- Conference date: 10–15 February 2008
- Location: Kolkata (India)
It is believed that Low and Intermediate frequency Quasi‐Periodic Oscillations (QPOs) may be generated due to the oscillations of the post‐shock region which Comptonizes soft photons. Any movement of these perturbations is expected to change the QPO frequency systematically. Here, we report the presence of such systematic drifts both during the onset phase from the of September 1998 to the September 1998, when the QPO frequency was increasing monotonically from 81mHz to 13.1Hz. It started to decrease at the onset of the decline phase. On the of September 1998, the QPO frequency gradually decreased to 2.62Hz and after that its value remains almost stable and no such systematic drift was observed. We therefore model the frequency drift with a propagatory oscillating shock solution. The systematic and predictable variation of the QPO frequency over a period of few weeks directly supports the view that it may due to the drifting of an oscillating shock rather than the movements of a blob inside a differentially rotating disk.
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