Observation of a cosmic gamma-ray burst on Apollo 16. I - Temporal variability and energy spectrum

Abstract

A cosmic gamma-ray event occurring April 27, 1972 at 10.68 UT was observed by gamma-ray and X-ray spectrometers on Apollo 16 as well as by Vela 6A. Analysis has yielded a detailed time profile of the entire event, an energy spectrum covering three order of magnitude (2.0 to 7.9 KeV and 0.067 to 5.1 MeV) and a source location. A well-defined onset prior to the main impulse period and a probable precursor are reported. The total energy of the event over the observed range was 2 x 10 to the minus 4th power ergs/sq cm. The data indicate the presence of a hard component which persists during the entire event, with a softer variable component becoming dominant during the most explosive burst portion.