Kazuhiro Hada, Motoki Kino, Akihiro Doi, Hiroshi Nagai, Mareki Honma, Yoshiaki Hagiwara, Marcello Giroletti, Gabriele Giovannini, Noriyuki Kawaguchi
2013 Astrophysical Journal  
We investigated the detailed inner jet structure of M87 using the Very Long Baseline Array data at 2, 5, 8.4, 15, 23.8, 43, and 86 GHz, especially focusing on the multi-frequency properties of the radio core at the jet base. First, we measured a size of the core region transverse to the jet axis, defined as W_ c, at each frequency ν, and found a relation between W_ c and ν as W_ c(ν) ∝ν^-0.71±0.05. Then, by combining W_ c(ν) and the frequency dependence of the core position r_ c(ν), which was
more » ... tained by our previous study, we have constructed a collimation profile of the innermost jet W_ c(r) down to 10 Schwarzschild radii (R_ s) from the central black hole. We found that W_ c(r) smoothly connects with the width profile of the outer edge-brightened, parabolic jet, and then follows a similar radial dependence down to several tens of R_ s. Closer to the black hole, the measured radial profile suggests a possible change of the jet collimation shape from the outer parabolic one, in which the jet shape tends to become more radially-oriented. This could be related to a magnetic collimation process or/and interaction with surrounding materials at the jet base. The present results shed light on the importance of higher-sensitivity/resolution imaging studies for M87 at 86, 43 and also 22 GHz, and should be examined more rigorously.
doi:10.1088/0004-637x/775/1/70 fatcat:fmkvhbl3zne2dkjmque55kw7xe