 nm and Si I 1082.7 nm spectral lines, covering the deep and upper photosphere. The t-SNE machine learning algorithm is employed to identify different classes of Si I Stokes-V profiles. The LCT technique derives horizontal proper motions around the pores. Both pores contain a thin light bridge, are stable during the observations, and never develop a penumbra. The isolated pore is three times smaller and significantly darker than the active-region pore, which is not predicted by simulations. The LCT maps show inflows around both pores, with lower velocities for the isolated pore. Both pores are embedded in the photospheric LOS velocity pattern of the granulation but filamentary structures are only visible in the chromospheric LOS maps of the active-region pore. The t-SNE identifies five clusters of Si I Stokes-V profiles, revealing an `onion-peel' magnetic field structure, despite the small size of the pores. The core with strong vertical magnetic fields is surrounded by concentric layers with lower and more inclined... Continued on ES/IODE ➡️ https://etcse.fr/niDES ------- If you find this interesting, feel free to follow, comment and share. We need your help to enhance our visibility, so that our platform continues to serve you.

📃Scientific paper: Can fallback accretion on magnetar model power the X-ray flares simultaneously observed with gamma-rays of Gamma-ray bursts? Abstract: The prompt emission, X-ray plateau, and X-ray flares of Gamma-ray bursts (GRB) are thought to be from internal dissipation, and the magnetar as the central engine with propeller fallback accretion is proposed to interpret the observed phenomena of GRBs. In this paper, by systematically searching for X-ray emission observed by Swift/Xry Telescope, we find that seven robust GRBs include both X-ray flares and plateau emissions with measured redshift. More interestingly, the X-ray flares/bumps for those seven GRBs are simultaneously observed in the gamma-ray band. By adopting the propeller fallback accretion model to fit the observed data, it is found that the free parameters of two GRBs (140512A and 180329B) can be constrained very well, while in the other five cases, more or less, they are not all sufficiently constrained. On the other hand, this requires that the conversion efficiency of the propeller is to be two or three times higher than that of the spindown dipole radiation of the magnetar. If this is the case, it is contradictory to the expectation from the propeller model: namely, a dirtier ejecta should be less efficient in producing gamma-ray emissions. Our results hint that at least the magnetar central engine with propeller fallback accretion model cannot interpret very well both the GRB X-ray flares simultaneously observed in the gamma-ray band and the X-ray flares of GRBs with a high Lorentz factor. ;Comment: 13 pages, 5 figures, 1 table, updated reference... Continued on ES/IODE ➡️ https://etcse.fr/KDuWM ------- If you find this interesting, feel free to follow, comment and share. We need your help to enhance our visibility, so that our platform continues to serve you.

📃Scientific paper: Detection of high-frequency pulsation in WR 135: investigation of stellar wind dynamics Abstract: We report the detection of high-frequency pulsations in WR\,135 from short cadence \(10\,minutes\) optical photometric and spectroscopic time series surveys. The harmonics up to $6^\{th\}$ order are detected from the integrated photometric flux variations while the comparatively weaker $8^\{th\}$ harmonic is detected from the strengths of the emission lines. We investigate the driving source of the stratified winds of WR\,135 using the radiative transfer modeling code, CMFGEN, and find the physical conditions that can explain the propagation of such pulsations. From our study, we find that the optically thick sub-sonic layers of the atmosphere are close to the Eddington limit and are launched by the Fe-opacity. The outer optically thin super-sonic winds \($\tau\_\{ross\}=0.1-0.01$\) are launched by the He\,$\textsc\{ii\}$ and C\,$\textsc\{iv\}$ opacities. The stratified winds above the sonic point undergo velocity perturbation that can lead to clumps. In the optically thin supersonic winds, dense clumps of smaller size \($f\_\{VFF\}=0.27-0.3$, where $f\_\{VFF\}$ is the volume filling factor\) pulsate with higher-order harmonics. The larger clumps \($f\_\{VFF\}=0.2$\) oscillate with lower-order harmonics of the pulsation and affect the overall wind variability. ;Comment: 18 pages, 13 figures and 4 tables. Accepted in The Astronomical Journal Continued on ES/IODE ➡️ https://etcse.fr/nG7bi ------- If you find this interesting, feel free to follow, comment and share. We need your help to enhance our visibility, so that our platform continues to serve you.

📃Scientific paper: Black Hole Spectroscopy for Precessing Binary Black Hole Coalescences Abstract: To accurately perform black hole spectroscopy, it is essential to know which quasinormal modes dominate astrophysical ringdown signals. In this Letter, we present a phenomenological description of the quasinormal modes that are excited in the ringdowns of comparable mass, quasi-circular precessing binary black hole coalescences. By analyzing an exhaustive catalog of numerical relativity simulations, we confirm that the relative fundamental quasinormal mode amplitudes of precessing systems are related to those of non-precessing systems by a simple rotation, and that additional structure in the spectrum is connected to the system's kick velocity and other asymmetries in the orbital dynamics. We find that the ringdowns of precessing systems need not be dominated by the $\{\(\ell,m\)=\(2,\pm 2\)\}$ quasinormal modes. These results build upon previous works on waveform modeling, and are consistent with a recent ringdown analysis of the LIGO-Virgo gravitational wave signal GW190521. ;Comment: Data Release and Analysis Scripts: https://lnkd.in/eJtzARgJ Continued on ES/IODE ➡️ https://etcse.fr/rXKf ------- If you find this interesting, feel free to follow, comment and share. We need your help to enhance our visibility, so that our platform continues to serve you.

🌌 CENTRA Research News! 🌌 Last week, Instituto Superior Técnico #MSc student David Fordham and #professor Ilídio Lopes published "Constraints on the axion-photon coupling using stellar modelling" in Physical Review D - American Physical Society! They have used #asteroseismology and #stellar modelling to explore the impact of #axionic production in late main-sequence stars. By comparing models with #observational data, they constrained the axion-photon #coupling parameter to an upper bound of 0.98×10−10 GeV−1 at 68% confidence and a conservative limit of 1.38×10−10 GeV−1 at 95% confidence. This method offers more stringent #bounds than most current direct axion detections and can be applied to #future asteroseismic data. Dive into the paper: https://lnkd.in/d8TuppJM