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 \sim 0.5 pc , as previously estimated from the time lag between X-ray dips and knot ejections ( 22 ; 8 ) .
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 .