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

  1. J. N. McCallum1,*,
  2. S. P. Ellingsen1,*,
  3. J. E. J. Lovell2,*

Article first published online: 22 FEB 2007

DOI: 10.1111/j.1365-2966.2007.11492.x

Issue

Monthly Notices of the Royal Astronomical Society

Monthly Notices of the Royal Astronomical Society

Volume 376, Issue 2, pages 549–556, April 2007

Additional Information

How to Cite

McCallum, J. N., Ellingsen, S. P. and Lovell, J. E. J. (2007), Magnetic field limits and spectral variability in the Circinus galaxy H2O megamasers. Monthly Notices of the Royal Astronomical Society, 376: 549–556. doi: 10.1111/j.1365-2966.2007.11492.x

Author Information

  1. 1

    School of Mathematics and Physics, University of Tasmania, Private Bag 21, Hobart, Tasmania 7001, Australia

  2. 2

    Australia Telescope National Facility, CSIRO, PO Box 76, Epping, NSW 2121, Australia

* E-mail: jmccallu@postoffice.utas.edu.au (JNM); Simon.Ellingsen@utas.edu.au (SPE); Jim.Lovell@csiro.au (JEJL)

Publication History

  1. Issue published online: 13 APR 2007
  2. Article first published online: 22 FEB 2007
  3. Accepted 2007 January 9. Received 2007 January 7; in original form 2006 September 21

SEARCH

SEARCH BY CITATION

ARTICLE TOOLS

View Full Article (HTML) Get PDF (552K)

Keywords:

  • masers;
  • polarization;
  • scattering;
  • galaxies: individual: Circinus

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.

View Full Article (HTML) Get PDF (552K)