We present the sensitivity of the Parkes Pulsar Timing Array to gravitational waves emitted by individual super-massive black-hole binary systems in the early phases of coalescing at the cores of merged galaxies .
Our analysis includes a detailed study of the effects of fitting a pulsar timing model to non-white timing residuals .
Pulsar timing is sensitive at nanoHertz frequencies and hence complementary to LIGO and LISA .
We place a sky-averaged constraint on the merger rate of nearby ( z < 0.6 ) black-hole binaries in the early phases of coalescence with a chirp mass of 10 ^ { 10 } \mathrm { M } _ { \odot } of less than one merger every seven years .
The prospects for future gravitational-wave astronomy of this type with the proposed Square Kilometre Array telescope are discussed .