In the non-relativistic regime, fluid composition do not affect solution of equations of motion, until explicit cooling is considered. One of the main reason is that the information of composition is not included in the equation of state. We show that indeed composition affects solutions of accretion and jets around compact objects where the temperatures are transrelativistic. We also discuss...
We present the general relativistic magneto-hydrodynamic (GRMHD) accretion flow in Kerr space-time in the presence of the shock waves. Adopting the relativistic equation of state, we solve the governing equations in the ideal MHD limit and obtain the shock-induced GRMHD accretion solution for the first time to the best of our knowledge. We find that the subsonic flow entering from the outer...
Viscosity plays a vital role in accretion flows around black holes. It helps in the transport of angular momentum outwards allowing matter to get accreted into the potential well formed by the central compact object. Apart from angular momentum transport, viscosity also heats up the matter. In viscous transonic flows, both with and without shock solutions are possible. Many numerical...
We examine the effect of variable viscosity parameter ($\alpha$) in relativistic, low angular momentum advective accretion flow around rotating black holes. Following the recent simulation studies of magnetohydrodynamic disk that reveal the radial variation of $\alpha(r)$, we theoretically investigate the properties of the global transonic accretion flow considering a one-dimensional power law...
We study the relativistic, inviscid accretion flow in a generic stationary axisymmetric Kerr-Taub-NUT (KTN) space-time in presence of the shock waves. Along with the mass, this KTN space-time contains the spin parameter or the Kerr parameter ($a_{\rm k}$) and the NUT parameter ($n$). Depending on the values of $a_{\rm k}$ and $n$ this space-time represents either black-hole or naked...
Accretion is one of the ubiquitous mechanisms involved in astrophysics. Underlying model was developed from its simplistic spherical symmetric. form, namely Bondi accretion, in 1952, to the disk accretion with nonzero angular momentum in 1990s, to modern magnetically arrested accretion disk flow in the last decade. I will try to touch upon how with the improved and novel observations the...
The radiation pressure supported standard accretion disk model (Shakura Sunyaev 1973 model) is prone to classical thermal and viscous instabilities. However, these instabilities are not observed in astrophysical systems as disks remain thermally stable for astronomical time periods. In this talk, I will show some of the key findings of strongly magnetized accretion disks simulated using 3D...
Observations of X-ray binaries containing black holes indicate the presence of geometrically thick, hot, dynamic Compton cloud around the black hole to satisfactorily explain it’s spectral and temporal properties. In this work, I present results of a few high resolution, 3D hydrodynamic simulations of such Compton cloud around a non-rotating black hole. Our results demonstrate that the...
The central engine in active galactic nuclei (AGNs) and microquasars
is a black hole. As the black hole does not have any hard surface the jet must originate from the inner part of the accretion disc. The radiation field of the accretion disc interacts with the jet material as the jet travels through the radiation field. Various steady-state investigations have shown that the radiation field...
We study the relativistic, inviscid, advective accretion flow around the black holes and investigate a key feature of the accretion flow, namely the shock waves. We observe that the shock-induced accretion solutions are prevalent and such solutions are commonly obtained for a wide range of the flow parameters, such as energy (${\cal E}$) and angular momentum ($\lambda$), around the black holes...
The study of X-ray binaries in the outbursting phase is crucial to understand the accretion process and the underlying physics. Every outburst is different regarding energy budget and the observed spectral-timing properties. In this presentation, I will summarise the lesson learned from the study of these systems. Also, I will discuss
some of the key issues in this topic based on our recent studies.
Extragalactic Black Hole X-ray Binaries (BH-XRBs) are the most intriguing X-ray sources as some of these systems are ‘home’ to the most massive stellar mass BHs ever found. Most of these sources accrete matter through a stellar wind, making them ideal for studying the dynamics of accretion disks in massive binary systems. In this work, we study the X-ray properties of three massive (MBH =...
Masses of most black holes discovered in X-ray binaries lie within a narrow range of 5 - 20 M$_\odot$. The formation of these black holes is understood using scenarios involving collapse of massive stars. Contrary to X-ray binaries, black holes discovered using gravitational waves from merger events have masses going up to 200 M$_\odot$. This apparent dichotomy had given rise to a belief of...
Studying the nature of type-B/C QPOs in different scenarios can decipher their production mechanism. We have analyzed the appearance or disappearance of type-B ~4.5 Hz and type-C ~9.5 Hz QPOs of BH source H1743-322 and found no change in the disk inner radius but power-law indices are varying. Quasi-simultaneous radio observations indicate that either a corona or a jet is responsible for the...
The Galactic BHC MAXI J1348-630 was discovered by MAXI/GSC and Swift/BAT satellites in 2019. The source had undergone two major outbursts in 2019, shortly after its discovery. Using archival data from multiple satellites (including Swift, MAXI, NICER, NuSTAR, and AstroSat) we have performed a detailed spectral and temporal analysis of both the outbursts. The first outburst lasted for four...
Cygnus X-1 is a well-known galactic accreting black hole binary that shows several observational features suggesting a complex interaction between the accretion disk, its atmosphere called Corona, and the jet. The polarisation characteristics of the Corona and the jet are different. To understand the high energy emission mechanism and the system's geometry, we have carried out a...
We present broadband X-ray spectral and timing analysis of the black hole X-ray binary MAXI J1348–630, performed using five AstroSat observations. The source was in the soft spectral state for the first three observations and in the hard state for the last two. The power density spectra are substantially weak in the soft state compared to the hard state. In addition, we detected quasi-periodic...
We present the results from X-ray broadband spectro-temporal analyses of recurrent outbursting sources GX 339$-$4 and H 1743$-$322 using AstroSat and NuSTAR archival observations carried out during $2016-2022$. GX 339$-$4 was found to be making transition from quiescence to outburst, and the wide-band spectral analyses results during outbursts shows that GX 339$-$4 was in hard ($kT_{\rm...
The enigmatic black hole X-ray binary GRS1915+105 exhibits diverse variability patterns (i.e., θ, β, δ, ρ, κ, ω, and γ classes) as observed with AstroSat. We present a generic feature of time-lag properties for the HFQPO observations which belong to the δ, ω, κ and γ variability class. For the first time, we detect soft-lag associated with the 67 Hz HFQPO for all four variability classes of...
We study the recent outburst of the black hole candidate EXO 1846-031 which went into an outburst in 2019 after almost 34 years in quiescence. We use archival data from Swift/XRT, MAXI/GSC, NICER/XTI and NuSTAR/FPMA satellites/instruments to study the evolution of the spectral and temporal properties of the source during the initial rising phase of the outburst. Evolving type-C quasi-periodic...
4U 1543-47 is a galactic low-mass X-ray binary discovered in 1971. It has undergone five outbursts. The fifth outburst that happened in 2021 marks the source as the brightest X-ray binary source ever reported with a peak X-ray intensity of $\sim$11 Crab in 2-4 keV with MAXI/GSC. We aim for a comprehensive analysis of the wideband spectral characteristics of the source using NICER, NuSTAR...
High-energy ($>$100 MeV) emission is one of the defining characteristics of active galactic nuclei (AGN) hosting closely aligned relativistic jets, i.e., blazars. One of the key research problems in jet physics is constraining the evolution of these enigmatic sources. This talk will briefly discuss some of the recent discoveries of detecting $\gamma$-ray emission from a variety of jetted AGN,...
The soft excess, an excess emission below 2 keV, is an extraordinary feature of the X-ray spectra for most of the Seyfert 1 AGNs. The origin of this feature remains debated, as several models have been suggested to explain it, including warm Comptonization, blurred ionized reflection and other models. From the long-term observations of Ark 120, a bare AGN, we found a strong correlation between...
We study the multi-wavelength properties of the bare Seyfert 1.5 galaxy MCG-2-58-22 using the multi-epoch AstroSat observations taken simultaneously in the X-ray and UV bands. Previous studies reported X-ray variability in MCG-2-58-22 on both short and long time scales. The source was in a high X-ray flux state in 2007 and 2016 with a 2-10 keV flux of ~5×10^-11 erg/cm^2/s. The AstroSat...
A detailed broadband spectral and timing analysis of a small flaring event of a120 ks in a narrow-line Seyfert 1 galaxy NGC 4051 using simultaneous XMM-Newton and NuSTAR observations has been performed. The ~300 ks long NuSTAR observation and the overlapping XMM-Newton exposure were segregated into pre-flare, flare and post-flare segments. We found that during the flare, the NuSTAR count rate...
Despite occupying ~ 40% of the local Universe, Low Luminosity Active Galactic Nuclei (LLAGNs) are less explored due to their faintness. Detection of a few in gamma rays by Fermi-LAT allows us to constrain the physical parameters of the jet by modeling their spectral energy distributions from radio to gamma-ray energies. While a one-zone model explains the broadband emission up to a few GeV,...
The radiative loss interpretation for the broken power-law spectra of blazars is often questioned since the difference between the indices does not support this inference. MKN 421 is one of the extensively studied high energy peaked blazars with its synchrotron component peaking at soft X-ray energies. The X-ray spectra, therefore, exhibits significant curvature and the spectrum is well...
The broadband spectral study of blazars has provided significant information regarding the emission processes and the blazar jet environment. Inputs derived from the temporal study are often conflicting with the processes responsible for the flux variation not being consistent with the statistical flux distribution. Besides these, even after decades of research, the matter content of blazar...
We studied the broadband X-ray spectra of Swift/BAT selected low-accreting AGNs using the observations from NuSTAR and Swift/BAT in the energy range of 3 − 150 keV. Our sample consists of 24 AGNs with Eddington ratio, $\lambda_{Edd} < 10^{−3}$. We extracted several coronal parameters from the spectral modelling, such as the photon index, hot electron plasma temperature, cutoff energy and...
Ultraluminous infrared galaxies (ULIRGs) are gas-rich merger remnants that are extremely luminous at infrared wavelengths, represent the final stage of the merging process of two comparable mass gas-rich galaxies that finally evolve into elliptical galaxies, and in some cases radio-loud AGN. Using the Giant Metrewave Radio Telescope (GMRT), we observed a large sample of ULIRGs that have...
In the radio-quiet category of active galactic nuclei (AGN), the observed X-ray emission is believed to originate in the hot corona close to the vicinity of the accretion disk. Despite the numerous X-ray studies on AGN, we still do not have a clear understanding of the nature of the corona, such as its geometry, shape, location and the physical processes that power it. Parameters that can put...
We present a multi-wavelength study of the active nucleus and the off-nuclear X-ray sources in the nearby spiral galaxy, NGC 1365 using three simultaneous UV/X-ray observations by AstroSat over a two months period and archival IR observations performed with Spitzer and Herschel. Utilising the data from the Soft X-ray Telescope (SXT) on-board AstroSat, we find spectral variability mainly caused...
An understanding of spin frequency evolution of neutron stars I the low-mass X-ray binary (LMXB) phase is essential to explain the observed spin distribution of millisecond pulsars (MSPs), and to probe the stellar and binary physics, including the possibility of continuous gravitational wave emission. I will discuss the crucial effects of transient accretion on the spin evolution of neutron...
With the advent of the time-domain astronomy brilliant transients have been discovered near the centers of the galaxies. Photometric and Spectroscopic follow-ups of these objects by transient surveys like ePESSTO, ZTF, ASASSN have shown that spectral evolutions of these objects are different from that of supernovae, and their temporal evolutions can be explained to some extent as a...
SMC X-2 is one of the high-mass X-ray binary (HMXB) pulsar in the Small Magellanic Cloud (SMC). After a long interval of 15 years, the source was observed in its third outburst in September 2015. The source reached a very high X-ray luminosity of ~5 × 10^38 erg s-1 at the peak of the outburst. The luminosity of the source slowly decayed over the course of a month. We will present results from...
LMC X-4 is a highly luminous and eclipsing high-mass X-ray binary pulsar which is known to exhibit variations in X-ray flux over a wide range of time scales. The Large Area X-ray Proportional Counter (LAXPC) and Soft X-ray Telescope (SXT) instruments onboard the AstroSat observed the source in August 2016. The source was found to emit an X-ray luminosity of $\sim 2 \times 10^{38}$ erg...
In Low Mass X-ray Binary (LMXB) sources, during the active accretion from the secondary star, the accumulated fuel (a mixture of Hydrogen and Helium) undergoes hydrostatic compression as more matter keeps piling up. When temperature and density conditions reach ignition levels (typically within a few hours to days), the entire fuel layer on the NS surface burns rapidly, leading to a...
In the past decades, several neutron stars (NSs), particularly pulsars, with mass $M>2M_\odot$ have been observed. On the other hand, the existence of massive white dwarfs (WDs), even violating Chandrasekhar mass-limit, was inferred from the peak luminosities of type Ia supernovae. Hence, there is a generic question of the origin of massive compact objects. Here we explore the existence of...
In May 2022, MAXI made the discovery of the millisecond pulsar MAXI J1816–195. The unstable burning of accreted material on the surface of neutron stars results in thermonuclear (Type-I) bursts. During the 2022 outburst, MAXI J1816–195 generated a number of thermonuclear bursts. An exponential decay function and a sharp linear rise are used to model the burst profiles. The faster decay of the...
Astrophysical black holes are remarkably simple objects, described completely by just two parameters – mass and spin. Although it is easy to determine the mass of a black hole from the far-field gravitational influence, the determination of spin is more subtle and it requires one to probe the strong gravity region close to the event horizon where the GR effects are prominent. However, to study...
The source XTE J1859+226 is a black hole X-ray binary, which underwent outburst in 1999-2000. This source serves as a rich astrophysical laboratory to understand the connection between accretion disk and radio jet since it exhibits different types of Low Frequency Quasi Periodic Oscillations (LFQPOs) along with multiple radio flares.
We re-investigate the timing and spectral propertise of...
Giant radio quasars (GRQs) are radio-loud active galactic nuclei (AGN) that propel megaparsec jets with projected linear sizes of more than 0.7 Mpc. We report the discovery of a sample consisting of more than a hundred giant radio quasars at high redshift (z >= 1) through crossmatching the TIFR GMRT Sky Survey Alternative Data Release 1 (TGSS ADR1). Due to the good sensitivity and high...
Type Ia supernova (SN Ia) arises from the thermonuclear explosion of at least one carbon-oxygen white dwarf in a binary system. The most favored explosion model is the delayed detonation in a Chandrasekhar mas WD (single degenerate scenario). This explosion produces a stratification in the abundance structure of the elements present in the ejecta. The heavier elements, like Ni-56 and Fe, are...
The time-averaged spectrum of Gamma-Ray Burst(GRB) is often well fitted by an empirical smooth broken power-law function term as the Band model. However, the physical interpretation of this Band function is still being debated. Two competitive models are the synchrotron emission from a non-thermal particle distribution accelerated at a shock front (synchrotron shock model) or a...
Intense X-ray bursts (type-I bursts) originating from unstable thermonuclear conflagration, are observed from the surface of neutron star low-mass X-ray binaries (LMXBs) and they offer a promising tool to constrain the equation of state of the supra-nuclear matter at the neutron star core and to probe gravity in strong regime near the compact object. Recent observations show the burst spectra...
GX 9+1, an atoll type neutron star low-mass X-ray binary (NS-LMXB), was observed by the Soft X-ray Telescope and the Large Area X-ray Proportional Counters on-board AstroSat during May 2 - 4, 2019. The hardness-intensity-diagram (HID) of the source showed it to be in the soft spectral state during the observation. Flux-resolved spectra of the source could be adequately modelled with an...
Low mass X-ray binaries hosting weakly magnetized neutron stars (NS-LMXB) are classified as atoll sources and Z sources, based on their correlated spectral and temporal variability properties. Some atoll sources have been reported to exhibit type I X-ray bursts, characterized by a Fast Rise Exponential Decay (FRED) profile. One such atoll source is GX 3+1, which was first discovered in 1964....
PSR J0026-1955 was recently independently discovered by the Murchison Widefield Array (MWA) and was quickly found to show both subpulse drifting and nulling. We have observed this pulsar with the upgraded Giant Metrewave Radio Telescope (uGMRT), covering a frequency range of 300-500 MHz. Our analysis shows that the pulsar exhibits two distinct subpulse drifting modes, with various evolutionary...
In the presence of strong magnetic fields, such as in the accretion columns of Neutron Stars, the electrons get quantized into circular orbits, and Cyclotron Resonant Scattering Feature (CRSF) is observed as absorption features in the X-ray spectrum as photons scatter off these electrons at the resonant energies. CRSF or cyclotron lines are the best diagnostic tools that we have to probe the...
Be/X-ray binaries represent the largest population of high
mass X-ray binaries (HMXBs) consist of a Be star and mainly a neutron star as a compact object. In this talk, I will discuss the results obtained from the X-ray studies of the Be/X-ray binary 1A 0535+262 during the 2020 October giant X-ray outburst using AstroSat. The pulsar was detected at a pulsation period of ∼103.55 s in the...
Asynchronous polars (APs) are an exceptional type of magnetic cataclysmic variables where there is a lack (~1-2%) of perfect synchronicity, unlike polars, between the spin period of the primary white dwarf star and the orbital period of the binary system. Also, there are a few unusual intermediate polars (IPs) where the difference between spin and orbital period is much less (~10-20%) compared...
Intermediate polars (IPs) are the low magnetic field strength ( B $\sim$10$^{6}$-10$^{7}$ G) subclass of magnetic cataclysmic variables. IPs are asynchronous systems, and they follow the asynchronism relation as the spin period of the white dwarf (WD) is relatively less than the orbital period of the binary system. Most IPs have orbital periods longer than the 'period gap' of 2-3 h. However,...
Nova outburst is an astronomical phenomenon accompanied by the ejection of matter, causing an increase in luminosity, leading to the appearance of a sudden bright star in the sky, which fades away over several weeks or months. They are interacting binary systems with a white dwarf (WD) primary and a main-sequence or sub/red-giant secondary. We have observed outbursts of the recurrent nova M31N...
The Ultra Violet Imaging Telescope (UVIT) is one of the payloads on board India's first multi-wavelength astronomical observatory AstroSat, launched by the Indian Space Research Organisation on 28th September 2015. Since its launch, UVIT has been observing several compact objects that includes X-ray binaries as well as active galactic nuclei (AGN). A systematic investigation is being carried...
We present the results of a comprehensive long-term spectro-temporal analysis of nine ultra-luminous X-ray sources (ULXs) with the central object being a black hole, using XMM-Newton monitoring of about a decade. Temporal studies reveal the existence of short-term variability in each source with fractional variance varying in the range of $1.42-27.28$ per cent. Five sources of the sample are...
Ultraluminous X-ray sources (ULXs) are the brightest known non-nuclear X-ray binaries with luminosities exceeding the classical Eddington limit of a 10 $\rm M_\odot$ black hole. Recent discoveries of neutron star cores in ULXs confirm that the Eddington ratio can be a few hundred. Broadband spectral studies are pivotal to deciphering the emission mechanism in these mysterious sources. Here we...
Be/X-ray binaries (BeXRBs) form a major subclass of high-mass X-ray binaries that consist of a Be star and a compact object. The possible compact objects can be neutron stars, white dwarfs or black holes. However, neutron stars are the most frequently observed companion than other types. We performed a follow-up study (Bhattacharyya et al. 2022) on the recent detection of two X-ray flaring...
The broadband spectral energy distribution (SED) of blazars shows a two-hump structure. Understanding blazar SEDs has become increasingly possible over the last decade due to the capability to acquire near-simultaneous data from low-energy radio to high-energy gamma rays. Though the low energy hump in the broadband SED of blazars is understood to be from synchrotron emission processes, the...
We report the analysis of the Z-track NS-LMXB GX 17+2 using the simultaneous data from the AstroSat (LAXPC/SXT) and NICER mission data. On segmenting the HID into three slices—horizontal branch, hard apex, and normal branch- we investigate the source's variability and spectral state evolution throughout the observation. We performed the timing analysis in all the branches separately to probe...
This study examines the inflows and outflows of stars and gas in double-barred discs. For this, a 3D gravitational model has been set up and studied from the viewpoint of chaotic scattering in open Hamiltonian systems. In the phase space, a bar-driven outflow mechanism has been identified near the primary bar ends and further visualized using Poincaré maps to locate regular or chaotic basins....
Hybrid Morphology Radio Galaxies (HyMoRS) are found to be very rare subclass of radio galaxies. HyMoRS exhibits differing Fanaroff & Riley morphologies (FR I/II) in each of the two lobes. FR-I jets are generally shorter, have a high proportion of entrainment of thermal plasma close to the core region of the galaxy. On the other hand, FR-II radio galaxies are much extended (in the order of...
TCP J18224935-2408280 is a transient discovered by Tadashi Kojima in May 2021 and later classified as a symbiotic star. Our follow-up study shows that the newly discovered symbiotic star (TCP J1822) was undergoing a Z-And type outburst (classical symbiotic outburst). To understand the nature of the outburst, low-resolution spectroscopic observations from HCT were obtained from May 2021 to...
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...
