Time variability of astrophysical masers

The time-dependent equations of radiative transfer are solved for a maser source much longer than it is wide. Transitions are assumed to occur between two energy levels only (this has previously been shown to be a justifiable approximation for the four-level hydroxyl (OH) maser, and is discussed bri...

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Bibliographic Details
Published in:Monthly notices of the Royal Astronomical Society 1978-07, Vol.183 (3), p.491-500
Main Authors: Salem, M., Middleton, M. S.
Format: Article
Language:English
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Summary:The time-dependent equations of radiative transfer are solved for a maser source much longer than it is wide. Transitions are assumed to occur between two energy levels only (this has previously been shown to be a justifiable approximation for the four-level hydroxyl (OH) maser, and is discussed briefly). It is found that the intensity may vary rapidly although the physical conditions in the masing region, including the rates of pumping and relaxation, are constant. Under certain circumstances the observed intensity of a saturated maser may vary quasi-periodically with large amplitude and a period (in years) equal to the maser length (in light years); the maser may seem to appear and disappear. All calculations are carried out for two of the four levels of the hydroxyl ground rotational-state maser, but the results are qualitatively valid for any system which is approximately equivalent to a two-level maser.
ISSN:0035-8711
1365-2966
DOI:10.1093/mnras/183.3.491