Upper limits on a radio halo in Abell 3667 at 1.4 GHz
  The presence of a radio halo in the massive, merging cluster Abell 3667 has
recently become a focus of debate in the literature following a putative halo
detection at 2.4 GHz despite a lack of detection at a range of lower
frequencies between 120 MHz and 1.8 GHz. Here we develop a new method to place
limits on radio haloes via generation of a realistic synthetic halo based on
the brightness distribution of real haloes. The model generated extends on
previous methods in the literature producing a single elliptical halo model,
capable of being injected into mosaic as well as single observations. Applying
this model to the deepest data available 1.4 GHz data for A3667 we derive an
upper limit halo power of P$_{1.4} \leq 5.55 \times 10^{23}$ W Hz$^{-1}$. We
discuss the result in the context of current scaling relation between the X-ray
and radio properties of galaxy clusters and find that the lack of a halo in
A3667 places the cluster on the border of the so-called `off-state' region in
which clusters are expected not to host any diffuse emission.
