A GAMMA-RAY MONTE-CARLO STUDY OF THE CLUMPY DEBRIS OF SN 1987A

We have performed Monte Carlo calculations of gamma-ray transport in m odels of the clumpy debris cloud of the LMC supernova, SN 1987A, to st udy the influence of composition mixing and heterogeneity on its emerg ent gamma-ray and X-ray fluxes. In particular, we have focused an the problematic Ginga band (16-28 keV) flux at day 600, whose measured val ue was an order of magnitude higher than predicted by previous theory. We find that the hydrogen of the envelope could not have been intimat ely mixed with the heavy elements of the core and that the hydrogen/he lium volume filling factor interior to 4000 km s(-1) must have been la rge (greater than or equal to 40%). Furthermore, we demonstrate that o ne cannot mimic the effects of clumping by artificially decreasing the photoelectric cross sections by some factor. A physical separation of the Compton scattering region and the regions occupied by the high-Z elements is required. The 600 day models that best fit both the line d ata at 847 keV and 1238 keV and the measured Ginga band fluxes suggest that as much as 50% of the explosively produced Ni-56 stayed interior to 1000 km s(-1) and 2 M.. The Ni-56 may have been more centrally con centrated than in the benchmark models. Ni-56 filling factors greater than 60% are not preferred, since such models are too good at absorbin g photons below 100 keV. Furthermore, a total envelope mass between 10 and 15 M. is favored.