Spectral Characteristics of Impulsive Solar-Flare X-Rays ???? 10 KeV

Abstract

Characteristics of the impulsive X-ray component are deduced from thirteen bursts of hard (> 10 keV) X-rays observed with the OGO-5 satellite during the period 1968 March 21-June 30. Most of These impulsive X-ray bursts were associated with impulsive microwave bursts and optical flares of importance <1. For ~40 keV X-rays the 6-folding rise time and decay time are found to be 2-5 and 3-10 sec, respectively. At maximum intensity the X-ray spectrum is consistent with the form ~Er y photons cm-2 sec-1 keV-1 , where 2.7 < 7 < 4.5 and 10 < ¿£ < 70 keV. The peak X-ray flux above 10 keV observed at the Earth was 10~ 6-10-5 ergs cm" 2 sec-1. Under the assumption that electron-proton bremsstrahlung is the mechanism for X-ray production, the spectrum of the energetic electrons in the X-ray source region has been deduced and is found to be consistent with the form electrons cm-2 sec" 1 keV" 1 , where 1.5 < delta <3.3 and 10 < E < 100 keV. The short rise time, the power-law energy spectrum, and the time of occurrence relative to the"optical flare indicate that the impulsive X-rays > 10 keV are a non thermal flash-phase phenomenon. There is evidence that the injection of energetic electrons into the X-ray source region occurs more or less continuously throughout the implusive X-ray burst. This injection, combined with the loss of energetic electrons through escape and collisions, probably determines the time-intensity profile of an impulsive X-ray burst.