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[11.07] X-ray spectra and quasi-periodic oscillations observed in the low hard states of the microquasar GRS 1915+105

R. B. Fiorito (Catholic University of America), C. B. Markwardt (University of Maryland, NASA-GSFC), J. H. Swank (NASA-GSFC)

Low frequency (1 - 10 Hz) quasi-periodic oscillations (QPO's) have been observed from the black hole candidate GRS 1915+105 by the Rossi X-ray Timing Explorer in 1996 and 1997 when this source was in a low luminosity hard state. The frequency of the QPO's is generally observed to increase with the total x-ray intensity but the relationship is not unique. We have performed a spectral and temporal analysis of a representative number of 1996 and 1997 PCA and HEXTE observations. We find that the time averaged x-ray spectral flux for 1997 can be fit with a power law and a small (less than 20 % of the total flux) disk black body component. For 1996 the thermal flux component is weaker, i.e. less than 10 % of the total. A correlation between QPO frequency and power law flux and index is observed for each data set. However, a correlation between thermal flux and the QPO frequency is observed only for the 1997 data. No correlation between disk temperature and frequency is observed for either data set.

Bulletin of the American Astronomical Society, 35#2
© 2003. The American Astronomical Soceity.