Spectral evolution of the galactic microquasars XTE J1550-564 and GRO J1655-40 during outbursts

We present results of a broadband spectroscopy of the galactic microquasars and black hole candidates XTE J1550-564 and GRO J1655-40, performed with the INTEGRAL and RXTE observatories during strong outbursts in 2003 and 2005, respectively. The spectral parameters evolution was traced during brightening and fading phases of each outburst to search a possible hysteresis and transitions from state to state. We estimated a size and optical depth of different regions around XTE J1550-564, like a hot plasma zone and optically thick accretion disk. Upper limits to the annihilation 511 keV line emission were obtained for both sources using data of the SPI spectrometer onboard the INTEGRAL observatory.