The energy spectra of solar flare electrons

ABSTRACT. A surveyof 50 electronenergy spectrafrom.itoI00MeVoriginatingfromsolarflareshasbeenmade by the combinationof datafromtwospectrometersonboardtheISEE-3(ICE)spacecraft.Theobservedspectralshapesofflareeventscanbedividedintotwo classesthroughthe criteriaof fit toanaccelerationmodel. This"standard"twostepaccelerationmodel,whichfitsthespectralshapeof thefirst classofflares,involvesan impulsivestepthatacceleratesparticlesuptoI00keVanda secondstepthatfurtheracceleratestheseparticlesup to 100MeV by a singleshock. This fit failsfor thesecondclassofflaresthatcanbecharacterizedashavin gexcessivelyhardspectraabove 1MeVrelativeto the predictionsofthemodel. Correlationswithsoftx-rayandmeterradioobservationsimply that theaccelerationof the highenergy particlesinthe secondclassof flaresis dominatedby theimpulsivephaseoftheflares.I. INTRODUCTION. Previoussurveysof electronflare spectrawithenergiesextendlnguptoI0MeVhavebeenconductedby Datlowe(1971),Simnett(1974),Line__tal.(1982),andEvensone__al.(tt 1984)."Thestudypresentedinthispaperhastheadvantageofnearlycontinuouscoverageover a four year period of high solaractivityinthe absenceofmagnetosphericeffectsdue to the orbit of the spacecraft. Twoindependentlywellcalibratedinstrumentsonthesamespacecraftareused