Intersteller masers: The influence of the geometrical shape on the radiation properties

The relation between the minimum and the maximum of the energy density of the microwave field is important in determining the internal physical conditions in a maser source and is directly connected with the size of the emission spot. This relation is investigated for models of homogeneous maser clouds for three different geometries: a thin tube, a thin disk and a sphere. For substantial degrees of saturation, an approximate analytical calculation scheme is presented. The radiation properties found satisfy the transfer and the rate equations well. As expected, the analysis supports the long standing view that the active medium is 10 to 100 times larger than the interferometer size. Here the real purpose is to provide some insight into the dependence of the radiation characteristics on the geometrical shape of the emission region. The luminosity is only slightly affected by the shape of the emitting region (for the same volume). However, the angular variation of the intensity and the peak intensity of the rays reflect sensitively on the geometrical shape.