SN 1991T: Gamma-Ray Observatory's first supernova?

The explosion of the Type la supernova SN 1991T in the nearby galaxy NGC 4527 may be detected in gamma-ray lines by the recently launched Gamma-Ray Observatory (GRO). We calculate the dominant gamma-line and continuum features of the new "delayed detonation" model FDEFA1 and compare them to those for standard deflagration models W7 and cdtg7. We show that there are many useful hard photon discriminants of the Type la explosion mechanism that can, in principle, be detected by the OSSE and COMPTEL instruments on the GRO. Either SN 1991T, if bright enough, or one of the several Type la supernovae expected to be within the GRO's range during its active life, may allow us to settle the detonation/ deflagration debate, verify the generic thermonuclear white dwarf model of Type la explosions, and calibrate the Type la B(max)/847 keV line flux ratio.