New 6 cm observations of the Cygnus Loop

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 λ6 cm wavelength were made with the Urumqi 25 m telescope. The λ6 cm map is analysed together with recently published maps from the Effelsberg 100 m telescope at λ21 cm and λ11 cm. The integrated flux density of the Cygnus Loop at λ6 cm is 90 ± 9 Jy, which implies a spectral index of  ± 0.06. This rules out any global spectral steepening up to λ6 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 λ6 cm show percentage polarizations up to 35% in some areas of the Cygnus Loop, exceeding those observed at λ11 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 λ21 cm emission is totally depolarized. Rotation Measures based on λ11 cm and λ6 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.