2010ApJ...720.1033M

We report on a year-long effort to monitor the central supermassive black hole in M81 in the X-ray and radio bands. Using Chandra and the Very Large Array, we obtained quasi-simultaneous observations of M81* on seven occasions during 2006. The X-ray and radio luminosity of M81* are not strongly correlated on the approximately 20 day sampling timescale of our observations, which is commensurate with viscous timescales in the inner flow and orbital timescales in a radially truncated disk. This suggests that short-term variations in black hole activity may not be rigidly governed by the "fundamental plane," but rather adhere to the plane in a time-averaged sense. Fits to the X-ray spectra of M81* with bremsstrahlung models give temperatures that are inconsistent with the outer regions of very simple advection-dominated inflows. However, our results are consistent with the X-ray emission originating in a transition region where a truncated disk and advective flow may overlap. We discuss our results in the context of models for black holes accreting at small fractions of their Eddington limit and the fundamental plane of black hole accretion.