2002A&A...394..517G

Supernova 1998bu in the galaxy M 96 was observed by COMPTEL for a total of 88 days starting 17 days after the explosion. We searched for a signal in the 847keV and 1238keV lines of radioactive ⁵⁶Co from this type Ia supernova. Using several different analysis methods, we did not detect SN 1998bu. Our measurements should have been sensitive enough to detect ⁶⁰Co gamma-rays as predicted from supernova models. Our 2σ flux limit is 2.3x10^–5photons/cm²/s; this would correspond to 0.35M_☉ of ejected ⁵⁶Ni, if SN 1998bu were at a distance of 11.3Mpc and transparent to MeV gamma rays for the period of our measurements. We discuss our measurements in the context of common supernova models, and conclude disfavoring a supernova event with large mixing and major parts of the freshly-generated radioactivity in outer layers.