A LIMIT ON THE CO-57 GAMMA-RAY FLUX FROM SN-1987A

We studied the gamma-ray flux from SN 1987A with a balloon-borne detector in Brazil on 1990 November 29. By comparing on- and off-source data, we obtained limits to the total gamma-ray flux due to Co-57 decays and presumed pulsar activity. If the pulsar contribution is neglected, an upper limit (90% confidence limit) is set to the total Co-57 contribution above 60 keV at 2.7 x 10(-4) cm-2 s-1 where the 122 keV line contribution is 1.0 x 10(-4) cm-2 s-1. The corresponding limit on the abundance ratio of Co-57 and Co-56 is 3.4 times that of the Sun. The present upper limit implies that the reported leveling off in the light curve of SN 1987A is primarily due to the pulsar activity. If the pulsar is Crab-like (photon index -2.2), the light curve requires an energy outflow greater than 0.95 x 10(37) ergs s-1 (above 1 keV) now being supplied to SN 1987A by its presumed pulsar.