Relativistic Precessing Jets and Cosmological Gamma-Ray Bursts

We discuss the possibility that gamma-ray bursts may result from cosmological relativistic blob-emitting neutron star jets that precess past the line of sight. Beaming reduces the energy requirements, so that the jet emission can last longer than the observed burst duration. One precession mode maintains a short-duration timescale while a second keeps the beam from returning to the line of sight, consistent with the paucity of repeaters. The long life of these objects reduces the number required for production as compared to short-lived jets. Blobs can account for the time structure of the bursts. Here we focus largely on kinematic and timescale considerations of beaming, precession, and blobs—issues that are reasonably independent of the acceleration and jet collimation mechanisms. We do suggest that large-amplitude electromagnetic waves could be a source of blob acceleration.