Radio polarization observations of large supernova remnants at λ6 cm

We have observed 79 supernova remnants (SNRs) with the Urumqi 25 m telescope at �6 cm during the Sino-German �6 cm polarization survey of the Galactic plane. We measured flux densities of SNRs at �6 cm, some of which are the first ever measured or the measurements at the highest frequency, so that we can determine or improve spectra of SNRs. Our observations have ruled out spectral breaks or spectral flattening that were suggested for a few SNRs, and confirmed the spectral break of S147. By combining our �6 cm maps with �11 cm and �21 cm maps from the Effelsberg 100 m telescope, we calculated the spectral index maps of several large SNRs. For many remnants we obtained for the first time polarization images, which show the intrinsic magnetic field structures at �6 cm. We disapproved three objects as being SNRs, OA184, G192.8 1.1 and G16.8 1.1, which show a thermal spectrum and no polarization. We have discovered two large supernova remnants, G178.2 4.2 and G25.1 2.3., in the survey maps.