Six Years of Fermi-Lat and Multi-Wavelength Monitoring of the Broad-Line Radio Galaxy 3c 120: Jet Dissipation at Sub-Parsec Scales From the Central Engine

Abstract

We present multi-wavelength monitoring results for the broad-line radio galaxy 3C 120 in the MeV/GeV, submillimeter, and 43 GHz bands over 6 yr. Over the past 2 yr, the Fermi-Large Area Telescope 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 Very Long Baseline Array (VLBA) monitoring revealed a brightening of the radio core, followed by the ejection of a superluminal knot. Since we observed the γ-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 γ-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 (BH), if we take the distance of the 43 GHz core from the central BH as ∼0.5 pc, as previously estimated from the time lag between X-ray dips and knot ejections. Based on our constraints on the relative locations of the emission regions and energetic arguments, we conclude that the γ 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.

Application of the spine-layer jet radiation model to outbursts in the broad-line radio galaxy 3C 120

“…Assuming that characteristic variability timescale tvar equals the shortest time bin for which the source has been detected with significance larger than 3σ we estimate tvar = 2 h for flare 1 and tvar = 30 min for flare 2. In a similar way 3C 120 γ-ray variability timescale for six years of Fermi/LAT data was estimated to be 5−10 days by Tanaka et al (2015). Variability timescale and causality arguments allow us to estimate radius of the emission region R cDtvar where…”

“…3C 120 γ-ray flux increase on very short timescale, observed spectral hardening, no flaring behaviour in X-rays and no indication of rapid changes in other wavelengths constitute a challenge for interpretation of those facts in terms of usual disk+jet models (Tanaka et al 2015). No indication of increased activity except for γ-rays suggest that high energy component and radiation at other wavelengths may be produced at different locations.…”

No Evidence of Intrinsic Optical/Near-Infrared Linear Polarization for V404 Cygni During Its Bright Outburst in 2015: Broadband Modeling and Constraint on Jet Parameters

“…To constrain the jet parameters and physical quantities in the emission region, we attempted to model the SED of V404 Cyg by using a one-zone synchrotron plus synchrotron selfCompton (SSC) model (Finke et al 2008), which is widely used for blazar SED modeling (e.g., Abdo et al 2009Abdo et al , 2011Tanaka et al 2014Tanaka et al , 2015. We show in Figure 6 (left panel) the quasi-simultaneous broadband SED of V404 Cyg during the K s -band flare.…”

Revisiting correlations between broad-line and jet emission variations for AGNs: 3C 120 and 3C 273

“…For 3C 120, Rjet ≫ RBLR, and then it is possible Rγ ≫ RBLR, which limits the EC component of gamma rays to be negligible compared to the SSC one. Tanaka et al (2015) derived a ratio of EC to SSC luminosity of ∼ 0.1 for 3C 120. The dominant SSC component deduced here is consistent with Tanaka et al (2015).…”