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We report about a 230 GHz very long baseline interferometry (VLBI) fringefinder observation of blazar 3C 279 with the APEX telescope in Chile, thephased submillimeter array (SMA), and the SMT of the Arizona Radio Observatory(ARO). We installed VLBI equipment and measured the APEX station position to 1cm accuracy (1 sigma). We then observed 3C 279 on 2012 May 7 in a 5 hour 230GHz VLBI track with baseline lengths of 2800 M$\lambda$ to 7200 M$\lambda$ anda finest fringe spacing of 28.6 micro-arcseconds. Fringes were detected on allbaselines with SNRs of 12 to 55 in 420 s. The correlated flux density on thelongest baseline was ~0.3 Jy/beam, out of a total flux density of 19.8 Jy.Visibility data suggest an emission region <38 uas in size, and at least twocomponents, possibly polarized. We find a lower limit of the brightnesstemperature of the inner jet region of about 10^10 K. Lastly, we find an upperlimit of 20% on the linear polarization fraction at a fringe spacing of ~38uas. With APEX the angular resolution of 230 GHz VLBI improves to 28.6 uas.This allows one to resolve the last-photon ring around the Galactic Centerblack hole event horizon, expected to be 40 uas in diameter, and probe radiojet launching at unprecedented resolution, down to a few gravitational radii ingalaxies like M 87. To probe the structure in the inner parsecs of 3C 279 indetail, follow-up observations with APEX and five other mm-VLBI stations havebeen conducted (March 2013) and are being analyzed.

First 230 GHz VLBI Fringes on 3C 279 using the APEX Telescope