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High-frequency quasi-periodic oscillations from GRS 1915+105 in its C state

2006; Oxford University Press; Volume: 369; Issue: 1 Linguagem: Inglês

10.1111/j.1365-2966.2006.10286.x

1365-2966

T. Belloni, Paolo Soleri, P. Casella, Mariano Méndez, S. Migliari,

Gamma-ray bursts and supernovae

We report the results of a systematic timing analysis of RXTE observations of GRS 1915+105 when the source was in its variability class theta, characterized by alternating soft and hard states on a time scale of a few hundred seconds. The aim was to examine the high-frequency part of the power spectrum in order to confirm the hecto-Hertz Quasi-Periodic Oscillations (QPO) previously reported from observations from mixed variability behaviours. During the hard intervals (corresponding to state C in the classification of Belloni et al., 2000, A&A, 35, 271), we find a significant QPO at a frequency of ~170 Hz, although much broader (Q~2) than previously reported. No other significant peak is observed at frequencies >30 Hz. A time-resolved spectral analysis of selected observations shows that the hard intervals from class theta show a stronger and steeper (Gamma=2.8-3.0) power-law component than hard intervals from other classes. We discuss these results in the framework of hecto-Hertz QPOs reported from GRS 1915+105 and other black-hole binaries.