RADIATIVE-TRANSFER IN ASTRONOMICAL MASERS .3. FILAMENTARY MASERS

This paper, the last in a series, presents the complete solution of a filamentary master. The contribution of rays emanating from the filament sidewall is essential for the solution self-consistency during saturation. We develop an integral equation to calculate this contribution, devise an iteration scheme to solve it, and perform the first two iterations. The solution provides complete expressions for the distributions of intensity and flux across the source as functions of position and direction with regard to the axis. One consequence of radiation beaming, somewhat surprising at first, is that the filament appears smaller when viewed off-axis, at angles exceeding the cap's opening angle. From the detailed results we devise the number distribution of brightness temperatures in a large sample of randomly oriented filaments with an arbitrary distribution of lengths. A thorough comparison of the filamentary and spherical geometries is presented with possible observational tests to differentiate between the two. The effects of external radiation on the maser structure and intensity are also studied. Explicit expressions for the brightness and flux in this situation are provided, including detailed analysis of two interacting filaments and a foreground slab amplifying a background filament. We propose that the two giant bursts of H2O maser emission observed in W49 and Orion were the result of such interactions. RApid time variations reported for the Orion burst may best be explained with amplification of a background maser filament by a foreground maser slab, initially unsaturated.