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Astron. Astrophys. 351, L15-L18 (1999)

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Letter to the Editor

The 1-12 Hz QPOs and dips in GRS 1915+105: tracers of Keplerian and viscous time scales?

S. Trudolyubov 1, E. Churazov 2,1 and M. Gilfanov 2,1

1 Space Research Institute, Russian Academy of Sciences Profsoyuznaya 84/32, 117810 Moscow, Russia
2 Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Strasse 1, 85740 Garching bei München, Germany

Received 3 August 1999 / Accepted 13 October 1999

Abstract

We analyzed 9 RXTE /PCA observations of GRS 1915+105 in the flaring state, when the hardness of the source spectrum was changing on the time scales from few seconds up to 1000 seconds. The quasi periodic oscillations (QPOs) with the frequency varying between [FORMULA] 1 and 12 Hz are associated with the episodes of harder source spectrum. In each observation we found tight correlation between the duration of the hard episode and the characteristic QPO frequency. For a half of the observations this correlation matches the relation between the viscous time scale and the Keplerian frequency, when both quantities are evaluated for various radii in the radiation pressure dominated accretion disk. Assuming that the QPO frequency is proportional to the Keplerian frequency at the boundary between an optically thick accretion disk and a hot comptonization region, the changes of the QPO frequency can then be understood as due to variations of this boundary position on the viscous time scales.

Key words: black hole physics – stars: binaries: general – X-rays: stars – stars: individual: GRS 1915+105

Send offprint requests to: trudolyubov@hea.iki.rssi.ru

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© European Southern Observatory (ESO) 1999

Online publication: November 3, 1999
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