ISRO Satellite Centre, Bangalore
E-mail: radhikad_isac@yahoo.in
Abstract.
Transient sources are seen to undergo a sudden increase in flux to
achieve its
peak within very few days and then slowly decay over several days or
months to
the quiescent level. These are binary systems which can be either a LMXB
or
HMXB. Here we explain the characteristics of two transient sources XTE
J1652-453 and XTE 1752-223, both first discovered by PCA on-board RXTE
(Rossi
X-ray Timing Explorer). XTE J1652-453 was detected during two PCA scans
on 28th
June, 2009 and 1st July 2009 and is located at an R.A of 16h52m20.33s
and Dec
of -45ˆ20'39.6'' in the galactic centre region; while
XTE J1752-223 was detected
on 23-10-2009 in the galactic bulge region at R.A = 17h52m13.2s and Dec
=
-22ˆ18'30''. XTE J1652-453 is observed to have a faster rise
to the peak,
while XTE J1752-223 had a very slow rise along with a precursor. The
spectral
study suggests that both the sources do have thermal and non-thermal
emissions
and show different characteristic spectral state transitions. From the
data
analyzed, it is understood that XTE J1752-223 rises from its quiescence
to the
Low/Hard state, then into the High/Soft state via the intermediate
state. Both
XTE J1652-453 and XTE J1752-223 remain in the High/Soft state while in
the peak,
and during decay exhibit intermediate state for a long period of 2
months and
enter the Low/Hard state before reaching the quiescence. Spectral study
of
both the sources also shows the presence of a relativistic Fe Kα
emission line.
Type C QPO's are seen in the case of XTE J1752-223 while in the
intermediate
state, but no characteristic features or QPO's are seen in XTE
J1652-453. An
estimation of the innermost radius of the accretion disc and equivalent
mass
proves that both the sources are LMXB's and black hole candidates. We
would
like to present a comparison of both these sources by spectral and
timing
analysis.