VLBA Observations of the Structure and Motions of the Inner Parsec of the M87 Jet
Abstract
Walker et al (2018, Ap.J. 855, 128) reported results from Very Long Baseline Array (VLBA) observations of M87 at 43 GHz which include intensive monitoring in 2007 and 2008 plus 17 years of roughly annual observations, for a total of 50 individual observations. The results from that study are reviewed in this poster. The central radio source in M87 provides the best opportunity to study jet formation because it has a large angular size for the gravitational radius of the black hole and has a bright jet that is well resolved by VLBI observations. The 43 GHz VLBA observations have a resolution of about 0.21 x 0.43 milli-arcseconds (mas) which is about 30 by 60 Schwarzchild radii (Rs) for D = 16.7 Mpc and Mbh = 6.1 X 109 Msun. Our high-dynamic-range images clearly show the wide-opening-angle structure of the jet and show the counter-jet. The jet and counter-jet are nearly symmetric in the inner 1.5 milli-arcseconds (0.12 pc in projection) with both being edge brightened. Both show deviations from parabolic shape in the form of an initial rapid expansion in width and subsequent contraction followed by further rapid expansion and, beyond the visible counter-jet, subsequent collimation. Proper motions and counter-jet/jet intensity ratios both indicate acceleration from apparent speeds of less than about 0.5c to greater than about 2c in the inner about 2 mas (0.16 pc or 240 Rs in projection) and suggest a helical flow. The jet displays a sideways shift with an approximately 8 to 10 year quasi-periodicity. The shift propagates outwards non-ballistically and significantly more slowly than the flow speed revealed by the fastest moving components. Polarization data show a systematic structure with magnetic field vectors that suggest a toroidal field close to the core.
- Publication:
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American Astronomical Society Meeting Abstracts #233
- Pub Date:
- January 2019
- Bibcode:
- 2019AAS...23336126W