Constraints on Circumnuclear Disk through Free-Free Absorption in the
  Nucleus of 3C 84 with KaVA and KVN at 43 and 86 GHz
  The nearby bright radio galaxy 3C 84 at the center of Perseus cluster is one
of the ideal targets to explore the jet in active galactic nuclei (AGNs) and
its parsec-scale environment. A recent research of Fujita & Nagai revealed the
existence of the northern counter-jet component (N1) located at $\sim$ 2 mas
north from the central core in 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 VERA (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 $\alpha$ ($S_{\nu}
\propto \nu^{\alpha}$) of $1.19 \pm 0.43$, while the approaching lobe component
has the steep spectrum with the index of $-0.54 \pm 0.30$. Based on the
measured flux asymmetry between the counter and approaching lobes, we constrain
the averaged number density of the FFA foreground $n_{\rm e}$ as $1.8 \times
10^{4}~{\rm cm^{-3}} \lesssim n_{\rm e} \lesssim 1.0 \times 10^{6}~{\rm
cm^{-3}}$. 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 $\sim 1$ pc region of 3C 84.
