A dark cloud associated with an unidentified EGRET source

CO J = 1-0 mapping observations of the dark nebula Lynds 227, which is poss ibly associated with the unidentified EGRET source 2EG J1811-2339, are pres ented. We detected a large amount of molecular gas along Lynds 227 with a t otal mass of (1-2) x 10(4) M-circle dot surrounding an X-ray synchrotron ne bula, which was detected by the ASCA within the error circle of 2EG J1811-2 339. Molecular gas along Lynds 227 shows spatial anticorrelation with the X -ray synchrotron nebula, suggesting that the synchrotron nebula is interact ing with the Lynds 227 cloud. We propose a gamma-ray emission mechanism for 2EG J1811-2339: high-energy electrons are injected from a rotation-powered pulsar and further accelerated in shock waves generated by the interaction with ambient matter. The high-energy electrons move into the molecular clo ud at the Lynds 227 and collide with dense interstellar matter to yield hig h-energy gamma-ray photons, mainly through relativistic bremsstrahlung.