Authors: S. Britzen, C. Fendt, A. Eckart, V. Karas
Journal: Transactions of IAA RAS vol. 40
Pages: 111 - 116
Keywords: VLBI, M87
The question how relativistic jets are launched in Active Galactic Nuclei (AGN) is still unsolved. Due to M87’s proximity, jet prominence, and the large BH mass, this giant radio galaxy is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. This source is one of the two prime objects to be studied in exquisite detail with the upcoming Event Horizon Telscope (EHT) observations. It promises to allow a direct view on the jet launching process itself which so far has not been possible to study observationally. Our investigations show, that the M87-jet visible at 15 GHz already probes a different physical zone compared to the standard blazar-zone we see in AGN jets. We remodeled and re-analyzed 31 VLBA observations at 15 GHz obtained within the MOJAVE programme. The data span a time range between 1995.6 and 2011.4. We performed a detailed investigation of the pc-scale jet kinematics, and the jet ridge line behavior. Special care has been taken to analyze the region close to the 15 GHz core. We find evidence for two different operating modes of the jet of M87: The jet switches between phases where the jet ridge line is (at least) double or the jet axis is displaced vertically and an unperturbed phase where the jet ridge line remains rather straight, only smoothly curved with the jet components aligned along a classical jet axis. The most likely scenario explaining the observed phenomena is a turbulent mass loading into the jet, most probably due to local reconnection processes of a tangled magnetic field, either generated in the accretion disk or the disk corona. In addition, on large scales, a global magnetic structure is required to channel the turbulent flow into what evolves into a large-scale jet. Large-scale jet instabilitites may explain the curved pattern of the observed jet flow.