Microstructure of Water Masers in W3 IRS 5

We report sub-milliarcsecond structures of water maser features in W3 IRS 5 observed with the Very Long Baseline Array (VLBA) at 22.2 GHz. A cluster of maser spots (emission spots in individual velocity channels) within a maser feature exhibits a simple velocity gradient but a complicated spatial alignment. Two-point spatial correlation functions for the spots can be fitted by power laws with an index of about 2 in both of the two ranges of 0.04-0.4 and 1-300 AU. This fact indicates a similar clustering of spots in the two very different ranges. The Doppler-velocity difference of the spots as a function of spot separation demonstrates a Kolmogorov-type turbulence in the range of 0.04-300 AU. Similar power laws in these functions have been reported for the W49N water masers. A unique difference of the W3 IRS 5 from the W49N masers is that on a scale above 1 AU, the Doppler-velocity difference of the spots in W3 IRS 5 (≤5 km s^-1) is much smaller than that in W49N (≤150 km s^-1). Very likely, this difference between the two sources arises because of different outflow velocities.