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OH Maser sources in W49N: probing differential anisotropic scattering with Zeeman pairs

Published online by Cambridge University Press:  24 July 2012

Avinash A. Deshpande ,
W. M. Goss  and
J. E. Mendoza-Torres
Avinash A. Deshpande
Affiliation:
Raman Research Institute, C. V. Raman Avenue, Sadashivanagar, Bangalore, 560080India email: [email protected]
W. M. Goss
Affiliation:
National Radio Astronomy Observatory, P.O. Box O, Socorro, NM 87801USA email: [email protected]
J. E. Mendoza-Torres
Affiliation:
Instituto Nacional de Astrofisica Optica y Electronica, 72840, Mexico email: [email protected]
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Abstract

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Our analysis of a VLBA 12-hour synthesis observations of the OH masers in W49N has provided detailed high angular-resolution images of the maser sources, at 1612, 1665 and 1667 MHz. The images, of several dozens of spots, reveal anisotropic scatter broadening; with typical sizes of a few tens of milli-arc-seconds and axial ratios between 1.5 to 3. The image position angles oriented perpendicular to the galactic plane are interpreted in terms of elongation of electron-density irregularities parallel to the galactic plane, due to a similarly aligned local magnetic field. However, we find the apparent angular sizes on the average a factor of 2.5 less than those reported by Desai et al., indicating significantly less scattering than inferred earlier. The average position angle of the scattered broadened images is also seen to deviate significantly (by about 10 degrees) from that implied by the magnetic field in the Galactic plane. More intriguingly, for a few Zeeman pairs in our set, we find significant differences in the scatter broadened images for the two hands of polarization, even when apparent velocity separation is less than 0.1 km/s. Here we present the details of our observations and analysis, and discuss the interesting implications of our results for the intervening anisotropic magneto-ionic medium, as well as a comparison with the expectations based on earlier work.

Keywords

masers; ISM: moleculesmagnetic fieldsindividual (W49N); radio lines: ISM
Type
Contributed Papers
Information
Proceedings of the International Astronomical Union , Volume 8 , Symposium S287: Cosmic Masers - from OH to H0 , January 2012 , pp. 470 - 474
Copyright
Copyright © International Astronomical Union 2012

References

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