Low and Intermediate Frequency Quasi-Periodic Oscillations ( QPOs ) are thought to be due to oscillations of Comptonizing regions or hot regions embedded in Keplerian discs .
Observational evidence of evolutions of QPOs would therefore be very important as they throw lights on the dynamics of the hotter region .
Our aim is to find systems in which there is a well defined correlation among the frequencies of the Quasi Periodic Oscillations over a range of time so as to understand the physical picture .
In this paper , we concentrate on the archival data of XTE J1550-564 obtained during 1998 outburst , and study the systematic drifts during the rising phase from the 7 ^ { th } of September 1998 to the 19 ^ { th } September 1998 , when the QPO frequency increased monotonically from 81 mHz to 13.1 Hz .
Immediately after that QPO frequency started to decrease and on the 26 ^ { th } of September 1998 , the QPO frequency became 2.62 Hz .
After that its value remained almost constant .
This frequency drift can be modeled satisfactorily with a propagatory oscillating shock solution where the post-shock region behaves as the Comptonized region .
Comparing with the nature of a more recent 2005 outburst of another black hole candidate GRO 1655-40 , where QPOs disappeared at the end of the rising phase , we conjecture that this so-called ’ outburst ’ may not be a full-fledged outburst .