Open AccessMagnetic field limits and spectral variability in the Circinus galaxy H 2 O megamasers
Author(s) -
McCallum J. N.,
Ellingsen S. P.,
Lovell J. E. J.
Publication year - 2007
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1111/j.1365-2966.2007.11492.x
Subject(s) - physics , astrophysics , megamaser , galaxy , maser , telescope , astronomy , magnetic field , radio telescope , field (mathematics) , mathematics , pure mathematics , quantum mechanics
We have used the Australia Telescope Compact Array (ATCA) to search for polarized emission from the Circinus galaxy H 2 O 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 H 2 O 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 H 2 O megamasers undergo diffractive interstellar scintillation, which has previously only been observed in pulsars and in one active galactic nucleus.