5 Conclusion

The analysis of 139 RXTE observations of GRS 1915+105 in the $\chi$-state revealed variable components and parameters of the X-ray spectra. The structure of the hard X-ray power law depends e.g. on the radio flux. Further, a two-branch correlation of the power law slope and the power law normalization was found. Theses branches show different pivoting behavior.

The most probable geometry is that of a hot corona above the accretion disk. A bulk motion comptonization seems to be ruled out for the $\chi$-states because of the time lags of hard and soft X-ray photons.

The continuous outflow of matter is not correlated with the accretion disk parameters as measured at X-rays. Neither the disk temperature nor the inner disk radius are connected with the radio flux. Therefore, the outflowing matter should not be provided by a disruption of the inner part of the accretion disk, as thought to be the case for the sporadic jets in GRS 1915+105, and a positive correlation between radio emission and power law slope is found. Because both the base of the jet and the corona are probably located near the black hole the correlation indicates an interaction of both structures. Whereas during low radio emission the hard X-ray component originates due to comptonization on a thermally-dominated corona, in radio loud states the comptonization should appear in the outflowing matter.

GRS 1915+105 shows a positive R($\Gamma$)-correlation as seen in other X-ray binaries and AGN. The large reflection amplitude suggests a highly anisotrophic inverse Compton scattering with the dominant part of the soft photons being scattered back into the disk plane.

Acknowledgements

The authors thank E. H. Morgan (MIT) and G. G. Pooley (MRAO) for providing the ASM and RT data and W. A. Heindl (RXTE) and K. A. Arnaud (XSPEC) for their comments. We thank the referee, A. Zdziarski, for the thorough reading and several suggestions which improved the presentation and T. Belloni for the constructive criticism. The Ryle Telescope is supported by PPARC. The Green Bank Interferometer is a facility of the National Science Foundation operated by the NRAO in support of NASA High Energy Astrophysics programs.