30th Annual Report 2017-18

The long term variability capabilities of LAXPC was shown by analysis of the enigmatic X-ray binary Cyg X-3 by the LAXPC team which included Ranjeev Misra . Apart from the orbital period 4.8 hrs, a slower oscillation of 36 days was observed. Further more complex variations with harmonics in 100s of seconds time-scales was detected in the observed light curves. More importantly AstroSat observed the source on the onset of a giant radio flare catching the behaviour of the X-ray variation during the event. The source made a state transition and the appearance of an hard power-law tail which was consistent with having the same origin as the radio emission. Figure 4: Dynamic power spectra of 4U 1728-34 in the energy range of 3–20 keV (top panel). A drifting kHz QPO whose frequency changes from ~815 Hz to ~850 Hz is clearly visible. The middle panel shows the variation of significance sigma showing that the QPO is significantly detected. The bottom panel shows the co-added power spectra after aligning the QPO frequency. No other features are detected in the 200–2000 Hz. (Figure taken fromVerdhan, et al.ApJ 841, 41). 34