RadioAstron reveals a spine-sheath jet structure in 3C 273
G. Bruni (Radio Observatory Medicina)
J. L. Gómez (Instituto de Astrofísica de Andalucía - CSIC)
L. Vega-García (Max-Planck-Institute for Radio Astronomy)
A. P. Lobanov (Max-Planck-Institute for Radio Astronomy, Moscow Institute of Physics and Technology)
A. Fuentes (Instituto de Astrofísica de Andalucía - CSIC)
T. Savolainen (Max-Planck-Institute for Radio Astronomy, Aalto University)
Y. Y. Kovalev (Russian Academy of Sciences, Max-Planck-Institute for Radio Astronomy, Moscow Institute of Physics and Technology)
M. Perucho (Universitat Politécnica de Valencia)
L. I. Gurvits (CSIRO - Oceans and Atmosphere, Wembley, TU Delft - Aerospace Engineering, Joint Institute for VLBI ERIC)
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Abstract
We present Space-VLBI RadioAstron observations at 1.6 GHz and 4.8 GHz of the flat spectrum radio quasar 3C 273, with detections on baselines up to 4.5 and 3.3 Earth Diameters, respectively. Achieving the best angular resolution at 1.6 GHz to date, we have imaged limb-brightening in the jet, not previously detected in this source. In contrast, at 4.8 GHz, we detected emission from a central stream of plasma, with a spatial distribution complementary to the limb-brightened emission, indicating an origin in the spine of the jet. While a stratification across the jet width in the flow density, internal energy, magnetic field, or bulk flow velocity are usually invoked to explain the limb-brightening, the different jet structure detected at the two frequencies probably requires a stratification in the emitting electron energy distribution. Future dedicated numerical simulations will allow the determination of which combination of physical parameters are needed to reproduce the spine-sheath structure observed by Space-VLBI with RadioAstron in 3C 273.