Millimeter-VLBI Observations of Low-luminosity Active Galactic Nuclei with Source-frequency Phase Referencing

We report millimeter-VLBI results of low-luminosity active galactic nuclei (M 84 and M 87) up to 88 GHz with source-frequency phase-referencing observations. detected the weak VLBI core obtained first image at GHz. The derived brightness temperature was about 7.2$\times$10$^9$ K, which could serve as a lower limit down 30 Schwarzschild radii still un-resolved in our successfully determined core-shifts 87 22-44 44-88 through technique. jet apex be deduced 46 $\mu$as upstream 43 from core-shift measurements. estimated magnetic field strength is 4.8$\pm$2.4 G, same magnitude 1-30 G near event horizon probed by Event Horizon Telescope.