Tracing low-mass galaxy clusters with radio relics: the discovery of
  Abell 3527-bis
  Galaxy clusters undergo mergers that can generate extended radio sources
called radio relics. Radio relics are the consequence of merger-induced shocks
that propagate in the intra cluster medium (ICM). In this paper we analyse the
radio, optical and X-ray data from a candidate galaxy cluster that has been
selected from the radio emission coming from a candidate radio relic detected
in NRAO VLA Sky Survey (NVSS). Our aim is to clarify the nature of this source
and prove that under certain conditions radio emission from radio relics can be
used to trace relatively low-mass galaxy clusters. We have observed the
candidate galaxy cluster with the Giant Meterwave Radio Telescope (GMRT) at
three different frequencies. These datasets have been analysed together with
archival data from ROSAT in the X-ray and with archival data from the Gamma-Ray
Burst Optical/Near-Infrared Detector (GROND) telescope in four different
optical bands. We confirm the presence of a 1 Mpc long radio relic located in
the outskirts of a previously unknown galaxy cluster. We confirm the presence
of the galaxy cluster through dedicated optical observations and using archival
X-ray data. Due to its proximity and similar redshift to a known Abell cluster,
we named it: Abell 3527-bis. The galaxy cluster is among the least massive
cluster known to host a radio relic. We showed that radio relics can be
effectively used to trace a subset of relatively low-mass galaxy clusters that
might have gone undetected in X-ray or Sunyaev-Zel'dovich (SZ) surveys. This
technique might be used in future deep, low-frequency surveys as those carried
on by LOFAR, uGMRT and, ultimately, SKA.
