Résumé du preprint Irfu-10-26

Suzaku Observation of GRS1915+105 : Evolution of Accretion Disc Structure during Limit-Cycle Oscillation
Y. Ueda, K. Honda, H. Takahashi, C. Done, H. Shirai, Y. Fukazawa, K. Yamaoka, S. Naik, H. Awaki, K. Ebisawa, J. Rodriguez, S. Chaty
We present results from the Suzaku observation of the microquasar GRS 1915+105 performed during the 2005Octobermultiwavelength campaign. The data include both stable state (class ) and limit-cycle oscillation (class ). Correct interstellar absorption as well as effects of dust scattering are fully taken into account in the spectral analysis. The energy spectra in the 2120 keV band in both states are all dominated by strong Comptonization of disk photons by an optically thick ( 710) and low temperature (Te 23 keV) hybrid plasmas containing non-thermal electrons produced with 1060% of the total power input. Absorption lines of highly ionized Fe ions detected during the oscillation indicate that a strong disk wind is developed. The ionization stage of the wind correlates with the X-ray flux, supporting the photoionization origin. The iron-K emission line shows a strong variability during the oscillation; the reflection is strongest during the dip but disappears during the flare. We interpret this as evidence for self-shielding that the Comptonizing corona becomes geometrically thick in the flare phase, preventing photons from irradiating the outer disk. The lowtemperature and high luminosity disk emission suggests that the disk structure is similar to that in the very high state of canonical black hole binaries. The spectral variability during the oscillation is explained by the change of the disk geometry and of the physical parameters of Comptonizing corona, particularly the fractional power supplied to the acceleration of non-thermal particles.