Observations of solar gamma ray continuum between 360 keV and 7 MeV on August 4, 1972

Measurements were made of the time-averaged gamma ray energy loss spectrum in the energy range 360 keV to 7 MeV by the gamma ray detector on the OSO-7 satellite during the 3B flare on August 4, 1972. The differential photon spectrum unfolded from this spectrum after subtracting the background spectrum and contributions from gamma ray lines is best described by a power law with spectral index of 3.4±0.3 between 360–700 keV and by an exponential law of the form exp (-E/E ₀) with E ₀ = 1.0±0.1 MeV above 700 keV. It is suggested that this spectrum is due to nonthermal electron bremsstrahlung from a population of electrons, with a strong break in the spectrum at 2 MeV. Since the observational data indicates that the matter number density must be n _H ? 5 × 10¹⁰ cm^-3 in the production region, the number of electrons above 100 keV required to explain the results is ?2 × 10³⁴.