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M. Feroci, P. Casella, E. Costa (IAS/CNR Rome, Italy), G. Matt (Univ. Roma 3, Italy), E. Massaro (Univ. Roma "La Sapienza", Italy), T. Belloni (Oss. Astr. Brera, Milan, Italy), M. Tavani (IFC/CNR, Milan, Italy)
The Galactic Microquasar GRS 1915+105 was observed by the Narrow Field Instruments onboard BeppoSAX in a series of short (~12 hours) and long (~2 days) pointings, during years 1996 to 2000. On April 1999 the source was detected in a relatively stable, oscillating state with timescale of about 50s, lasting more than one day. The temporal properties of the oscillation show smooth variations during the observation and appear to be correlated to the variations in intensity in the 2-10 keV energy range.
We have carried a phase-resolved, wide-band (1-200 keV) spectral analysis of this state describing the spectrum of the emitted radiation as due to an absorbed multi-temperature disk and a non-thermal component. We have found a characteristic phase-dependent behaviour of the parameters of the individual spectral components suggesting a complex phenomenology in the close environment of the source during this state.