Probing the Radio Counterpart of Gamma-ray Flaring Region in 3C 84

Abstract

The radio source 3C 84 associated with the radio/giant elliptical galaxy NGC 1275 is one of the best targets to probe the radio counterpart of the γ-ray emitting region. Although this source shows clear time variability in γ-ray bands, no clear correlation in radio light curve was found on the timescale of –ray variability. The location of the γ-ray flaring region has been an open question. In this proceeding, we firstly review our previous findings from radio observations. Next we present our new results based on the Very Long Baseline Array (VLBA) data at 43 GHz. We discover the limb-brightened structure in the “restarted” jet associated with the 2005 radio outburst. In 1990s, the jet structure was rather ridge-brightening than limbbrightening, despite the observations were done with similar angular resolution. This indicates that the radio jet morphology in terms of the transverse structure has been indeed changed recently. This change in the morphology shows an interesting agreement with the time variation of the γ-ray flux density, i.e., the γ-ray flux density in 1990s was more than 7 times lower than the current one. We argue the possibility that the transition from ridge-brightening to limb-brightening is related to the γ-ray time variability.