Mapping The Supermassive Binary Black-Hole Sky With Pulsar Timing Arrays

Within the next several years, pulsar-timing array programs such as NANOGrav and the International Pulsar Timing Array will usher in the next era of gravitational-wave astronomy through the detection of a stochastic background of nanohertz-frequency gravitational waves, originating from a cosmological population of inspiraling supermassive binary black holes. While the source positions will likely be isotropic to a good approximation, the gravitational-wave angular power distribution will be anisotropic, with the most massive and nearby binaries producing signals that resound above the background. We show how tailored Bayesian searches can reconstruct maps of the gravitational-wave sky at nanohertz frequencies, localizing bright binaries while simultaneously modeling the background signal from the less massive and more distant ensemble. We discuss the prospects for measuring gravitational-wave anisotropy in the near future, and the modeling optimizations that will take us there.