Radio jet precession in M 81

Abstract

We report four novel position angle measurements of the core region M 81∗ at 5 GHz and 8 GHz, which confirm the presence of sinusoidal jet precession in the M 81 jet region, as suggested by Martí-Vidal et al. (2011, A&A, 533, A111). The model makes three testable predictions regarding the evolution of the jet precession, which we test in our data with observations from 2017, 2018, and 2019. Our data confirm a precession period of ∼7 yr on top of a small linear drift. We further show that two 8 GHz observation are consistent with a precession period of ∼7 yr but show a different time lag with respect to the 5 GHz and 1.7 GHz observations. We do not find a periodic modulation of the light curve with the jet precession and therefore rule out a Doppler nature for the historic 1998-2002 flare. Our observations are consistent with either a binary black hole origin for the precession or the Lense-Thirring effect.