CORRELATIONS BETWEEN X-RAY OUTBURSTS AND RELATIVISTIC EJECTIONS IN THE X-RAY TRANSIENT GRO J1655-40

ALTHOUGH objects that emit radio jets have been known for many years, the physical mechanism responsible for the jets has been unclear. Accr etion of mass onto a compact object (such as a black hole) has often b een invoked in models of their formation(1). X-ray emission from such sources is a potentially powerful probe of the processes taking place, because it seems to arise much closer to the central object. Here se report the detection of X-ray and radio emission from the recently dis covered(2,3) transient source X-ray Nova Scorpii 1994 (GRO J1655-40). The radio outbursts, presumably reflecting the feeding of material int o relativistic jets, generally follow bursts of hard X-ray emission (2 0-400 keV) with a delay that varies from a few days to about two weeks . This suggests that the mechanism behind the X-ray emission is not re lated to the ejection process in a simple way. Nevertheless, GRO J1655 -40 may be the best example of a compact object/accretion-disk system in which models of jet formation and X-ray production can be tested di rectly.