The solar X-ray flare of July 7, 1966

By means of a mica window Geiger-Mueller tube on earth satellite Explorer 33, a major solar X-ray flare was observed with 81.8-sec time resolution on July 7, 1966. The flare had its onset at 0023, its maximum intensity at 0042, and a total duration of about 200 minutes. The maximum energy flux was 3 × 10−2 erg/cm² sec, and the time integrated flux was 97 erg/cm² (2 < λ < 12 A). Assuming equal intensity over 2 π steradians at the sun, the total emission in this wavelength band was 1.4 × 1029 ergs, and the maximum surface luminosity of the sun was 2.9 × 106 erg/cm² sec or 4.5 × 10−5 of the whole radiant luminosity of the average solar surface. Charged particles began to arrive at the satellite at 0058, or 35 minutes after the first detection of the X-ray enhancement, and remained in the interplanetary system for at least ten days thereafter. The intensity-time curve of the soft X rays is compared with those of 2700-Mhz solar radio noise flux and of ionospheric absorption at 22 Mhz as observed at Penticton.