Evidence for e−/e+ annihilation mechanism as an initial radiation process in gamma-ray bursts

An unusual spectrum has been obtained over 126 ms at the onset of the intense 1978 November 19 gamma-ray burst recorded by the Franco-Soviet Signe experiments. Evidence is presented for two distinct components above and below 200 keV : a soft emission with a possible low-energy cutoff and a peak around 400 keV with an accompanying high-energy tail. As this peak contains > 95 percent of the total fluence at this time, we suggest the role of the e⁻/e⁺ annihilation as an initial radiation process in gamma-ray bursts and we propose a possible interpretation of the high-energy tail.