Please use this identifier to cite or link to this item: http://hdl.handle.net/2289/5858
Title: OH Maser Sources in W49N: Probing magnetic field and differential anisotropic scattering with Zeeman pairs using the very long baseline array
Authors: Deshpande, A.A.
Gross, W.M.
Mendoza-Torres, Jose E.
Keywords: ISM: individual objects
W49N, ISM
structure, magnetic fields
Issue Date: Sep-2013
Publisher: IOP Sciences for The American Astronomical Society
Citation: The Astrophysical journal, 2013, Vol.775, p36
Abstract: Our analysis of a Very Long Baseline Array 12 hr synthesis observation of the OH masers in the well-known star-forming region W49N has yielded valuable data that enable us to probe distributions of magnetic fields in both the maser columns and the intervening interstellar medium (ISM). The data, consisting of detailed high angular resolution images (with beam width ~20 mas) of several dozen OH maser sources, or spots, at 1612, 1665, and 1667 MHz, reveal anisotropic scatter broadening with typical sizes of a few tens of milliarcseconds and axial ratios between 1.5 and 3. Such anisotropies have been reported previously by Desai et al. and have been interpreted as being induced by the local magnetic field parallel to the Galactic plane. However, we find (1) apparent angular sizes of, on average, a factor of about 2.5 less than those reported by Desai et al., indicating significantly less scattering than inferred previously, and (2) a significant deviation in the average orientation of the scatter-broadened images (by ~10°) from that implied by the magnetic field in the Galactic plane. More intriguingly, for a few Zeeman pairs in our set, significant differences (up to 6σ) are apparent in the scatter-broadened images for the two hands of circular polarization, even when the apparent velocity separation is less than 0.1 km s-1. This may possibly be the first example of a Faraday rotation contribution to the diffractive effects in the ISM. Using the Zeeman pairs, we also study the distribution of the magnetic field in the W49N complex, finding no significant trend in the spatial structure function. In this paper, we present the details of our observations and analysis leading to these findings, discuss implications of our results for the intervening anisotropic magneto-ionic medium, and suggest possible implications for the structure of magnetic fields within this star-forming region.
Description: Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations)
URI: http://hdl.handle.net/2289/5858
ISSN: 0004-637X
1538-4357-(Online)
Alternative Location: http://adsabs.harvard.edu/abs/2013ApJ...775...36D
http://arxiv.org/abs/1307.7966
http://dx.doi.org/10.1088/0004-637X/775/1/36
Copyright: 2013 American Astronomical Society
Appears in Collections:Research Papers (A&A)

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