Detection of HC 3 N Maser Emission in NGC 253

We report the detection of maser emission from the J = 4-3 transition of HC3N at 36.4 GHz toward the nearby starburst galaxy NGC 253. This is the first detection of maser emission from this transition in either a Galactic or extragalactic source. The HC3N maser emission has a brightness temperature in excess of 2500 K and is offset from the center of the galaxy by approximately 18'' (300 pc), but close to a previously reported class I methanol maser. Both the HC3N and methanol masers appear to arise near the interface between the galactic bar and the central molecular zone, where it is thought that molecular gas is being transported inwards, producing a region of extensive low-velocity shocks.