Discovery of Millimeter-Wave Excess Emission in Radio-Quiet Active
  Galactic Nuclei
  The physical origin of radio emission in Radio Quiet Active Galactic Nuclei
(RQ AGN) remains unclear, whether it is a downscaled version of the
relativistic jets typical of Radio Loud (RL) AGN, or whether it originates from
the accretion disk. The correlation between 5 GHz and X-ray luminosities of RQ
AGN, which follows $L_R = 10^{-5}L_X$ observed also in stellar coronae,
suggests an association of both X-ray and radio sources with the accretion disk
corona. Observing RQ AGN at higher (mm-wave) frequencies, where synchrotron
self absorption is diminished, and smaller regions can be probed, is key to
exploring this association. Eight RQ AGN, selected based on their high X-ray
brightness and variability, were observed at 95 GHz with the CARMA and ATCA
telescopes. All targets were detected at the $1-10$ mJy level. Emission excess
at 95~GHz of up to $\times 7$ is found with respect to archival low-frequency
steep spectra, suggesting a compact, optically-thick core superimposed on the
more extended structures that dominate at low frequencies. Though unresolved,
the 95 GHz fluxes imply optically thick source sizes of $10^{-4}-10^{-3}$ pc,
or $\sim 10 - 1000$ gravitational radii. The present sources lie tightly along
an $L_R$ (95 GHz) = $10^{-4}L_X$ (2$-$10 keV) correlation, analogous to that of
stellar coronae and RQ AGN at 5 GHz, while RL AGN are shown to have higher $L_R
/ L_X$ ratios. The present observations argue that simultaneous mm-wave and
X-ray monitoring of RQ AGN features a promising method for understanding
accretion disk coronal emission.
