Abstract
The high radio frequency polarization imaging of non-thermal emission from active galactic nuclei (AGN) is a direct way to probe the magnetic field strength and structure in the immediate vicinity of supermassive black holes (SMBHs) and is crucial in testing the jet-launching scenario. To explore the the magnetic field configuration at the base of jets in blazars, we took advantage of the full polarization capabilities of the Global Millimeter VLBI Array (GMVA). With an angular resolution of ∼50 micro-arcseconds (μas) at 86 GHz, one could resolve scales up to ∼450 gravitational radii (for a 10 9 solar mass black hole at a redshift of 0.1). We present here the preliminary results of our study on the blazar BL Lac. Our results suggest that on sub-mas scales the core and the central jet of BL Lac are significantly polarized with two distinct regions of polarized intensity. We also noted a great morphological similarity between the 7 mm/3 mm VLBI images at very similar angular resolution.
Highlights
Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, Bonn 53121, Germany; Korea Astronomy and Space Institute, 776 Daedeokdae-ro, Yuseong-gu, Daejeon 34055, Korea; Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, NASA Postdoctoral Program (NPP) Fellow
The 3 mm map is convolved with the 7 mm beam to compare the extended jet morphology
In the top left corner, we show a zoomed version of the inner jet region
Summary
Polarization study of non-thermal emission from AGN is a direct way to probe the magnetic field strength and structure in the immediate vicinity of a black hole, i.e., in a region where plasma is being injected and accelerated into the main jet stream. High-frequency polarimetric observations are essential in order to have a better understanding of the role of magnetic field in AGN accretion and jet production. High-resolution observations have been proven to be quite important in pinpointing the radiation processes responsible for the γ-ray emission in blazars [1,2,3,4,5]. For a recent flare in 2006, a combination of high-resolution images with the associated broadband flux and optical polarization measurements of the source provided evidence for a helical magnetic field, well within the jet acceleration zone. BL Lac is an excellent candidate to study the relation between jet formation, γ-ray emission, shock propagation and polarization variability
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