Rapid Multiwaveband Polarization Variability in the Quasar PKS 0420–014: Optical Emission from the Compact Radio Jet

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 VLBA (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 9 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 wave bands 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 wave bands, 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.

[1]  J. Bregman,et al.  Relativistic jets : the common physics of AGN, microquasars, and gamma-ray bursts : Ann Arbor, Michigan, 14-17 December 2005 , 2006 .

[2]  Paul S. Smith,et al.  Evidence for cospatial optical and radio polarized emission in active galactic nuclei , 2006 .

[3]  T. Cawthorne.  Polarization of synchrotron radiation from conical shock waves , 2006 .

[4]  M. Cohen,et al.  ACCEPTED FOR PUBLICATION IN APJ LETTERS Preprint typeset using LATEX style emulateapj v. 12/14/05 INTRINSIC BRIGHTNESS TEMPERATURES OF AGN JETS , 2006 .

[5]  C. Aspin,et al.  Astronomical Polarimetry: Current Status and Future Directions , 2005 .

[6]  Paul S. Smith,et al.  Polarimetric Observations of 15 Active Galactic Nuclei at High Frequencies: Jet Kinematics from Bimonthly Monitoring with the Very Long Baseline Array , 2005, astro-ph/0502501.

[7]  P. Hughes.  The Origin of Complex Behavior of Linearly Polarized Components in Parsec-Scale Jets , 2004, astro-ph/0411725.

[8]  N. Vlahakis,et al.  Magnetic Driving of Relativistic Outflows in Active Galactic Nuclei. I. Interpretation of Parsec-Scale Accelerations , 2003, astro-ph/0310747.

[9]  Paul S. Smith,et al.  Optical Spectropolarimetry of Quasi-stellar Objects Discovered by the Two-Micron All Sky Survey , 2003, astro-ph/0305098.

[10]  A. Marscher,et al.  High-Frequency VLBA Total and Polarized Intensity Images of Gamma-Ray Bright Blazars , 2002 .

[11]  A. V. Yurchenko,et al.  Multiepoch Very Long Baseline Array Observations of EGRET-detected Quasars and BL Lacertae Objects: Superluminal Motion of Gamma-Ray Bright Blazars , 2001, astro-ph/0101570.

[12]  Paul S. Smith,et al.  Intrinsic Differences in the Inner Jets of High and Low Optically Polarized Radio Quasars , 2000, astro-ph/0003309.

[13]  Paul S. Smith,et al.  Photometric Calibration of Stars in the Fields of Selected BL Lacertae Objects and Quasars , 1998 .

[14]  A. Marscher,et al.  Parsec-Scale Synchrotron Emission from Hydrodynamic Relativistic Jets in Active Galactic Nuclei , 1995 .

[15]  A. Marscher,et al.  Radio, millimeter-submillimeter, and infrared spectra of flat-spectrum extragalactic radio sources , 1994 .

[16]  M. Sitko,et al.  Nearly Simultaneous Very Long Baseline Interferometry and Optical Polarimetry of Blazars , 1994 .

[17]  Geoffrey Burbidge,et al.  A revised and updated catalog of quasi-stellar objects , 1993 .

[18]  Paul S. Smith,et al.  Discovery of a sub-megagauss magnetic white dwarf through spectropolarimetry , 1992 .

[19]  P. Hughes.  Beams and jets in astrophysics , 1991 .

[20]  A. Marscher,et al.  The Gasdynamics of Compact Relativistic Jets , 1988 .

[21]  T. W. Jones,et al.  Polarization as a probe of magnetic field and plasma properties of compact radio sources: simulation of relativistic jets , 1988 .

[22]  Walter Kieran Gear,et al.  Models for high-frequency radio outbursts in extragalactic sources, with application to the early 1983 millimeter-to-infrared flare of 3C 273. , 1985 .

[23]  T. Jones,et al.  Magnetic field structures in active compact radio sources , 1985 .

[24]  M. Sitko,et al.  Optical polarimetry of BL Lacertae objects and violent variable quasars. , 1984 .

[25]  J. Angel,et al.  The radio morphology of blazars and relationships to optical polarization and to normal radio galaxies. , 1984 .

[26]  A. Konigl.  Relativistic jets as X-ray and gamma-ray sources. , 1981 .

[27]  Roger D. Blandford,et al.  Relativistic jets as compact radio sources , 1979 .

[28]  A. Marscher,et al.  Relativistic jets and the continuum emission in QSOs , 1979 .

[29]  J. Wardle,et al.  The linear polarization of quasi-stellar radio sources at 3.71 and 11.1 centimeters. , 1974 .

[30]  B. Burn.  On the Depolarization of Discrete Radio Sources by Faraday Dispersion , 1965 .