A possible lateral gamma-ray burst jet from SN 1987A

There was a bright, transient companion spot to SN 1987A with a projected d istance of about 17 light-days, observed by optical speckle interferometry 1-2 months after explosion. It is shown here that the bright spot may be du e to a receding ultrarelativistic jet traveling at similar to 53 degrees wi th respect to the observer-to-SN 1987A vector, through a circumstellar medi um with a density profile of rho(r) proportional to r(-2). If it had approa ched us along the line of sight, a very bright gamma-ray burst (GRB) would have been seen with an apparent isotropic energy of similar to 10(54) ergs and an opening angle of a few degrees. The model provides an adequate expla nation for the evolution of the spot, although there are still problems in explaining its observed color. This model implies that at least some GRBs w ould be seen as going through a medium with a density of rho(r) proportiona l to r(-2) rather than through a uniform medium, which is frequently adopte d in GRB calculations. Improved analysis of the speckle data has revealed a nother, fainter spot on the opposite side.