LOFAR discovery of a double radio halo system in Abell 1758 and
  radio/X-ray study of the cluster pair
  Radio halos and radio relics are diffuse synchrotron sources that extend over
Mpc-scales and are found in a number of merger galaxy clusters. They are
believed to form as a consequence of the energy that is dissipated by
turbulence and shocks in the intra-cluster medium (ICM). However, the precise
physical processes that generate these steep synchrotron spectrum sources are
still poorly constrained. We present a new LOFAR observation of the double
galaxy cluster Abell 1758. This system is composed of A1758N, a massive cluster
hosting a known giant radio halo, and A1758S, which is a less massive cluster
whose diffuse radio emission is confirmed here for the first time. Our
observations have revealed a radio halo and a candidate radio relic in A1758S,
and a suggestion of emission along the bridge connecting the two systems which
deserves confirmation. We combined the LOFAR data with archival VLA and GMRT
observations to constrain the spectral properties of the diffuse emission. We
also analyzed a deep archival Chandra observation and used this to provide
evidence that A1758N and A1758S are in a pre-merger phase. The ICM temperature
across the bridge that connects the two systems shows a jump which might
indicate the presence of a transversal shock generated in the initial stage of
the merger.
