  We present the results of simulated injections testing the first Bayesian
search-pipeline capable of investigating the angular-structure of a
gravitational-wave (GW) background influencing pulsar signals. A stochastic
background of GWs from the incoherent superposition of many inspiraling
supermassive black hole binaries at nHz frequencies is likely to be the
dominant GW signal detectable by pulsar timing arrays (PTAs). Even though one
might expect a background composed of a high-redshift cosmological population
of sources to be fairly isotropic, deviations from isotropy may be indicative
of local GW hotspots or some form of continuous anisotropy in the
angular-distribution of GW-power. A GWB induces time-of-arrival deviations in
pulsar signals which are correlated between separated pulsars. In an isotropic
background this cross-correlation follows a distinctive relationship, known as
the Hellings and Downs curve, that depends only on the angular separation of
the pulsars. If the background is anisotropic, the cross-correlation is
different, but predictable, and also depends on the absolute position of the
pulsars. By simulating datasets containing GWBs with various anisotropic
configurations, we have explored the prospects for constraining anisotropy
using near future data. We find that at moderate to high signal to noise ratio
the assumption of isotropy is no longer an appropriate description of the
simulated background. Furthermore, we can recover the nature of the injected
anisotropy in a Bayesian parameter-estimation search, and propose a prior on
the anisotropy search-space motivated by the physicality of the implied
distribution of sources.
