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 2₁ → 3₀ 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 ≤ 5 observations for G3345.01+1.79 and W48, in which both J ₀ → J _-1 E and 2₁ → 3₀ A ⁺ methanol masers are detected coincidentally. Other astronomical conditions, such as magnetic field, 2₁ → 3₀ 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. This revised version was published online in July 2006 with corrections to the Cover Date.