A search for variable and transient radio sources in the extended
  Chandra Deep Field South at 5.5 GHz
  We present a three epoch survey for transient and variables in the extended
Chandra Deep Field South at 5.5 GHz with the Australia Telescope Compact Array.
A region covering $\sim$0.3 deg$^{2}$ was observed on timescales of 2.5 months
and 2.5 years and typical sensitivities 12.1 $-$ 17.1 $\mu$Jy beam$^{-1}$
(1$\sigma$) were achieved. This survey represents the deepest search for
transient and variable radio sources at 5.5 GHz. In total 124 sources were
detected above the 5.5$\sigma$ level. One highly variable radio source was
found with $\Delta S > 50%$ implying a surface density of $\sim$3 deg$^{-2}$. A
further three radio sources were found with lower levels of variability
equating to a surface density of $\sim$13 deg$^{-2}$ above a detection
threshold of 82.3 $\mu$Jy. All of the variable sources have inverted radio
spectra (between 1.4 and 5.5 GHz) and are associated with active galactic
nuclei. We conclude that these variables are young gigahertz peaked-spectrum
sources with active and self-absorbed radio jets. We explore the variability
completeness of this sample and conclude that the fairly low levels of
variability would only be detectable in 3$-$25% of all sources within the
field. No radio transients were detected in this survey and we place an upper
limit on the surface density of transient events $ < 7.5$ deg$^{-2}$ above a
detection threshold of 68.8~$\mu$Jy.
