2010MNRAS.402.1816C

We present RXTE observations covering six normal outbursts of the dwarf nova SU UMa, the prototype of its class. The outbursts showed consistent X-ray behaviour with the X-ray count rate dropping suddenly by a factor of 4, and with evidence for a half-day delay between the optical rise and the X-ray suppression. In contrast to SS Cygni, an X-ray flux increase at the beginning of outburst was not observed, although it is expected from boundary-layer models. The X-ray flux was high and decreasing during quiescence, in conflict with the disc instability model. The X-ray spectrum of SU UMa was softer in outburst than during quiescence, and it was consistent with constant reflection.