  Highly accreting quasars are quite luminous in the X-ray and optical regimes.
While, they tend to become radio quiet and have optically thin radio spectra.
Among the known quasars, IRAS F11119+3257 is a supercritical accretion source
because it has a bolometric luminosity above the Eddington limit and extremely
powerful X-ray outflows. To probe its radio structure, we investigated its
radio spectrum between 0.15 and 96.15 GHz and performed very-long-baseline
interferometric (VLBI) observations with the European VLBI Network (EVN) at
1.66 and 4.93 GHz. The deep EVN image at 1.66 GHz shows a two-sided jet with a
projected separation about two hundred parsec and a very high flux density
ratio of about 290. Together with the best-fit value of the integrated spectral
index of -1.31+/-0.02 in the optically thin part, we infer that the approaching
jet has an intrinsic speed at least 0.57 times of the light speed. This is a
new record among the known all kinds of super-Eddington accreting sources and
unlikely accelerated by the radiation pressure. We propose a scenario in which
IRAS F11119+3257 is an unusual compact symmetric object with a small jet
viewing angle and a radio spectrum peaking at 0.53+/-0.06 GHz mainly due to the
synchrotron self-absorption.
