Imaging observations of SN1987A at gamma‐ray energies

Abstract

The Caltech imaging γ‐ray telescope was launched by balloon from Alice Springs, NT, Australia for observations of SN1987A during the period 18.60–18.87 November 1987 UT. The preliminary results presented here are derived from 8200 seconds of instrument livetime on the supernova and 2500 seconds on the Crab Nebula and pulsar at a float altitude of 37 km. We have obtained the first images of the SN1987A region at γ‐ray energies confirming that the bulk of the γ‐ray emission comes from the supernova and not from LMC X‐1. A count excess is detected between 300 and 1300 keV from the direction of the supernova, one third of which comes from energy bands of width 80 and 92 keV centered on 847 and 1238 keV, respectively. The excess can be interpreted as a line photon flux plus scattered photon continuum from the radioactive decay of ^(56)Co synthesized in the supernova explosion. We compare our data to recent predictions and find it to be consistent with models invoking moderate mixing of core material into the envelope.