The discovery of a new, very strong, and widespread interstellar methanol maser line

Abstract

The first detection of very strong maser emission in the 6.6 GHz 5 1 → 6 0 A + transition of methanol toward a large number of star-forming regions is reported. Essentially all 6.6 GHz maser sources found are associated with interstellar OH masers. Toward a number of sources, the 6.6 GHz emission has flux densities of several thousand Jy, exceeding that of any known OH maser. Since all known masers in the 12 GHz 2 0 → 3 −1 E transition observationally accessible to us have been found to have 6.6 GHz counterparts, the latter line is undoubtedly a Class II methanol maser transition. In all cases the 6.6 GHz luminosity exceeds the 12 GHz luminosity, often by large factors