A model for the Z-track phenomenon, jet formation and the kilohertz QPO based on Rossi-XTE observations of the Z-track sources

We present a new model for the Z-track phenomenon, based on analysis of the spectral evolution around the Z-track in several Z-track sources, in which radi ation pressure plays a major role. Increasing mass accretion rate on the normal branch causes heating of the neutron star with the emissive flux from the surface increasing by an order of magni tude to become super-Eddington at the horizontal branch where radio detection shows the pre sence of jets. We propose that the radiation pressure disrupts the inner disk leading to the la unching of the jets. Secondly, by timing analysis of the same data we find a correlation of the frequenc y of kHz QPO with the emissive flux and propose that the higher frequency QPO is an oscillati on at the inner disk edge which progressively moves to larger radial positions as the disk i s disrupted by radiation pressure.