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Astron. Astrophys. 360, L25-L29 (2000)

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Letter to the Editor

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

A.R. Rao 1, S. Naik 1, S.V. Vadawale 1 and S.K. Chakrabarti 2

1 Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai (Bombay) 400 005, India
2 S.N. Bose National Centre for Basic Sciences, Salt Lake, Calcutta 7000091, India

Received 26 June 2000 / Accepted 26 July 2000


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.

Key words: X-rays: stars – accretion, accretion disks – black hole physics – stars: winds, outflows – stars: individual (GRS 1915+105)

Send offprint requests to: A.R. Rao arrao@tifr.res.in

© European Southern Observatory (ESO) 2000

Online publication: August 17, 2000