DETECTION OF A SERIES OF METHANOL MASER LINES AT 1.9-MILLIMETER WAVELENGTH

The series of methanol J(0)-J(-1)E lines at 157 GHz has been detected in known methanol line sources together with the 2(1)-3(0) A(+) line of A-type methanol. In W3(OH), 345.01 + 1.79, W48, and Cep A the J(0)-J(-1), lines are intense and narrow and are believed to be maser lines. The radial velocities and profiles are similar to those of other class II methanol lines in these sources. The intensity of the lines increases with rotational number J, in contrast to thermal methanol features which were detected in the same sources at slightly different radial velocities. It is suggested that the new maser line sources are the class II methanol masers but are excited with higher radiation temperature than the lower frequency class II masers at 6.7 and 12.2 GHz. The masers may be related to molecular outflows or cometary bow shocks of ultracompact H II regions as is evidenced by their velocity shift relative to the parent molecular clouds.