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Volume 398, Number 3, February II 2003
Page(s) 993 - 1005
Section Stellar clusters and associations
DOI http://dx.doi.org/10.1051/0004-6361:20021702

A&A 398, 993-1005 (2003)
DOI: 10.1051/0004-6361:20021702

The effect of HII regions on rotation measure of pulsars

D. Mitra1, R. Wielebinski1, M. Kramer2 and A. Jessner1

1  Max-Planck Institute für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
2  University of Manchester, Jodrell Bank Observatory, Macclesfield SK11 9DL, UK

(Received 15 July 2002 / Accepted 12 November 2002)

We have obtained new rotation measures for 11 pulsars observed with the Effelsberg 100-m radio telescope, in the direction of the Perseus arm. Using a combination of 34 published and the 11 newly measured pulsar rotation measures we study the magnetic field structure towards the Perseus arm. We find that two pulsars towards $l\sim 149^{\circ}$ (Region 1) and four pulsars towards $l\sim 113^{\circ}$ (Region 2) lie behind HII regions which seriously affect the pulsar rotation measures. The rotation measure of PSR J2337+6151 seems to be affected by its passage through the supernova remnant G114.3+0.3. For Region 1, we are able to constrain the random component of the magnetic field to $5.7~\mu$G. For the large-scale component of the Galactic magnetic field we determine a field strength of $1.7\pm1.0~\mu$G. This average field is constant on Galactic scales lying within the Galactic longitude range of $85^{\circ} < l < 240^{\circ}$ and we find no evidence for large scale field reversal upto 5-6 kpc. We highlight the great importance to include the effects of foreground emission in any systematic study.

Key words: Galaxy: structure -- magnetic fields -- ISM: HII regions -- stars: pulsars: general

Offprint request: D. Mitra, dmitra@mpifr-bonn.mpg.de

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