  Super-massive black hole binaries are expected to produce a GW signal in the
nano-Hertz frequency band which may be detected by PTAs in the coming years.
The signal is composed of both stochastic and individually resolvable
components. Here we develop a generic Bayesian method for the analysis of
resolvable sources based on the construction of `null-streams' which cancel the
part of the signal held in common for each pulsar (the Earth-term). For an
array of $N$ pulsars there are $N-2$ independent null-streams that cancel the
GW signal from a particular sky location. This method is applied to the
localisation of quasi-circular binaries undergoing adiabatic inspiral. We carry
out a systematic investigation of the scaling of the localisation accuracy with
signal strength and number of pulsars in the PTA. Additionally, we find that
source sky localisation with the International PTA data release one is vastly
superior than what is achieved by its constituent regional PTAs.
