Search for millisecond periodicities in type I X-ray bursts of the Rapid Burster

We have searched the rising portion of type I X-ray bursts observed from the Rapid Burster with the Rossi X-ray Timing Explorer for the presence of periodicities. The 95per cent confidence upper limit on the average rms variation of near coherent pulsations with a width of &1Hz (in 60±2048Hz) during the first second of the bursts is ,8.8per cent. We find a possible detection (.98per cent significance) at 306.5Hz.