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Abstract

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 Type:	Article
Authors/Creators:	McCallum, JN and Ellingsen, SP and Lovell, JEJ
Keywords:	masers – polarization – scattering – galaxies: individual: Circinus.
Journal or Publication Title:	Monthly Notices of the Royal Astronomical Society
Publisher:	Blackwell Publishing
ISSN:	0035-8711
DOI / ID Number:	https://doi.org/10.1111/j.1365-2966.2007.11492.x
Additional Information:	The definitive version is available at www.blackwell-synergy.com
Item Statistics:	View statistics for this item

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