Will GRB 990123 Perform an Encore?

The recent gamma ray burst, GRB 990123 has a redshift $z_s=1.61$ and appears to have an energy $E\sim3\times10^{54}$ erg, and a peak luminosity $L_{max} \sim6\times10^{53}$ erg/s \sim 2\times10^{-6}c^5/G$, assuming isotropic emission. This is ten times larger than hitherto reported and in excess of the rest mass of a solar mass object. Optical observations have revealed an intervening galaxy with redshift $z_d=0.286$ displaced from the line of sight by $1.8\pm0.4''$. This raises the possibility that the burst is enhanced by gravitational lensing. We argue that multiple images are not present within the burst profile or within 15 minutes of the burst trigger. Preliminary inspection of the intervening galaxy image allows us to set a limit on the magnification of $\mu<60$; if subsequent analysis of Ulysses data extends this window to $\sim 1$ day, and/or if a fainter burst is not observed within a few weeks, the magnification is at most modest ($\mu<10$), and the burst remains the most intrinsically luminous event yet observed.