Ultra-steep spectrum emission in the merging galaxy cluster Abell 1914
  A number of radio observations have revealed the presence of large
synchrotron-emitting sources associated with the intra-cluster medium. There is
strong observational evidence that the emitting particles have been
(re-)accelerated by shocks and turbulence generated during merger events. The
particles that are accelerated are thought to have higher initial energies than
those in the thermal pool but the origin of such mildly relativistic particles
remains uncertain and needs to be further investigated. The galaxy cluster
Abell 1914 is a massive galaxy cluster in which X-ray observations show clear
evidence of merging activity. We carried out radio observations of this cluster
with the LOw Frequency ARay (LOFAR) at 150 MHz and the Giant Metrewave Radio
Telescope (GMRT) at 610 MHz. We also analysed Very Large Array (VLA) 1.4 GHz
data, archival GMRT 325 MHz data, CFHT weak lensing data and Chandra
observations. Our analysis shows that the ultra-steep spectrum source (4C38.39;
$\alpha \lesssim -2$), previously thought to be part of a radio halo, is a
distinct source with properties that are consistent with revived fossil plasma
sources. Finally, we detect some diffuse emission to the west of the source
4C38.39 that could belong to a radio halo.
