S E M I N A R IDepartament d'Astronomia i Astrofísica
Universitat de València
Jet Precesion in the AGN of M81. Physical Parameters and Evidence of a Binary Black Hole
Onsala Space Observatory (Chalmers University), Onsala, Suècia
Seminari del departament d'Astronomia i Astrofísica
Dimecres 18 juliol 2012
We report on a full campaign of multi-frequency global-VLBI observations of M81, phase-referenced to the closeby supernova SN1993J. From these observations, we find a systematic drift in the intensity peak of M81 among the different frequencies (possibly due to opacity effects in the radio jet). From these results, we can estimate the mass of the central black hole and the strength of the magnetic field at the jet base. The former is compatible with previous estimates using independent approaches; the latter is about 4 orders of magnitude higher than previous estimates. Furthermore, from the astrometry to SN1993J, we also detect an evolution in the jet position angle that is correlated to changes in the total flux density of M81 and to changes in the orientation of the jet cores at all frequencies. These results can be interpreted as due to jet precesion, with a period of a few decades. Indeed, from the modelling of the core orientation vs. time, we also detect strong evidence of two different period contributions to the jet precesion (binary black hole in M81?!). Further results on the astrometry monitoring of M81, now phase-referenced to a new closeby supernova, are also being analyzed. We are also analyzing radio light curves of M81 (with the VLA, covering almost 12 years at frequencies ranging from 300MHz to 22GHz), to help us better constrain the physical parameters and evolution of the jet in M81.