A Sino-German λ6 cm polarization survey of the Galactic plane

VII. Small supernova remnants

¹ National Astronomical Observatories, CAS, Jia-20 Datun Road, Chaoyang District, 100012 Beijing, PR China
e-mail: xhsun@nao.cas.cn; hjl@nao.cas.cn
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: preich@mpifr-bonn.mpg.de; wreich@mpifr-bonn.mpg.de

Received: 13 July 2011
Accepted: 30 September 2011

Abstract

Aims. We study the spectral and polarization properties of supernova remnants (SNRs) using our λ6 cm survey data.

Methods. We analyse data from observations taken as part of the Sino-German λ6 cm polarization survey of the Galactic plane. By using the integrated flux densities at λ6 cm together with measurements at other wavelengths from the literature, we derive the global spectra of 50 SNRs. In addition, from the observations at λ6 cm we obtain the polarization images of 24 SNRs.

Results. We derive integrated flux densities at λ6 cm for 51 small SNRs with angular sizes smaller than 1°. 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 H ii 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 λ6 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.