O'Sullivan, Shane

Broadband radio circular polarization observations of the quasar PKS B2126-158.

Author list: Shane O’Sullivan

I will present full-polarization observations of the quasar PKS B2126-158 from 1 to 10 GHz using the Australia Telescope Compact Array. Large fractional circular polarization (m_c) is detected at high significance across the entire band at 128 MHz intervals; which allows us to construct a very robust circular polarization (CP) spectrum. We find m_c is proportional to frequency to the power of +0.6 +/- 0.1 from 1.5 to 6.5 GHz, with a peak of m_c ~ 1% before the spectrum turns over somewhere between 6.5 and 8 GHz, above which m_c goes as frequency to the power of -3.2 +/- 0.3. The frequency dependence of the linear polarization (LP) is well modelled by external Faraday rotation in which large gradients in RM exist on scales much smaller than our resolution. Overall, our results are consistent with the hypothesis of little or no thermal plasma within the jet, with conversion of LP to CP caused by a small amount of Faraday rotation from the low-energy end of the relativistic electron energy spectrum in an electron-proton dominated jet.