Black holes (BH) represent the end stages of the evolution of stars with ZAMS > 15.0 M_{\odot}. These BHs are formed by the gravitational collapse of a massive star. BHs cannot be seen, but the effects of their strong gravity on the stars and the gases nearby can give us a lot of information. Astronomers' best hope has been to discover a BH in a nearby binary system. If the BH is in such a...
We have carried detailed time-resolved timing analysis of an intermediate polar V709 Cas, using the long-baseline, short cadence optical photometric data from the Transiting Exoplanet Survey Satellite(TESS). We found an orbital period of $5.332965\pm0.000007$ hr, a spin period of $312.7488\pm0.0004$ sec and a beat period of $317.9265\pm0.0004$ sec, which are similar and more precise than the...
We check if the first significant digit of the dispersion measure of pulsars and Fast Radio Bursts (using the CHIME catalog) is consistent with the Benford distribution. We find a large disagreement with Benford’s law with ${\chi}^2$ close to $80$ for $8$ degrees of freedom for both these aforementioned datasets. This corresponds to a discrepancy of about $7𝜎$. Therefore, we conclude that the...
Time-dependent fluid equations can describe a wide range of astrophysical problems like accretion flow around a compact object, outflows emanating from Young stars, or Active Galactic Nuclei (AGN). The strong gravity and high magnetic fields present in these flows make them particularly interesting for study. Numerical simulation of fluid equations provides an efficient way to study these...
PSR J1713+0747 is one of the most precisely timed pulsars in the international pulsar timing array experiment. This pulsar showed an abrupt profile shape change between 2021 April 16, (MJD 59320) and 2021 April 17 (MJD 59321). In this study, we report the results from multi-frequency observations of this pulsar carried out with the upgraded Giant Metrewave Radio Telescope (uGMRT) before and...
The evolution of time-lag and low frequency quasi-periodic oscillations (LFQPOs) in outbursting black hole sources can be explained by the systematic drifting of the outer boundary of the Compton cloud during rising and declining phases of the outburst. We study the fast variability properties of Galactic Soft X-ray Transient (SXT) XTE J1550-564 during 2000 outburst using RXTE instruments and...
The Galactic black hole X-ray binary candidate MAXI J1803−298 was first discovered with the nova search system of MAXI (Serino et al. 2021). NuSTAR and NICER found periodic absorption dips, and Swift detected absorption lines likely originating in a disk wind, both suggestive of a high inclination angle above ∼ 70$^{\circ}$. A sign of an outflow was also detected in optical spectroscopy, where...
The study examines the radio properties of quasars discovered in the data release 17 of Sloan Digital Sky survey(SDSS).The main idea of the study is to find how many of the SDSS quasars emit in the radio band, what fraction of quasars are radio-loud, is there a radio loud/radio-quiet dichotomy and what is the radio morphology of the radio loud quasars in SDSS. This involves searching for the...
We present the result of the spectral and timing study of GX 340+0 which is a Cyg X-2-like source using AstroSat’s SXT and LAXPC data. The source is found to be proceeding towards the flaring branch from the horizontal branch via normal branch as the observation progresses. Spectral analysis of SXT [1-7keV] and LAXPC data [4-25keV] in 1-25keV, reveals that the black body flux and flux ratio...
Weakly magnetized low mass X-ray binaries (LMXB) with neutron star (NS) as a compact object are classified into Z sources and atoll sources based on their correlated spectral and temporal variability properties. The colour-colour diagrams (CDs)/hardness-intensity diagrams (HIDs) of atoll sources are characterized by isolated clumps called ‘island states’ which at times extend to form an...
4U 1636–536 is an atoll type neutron star low mass X-ray binary (NS-LMXB) first observed by the Uhuru and Copernicus missions in 1974. It is a frequent burster which has shown a total of 664 unique bursts between 1996 to 2012. Some of these bursts have been short waiting time bursts with a mean burst rate of 0.26 $hr^{-1}$. Given its frequent bursting nature, this source provides us with an...
Low mass X-ray binaries hosting a neutron star (NS-LMXBs) have been classified as ‘Z’ and ‘atoll’ sources based on the tracks they trace out in the hardness-intensity-diagram (HID) and their correlated X-ray spectral and X-ray fast-variability characteristics. Atoll sources have lower mass accretion rates and host a neutron star having lower magnetic field (< 10^9 G). The exact physical...
Blazars are highly variable on all timescales ranging from a few minutes to years. Variability studies in blazars is one of the important tools to understand the blazar jets. To study flux and spectral variability on intra-day and long term timescales we have used XMM-Newton and SWIFT satellite X-ray data. On short-term timescales emission from jets are dominating whereas on longterm...
In this work, we present a detailed study and a complete analytical investigation of the critical behavior of the accretion flow and the nature of the phase trajectories corresponding to the transonic accretion in the context of these massive elliptical galaxies by incorporating the effect of the entire gravitational potential of the host galaxy in the presence of cosmological constant.
To understand the X-ray spectra of one of the superluminal X-ray binaries, we used RXTE/PCA and AstroSat/LAXPC data of GRS 1915+105.Where we can see significant photon counts variability in the X-ray light curves within 3.0–80.0 keV energy range.Out of 12 classes of X-ray variability, only few classes have significant higher and lower photons count.So We extract the higher(High flux) and...
Based on the X-ray flux variability on color-color diagrams (CDs)/hardness-intensity diagrams(HID) of low mass X-ray binaries hosting neutron stars as compact objects (NS-LMXBs) classified as Z and atoll sources. 4U 1820-30 is an atoll type NS-LMXB located in the globular cluster NGC 6624. It is one of the most well-studied NS-LMXBs and is reported to have kilohertz quasi periodic...
We provide a complete general relativistic and fluid dynamical treatment to derive an expression of the relativistic accretion rate in curved space-time. We exploit the killing symmetry of stationary-axisymmetric space-time to obtain the conserved current using which we find an integral relation between mass flux and height of the accretion disk. In comparison with the existing different...
Active Galactic Nuclei (AGNs) are one of the most interesting objects in the extragalactic sky. They emit radiation in all wavelength ranging from radio to X-ray and Gamma rays. Through X-ray study we can probe very deep into AGNs because it comes from the vicinity of central Super Massive Black-Holes. Although the inverse compton scattering of the accretion disc’s UV/Optical photon by hot...
