Rapid time variations of water maser emission in W3(OH) and NGC 6334C

We report the observed results of a short time scale monitoring of the 22 GHz water maser emission in W3(OH) and NGC 6334C. Both sources were monitored daily for about a month. The aim of the observations is to investigate the possible presence of very short interval variations on time scales of hours or days. Our observations showed that the flux density of the component at -52.8 km s(-1) in W3(OH) decayed linearly with a timescale of about 19 days, and a maser in NGC 6334C flared rapidly, doubling the flux with a timescale of about 4 days. The rapid time variability of the observed water maser features may be caused by an external pumping event. The collision among dense clumps at sufficient relative velocities supplies the powerful energy required to excite H2O maser emission and then quenches the pump in the following days or longer period.