2009A&A...503..827X

SNR G65.2+5.7 is one of few supernova remnants (SNRs) that have been optically detected. It is exceptionally bright in X-rays and the optical [O III]-line. Its low surface brightness and large diameter ensure that radio observations of SNR G65.2+5.7 are technically difficult and thus have hardly been completed. Many physical properties of this SNR, such as spectrum and polarization, can only be investigated by radio observations. The λ11cm and λ6cm continuum and polarization observations of SNR G65.2+5.7 were completed with the Effelsberg 100-m and the Urumqi 25-m telescopes, respectively, to investigate the integrated spectrum, the spectral index distribution, and the magnetic field properties. Archival λ21cm data of the Effelsberg 100-m telescope were also used. The integrated flux densities of G65.2+5.7 at λ11cm and λ6cm are 21.9±3.1Jy and 16.8±1.8Jy, respectively. The power-law spectrum (S~ν^α) is well fitted by α=-0.58±0.07 from 83MHz to 4.8GHz. Spatial spectral variations are small. Along the northern shell, strong depolarizion is observed at both wavelengths. The southern filamentary shell of SNR G65.2+5.7 is polarized by as much as 54% at λ6cm. There is significant depolarization at λ11cm and confusion with diffuse polarized Galactic emission. Using equipartition principle, we estimated the magnetic field strength for the southern filamentary shell to be between 20µG (filling factor 1) and 50µG (filling factor 0.1). A faint HI shell may be associated with the SNR. Despite its unusually strong X-ray and optical emission and its very low surface brightness, the radio properties of SNR G65.2+5.7 are found to be typical of evolved shell-type SNRs. SNR G65.2+5.7 may be expanding in a pre-blown cavity as indicated by a deficit of HI gas and a possible HI-shell.