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Magnetic field limits and spectral variability in the Circinus galaxy H2O megamasers


McCallum, J and Ellingsen, SP and Lovell, JEJ, Magnetic field limits and spectral variability in the Circinus galaxy H2O megamasers, Royal Astronomical Society. Monthly Notices, 376, (2) pp. 549-556. ISSN 0035-8711 (2007) [Refereed Article]

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The definitive published version is available online at:

DOI: doi:10.1111/j.1365-2966.2007.11492.x


We have used the Australia Telescope Compact Array (ATCA) to search for polarized emission from the Circinus galaxy H2O megamasers. No linear or circular polarized emission was detected with 3σ upper limits of 24 and 39 mJy, respectively, corresponding to fractional polarizations of 0.6 and 0.9 per cent for the strongest line. These results allow us to place upper limits on the strength of the nuclear magnetic field of ≤150 mG near the outer edge of the masing disc and ≤360 mG at the inner edge.

Rapid variability, thought to be due to interstellar scintillation, is a well-known feature of the Circinus H2O megamasers. Our Stokes-I data show evidence for changes in the shape of the maser line spectral profiles, as well as their intensity. In addition to the rapid variations, the maser light curves also exhibit variations with a time-scale of the order of days (although our observations are too short to characterize this well). These behaviours support the hypothesis that the Circinus H2O megamasers undergo diffractive interstellar scintillation, which has previously only been observed in pulsars and in one active galactic nucleus.

Item Details

Item Type:Refereed Article
Research Division:Physical Sciences
Research Group:Astronomical sciences
Research Field:Galactic astronomy
Objective Division:Expanding Knowledge
Objective Group:Expanding knowledge
Objective Field:Expanding knowledge in the physical sciences
UTAS Author:McCallum, J (Dr Jamie McCallum)
UTAS Author:Ellingsen, SP (Professor Simon Ellingsen)
ID Code:44267
Year Published:2007
Funding Support:Australian Research Council (DP0342478)
Web of Science® Times Cited:10
Deposited By:Physics
Deposited On:2007-08-01
Last Modified:2019-02-19

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