Z-CAM IN OUTBURST DURING THE ROSAT ALL-SKY SURVEY

We present the first X-ray observations of the dwarf nova Z Cam taken during outburst. ROSAT Survey observations show that Z Cam conforms to the pattern of X-ray behaviour seen in other dwarf novae, i.e., the q uiescent hard X-ray emission is suppressed during outburst and replace d by extreme-ultraviolet emission which declines more rapidly than the optical flux. The timing of the hard X-ray suppression is measured wi th precision for the first time in any system.