Evolution of the H2O maser emission in IRAS 20126+4104

We present the results of our investigation of the H2O maser emission from individual features in IRAS 20126+4104, which is a cold infrared source. The observations were performed at the 22-m radio telescope of the Pushchino Radio Astronomy Observatory. A radial-velocity drift of the features caused by their deceleration at the interface between between an accelerated jet and the surrounding molecular environment has been detected. The observed tendency for the H2O emission as a whole to drift is associated with the successive excitation of maser features or their clusters by the front of a shock (or magnetohydrodynamic) wave. An estimate of the jet rotation period is provided (similar to 150 years).