The great Kite in the sky: a LOFAR observation of the radio source in
  Abell 2626
  The radio source at the center of the galaxy cluster Abell 2626, also known
as the Kite, stands out for its unique morphology composed of four, symmetric
arcs. Previous studies have probed the properties of this source at different
frequencies and its interplay with the surrounding thermal plasma, but the
puzzle of its origin is still unsolved. We use new LOw Frequency ARray (LOFAR)
observation from the LOFAR Two-meter Sky Survey at 144 MHz to investigate the
origin of the Kite.} We present a detailed analysis of the new radio data which
we combined with archival radio and X-ray observations. We have produced a new,
resolved spectral index map of the source with a resolution of 7$''$ and we
studied the spatial correlation of radio and X-ray emission to investigate the
interplay between thermal and non-thermal plasma. The new LOFAR data have
changed our view of the Kite by discovering two steep-spectrum ($\alpha<-1.5$)
plumes of emission connected to the arcs. The spectral analysis shows, for the
first time, a spatial trend of the spectrum along the arcs with evidence of
curved synchrotron spectra and a spatial correlation with the X-ray surface
brightness. On the basis of our results, we propose that the Kite was
originally an X-shaped radio galaxy whose fossil radio plasma, after the end of
the activity of the central active galactic nucleus, has been compressed due to
motions of the thermal plasma in which it is encompassed. The interplay between
the compression and advection of the fossil plasma, with the restarting of the
nuclear activity of the central galaxy, could have enhanced the radio emission
of the fossil plasma producing the arcs of the Kite. We present also the first,
low-frequency observation of a jellyfish galaxy in the same field, in which we
detect extended, low-frequency emission without a counterpart at higher
frequencies.
