Gamma-ray burst observations by the HEAO-3 high-resolution gamma-ray spectrometer

Observations of cosmic gamma-ray bursts with the JPL High-Resolution Gamma-Ray Spectrometer on HEAO-3 are discussed. Two bursts seen on 1979 November 16 are of particular interest. The first event occurred at 14:16:41 UT and lasted for eight seconds. This event was detected only by the instrument's five CsI shield segments. The second event occurred 61 sec later, at 14:17:42 UT, and lasted 18 sec. This event was clearly detected by the high-resolution germanium detectors. Because of the close temporal coincidence of the two events, we consider the possibility that both originated from one celestial source, and that the scanning motion of HEAO, 3 (nominal spin period 20 min) was such as to exclude the first from the (approximately 30° FWHM) field of view of the germanium detectors and include the second. Directional information from the relative response of the shield pieces and Earth occulation constraint are all consistent with this interpretation and high-resolution spectral data from the second burst are discussed in this light.

Recent unpublished analyses of long-baseline timing data from interplanetary spacecraft show that the response in the HEAO high-resolution detectors was probably Earth albedo scattering, which can be an important systematic effect in low-Earth orbit.