Long-term observations of outbursts and variability of the W49N water masers

Abstract

A long-term monitoring of the 22 GHz water masers in W49N has been carried out with the 14-m Metsahovi radio telescope during November 1980-June 1983 and February-April 1985. Here some new results are presented: (1) some basic statistics of the H2O outbursts, (2) the locations of the correlated outbursts on the VLBI maps obtained from the same time period as our observations, (3) the long-term total flux variability, and (4) the observed line narrowing relation Delta V(maser) proportional to F(0) exp -0.5 of saturated masers has been interpreted according to the suggestion of Strelnitskij (1986) that it may result from changes in the kinetic temperature Tk. Using this approach upper limits to Tk can be derived from three outbursts of the flare feature and are some 940 K at F(0)(max) and 1160 K at Delta F(outburst)/2. If a 75 percent turbulence is assumed in Delta V(D) the above temperatures are 408 K and 509 K, respectively, yielding a cooling rate of some 4.8 K/day during a time period of three weeks. The big majority of the outbursts does, however, not show any line narrowing suggesting that these masers are in the constant temperature plateau of postshocked gas. (Author (revised))