creators_name: McCallum, JN
creators_name: Ellingsen, SP
creators_name: Lovell, JEJ
creators_id: 
creators_id: Simon.Ellingsen@utas.edu.au
creators_id: 
type: article
datestamp: 2008-04-07 14:20:44
lastmod: 2008-09-01 01:51:55
metadata_visibility: show
title: Magnetic field limits and spectral variability in the Circinus galaxy H2O megamasers
ispublished: pub
subjects: 240101
full_text_status: restricted
keywords: masers – polarization – scattering – galaxies: individual: Circinus.
note: The definitive version is available at www.blackwell-synergy.com
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.
date: 2007
date_type: published
publication: Monthly Notices of the Royal Astronomical Society
volume: 376
number: 2
publisher: Blackwell Publishing
pagerange: 549-556
id_number: 10.1111/j.1365-2966.2007.11492.x
refereed: TRUE
issn: 0035-8711
official_url: http://dx.doi.org/10.1111/j.1365-2966.2007.11492.x
citation: McCallum, JN and Ellingsen, SP and Lovell, JEJ (2007) Magnetic field limits and spectral variability in the Circinus galaxy H2O megamasers. Monthly Notices of the Royal Astronomical Society, 376 (2). pp. 549-556. ISSN 0035-8711
document_url: http://eprints.utas.edu.au/4064/1/4064.pdf