  We present multi-wavelength monitoring results for the broad-line radio
galaxy 3C 120 in the MeV/GeV, sub-millimeter, and 43 GHz bands over six years.
Over the past two years, Fermi-LAT sporadically detected 3C 120 with high
significance and the 230 GHz data also suggest an enhanced activity of the
source. After the MeV/GeV detection from 3C 120 in MJD 56240-56300, 43 GHz VLBA
monitoring revealed a brightening of the radio core, followed by the ejection
of a superluminal knot. Since we observed the gamma-ray and VLBA phenomena in
temporal proximity to each other, it is naturally assumed that they are
physically connected. This assumption was further supported by the subsequent
observation that the 43 GHz core brightened again after a gamma-ray flare
occurred around MJD 56560. We can then infer that the MeV/GeV emission took
place inside an unresolved 43 GHz core of 3C 120 and that the jet dissipation
occurred at sub-parsec distances from the central black hole, if we take the
distance of the 43 GHz core from the central black hole as ~ 0.5 pc, as
previously estimated from the time lag between X-ray dips and knot ejections
(Marscher et al. 2002; Chatterjee et al. 2009). Based on our constraints on the
relative locations of the emission regions and energetic arguments, we conclude
that the gamma rays are more favorably produced via the synchrotron
self-Compton process, rather than inverse Compton scattering of external
photons coming from the broad line region or hot dusty torus. We also derived
the electron distribution and magnetic field by modeling the simultaneous
broadband spectrum.
