Belloni, T.Soleri, P.Casella, P.Méndez, M.Migliari, Simone2016-06-132016-06-132006-060035-8711https://hdl.handle.net/2445/99492We report the results of a systematic timing analysis of RXTE observations of GRS 1915+105 when the source was in its variability class θ, 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 hectohertz 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.), 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 θ show a stronger and steeper (Γ = 2.8-3.0) power-law component than hard intervals from other classes. We discuss these results in the framework of hectohertz QPOs reported from GRS 1915+105 and other black hole binaries.6 p.application/pdfeng(c) Belloni, T. et al., 2006Observacions astronòmiquesAstronomia de raigs XOscil·lacionsAstronomical observationsX-ray astronomyOscillationsinfo:eu-repo/semantics/article6340422016-06-13info:eu-repo/semantics/openAccess