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. 
A. R. Rao (1), S. Naik (1), S. V. Vadawale (1) and S. K. Chakrabarti   (2) ((1)TIFR, Mumbai, India. (2)SNBNCBS, Calcutta, In...