Constraints on the Circumnuclear Disk through Free–Free Absorption in the Nucleus of 3C 84 with KaVA and KVN at 43 and 86 GHz
Kiyoaki Wajima, Motoki Kino, Nozomu Kawakatu
Abstract
Abstract The nearby bright radio galaxy 3C 84 at the center of the Perseus cluster is an ideal target to explore the jet in an active galactic nucleus and its parsec-scale environment. The recent research of Fujita & Nagai revealed the existence of the northern counter-jet component (N1) located 2 mas north from the central core in very long baseline interferometer (VLBI) images at 15 and 43 GHz and they are explained by the free–free absorption (FFA) due to an ionized plasma foreground. Here we report a new quasi-simultaneous observation of 3C 84 with the Korean VLBI Network (KVN) at 86 GHz and the KVN and VLBI Exploration of Radio Astrometry Array (KaVA) at 43 GHz in 2016 February. We succeeded the first detection of N1 at 86 GHz and the data show that N1 still has an inverted spectrum between 43 and 86 GHz with its spectral index α ( ) of 1.19 ± 0.43, while the approaching lobe component has a steep spectrum with an index of −0.54 ± 0.30. Based on the measured flux asymmetry between the counter and approaching lobes, we constrain the averaged number density of the FFA foreground n e as . Those results suggest that the observational properties of the FFA foreground can be explained by the dense ionized gas in the circumnuclear disk and/or assembly of clumpy clouds at the central ∼1 pc region of 3C 84.