VLBA Polarization Observations of Markarian 421 After a Gamma-Ray High State

Abstract

We present four high dynamic range, dual-circular polarization, Very Long Baseline Array (VLBA) observations at 22 GHz of Markarian 421, taken throughout the year following the source's unprecedented gamma-ray high state in early 2001. These four new VLBA observations are combined with data from our earlier 1999 paper and archival VLBA data-sets that have become available since 1999 to produce a combined 28 epoch VLBA data-set on Mrk 421 spanning the years 1994 to 2002. No new component associated with the 2001 flares was seen on the total intensity images, but the combined data-set allowed precise measurements of the apparent speeds of the existing components. The peak measured apparent speed was for component C5, which has an apparent speed of 0.1 +/- 0.02 c (H_0=71 km s^{-1} Mpc^{-1}, Omega_m=0.27, and Omega_Lambda=0.73). No counterjet is seen with a limit on the jet to counterjet brightness ratio J >~ 100. These observed VLBI properties of Markarian 421 are consistent with a jet with a bulk Lorentz factor of about 2 and an angle to the line-of-sight of about 1 degree, suggesting a jet that decelerates between the gamma-ray producing region and the parsec scale. The VLBI core and inner jet (component C7) have fractional polarizations of about 5%, and an electric vector position angle (EVPA) aligned with the jet axis. Component C5 (at 1.5 mas from the core) has a higher fractional polarization of about 15%, and an EVPA nearly orthogonal to the jet axis. Significant variability is detected in the EVPA of component C6, which at two of the four epochs shows an EVPA aligned with the jet axis, possibly a sign of propagating disturbances that are only visible on the polarization images. If these propagating disturbances are linked to the 2001 gamma-ray high state, then their inferred apparent speed is between 1 and 3 c.

11 pages, accepted to ApJ

References in corpus (26)

• First Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Preliminary Maps and Basic Results
• Sub-milliarcsecond Imaging of Quasars and Active Galactic Nuclei III. Kinematics of Parsec-Scale Radio Jets
• Multi-Epoch VLBA Observations of EGRET-Detected Quasars and BL Lac Objects: Superluminal Motion of Gamma-Ray Bright Blazars
• Internal shocks in the jets of radio-loud quasars
• Parsec Scale Properties of Markarian 501
• Decelerating Flows in TeV Blazars: A Resolution to the BL Lac -- FR I Unification Problem
• Multi-Epoch VLBA Observations of EGRET-Detected Quasars and BL Lac Objects: Connection between Superluminal Ejections and Gamma-Ray Flares in Blazars
• Modelling the TeV gamma-ray spectra of two low redshift AGNs: Mkn 501 and Mkn 421
• A View through Faraday's Fog 2: Parsec Scale Rotation Measures in 40 AGN
• The Parsec-Scale Structure and Jet Motions of the TeV Blazars 1ES 1959+650, PKS 2155-304, and 1ES 2344+514
• Survey of Instantaneous 1-22 GHz Spectra of 550 Compact Extragalactic Objects with Declinations from -30deg to +43deg
• Simultaneous X-Ray and TeV Gamma-Ray Observations of the TeV Blazar Markarian 421 during February and May 2000
• Discovery of Spectral Variability of Markarian 421 at TeV Energies
• A View through Faraday's fog: Parsec scale rotation measures in AGN
• Parsec-Scale Blazar Monitoring: Flux and Polarization Variability
• Measurement of the Multi-TeV gamma-ray Flare-Spectra of Markarian 421 and Markarian 501
• Parsec-Scale Jet Polarization Properties of a Complete Sample of Active Galactic Nuclei at 43 GHz
• Kinematics of the Parsec-Scale Relativistic Jet in Quasar 3C 279: 1991 - 1997
• Cutoff in the TeV Energy Spectrum of Markarian 421 During Strong Flares in 2001
• VLBI Polarimetry of 177 Sources from the Caltech-Jodrell Bank Flat-spectrum Survey
• The Sub-Luminal Parsec-scale Jet of Mkn 501
• Implications of Variability Patterns observed in TeV Blazars on the Structure of the Inner Jet
• VSOP and Ground-based VLBI Imaging of the TeV Blazar Markarian 421 at Multiple Epochs
• Extragalactic Sources of TeV Gamma Rays: A Summary
• Internal shocks and the blazar sequence. Low and intermediate power BL Lac objects
• Do the mildly superluminal VLBI knots exclude ultrarelativistic blazar jets?

Cited by in corpus (31)

• Synchrotron Self-Compton Analysis of TeV X-ray Selected BL Lacertae Objects
• The Jets of TeV Blazars at Higher Resolution: 43 GHz and Polarimetric VLBA Observations from 2005-2009
• The X-ray Polarization View of Mrk~421 in an Average Flux State as Observed by the Imaging X-ray Polarimetry Explorer
• The Parsec-Scale Jets of the TeV Blazars H 1426+428, 1ES 1959+650, and PKS 2155-304: 2001-2004
• Intrinsic $\gamma$-ray luminosity, black hole mass, jet and accretion in Fermi blazars
• Is the core of M87 the source of its TeV emission? Implications for unified schemes
• A sample of low-redshift BL Lacertae objects. II. EVN and MERLIN data and multi-wavelength analysis
• Unveiling the X-ray/TeV engine in Mkn 421
• Multiwavelength Observations of the Blazar Mrk 421 in December 2002 and January 2003
• INTEGRAL observations of the blazar Mrk 421 in outburst (Results of a multi-wavelength campaign)
• VLBA monitoring of Mrk 421 at 15 GHz and 24 GHz during 2011
• On the Origin of Rapid Flares in TeV Blazars
• Radiation from relativistic jets in blazars and the efficient dissipation of their bulk energy via photon breeding
• High-Energy Aspects of Astrophysical Jets
• Very Long Baseline polarimetry and the gamma-ray connection in Markarian 421 during the broadband campaign in 2011
• The TeV blazar Markarian 421 at the highest spatial resolution
• Parsec-scale Magnetic-Field Structures in HEAO-1 BL Lacs
• The Properties of Parsec-Scale Blazar Jets
• A Suzaku X-Ray Study of the Particle Acceleration Processes in the Relativistic Jet of Blazar Mrk 421
• Probing an X-ray flare pattern in Mrk 421 induced by multiple stationary shocks: a solution to the bulk Lorentz factor crisis
• Simultaneous radio-interferometric and high-energy TeV observations of the gamma-ray blazar Mkn 421
• Possible Detection of Apparent Superluminal inward motion in Markarian 421 after the Giant X-ray flare in February, 2010
• Influence of the jet opening angle on the derived kinematical parameters of blazar jets having uniform and stratified bulk motion
• X-ray and TeV Gamma-Ray Emission from Parallel Electron-Positron or Electron-Proton Beams in BL Lac Objects
• An Exceptional Radio Flare in Markarian 421
• Astrophysics in 2005
• The Parsec-Scale Structure of the Newer TeV Blazars
• VLBI observations of a flared optical quasar CGRaBS J0809+5341
• An emergence of new polarized emission region in blazar Mrk 421 associated with X-ray flare
• Photon breeding mechanism in relativistic jets: astrophysical implications
• Parsec-scale Structure and Kinematics of Faint TeV HBLs