A search for evidence of energetic protons immediately prior to the impulsive phase of solar flares

Abstract

Studies of gamma ray flares from the Solar Maximum Mission (SMM) show that energetic protons are present close, if not simultaneous, to the onset of the impulsive phase. It is important to flare models to know if such protons are (a) accelerated rapidly at the impulsive phase; (b) present as a non-thermal seed population and finally accelerated at the impulsive phase or (c) accelerated slowly prior to the flare. We have analysed data from the Gamma Ray Spectrometer on SMM for evidence of nuclear line emission prior to the impulsive phase, which would indicate the presence of protons > 5–10 MeV. The selected flares were accompanied by one or more of the following: extensive pre-cursor activity in soft X-rays; coronal activity; energetic protons in interplanetary space from a preceding flare. No evidence for any statistically-significant line emission prior to the impulsive phase was found, which lends support to (a) above, while putting limits on the spectrum of the seed population in (b). An upper limit of ≃ 10 25 erg −1 is placed on the power in non-thermal protons above 10 MeV in the pre-flare phase.