DR. BROJA DUTTA

The complex behavior of Quasi-Periodic Oscillations (QPOs) and Fourier phase lags have significant observational effects in the Galactic black hole sources. These temporal properties can diagnose the dynamics of accretion flow around the black holes. We analyze RXTE/PCA data of the black hole sources GX 339-4, XTE J1550-564 and GRO J1655-40 to study the behavior of Low Frequency Quasi Periodic Oscillations (QPOs) frequency and phase/time lag properties during the rising and declining phases of the outbursts. We find a systematic variation in QPO frequency with time in the onset and declining phases of the outbursts. These frequency evolutions could be clearly interpreted with the propagatory shock oscillations solution where the post-shock region behaves as the Comptonized region. The evolution of time lag is correlated with the QPO frequency for all the outbursts and suggests towards a common evolution scenario of the black hole transients through their outbursts.