Research Note

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

¹ Max Planck Institute for Radio Astronomy (MPIfR), Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: aroy@mpifr.de; tkrichbaum@mpifr.de
² European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Vitacura, Santiago 19, Chile
³ Atacama Pathfinder Experiment, Parcela #85, Sequitor, San Pedro de Atacama, Chile
⁴ Department of Earth and Space Sciences, Chalmers University of Technology, Onsala Space Observatory, 439 92 Onsala, Sweden
⁵ Istituto di Radioastronomia, Istituto Nazionale di Astrofisica, 96017 Noto, Italy
⁶ MIT Haystack Observatory, Westford, MA 01886, USA
⁷ Arizona Radio Observatory (ARO), University of Arizona, Tucson, 85721 Arizona, USA
⁸ Harvard Smithsonian Center for Astrophysics (CfA), Cambridge, MA 02138, USA
⁹ Institut de Radioastronomie Millimétrique (IRAM), 38400 Saint Martin d’ Hères, France
¹⁰ Observatorio del Pico Veleta, Estación RadioAstronómica IRAM-IGN, Granada, Spain
¹¹ SP Technical Research Institute of Sweden, 50115 Borås, Sweden
¹² Institute for Astrophysical Research, Boston University, Boston, MA 02215, USA
¹³ Institute of Geodesy and Geoinformation, University of Bonn, 53113 Bonn, Germany
¹⁴ Institute of Astronomy and Astrophysics, Academia Sinica, PO Box 23-141, 10617 Taipei, Taiwan
¹⁵ Korea Astronomy and Space Science Institute, 776, Daedeokdae-ro, Yuseong-gu, 305-348 Daejeon, Republic of Korea
e-mail: jwagner@kasi.re.kr

Received: 10 February 2014
Accepted: 10 June 2015

Abstract

Aims. We report about a 230 GHz very long baseline interferometry (VLBI) fringe finder observation of blazar 3C 279 with the APEX telescope in Chile, the phased submillimeter array (SMA), and the SMT of the Arizona Radio Observatory (ARO).

Methods. We installed VLBI equipment and measured the APEX station position to 1 cm accuracy (1σ). We then observed 3C 279 on 2012 May 7 in a 5 h 230 GHz VLBI track with baseline lengths of 2800 Mλ to 7200 Mλ and a finest fringe spacing of 28.6 μas.

Results. Fringes were detected on all baselines with signal-to-noise ratios of 12 to 55 in 420 s. The correlated flux density on the longest baseline was ~0.3 Jy beam^-1, out of a total flux density of 19.8 Jy. Visibility data suggest an emission region ≲ 38 μas in size, and at least two components, possibly polarized. We find a lower limit of the brightness temperature of the inner jet region of about 10¹⁰ K. Lastly, we find an upper limit of 20% on the linear polarization fraction at a fringe spacing of ~ 38 μas.

Conclusions. With APEX the angular resolution of 230 GHz VLBI improves to 28.6 μas. This allows one to resolve the last-photon ring around the Galactic Center black hole event horizon, expected to be 40 μas in diameter, and probe radio jet launching at unprecedented resolution, down to a few gravitational radii in galaxies like M 87. To probe the structure in the inner parsecs of 3C 279 in detail, follow-up observations with APEX and five other mm-VLBI stations have been conducted (March 2013) and are being analyzed.