Brunthaler, Bower, Falcke, Melon 2001: Circular Polarization in M81
Detection of Circular Polarization in M81
Andreas Brunthaler 1,2
Geoffrey C. Bower3,
Rick R. Melon4,
1Harvard-Smithsonian Center for Astrophysics, 60 Garden Street MS 42, Cambridge, MA 02138 (email@example.com)
2Max-Planck-Institut für Radioastronomie, Auf den Hüugel 69, D-53121 Bonn, Germany
3UC Berkeley, RAL, 601 Campbell Hall, Berkeley CA 94720
4Department of Astronomy and Astrophysics, 525 Davey Lab, The Pennsylvania State University, University Park, PA 16802
We report the detection of circular polarization in the compact radio
jet of the nearby spiral galaxy M81 (M81*). The observations were made
with the Very Large Array at 4.8 and 8.4 GHz and circular polarization
was detected at both frequencies. We estimated a value of
m_c=0.54% at 8.4 GHz and m_c=0.26% at 4.8 GHz for the
fractional circular polarization. The spectrum of the circular
polarization is inverted which is unusual for AGN. We also detected
no linear polarization in M81* to a level of 0.01% implying that the
source has a very high circular-to-linear polarization ratio found so
far only in Sgr A*, the central radio source in our Galaxy. This
further supports the idea that M81* is a scaled-up version of Sgr A*
and suggests that the polarization properties are intrinsic to the two
sources and are not caused by a foreground screen in the Galaxy.
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