A Sino-German ℷ6 cm polarization survey of the Galactic plane VII. Small supernova remnants

Aims. We study the spectral and polarization properties of supernova remnants (SNRs) using our gimel 6 cm survey data. Methods. We analyse data from observations taken as part of the Sino-German gimel 6 cm polarization survey of the Galactic plane. By using the integrated flux densities at gimel 6 cm together with measurements at other wavelengths from the literature, we derive the global spectra of 50 SNRs. In addition, from the observations at gimel 6 cm we obtain the polarization images of 24 SNRs. Results. We derive integrated flux densities at gimel 6 cm for 51 small SNRs with angular sizes smaller than 1 degrees. We are able to derive global radio spectral indices in all the cases except for Cas A. For the SNRs G15.1-1.6, G16.2-2.7, G16.4-0.5, G17.4-2.3, G17.8-2.6, G20.4+0.1, G36.6+2.6, G43.9+1.6, G53.6-2.2, G55.7+3.4, G59.8+1.2, G68.6-1.2, and G113.0+0.2, the spectra have been significantly improved. From our analysis, we argue that the object G16.8-1.1 is probably an HII region instead of a SNR. Cas A shows a secular decrease in total intensity, and we measure a flux density of 688 +/- 35 Jy at gimel 6 cm between 2004 and 2008. We detect polarized emission from 25 SNRs. For G16.2-2.7, G69.7+1.0, G84.2-0.8, and G85.9-0.6, the polarized emission is detected for the first time confirming that they are SNRs. Conclusions. High-frequency observations of SNRs are difficult but essential to determine their spectra and measure their polarization in particular towards the inner Galaxy, where Faraday effects are important.