Maser Emission toward the Infrared Dark Cloud G359.94+0.17 Seen in Silhouette against the Galactic Center

The infrared dark cloud G359.94$+$0.17 is a conspicuous, opaque cloud, which is seen in silhouette against the Galactic center. We found unexpectedly strong ($\sim\ $50 Jy) maser emission of CH$_3$OH at 44 GHz with additional weak 22 GHz H$_2$O maser and 43 GHz SiO thermal emissions toward this cloud. Detections of these molecular lines indicate that strong star-forming activities are proceeding in this cloud, which was not reported previously despite of numerous studies toward the Galactic center. The line profiles of the NH$_3$inversion lines at 23 GHz indicate that G359.94$+$0.17 is composed of mainly two clouds with $V_{\rm lsr}$$=$0, and 15 km s$^{-1}$overlapped on the line of sight. The maser emission is associated with the 15 km s$^{-1}$cloud, suggesting that it is located at the Norma spiral arm.