A Possible Lateral Gamma-Ray Burst Jet from Supernova 1987A

Abstract

There was a bright, transient companion spot to SN1987A with a projected distance of about 17 light-days, observed by optical speckle interferometry one to two months after explosion. It is shown here that the bright spot may be due to a receding ultra-relativistic jet traveling at 53 degress to the observer-to-SN1987A vector, through a circumstellar medium of density profile rho(r) ~ r^-2. If it had approached us along the line of sight, a very bright gamma-ray burst would have been seen with an apparent isotropic energy of about 10^54 erg and an openning angle of a few degrees. The model provides an adequate explanation for the evolution of the spot, although there are still problems in explaining its observed color. This model implies that at least some GRBs would be seen as going through a medium with density rho(r) ~ r^-2 rather than a uniform medium, which is frequently adopted in GRB calculations. Improved analysis of the speckle data has revealed another and fainter spot on the opposite side.