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

There was a bright, transient companion spot to SN1987A with a projected distance of about 17 light-days, observed by speckle interferometry in the optical 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 $\sim 45^\circ$ to the observer-to-SN1987A vector, through a circumstellar medium of density profile $\rho (r)\propto r^{-2}$. If it had approached us along the line of sight, a very bright gamma-ray burst would have been seen. The model provides an adequate explanation for the evolution of the spot and is consistent with observations of SN1987A from infrared to ultraviolet. This model implies that at least some GRBs would be seen as going through a medium with density $\rho(r)\propto r^{-2}$.