Gamma-ray burst observations from Helios-2

Observations of five ..gamma..-ray bursts made with the solar orbiter Helios 2 are reported. Wave front timing from Helios 2, at distances of up to 1.98 AU, to Vela 5 A and 6A, in Earth orbit, provides source location bands as narrow as 2', although several degrees in length. The burst intensities and time profiles measured in interplanetary space by Helios 2 are the same as those observed near the Earth, ruling out a narrow-beam interplanetary origin model. Also, the source direction bands for these events are inconsistent with the directions of all known celestial X-ray objects, X-ray bursters, and high-energy ..gamma..-ray source regions. The ..gamma..-ray burst source objects therefore appear to form a distinct class from all lower-energy X-ray or higher-energy ..gamma..-ray emitters.