A Probable Precursor to the X-Ray Nova Centaurus XR-4

A short-lived burst of X-rays from a region of the sky containing Cen XR4 occurred on 1969 July 7 at 0152 UT, about 50 hours before the first reported observation of the X-ray nova outburst of Cen XR-4. The event was observable above background for a period of about 10 minutes. If the event was due to Cen XR-4, its maximum intensity was more than twice the maximum reported for the subsequent X-ray nova and more than 4 times that of Sco X-1 in a nonflaring state.