Indian Centre for Space Physics
43, Chalantika, Garia Station Road, Kolkata, India, 700084.


Research Topics

Theory :
Observation :

List of Publications

Faculty Members :

Prof. Sandip K. Chakrabarti

Dr. Dipak Debnath

Research Fellows :

Head of the Department :

Dr. Dipak Debnath

High Energy Astrophysics

    Black Hole astrophysics consists of studies of how matter is accreted into the black holes, how matter is ejected from accretion disks in the form of jets and outflows, how radiation is emitted from these disks and outflows and what is the time dependence of the spectrum of radiation. All these works are done at ICSP. There are two branches of black hole astrophysics: Theoretical and Observational.

Theoretical Astrophysics :

    It is well known that in compact objects, such as black holes and neutron stars, the gravitational force plays the most powerful role to produce electromagnetic radiation from accreting matter. Observing this radiation is crucial in astronomy and understanding the spectrum is crucial for model builders and theorists. In a binary system, matter from the companion star accrets into the black holes via Roche-Lobe and produces a disk like structure. There are a large number of theoretical models which are present in the literature to explain the accretion physics around the black holes. In order to study physical processes related to the accretion disk, outflows, jets, QPOs, etc., we consider two component advective flow (TCAF) model (Chakrabarti, 1989; Chakrabarti & Titarchuk, 1995; Chakrabarti, 1997). Here, we try to couple the radiative transfer processes along with hydrodymanic processes in a self-consistent manner. Also, in order to find origin of the temporal and the spectral variabilities in black hole candidates, we use model dependent / independent Monte-Carlo simulation methods. Also, we are trying to develop a radiatively efficient accretion disk model for the visualization of black hole candidates.

Observational Astrophysics :

    Observational study of astronomical objects is a very much challenging and interesting task to do. Galactic stellar massive black hole candidates are most fascinating objects to study in X-ray domain as because of these sources show variabilities in a short time scales in X-rays. We mainly study temporal and spectral properties and their evolutions during the outbursts, we mainly use archival data of NASA's astronomy satellite RXTE. In order find the origin and day-wise evolutions of quasi-periodic oscillation (QPO) frequencies, in 2005, we develop a new model, named as Propagating Oscillatory Shock (POS) model, which is a time varying form of shock oscillation model (SOM), introduced by Chakrabarti and his collaborators in mid-90s (Molteni, Sponholtz, & Chakrabarti, 1996; Ryu, Chakrabarti, & Molteni, 1997). Also to find direct evidences of two component advective flows (Keplerian and sub-Keplerian) in the accretion disk around the black holes, recently we have included the TCAF model in HEASARC's spectral analysis software package XSPEC as a local additive model (Debnath et al. 2013). We found that TCAF model can fit observational data obtained from different spectral states of few transonic black hole candidates (GRO J1655-40, GX 339-4, H 1743-322, etc). Variation of two component accretion rates are also found to be consistent with the disk black body and the power-law model fluxes, obtained from the spectral fit using a combined disk black body and power law model components. Also, from the TCAF model fit of black hole spectra, shock parameters such as location and strength can be extracted directly. From these two important shock parameters, we have predicted observed low-frequency QPOs (Debnath et al. 2013).