A new pumping mechanism for a series of class II methanol masers in the J(0)-J(-1) E transitions

A new pumping mechanism - methanol masers without population inversion is presented in this paper. It can be used to explain the formation of a series of J(0) --> J(-)1 E methanol masers, while the 2(1) --> 3(0) A(+) methanol masers are regarded as a driving coherent micrwave field. In the new mechanism, the intensities of J(0) - J(-)1 E methanol masers are increased with the decreasing transition frequencies (or with rotational number J, approximately). These results agree with Slysh et al. (1995) and Slysh et al. (1999) J less than or equal to 5 observations for G3345.01+1.79 and W48, in which both J(0) --> J(-)1 E and 2(1) --> 3(0) A(+) methanol masers are detected coincidentally. Other astronomical conditions, such as magnetic field, 2(1) --> 3(0) A(+) coherent radition, incoherent pumping rate by thermal radition and so on are also discussed. The new mechanism can operate as a complement to other ordinary maser pumping mechanisms for some class II methonal maser sources.Astronomy & AstrophysicsSCI(E)3ARTICLE4367-37527