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 coincident 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 ( n _ { H } = 10 ^ { 3 } cm ^ { -3 } ) , strong magnetized ( B \sim 0.18 mG ) environment in which it is located .