Solai X-rays, observed by an experiment on Explorer 34, have been compared with He flares and microwave bursts. The X-rays were detected by a xenon-methane filled proportional counter with 9.4 mg/cm 2 beryllium window of area 2.2 cm 2. The proportional counter was part of the Cosmic Ray Anisotropy experiment of the Southwest Center for Advanced Studies (now University of Texas at Dallas), Dallas, Texas.
The spin of the spacecraft caused the proportional counter to scan across the Sun and around the ecliptic plane. The azimuth of the proportional counter was divided into eight sectors and the counts received from each sector were recorded separately. Solar X-rays were observed as an enhanced count rate in the octant centred on the Sun while the adjacent octants gave the background count rate. The integrated solar X-ray flux above 2.7 keV was measured every 81.96 sec.
The X-ray bursts for 52 days in June and July 1967 were compared with the reported He flares in the revised listing of the ESSA Solar Geophysical Data Bulletins 1967. Data were used at all times for which the following conditions held, (1) the satellite was beyond the radiation belts, (2) the received data was of good quality as determined by the tracking station, (3) no charged particle flare effects were present, (4) the solar activity was not too high, so that it was possible to associate a particular X-ray burst with a unique listed He flare, and (5) there was both visual and cinematographic He flare patrol coverage. For 80}/0 of the time all of these conditions were satisfied, and yielded 472 X-ray bursts to be compared with 687 He flares.
This comparison showed that He flares of larger areas and greater brightness tended to occur with the more intense X-ray bursts but there was no one-to-one correspondence between the two phenomena. Only 29% of the -f He flares were associated with X-ray bursts intense enough to be observed by this experiment, but the association improved to 100% for lb flares.
The number of X-ray bursts not accompanied by reported He flares varied from (29__+4) % of low intensity X-ray bursts to (18_ 5) % of intense bursts. Either these X-ray bursts occurred without any significant associated He emission or the flare occurred close to or around the solar limb where the He emission would be obscured. The probability of a flare occurring within + 20 ~ longitude of either limb on a given day was assumed to be proportional to the total sum of the number of normal and bright flares that occurred on the east limb (radial distances greater than 0.95) on the Solar Physics 13 (1970) 467-470.