The B3-VLA CSS sample

VII. WSRT polarisation observations and the ambient Faraday medium properties revisited

¹ Istituto di Radioastronomia – INAF, via Gobetti 101, 40129 Bologna, Italy e-mail: rossetti@ira.inaf.it
² Dipartimento di Astronomia, Università di Bologna, via Ranzani 1, 40127 Bologna, Italy

Received: 12 November 2007
Accepted: 11 February 2008

Abstract

We present new polarisation observations at 13 cm, acquired using the Westerbork Synthesis Radio Telescope (WSRT), of 65 sources, from the B3-VLA sample of Compact Steep-Spectrum sources. These new data are combined with our VLA polarisation data, at 3.6, 6 and, 21 cm, presented in a previous paper. Due to the multi-channel frequency capabilities of the WSRT, these new 13 cm observations enable a more reliable determination of integrated Rotation Measures, and of depolarisation behaviour with wavelength. The new data are inconsistent with the depolarisation models that we used earlier, and we propose an alternative model which seems to work properly. We also revise our previous model for the external Faraday screen, and its dependence on the source redshift.