Restarting activity in the nucleus of PBC J2333.9-2343: an extreme case
  of jet realignment
  PBC J2333.9-2343 is a giant radio galaxy which shows different
characteristics at different wavebands that are difficult to explain within the
actual generic schemes of unification of active galactic nuclei (AGN), thus
being a good candidate to host different phases of nuclear activity. We aim at
disentangling the nature of this AGN by using simultaneous multiwavelength
data. We obtained data in 2015 from the Very Long Baseline Array (VLBA), the
San Pedro M\'{a}rtir telescope, and the XMM-Newton}observatories. This allows
the study of the nuclear parts of the galaxy through its morphology and
spectra, as well as the analysis of the spectral energy distribution (SED). We
also reanalysed optical data from the San Pedro M\'{a}rtir telescope from 2009
previously presented in Parisi et al. (2012) for a homogeneous comparison. At
X-ray frequencies, the source is unabsorbed. The optical spectra are of a type
1.9 AGN, both in 2009 and 2015, although showing a broader component in 2015.
The VLBA radio images show an inverted spectrum with self-absorbed, optically
thick compact core and steep spectrum, optically thin jet. The SED resembles
that of typical blazars and is best represented by an external Compton (EC)
model with a viewing angle of $\sim$ 3-6 degrees. The apparent size of the
large scale structure of PBC J2333.9-2343 must correspond to an intrinsic
deprojected value of $\sim 7$ Mpc for $\theta_v<10^\circ$, and to $> 13$ Mpc
for $\theta_v<5^\circ$, a value much larger than the bigger giant radio galaxy
known (4.5 Mpc). The above arguments suggest that PBC J2333.9-2343 has
undergone through a new episode of nuclear activity and that the direction of
the new jet has changed, in the plane of the sky and is now pointing towards
us, making this source from being a radio galaxy to become a blazar, a very
exceptional case of restarting activity.
