A Kinship between the EGRET SNR's and Sgr A East

Abstract

Sgr A East appears to be a single, mixed morphology 10,000 year-old supernova remnant (SNR) at the Galactic Center. It also appears to belong to a class of remnants that have been observed and detected at 1720 MHz, the transition frequency of OH maser emission. However, if the EGRET source 3EG J1746-2852 conincident with the Galactic center is itself associated with this object, it would endow it with a gamma-ray luminosity almost two orders of magnitude greater than that of the other EGRET-detected SNR's. We here reconsider the viability of a pion-production mechanism as the source of the broadband emission observed from Sgr A East, and show that what connects these objects -- and ultimately also accounts for their different gamma-ray emissivity -- is the very important interaction between the expanding SNR shell and the surrounding molecular cloud environment. The singularly high gamma-ray luminosity of Sgr A East, as well as its unusually steep radio spectral index, can thereby be attributed to the high-density, strong magnetized environment in which it is located.