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Astron. Astrophys. 322, 98-102 (1997)


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Antisymmetric rotation measures in our Galaxy: evidence for an A0 dynamo

J.L. Han 1, R.N. Manchester 2, E.M. Berkhuijsen 3 and R. Beck 3

1 Beijing Astronomical Observatory, Chinese Academy of Sciences, Beijing 100080, China (hjl@bao01.bao.ac.cn)
2 Australia Telescope National Facility, CSIRO, PO Box 76, Epping, NSW 2121, Australia
3 Max-Planck-Institute für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany

Received 12 September 1996 / Accepted 22 November 1996

Abstract

Rotation measures for extragalactic sources, after selection to emphasize the large-scale structure of the Galactic magnetic field, reveal a striking antisymmetric pattern about the Galactic plane and the meridian through the Galactic Centre. This pattern is also observed in the rotation measures of pulsars with [FORMULA]. The symmetry of the pattern, the magnitude of the rotation measures and the distance dependence of the pulsar rotation measures show that this pattern is not the result of local perturbations, but is on a large and possibly Galactic scale. This antisymmetric pattern and the existence of magnetic fields perpendicular to the plane in the Galactic Centre region, indicate that a dynamo mode of odd symmetry, possibly of A0 type, makes a substantial contribution to the magnetic fields in the thick disk and halo of our Galaxy, at least inside the Solar circle.

Key words: ISM: magnetic fields – Galaxy: structure – pulsars – polarization

Send offprint requests to: J.L. Han

© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998

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