Multiband RadioAstron space VLBI imaging of the jet in quasar S5 0836+710^⋆

¹ Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
e-mail: alobanov@mpifr-bonn.mpg.de
² Institut für Experimentalphysik, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg, Germany
³ Departament d’Astronomia i Astrofísica, Universitat de València, C/ Dr. Moliner, 50, 46100 Burjassot, València, Spain
⁴ Observatori Astronòmic, Universitat de València, C/ Catedràtic Beltrán 2, 46091 Paterna, València, Spain
⁵ INAF – Istituto di Astrofisica e Planetologia Spaziali, Via Fosso del Cavaliere 100, 00133 Rome, Italy
⁶ Deutsches GeoForschungsZentrum, Telegrafenberg, 14473 Potsdam, Germany
⁷ Technical University of Berlin, Straße des 17. Juni 135, 10623 Berlin, Germany
⁸ Instituto de Astrofísica de Andalucía, CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
⁹ Jodrell Bank Observatory (JBO), The University of Manchester, Macclesfield SK11 9DL, UK
¹⁰ Astro Space Center of Lebedev Physical Institute, Profsoyuznaya 84/32, 117997 Moscow, Russia
¹¹ Moscow Institute of Physics and Technology, Dolgoprudny, Institutsky Per., 9, Moscow Region 141700, Russia
¹² Aalto University Department of Electronics and Nanoengineering, PL 15500, 00076 Aalto, Finland
¹³ Aalto University Metsähovi Radio Observatory, 02540 Kylmälä, Finland
¹⁴ National Radio Astronomy Observatory, PO Box O, Socorro, NM 87801, USA
¹⁵ Department of Physics and Astronomy, University of New Mexico, Albuquerque, NM 87131, USA

Received: 30 January 2019
Accepted: 25 October 2019

Abstract

Context. Detailed studies of relativistic jets in active galactic nuclei (AGN) require high-fidelity imaging at the highest possible resolution. This can be achieved using very long baseline interferometry (VLBI) at radio frequencies, combining worldwide (global) VLBI arrays of radio telescopes with a space-borne antenna on board a satellite.

Aims. We present multiwavelength images made of the radio emission in the powerful quasar S5 0836+710, obtained using a global VLBI array and the antenna Spektr-R of the RadioAstron mission of the Russian Space Agency, with the goal of studying the internal structure and physics of the relativistic jet in this object.

Methods. The RadioAstron observations at wavelengths of 18 cm, 6 cm, and 1.3 cm are part of the Key Science Program for imaging radio emission in strong AGN. The internal structure of the jet is studied by analyzing transverse intensity profiles and modeling the structural patterns developing in the flow.

Results. The RadioAstron images reveal a wealth of structural detail in the jet of S5 0836+710 on angular scales ranging from 0.02 mas to 200 mas. Brightness temperatures in excess of 10¹³ K are measured in the jet, requiring Doppler factors of ≥100 for reconciling them with the inverse Compton limit. Several oscillatory patterns are identified in the ridge line of the jet and can be explained in terms of the Kelvin–Helmholtz (KH) instability. The oscillatory patterns are interpreted as the surface and body wavelengths of the helical mode of the KH instability. The interpretation provides estimates of the jet Mach number and of the ratio of the jet to the ambient density, which are found to be M_j ≈ 12 and η ≈ 0.33. The ratio of the jet to the ambient density should be conservatively considered an upper limit because its estimate relies on approximations.