The radiation of astronomical masers fluctuates on the time scale 1/Gamma, where Gamma is the levels' loss rate. These intensity fluctuations reflect fluctuations of the level poulations around their mean, steady state values over the length scale λc = c/Γ. In saturated masers, the intensity fluctuations are dominated by passage through the unsaturated core. The effects of the saturated zones and of the seed radiation that the masers amplify can be neglected.

These fluctuations may have been detected in recent observations by Clegg and Cordes (1991) of Galactic H II/OH masers, providing a possible direct determination of the saturation intensity Js (= Γ/2B), an important input parameter for theoretical modeling. Long time-scale variations in the fluctuation amplitudes can provide information on phenomena such as passage of hydrodynamic waves in the maser region.

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Published in The Astrophysical Journal Letters, v. 370, no. 1, p. L45-L48.

©1991. The American Astronomical Society. All rights reserved.

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