Unmasking the history of 3C 293 with LOFAR sub-arcsecond imaging
  Active galactic nuclei (AGNs) show episodic activity, evident in galaxies
that exhibit restarted radio jets. These restarted jets can interact with their
environment, leaving signatures on the radio spectral energy distribution.
Tracing these signatures requires resolved spectral index measurements over a
broad frequency range including low frequencies. We present such a study for
the radio galaxy 3C 293. Using the International LOFAR telescope (ILT) we
probed spatial scales as fine as ~0.2" at 144 MHz, and to constrain the
spectrum we combined these data with Multi-Element Radio Linked Interferometer
Network (MERLIN) and Very Large Array (VLA) archival data. In the inner lobes
(~2 kpc), we detect the presence of a spectral turnover that peaks at ~225 MHz
and is most likely caused by free-free absorption from the rich surrounding
medium. We confirm that these inner lobes are part of a jet-dominated young
radio source (spectral age $\lesssim$0.17 Myr), which is strongly interacting
with the rich interstellar medium (ISM) of the host galaxy. The outer lobes
(~100 kpc) have a spectral index of $\alpha$~0.6-0.8 from 144-4850 MHz with a
remarkably uniform spatial distribution and only mild spectral curvature
($\Delta\alpha\lesssim$ 0.2). We propose that intermittent fuelling and jet
flow disruptions are powering the mechanisms that keep the spectral index in
the outer lobes from steepening and maintain the spatial uniformity of the
spectral index. Overall, it appears that 3C 293 has gone through multiple (two
to three) epochs of activity. This study adds 3C 293 to the new sub-group of
restarted galaxies with short interruption time periods. This is the first time
a spatially resolved study simultaneously studies a young source as well as the
older outer lobes at such low frequencies. This illustrates the potential of
the ILT to expand such studies to a larger sample of radio galaxies.
