X-ray spectral components in the hard state of GRS 1915+105: origin of the 0.5 - 10 Hz QPO

We investigate the origin of the ubiquitous 0.5 - 10 Hz QPO in the Galactic microquasar GRS 1915+105. Using the archival X-ray data from RXTE, we make a wide band X-ray spectral fitting to the source during a low-hard state observed in 1999 June. We resolve the X-ray spectra into three components, namely a multi-color disk component, a Comptonised component and a power-law at higher energies. This spectral description is favored compared to other normally used spectra like a cut-off power law, hard components with reflection etc. We find that the 0.5 - 10 Hz QPO is predominantly due to variations in the Comptonised component. We use this result to constrain the location of the various spectral components in the source.