THE VIABILITY OF ENERGETIC PROTONS AS AN AGENT FOR ATMOSPHERIC HEATING DURING THE IMPULSIVE PHASE OF SOLAR-FLARES

Recent observations of gamma-ray line intensities in solar flares resu lts have led to the suggestion that the energy content in accelerated protons may rival that of accelerated electrons. However, simply havin g a large energy content in accelerated protons is not sufficient to e nsure an important role for protons in driving the response of the atm osphere to flare energy input: a viable model must also deposit a larg e fraction of the particle energy at the top of the chromosphere to ac count for the large increase in soft X-ray emission measure that chara cterizes the main phase of a flare. While hard X-ray producing electro ns indeed deposit a sufficient amount of energy at the appropriate dep ths in the atmosphere, only protons with a characteristic energy of or der 1 MeV do likewise. It is intriguing that a characteristic energy o f just this value has been obtained through independent analysis of ga mma-ray line intensities. However, it must be noted that protons of th is energy do not have a signature in hard X-rays, leading us to conclu de that a substantial fraction of the flare energy budget must still r eside in deka-keV electrons. In order to complete the global energetic picture, further corroborating observational diagnostics for MeV prot ons are desirable. In this Letter, we discuss such suitable observatio ns.