183 GHz H2O MASER EMISSION AROUND THE LOW-MASS PROTOSTAR SERPENS SMM1

We report the first interferometric detection of 183 GHz water emission in the low-mass protostar Serpens SMM1 using the Submillimeter Array with a resolution of 3 '' and rms of similar to 7 Jy in a 3 km s(-1) bin. Due to the small size and high brightness of more than 240 Jy beam(-1), it appears to be maser emission. In total, three maser spots were detected out to similar to 700 AU from the central protostar, lying along the redshifted outflow axis, outside the circumstellar disk but within the envelope region as evidenced by the continuum measurements. Two of the maser spots appear to be blueshifted by about 1-2 km s(-1). No extended or compact thermal emission from a passively heated protostellar envelope was detected with a limit of 7 Jy ( 16 K), in agreement with recent modeling efforts. We propose that the maser spots originate within the cavity walls due to the interaction of the outflow jet with the surrounding protostellar envelope. Hydrodynamical models predict that such regions can be dense and warm enough to invert the 183 GHz water transition.