X-ray and gamma-ray observations of a white-light flare

Hard radiations (X-ray and gamma-ray) from a major solar flare observed by HEAO-1 on July 11, 1978, are discussed. It is noted that the observations showed gamma-ray line and continuum emission extending to the highest energy observed. The lines are identified with the 2.2 MeV line of deuterium formation and the 4.4 MeV line of inelastic scattering on C-12, both of which were previously observed in the flares of August 1972. The flare of July 11 is identified as a white-light flare. It therefore provides the first opportunity for a detailed examination of white-light flare theories that depend on proton heating of the photosphere. The line strength over a four-minute integration at 2.2 MeV is found to be 1.00 + or - 0.29 ph/sq cm-sec; the gamma-ray emission (excluding the 2.2 MeV line which was appreciably delayed) lagged by less than 20 sec approximately after the hard X-ray and microwave fluxes. It is concluded that the 'second-stage' acceleration of high-energy solar particles must commence promptly after the impulsive phase.