The 1979 March 5 gamma-ray transient: Was it a classic gamma-ray burst?

The 1979 March 5 gamma-ray transient has long been thought to be fundamentally different 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 the March 5 transient were detectable primarily because it was extremely bright. Computer limitations, satellite transmission effects or pulse pileup, and dead-time effects have prevented, until now, the analysis of spectra from the {ital International} {ital Cometary} {ital Explorer} ({ital ICE}) and the {ital Pioneer} {ital Venus} {ital Orbiter} ({ital PVO}). The {ital ICE}-{ital PVO} spectrum of the main peak differs 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 {ital ICE}-{ital 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 {approximately}200 keV, somewhat soft but within the range of classic GRBs. We believe that, given the {ital ICE}-{ital PVO} spectral observations, the March 5 transient would have been classified as a classic GRB when itmore » was discovered. Although a formal analysis has not been done, the pulsations and recurrences might still be unique features that distinguish the March 5 transient from GRBs. The {ital ICE} spectrum provides evidence for a low-energy cutoff 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 when they are young their spatial distribution will be similar to the SGRs. If torques can align the field with the spin axis, then when they are old their spatial distribution will be isotropic like classic GRBs. (Abstract Truncated)« less