Study of Spectro-Temporal behaviour in X-ray binaries with AstroSat/LAXPC

Large Area X-ray Proportional Counter (LAXPC) on-board AstroSat, with its higher efficiency and unprecedented time resolution (~ 10 micro-seconds), provides a rare opportunity to study X-ray spectro-timing variability of X-ray binaries up to 80 keV. In this talk, I shall focus on results obtained from the X-ray variability study of four X-ray binaries: H 1743-322, 4U 1728-34, GRS 1915+105 and GRS 1716-249 which were  monitored by LAXPC during last one year. Such studies provide valuable information about the source accretion properties in the hard X-ray regime at different spectral states, namely hard/hard-intermediate and soft/soft-intermediate. Till date, many attempts have been made to connect spectral and temporal variability in these X-ray binaries but unfortunately most of them are limited to 20 keV which is the upper threshold with the most reliable calibration in RXTE/PCA. With the launch of AstroSat, LAXPC reliably extends the higher energy limit to 80 keV. This allows us to test and extend our knowledge of source spectral state evolution from the soft X-ray band to the hard X-ray band. We have detected QPOs in these X-ray binaries at various frequencies and also in high energy regime. We also studied rms and time lag for these QPOs. In GRS 1915+105 we found a new X-ray class based on rate and color. GRS 1716-249 has gone into outburst after ~ 24 years. We have found high quality spectro-temporal results for this source.