Determination of the Kerr parameter of the central Black Hole in BL Lacertae objects

Presentation duration: 30 minutes

Presenter: Till Steinbring

We present an observational test of the Blandford-Znajek mechanism (1977), according to which extragalactic jets are driven by the extraction of rotational energy from the central supermassive black hole. In this model the jet luminosity depends on the Kerr parameter and the magnetic field. To prove whether this relation holds for BL Lacertae objects, we determine the jet parameters using VLBI radio data from the MOJAVE monitoring program. By fitting the broadband spectral energy distribution, we can derive luminosity and magnetic field on parsec scales. The jet geometry can be constrained connecting the VLBI scale jet with the central engine. The inferred Kerr parameter values are in line with the Blandford Znajek scenario.