Research Topics
Theory :
Observation :
List of
Publications
Faculty
Members :
Prof. Sandip K. Chakrabarti
Dr. Dipak Debnath
Research Fellows :
Visiting Fellows :
Dr. Broja
Gopal Dutta
Head of the
Department :
Dr.
Dipak Debnath
Past Ph.D. Students


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 RocheLobe 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 selfconsistent
manner. Also, in order to
find origin of the
temporal and the spectral
variabilities in black hole candidates,
we use model dependent / independent MonteCarlo
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 Xray domain as
because of these sources show variabilities in a
short time scales in Xrays. 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 daywise evolutions
of quasiperiodic 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 mid90s (Molteni, Sponholtz,
& Chakrabarti, 1996; Ryu, Chakrabarti, &
Molteni, 1997). Also to find direct evidences of
two component advective flows (Keplerian and
subKeplerian) 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 J165540, GX 3394, H 1743322,
etc). Variation of two component accretion rates
are also found to be consistent with the disk
black body and the powerlaw 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 lowfrequency QPOs (Debnath et al. 2013).
