Observational constraints of relativistic jets from black holes has largely come from the most powerful and extended jets [ 42 , 2 ] , leaving the nature of the low luminosity jets a mystery [ 3 ] .
M81* is one of the nearest low-luminosity jets , which underwent an extremely large radio flare in 2011 , allowing us to study compact core emission with unprecedented sensitivity and linear resolution .
Utilizing a multi-wavelength campaign , we were able to track the flare as it re-brightened and became optically thick .
Simultaneous X-ray observations indicated the radio re-brightening was preceded by a low energy X-ray flare at least t _ { delay } > 12 { days } prior .
Associating the time delay between the two bands as the cooling time in a synchrotron flare [ 39 , 38 ] , we find the magnetic field strength was 1.9 < B < 9.2 { G } , which is consistent with magnetic field estimate from spectral-energy distribution modeling [ 44 ] , B < 10.2 { G } .
In addition , VLBA observations at 23 GHz clearly illustrate a discrete knot moving mildly relativistically at v _ { app } / c = 0.51 \pm 0.17 associated with the initial radio flare .
The observations indicate radial jet motions for the first time in M81* .
This has profound implications for jet production , as it means radial motion can be observed in even the lowest-luminosity AGN , but at slower velocities and smaller radial extents ( \approx 10 ^ { 4 } R _ { G } ) .