Rapid Multiwaveband Polarization Variability in the Quasar PKS 0420−014: Optical Emission from the Compact Radio Jet
نویسندگان
چکیده
An 11-day monitoring campaign in late 2005 reveals clear correlation in polarization between the optical emission and the region of the intensity peak (the “pseudocore”) at the upstream end of the jet in 43 GHz Very Long Baseline Array images in the highly variable quasar PKS 0420−014. The electric-vector position angle (EVPA) of the pseudocore rotated by about 80 in four VLBA observations over a period of nine days, matching the trend of the optical EVPA. In addition, the 43 GHz EVPAs agree well with the optical values when we correct the former for Faraday rotation. Fluctuations in the polarization at both wavebands are consistent with the variable emission arising from a standing conical shock wave that compresses magnetically turbulent plasma in the ambient jet. The volume of the variable component is the same at both wavebands, although only ∼ 20% of the total 43 GHz emission arises from this site. The remainder of the 43 GHz flux density must originate in a separate region with very low polarization. If 0420−014 is a typical case, the nonthermal optical emission from blazars originates primarily in and near the pseudocore rather than closer to the central engine where the flow collimates and accelerates. Subject headings: galaxies: quasars: general — galaxies: quasars: individual (PKS 0420−014) — physical data and processes: polarization Institute for Astrophysical Research, Boston University, Boston, MA 02215; [email protected], [email protected], [email protected] Sobolev Astronomical Institute, St. Petersburg State University, Universitetskij pr. 28, 198504 St. Petersburg, Russia; [email protected], [email protected], [email protected] Steward Observatory, The University of Arizona, Tucson, AZ 85721-0065; [email protected] Multiple Mirror Telescope Observatory, The University of Arizona, Tucson, AZ 85721-0065; [email protected] School of Physics and Astronomy, Cardiff University, 5 The Parade, Cardiff CF2 3YB, Wales, UK; [email protected]
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