Resolving multiple supermassive black hole binaries with pulsar timing
  arrays
  We study the capability of a pulsar timing array (PTA) to individually
resolve and localize in the sky monochromatic gravitational wave (GW) sources.
Given a cosmological population of inspiralling massive black hole binaries,
their observable signal in the PTA domain is expected to be a superposition of
several nearly-monochromatic GWs of different strength. In each frequency bin,
the signal is neither a stochastic background nor perfectly resolvable in its
individual components. In this context, it is crucial to explore how the
information encoded in the spatial distribution of the array of pulsars might
help recovering the origin of the GW signal, by resolving individually and
locating in the sky the strongest sources. In this paper we develop a
maximum-likelihood based method finalized to this purpose. We test the
algorithm against noiseless data showing that up to P/3 sources can be resolved
and localized in the sky by an array of P pulsars. We validate the code by
performing blind searches on both noiseless and noisy data containing an
unknown number of signals with different strengths. Even without employing any
proper search algorithm, our analysis procedure performs well, recovering and
correctly locating in the sky almost all the injected sources.
