• ANUJ NANDI

Articles written in Journal of Astrophysics and Astronomy

• Early In-orbit Performance of Scanning Sky Monitor Onboard AstroSat

We report the in-orbit performance of Scanning Sky Monitor (SSM) onboard AstroSat. The SSM operates in the energy range 2.5 to 10 keV and scans the sky to detect and locate transient X-ray sources. This information of any interesting phenomenon in the X-ray sky as observed by SSM is provided to the astronomical community for follow-up observations. Following the launch of AstroSat on 28th September, 2015, SSM was commissioned on October 12th, 2015. The first power ON of the instrument was with the standard X-ray source, Crab in the field-of-view. The first orbit data revealed the basic expected performance of one of the detectors of SSM, SSM1. Following this in the subsequent orbits, the other detectors were also powered ON to find them perform in good health. Quick checks of the data from the first few orbits revealed that the instrument performed with the expected angular resolution of 12’ × 2.5 and effective area in the energy range of interest. This paper discusses the instrument aspects along with few on-board results immediately after power ON.

• Editorial

• Observational aspects of outbursting black hole sources: Evolution of spectro-temporal features and X-ray variability

We report on our attempt to understand the outbursting profile of Galactic Black Hole sources, keeping in mind the evolution of temporal and spectral features during the outburst. We present results of evolution of quasi-periodic oscillations, spectral states and possible connection with jet ejections during the out burst phase. Further,we attempt to connect the observed X-ray variabilities (i.e., ‘class’/‘structured’ variabilities, similar to GRS 1915$+$105) with spectral states of black hole sources. Towards these studies, we consider three black hole sources that have undergone single (XTE J1859$+$226), a few (IGR J17091$-$3624) and many (GX 339-4) outbursts since the start of $RXTE$ era. Finally, we model the broadband energy spectra (3–150 keV) of different spectral states using $RXTE$ and $NuSTAR$ observations. Results are discussed in the context oftwo-component advective flow model, while constraining the mass of the three black hole sources.

• Study of X-ray transients with Scanning Sky Monitor (SSM) onboard AstroSat

Scanning Sky Monitor (SSM) onboard AstroSat is an X-ray sky monitor in the energy range 2.5–10 keV. SSM scans the sky for X-ray transient sources in this energy range of interest. If an X-ray transient source is detected in outburst by SSM, the information will be provided to the astronomical community for follow-up observations to do a detailed study of the source in various other bands. SSM instrument, since its power-ON in orbit, has observed a number of X-ray sources. This paper discusses observations of few X-ray transients by SSM. The flux reported by SSM for few sources during its Performance Verification phase (PV phase) is studied and the results are discussed.

• Advective accretion flow properties around rotating black holes – application to GRO J1655-40

We examine the properties of the viscous dissipative accretion flow around rotating black holes in the presence of mass loss. Considering the thin disc approximation, we self-consistently calculate the inflow-outflow solutions and observe that the mass outflow rates decrease with the increase in viscosity parameter ($\alpha$). Further, we carry out the model calculation of quasi-periodic oscillation frequency ($\nu_{\rm QPO}$) that is frequentlyobserved in black hole sources and observe that $\nu^{\max}_{\rm QPO}$ increases with the increase of black hole spin ($a_{\rm k}$). Then, we employ our model in order to explain the High Frequency Quasi-Periodic Oscillations (HFQPOs) observedin black hole source GROJ1655-40. While doing this, we attempt to constrain the range of $a_k$ based on observed HFQPOs ($\sim$300 Hz and $\sim$450 Hz) for the black hole source GRO J1655-40.

• # Journal of Astrophysics and Astronomy

Current Issue
Volume 40 | Issue 4
August 2019

• # Continuous Article Publication

Posted on January 27, 2016

Since January 2016, the Journal of Astrophysics and Astronomy has moved to Continuous Article Publishing (CAP) mode. This means that each accepted article is being published immediately online with DOI and article citation ID with starting page number 1. Articles are also visible in Web of Science immediately. All these have helped shorten the publication time and have improved the visibility of the articles.

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019