Accretion-ejection morphology of the microquasar SS 433 resolved at sub-au scale^⋆

¹ Univ. Grenoble Alpes, CNRS, IPAG, 38000 Grenoble, France
e-mail: pierre-olivier.petrucci@univ-grenoble-alpes.fr
² Max Planck Institute for extraterrestrial Physics, Giessenbachstr., 85748 Garching, Germany
³ LESIA, Observatoire de Paris, PSL Research University, CNRS, Sorbonne Universités, UPMC Univ. Paris 06, Univ. Paris Diderot, Sorbonne Paris Cité, 75005 Paris, France
⁴ Unidad Mixta Internacional Franco-Chilena de Astronomía (CNRS UMI 3386), Departamento de Astronomía, Universidad de Chile, Camino El Observatorio 1515, Las Condes, Santiago, Chile
⁵ European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
⁶ CENTRA and Universidade de Lisboa – Faculdade de Ciências, Campo Grande, 1749-016 Lisboa, Portugal
⁷ CENTRA and Universidade do Porto – Faculdade de Engenharia, 4200-465 Porto, Portugal
⁸ Observatoire de Genève, Université de Genève, 51 Ch. des Maillettes, 1290 Versoix, Switzerland
⁹ Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
¹⁰ Hubble Fellow, Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
¹¹ European Southern Observatory, Casilla 19001, Santiago 19, Chile
¹² 1. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
¹³ Max-Planck-Institute for Radio Astronomy, Auf dem Hügel 69, 53121 Bonn, Germany
¹⁴ Department of Physics, Le Conte Hall, University of California, Berkeley, CA 94720, USA

Received: 25 April 2017
Accepted: 12 May 2017

Abstract

We present the first optical observation of the microquasar SS 433 at sub-milliarcsecond (mas) scale obtained with the GRAVITY instrument on the Very Large Telescope interferometer (VLTI). The 3.5-h exposure reveals a rich K-band spectrum dominated by hydrogen Brγand He i lines, as well as (red-shifted)emission lines coming from the jets. The K-band-continuum-emitting region is dominated by a marginally resolved point source (<1 mas) embedded inside a diffuse background accounting for 10% of the total flux. The jet line positions agree well with the ones expected from the jet kinematic model, an interpretation also supported by the consistent sign (i.e., negative/positive for the receding/approaching jet component) of the phase shifts observed in the lines. The significant visibility drop across the jet lines, together with the small and nearly identical phases for all baselines, point toward a jet that is offset by less than 0.5 mas from the continuum source and resolved in the direction of propagation, with a typical size of 2 mas. The jet position angle of ~80° is consistent with the expected one at the observation date. Jet emission so close to the central binary system would suggest that line locking, if relevant to explain the amplitude and stability of the 0.26c jet velocity, operates on elements heavier than hydrogen. The Brγprofile is broad and double peaked. It is better resolved than the continuum and the change of the phase signal sign across the line on all baselines suggests an East-West-oriented geometry similar to the jet direction and supporting a (polar) disk wind origin.