Limit on X-ray emission from a supernova during maximum light

The MIT 1-60 keV X-ray detector on the OSO-7 satellite observed the supernova SN 1971s in NGC 493 during the period of its optical rise and maximum. The data were examined for steady and pulsed X-ray emission. Analysis of the light curve shows that the supernova was most likely of Type II. The upper limit (3 a) to the continuous X-ray luminosity during the week of the optical rise and maximum is 5 >c 10 ergs s ' (1-5 keY), a factor of 40 less than previous upper limits for this portion of the light curve. The upper limit to the energy of an X-ray pulse of duration between 2 seconds and 3 minutes is 5 x 1048 ergs (1-9 keV). The data examined for such a pulse covered 31 percent of the total observation time. Subject headings: supernova - X-ray sources