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R. Misra (Northwestern Univ.)
A generic model for alternating lags in QPO harmonics is presented where variations in the photon spectrum are caused by oscillations in two parameters that characterize the spectrum. It is further assumed that variations in one of the parameters is linearly driven by variations in the other after a time delay td. It is shown that alternating lags will be observed for a range of td values. A phenomenological model based on this generic one is developed which can explain the amplitude and phase lag variation with energy of the fundamental and three harmonics of the 67 mHz QPO observed in GRS 1915+105. The phenomenological model also predicts the variation of the Bicoherence phase with energy, which can be checked by further analysis of the observational data.
The author(s) of this abstract have provided an email address for comments about the abstract: ranjeev@finesse.astro.nwu.edu