Evidence for two-component flows around the black hole candidate XTE J1550-564 from spectral features during its 1998-1999 outburst

We study the spectral properties of the accretion disc in the Galactic black hole candidate XTE J1550-564 during the 1998-1999 outburst when the source exhibited double-peaked eruptions. This outburst lasted for 250 d and the 2.5-25.0 keV spectral state varied smoothly from one to another several times. We show that the spectral features of the 1998-1999 outburst could be clearly understood by a two-component (Keplerian and sub-Keplerian) advective flow (TCAF). We concentrate on the spectral data from a Proportional Counter Array instrument on the RXTE satellite for the black hole XTE J1550-564 and fit them quite satisfactorily using TCAF model. From the spectral fit we calculate the disc parameters, such as the Keplerian rate, the sub-Keplerian rate (halo rate), the shock location and the inner edge of the Keplerian disc. This observation points to the presence of two independent components in the accretion flow and that the accretion rate at all radii need not be constant in an evolving disc.