Detection of millimeter-wavelength intraday variability in polarized emission from S5 0716+714

Abstract

We report the detection of millimeter-wavelength intraday variability in polarized emission from S5 0716+714 based on multifrequency polarization observations using the Korean VLBI Network (KVN) radio telescopes. The observations were conducted on November 7, 2013 at 22, 43, and 86 GHz in dual polarization using two 21 m radio telescopes belonging to KVN Yonsei and Ulsan. We found significant variations in the degree of linear polarization at 86 GHz and in polarization angle at 43 and 86 GHz during ~10 h. We measured mean flux densities of 2.8 Jy, 2.8 Jy, and 2.7 Jy at 22, 43, and 86 GHz, respectively, with a flux modulation index ranging from 1.5% to 7.2% at the frequencies. The spectrum of the source is quite flat with spectral indices of −0.07 to 0.07 at 22−43 GHz and −0.23 to 0.04 at 43−86 GHz. The measured degree of the linear polarization ranges from 2.3% to 3.3% at 22 GHz from 0.9% to 2.2% at 43 GHz and from 0.4% to 4.0% at 86 GHz, yielding prominent variations at 86 GHz over 4−5 h. The linear polarization angle is in the range of 4° to 12° at 22 GHz, −39° to 81° at 43 GHz, and 66° to 119° at 86 GHz with a maximum rotation of 110° at 43 GHz over ~4 h. We estimated the Faraday rotation measures (RM) ranging from −9200 to 6300 rad m -2 between 22 and 43 GHz, and from −71 000 to 7300 rad m -2 between 43 and 86 GHz, respectively. The frequency dependency of RM was investigated, yielding a mean power-law index, a , of 2.0. This implies that the polarized emission from S5 0716+714 at 22−86 GHz moves through a Faraday screen in or near the jet of the source.