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Issue A&A
Volume 447, Number 3, March I 2006
Page(s) 937 - 947
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:20054133



A&A 447, 937-947 (2006)
DOI: 10.1051/0004-6361:20054133

New $\mathsf{\lambda}$6 cm observations of the Cygnus Loop

X. H. Sun1, W. Reich2, J. L. Han1, P. Reich2 and R. Wielebinski2

1  National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100012, PR China
    e-mail: [xhsun;hjl]@bao.ac.cn
2  Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, Bonn 53121, Germany
    e-mail: [wreich;preich;rwielebinski]@mpifr-bonn.mpg.de

(Received 31 August 2005 / Accepted 4 October 2005 )

Abstract
Radio continuum and polarization observations of the entire Cygnus Loop at $\lambda$6 cm wavelength were made with the Urumqi 25 m telescope. The $\lambda$6 cm map is analysed together with recently published maps from the Effelsberg 100 m telescope at $\lambda$21 cm and $\lambda$11 cm. The integrated flux density of the Cygnus Loop at $\lambda$6 cm is 90 $\pm$ 9 Jy, which implies a spectral index of $\alpha=-0.40$ $\pm$ 0.06. This rules out any global spectral steepening up to $\lambda$6 cm. However, small spectral index variations in some regions of the source are possible, but there are no indications for any spectral curvature. The linear polarization data at $\lambda$6 cm show percentage polarizations up to 35% in some areas of the Cygnus Loop, exceeding those observed at $\lambda$11 cm. The Rotation Measure is around -21 rad m-2 in the southern area, which agrees with previous observations. However, the distribution of Rotation Measures is rather complex in the northern part of the Cygnus Loop, where the $\lambda$21 cm emission is totally depolarized. Rotation Measures based on $\lambda$11 cm and $\lambda$6 cm data are significantly larger than in the southern part. The difference in the polarization characteristics between the northern and southern part supports previous ideas that the Cygnus Loop consists of two supernova remnants.


Key words: ISM: magnetic fields -- ISM: supernova remnants -- radio continuum: ISM -- techniques: polarimetric

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© ESO 2006


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