5 Conclusions

1.

We argue that X-ray data are broadly consistent with the assumption that 1999 September outburst of V4641 was caused by the episode of super-Eddington accretion onto a black hole accompanied by a formation of an extended envelope. The properties of the source during this outburst are similar to those of SS433 suggesting that formation of the envelope/outflow is a generic characteristic of the supercritical accretion as predicted by many theoretical models.

2.

It is interesting however that hard spectrum, resembling the spectrum of Cygnus X-1 during low state, was observed from V4641 at the luminosity level more than order of magnitude larger than in Cygnus X-1.

3.

Using ASM data during the extended period of relatively quiescent state of the source prior to the giant outburst we marginally detected periodicity in the 1.5-12 keV energy band, consistent with the optically determined orbital period.

4.

Almost two weeks prior to outburst dramatic evolution of spectrum is observed, associated with the significant decrease of the source X-ray flux. If the subsequently observed extended radio source is due to ejection happened at this time (and not during the major outburst), then expansion velocity would be at the level of 0.7-0.8 c - similar to the velocity observed in several galactic jet sources.

Acknowledgements

This research has made use of data obtained through the High Energy Astrophysics Science Archive Research Center Online Service, provided by the NASA/Goddard Space Flight Center.