Dynamical analysis of the complex radio structure in 3C 293: Clues on a
  rapid jet realignment in X-shaped radio galaxies
  Radio galaxies classified as X-shaped/winged, are characterised by two pairs
of extended and misaligned lobes, which suggest a rapid realignment of the jet
axis, for which a potential cause is still under debate. Here we analyse the
complex radio structure of 3C 293 winged source hosted by the post-merger
galaxy, which uniquely displays a significant asymmetry between the sizes of
the two pairs of lobes, indicating that an episode of jet realignment took
place only very recently. Based on all the available radio data for 3C 293, we
have performed a detailed spectral modelling for the older and younger lobes in
the system. In this way we derived the lobes' ages and jet energetics, which we
then compared to the accretion power in the source. We found that the 200
kpc-scale outer lobes of 3C 293 are ~60 Myr old and that jet activity related
to the formation of the outer lobes ceased within the last Myr. Meanwhile, the
inner 4 kpc-scale lobes, tilted by ~40 deg with respect to the outer ones, are
only about ~0.3 Myr old. The best model fits also return identical values of
the jet power supplying the outer and the inner structures. This power is of
the order of the maximum kinetic luminosity of a Blandford-Znajek jet for a
given black hole mass and accretion rate, but only in the case of relatively
low values of a black hole spin, a~0.2. The derived jet energetics and
timescales, along with the presence of two optical nuclei in 3C 293, all
provide a strong support to the Lense-Thirring precession model in which the
supermassive black hole spin, and therefore the jet axis, flips rapidly owing
to the interactions with the tilted accretion disk in a new tidal interaction
episode of the merging process. We further speculate that, in general, X-shape
radio morphology forms in post-merger systems that are rich in cold molecular
gas, and only host slowly spinning supermassive black holes.
