Journal of Astrophysics and Astronomy最新文献

We report a detailed spectro-temporal analysis of the black hole low mass X-ray binary 4U 1543−475 during its 2021 outburst using the data from the Large Area X-ray Proportional Counter and the Soft X-ray Telescope instruments on board AstroSat. We studied the energy and frequency dependency of the source variability to probe the origin of the disc/coronal fluctuations. Following the state transition (from soft to intermediate state), the emergence of a band-limited noise component is observed along with the power law noise when the disk is recovering from a sudden decrease in the inner disk radius. A possible correlation between the low-frequency root mean square (RMS) variability amplitude and the covering fraction of the non-thermal component is detected. During the final AstroSat observation, a flip-flop phenomenon is reported, where rapid variation in RMS occurs in concurrence with sudden flux transition. An indication of the evolution of inner disk temperature along with a significant change in thermal flux was observed during the flip-flop phase, arguing for a disk instability-driven origin for this phenomenon. Our results suggest that the long-term variability evolution is primarily affected by the coronal changes, whereas the disk behavior governs the short-term variability evolution.

This work presents the first-ever broadband (0.7–25.0 keV) timing and spectral analysis of Be-HMXB 2S 1417–624 during its 2021 outburst. Using AstroSat observations, coherent pulsations at (sim )17.36633 s (MJD 59239.082) were detected in 0.7–7.0 keV SXT and 3.0–25.0 keV LAXPC data. The pulse profile was dual peaked at all energies, with the relative intensity of the main peak increasing with energy. The peaks in the SXT profiles were broad and comprised of several mini-structures. The LAXPC profiles were relatively smooth and had higher pulsed fractions, which increased with energy. The SXT(+)LAXPC simultaneous energy spectrum is well described by an absorbed power-law with exponential cut-off, a (sim )1.6 keV black body component, and a 6.47 keV emission line. A model comprising of an absorbed power law with high energy cut-off plus a partial covering absorber and Gaussian emission line fits the spectrum quite well. These results have been compared with timing and spectral features during the previous outbursts of this transient pulsar.

An analysis of the high-resolution ((Rsim 48000)) optical spectrum of hot (B1Ibe) post-AGB star LS 4331 (IRAS 17381−1616) is presented. The detailed identification of the observed absorption and emission features in the wavelength range 3700–9200 Å is carried out for the first time. The atmospheric parameters and chemical composition of the star are derived from the non-LTE analysis of absorption lines. We estimated (T_textrm{eff}=20900pm 500) K, (log g=2.57,pm ,0.08), (V_r=-51.7,pm ,0.8) km s(^{-1}), (xi _textrm{t}=24,pm ,4) km s(^{-1})  and (v sin i=30,pm ,5) km s(^{-1}). An abundance analysis for C, N, O, Mg, Al, S, and Si reveals that the N and O abundance is close to solar while metal underabundances relative to the solar value (i.e., ([mathrm{Mg/H}] = -1.04) dex, ([mathrm{Al/H}] = -1.20) dex, ([mathrm{Si/H}] = -0.46) dex) are found. LS 4331 is a high galactic latitude metal-poor and carbon-deficient hot post-AGB star. The underabundance of carbon (([mathrm{C/H}]=-0.64) dex) is similar to that found in other hot post-AGB stars and indicates that the star’s AGB phase of evolution was terminated before the third dredge-up. Plasma diagnostics are derived from the nebular emission lines. The presence of nebular emission lines in the spectrum of LS 4331 indicates that the photoionization of the circumstellar envelope has already started. The nebular parameters and expansion velocity of the nebula are derived. Using the Gaia DR3 distance, the absolute luminosity of the star is derived, and the star’s position on the post-AGB evolutionary tracks suggests that its initial main sequence mass is about 1.2 (M_{odot }). It is also reported that fast irregular brightness variations with an amplitude of up to 0.3 mag in the V band have been found in the star, typical of hot post-AGB objects.

The effect of finite non-zero temperature on the masses and radii of anisotropic deformed magnetized white dwarfs in the parameterized (gamma )-metric formalism is investigated. The equation of state (EoS) for a relativistic free Fermi gas of electrons surrounding a lattice of nuclei, considering the effects of finite temperature, Landau quantization, and anisotropic pressure is developed. We found stable super-Chandrasekhar masses of white dwarfs (above ({sim }5) (M_{odot })). At a fixed central density and temperature, the masses decrease monotonically as the central magnetic field increases, and equatorial radii increase monotonically. We also observed that the maximum mass and its corresponding equatorial radius decrease with the increase of the central magnetic field. Moreover, the maximum mass occurs at a higher central density as the magnetic field increases. This shows that increasing the magnetic field (hence increasing anisotropy) softens the EoS and makes the star more compact. We also found that the mass and equatorial radius increase with increasing temperature at a fixed central density and central magnetic field strength. This effect is significant for low central magnetic fields and low central densities. In essence, the finite temperature has an opposing effect to that of the magnetic field by decreasing the anisotropy of the system, thereby making the EoS stiffer and the star less compact.

Since the Fermi Large Area Telescope launch, a large sample of blazars has been detected in the (gamma )-ray band. One of the important parameters, the variability index (VI), is adopted to quantify the (gamma )-ray blazar variability. The variability of blazars can be affected by the geometric jet structure, accretions, source sizes, or evolutions of particles. In this paper, we compiled a sample of 2250 blazars (792 flat spectrum radio quasars, 1458 BL Lacertae objects) with some physical parameters to investigate the correlations between the VI and beaming effects. The VI shows positive correlations with the Doppler factors, (gamma )-ray luminosities, core dominances, and superluminal motions for both FSRQs and BL Lacs but only holds a positive correlation on polarizations for BL Lacs. The close correlations between VI and the beaming indicators reinforced the previous results that the (gamma )-ray variability is related to the jet, and the VI can be regarded as an effective indicator for the jet beaming effects of Fermi blazars.

Spatial, kinematic, and orbital properties, along with ages and chemical compositions of the thin disc, thick disc, and various stellar substructures in the halo, are studied based on data from the LAMOST and Gaia surveys. The star formation in the Galactic thin and thick disc, with peak metallicities of − 0.20 and − 0.45 dex, is found to have peaked about 5.5 and 12.5 Gyr ago, respectively. The thin disc is also found to have experienced an initial star formation burst about 12.5 Gyr ago. The pro-grade population Splash and hot-disc (HD), with peak metallicity of about − 0.60 and − 0.43, are found to be about 13.03 and 12.21 Gyr old, respectively, with peak eccentricity of 0.70 and 0.35, are understood to be of in situ origin. The Gaia-Enceladus/Sausage (GE/S), Thamnos and Sequoia, with peak metallicity of about − 1.31, − 1.36, and − 1.56, are found to be about 11.66, 12.89, and 12.18 Gyr, respectively, and are understood to be remnants of dwarf galaxies merged with the Milky Way. The HD, Splash, and Thamnos have experienced chemical evolution similar to the thick disc, while GE/S, Sequoia, and Helmi stream have experienced distinct chemical enrichment of iron and (alpha )-process elements.

Determination of cosmological parameters is a major goal in cosmology at present. The availability of improved data sets necessitates the development of novel statistical tools to interpret the inference from a cosmological model. In this paper, we combine the principal component analysis (PCA) and Markov Chain Monte Carlo (MCMC) method to infer the parameters of cosmological models. We use the No U-Turn Sampler (NUTS) to run the MCMC chains in the model parameter space. After determining the observable by PCA, we replace the observational and error parts of the likelihood analysis with the PCA reconstructed observable and find the most preferred model parameter set. To demonstrate our methodology, we assume a polynomial expansion as the parametrization of the dark energy equation of state and plug it into the reconstruction algorithm as our model. After testing our methodology with simulated data, we apply the same to the observed data sets, the Hubble parameter data, Supernova Type Ia data, and the Baryon acoustic oscillation data. This method effectively constrains cosmological parameters from data, including sparse data sets.

This paper presents a comprehensive analysis of 30 ks Chandra and 46.8 ks (13 h) 1.4 GHz GMRT radio data on the cool-core cluster RXCJ0352.9(+)1941 to investigate AGN activities at its core. This study confirms a pair of X-ray cavities at projected distances of about 10.30 and 20.80 kpc, respectively, on the NW and SE of the X-ray peak. GMRT L band (1.4 GHz) data revealed a bright radio source associated with the core of this cluster hosting multiple jet-like emissions. The spatial association of the X-ray cavities with the inner pair of radio jets confirms their origin due to AGN outbursts. The 1.4 GHz radio power (7.4 pm 0.8 times 10^{39}) erg s(^{-1}) is correlated with the mechanical power stored in the X-ray cavities (({sim }7.90times 10^{44}) erg s(^{-1})), implying that the power injected by radio jets in the ICM is sufficient enough to offset the radiative losses. The X-shaped morphology of diffuse radio emission seems to be comprised of two pairs of orthogonal radio jets, likely formed due to a spin-flip of jets due to the merger of two systems. The X-ray surface brightness analysis of the ICM in its environment revealed two non-uniform, extended spiral-like emission structures on either side of the core, pointing towards gas sloshing due to a minor merger. It might have resulted in a cold front at (sim )31 arcsec (62 kpc) with a temperature jump of 1.44 keV.

We have studied two manuscripts as commentaries called Laghu Mānasa Vyākhyā and titled grahaṇānayanam. Our attempts to decipher the contents have revealed that they are commentaries in Sanskrit (the script is Kannada) on the 9th century manuscript called Laghu Mānasa by Munjalācarya. These two manuscripts have solved examples of eclipses of śaka 1528 (1606CE) and 1549 (1627CE); the procedure gives all the details to get the mean positions of the Sun, the Moon, and the nodes and subsequently, the timings and magnitude of eclipses. The first text is incomplete; the second has complete calculations. With the details provided for the procedure, we find that the method for finding the sine is unique and differs from that of Bhaskarācārya and Ganeśha Daivajnya. We present the calculations, verify them, and compare them with online software computations. The agreement is within the error limits of observations.

Solar loops are hot and magnetic structures that often have transverse displacements. In this research, we study the characteristics of three solar loops using the images observed in the radiation region with the Hinode/XRT telescope on 11 September 2017. Fluctuations of solar loops can be traced using two methods: image and spectral processing. In the first method, displacements and disturbances are measured in images, while in the second method, periodic patterns are searched in Doppler shifts by spectrometers. Our analysis method is based on image processing and solar loop seismology. In this method, the time slices can be prepared from the images and then analyzed using the wavelet method. The measurement results of time series for three loops with lengths of 113040, 79128, and 62800 km were obtained in the range of 3–18, 3–6, and 3–16 min, respectively. The phase velocity of these oscillations was calculated in the range of 209–1256, 438–879.2, and 130–697.7 km s⁻¹ for three loops, respectively. Also, Alfven speeds were determined as 150–1012, 316–708.8, and 94–562.5 km s⁻¹. The magnetic field related to these fluctuations was calculated by the seismological method with the approximation of the thin cylindrical model for the loops measuring 2.47–16.52, 3.6–11.56, and 1.1–9.18 Gauss. Our findings suggest that oscillating movements in the loops can be interpreted as Kink transverse oscillations.