0120236

A hard X-ray component extending up to several hundred keV has been recently discovered in Sco X-1 and a few others Z-sources i.e. low mass X-ray binaries LMXRBs which host an old weakly magnetized and fastly spinning neutron star accreting at rates close to the Eddington limit. Among sources accreting at near-Eddington rates only black hole candidates (BHC) were known to possess similar high energy tails. A variety of models for the hard X-ray components of BHCs has been proposed including thermal non thermal and bulk motion COmptonisation shock emission or annihilation in a pair dominated plasma cloud. The presence of a similar hard component in Z-sources opens up a new area of investigation for neutron stars accreting at high rates. Z-sources are known to have highly variable radio counterparts indicating episodic ejection of matter at relativistic energies. Recent observations of the radio source associated with Sco X-1 revealed variable lobes on opposite sidesof the central source propagating outwards at about 0.4-0.5 c. A detailed investigation of these phenomena in Sco X-1 and the extent to which they parallel those observed in stellar mass BHCs is the main aim of our program. This is based on coordinated observations to be carried out simultaneously from soft gamma ray to X-ray energies and in the V-band near-IR and radio. We request a sigle 300 ksec INTEGRAL observation. In particular we will:(a) study the correlated variability from the soft gamma rays to the radio (b) investigate the hard X-ray continuum of the source up to energies of ~ 700-800 keV and its relation to the source state as determined through multiwavelength observations (c) search for high energy emission lines similar to those observed in Nova Muscae 1991. [truncated! Please see actual data for full text]