2016A&A...592L..10L

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 86GHz 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 86GHz and in polarization angle at 43 and 86GHz during ∼10h. We measured mean flux densities of 2.8Jy, 2.8Jy, and 2.7Jy at 22, 43, and 86GHz, 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 22-43GHz and -0.23 to 0.04 at 43-86GHz. The measured degree of the linear polarization ranges from 2.3% to 3.3% at 22GHz from 0.9% to 2.2% at 43GHz and from 0.4% to 4.0% at 86GHz, yielding prominent variations at 86GHz over 4-5h. The linear polarization angle is in the range of 4° to 12° at 22GHz, -39° to 81° at 43GHz, and 66° to 119° at 86GHz with a maximum rotation of 110° at 43GHz over ∼4h. We estimated the Faraday rotation measures (RM) ranging from -9200 to 6300rad/m² between 22 and 43GHz, and from -71000 to 7300rad/m² between 43 and 86GHz, 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 22-86GHz moves through a Faraday screen in or near the jet of the source.