Was It a Classic Gamma - Ray Burst ?

The March 5th, 1979 gamma-ray transient has long been thought to be fundamentally di erent from the classic gamma-ray bursts (GRBs). It had recurrences, pulsations, and a soft spectral component unlike classic GRBs. With the exception of the soft component reported from the Konus experiment, the unusual characteristics of March 5th were detectable primarily because it was extremely bright. Computer limitations, satellite transmission e ects or pulse pileup and dead-time e ects have prevented, until now, the analysis of spectra from the International Comet Explorer (ICE) and the Pioneer Venus Orbiter (PVO). The ICE-PVO spectrum of the main peak di ers markedly from the published Konus spectrum. Rather than being dominated by a soft component similar to that observed in the soft gamma repeaters (SGRs), the ICE-PVO spectrum appears to be consistent with a classic GRB spectrum, especially above 100 keV. Above 100 keV, the spectrum is consistent with thermal bremsstrahlung with a temperature of 200 keV, somewhat soft but within the range of classic GRBs. We believe that, given the ICE-PVO spectral observations, the March 5th transient would have been classi ed as a classic GRB when it was discovered. Although an formal analysis has not been done, the pulsations and recurrences might still be unique features that distinguish March 5th from GRBs. The ICE spectrum provides evidence for a low-energy cuto at 100 keV. If high-velocity neutron stars are born as misaligned rotators with their velocities aligned with their spin axes and if their emissions are beamed, then