A 2.2 second period in the 1984 August 5 gamma-ray burst

A time history and Fourier power spectrum are presented for the August 5, 1984 gamma-ray burst (GRB) observed with the SMM Hard X-ray Burst Spectrometer and the Pioneer Venus Orbiter spacecraft. A significant complex feature of the event is identifiable in both data sets: a gradual ripple with a well-defined 2.2-sec period lasting for seven cycles, with a series of narrow spikes, which appear always on the ascending phase of the sinusoidal ripple. This event is unusual in both its temporal and spectral attributes: it exhibits coexistence of periodic and nonperiodic features, and it was also reported as the most intense GRB event observed with the SMM Gamma-Ray Spectrometer, extending up to 100 MeV.