A ten-day observation of Hercules X-1 from the OSO-7 satellite.

The MIT X-ray detectors aboard the 0S0-7 spacecraft viewed Hercules X-1 from 1972 November 14 to November 24. X-ray turn-on in the 35-day cycle was observed to occur between phases 0.67 and 0.70 (November 18.64-18.70). A significant decrease in the X-ray intensity occurred near mid-orbital phase, approximately 1.5 days after X-ray turn-on. Using the 1-6 keV data obtained during the 35-day OFF state, we conclude that if the optical light curve is due to heating of the large star by a blackbody source of soft X-rays, then the source must be large, radius > 5 x 108 cm, and cool, temperature (kT) < 90 eV. During one eclipse period (November 20.8-21.0), we find evidence for 1-6 keV X-ray emission. Subject headings: binaries - stars, individual - X-ray sources