Note the narrowness of the sensitivity region (bounded by the functions γ max, γ min) within which the sensitivity of the data combination I ( t ) is defined. The sensitivity of a single-telescope experiment (blue curve), as well as the current estimates of the upper- and lower bounds (green and red line respectively) on the amplitude radiated by an ensemble of super-massive black-hole binaries are included. The pulsars have been assumed to be at equal distances from Earth (1 kpc). Gravitational wave sensitivity expressed as the ratio between the square-root of the one-sided power spectral density of the noise and the r.m.s. We find the resulting optimal signal-to-noise ratio to be more than one order of magnitude larger than that obtainable by correlating pairs of timing data from arrays of equal size. Since arrays can generate pairs of clock and ephemeris-free timing combinations that are no longer affected by correlated noises, we implement with them the cross-correlation statistic to search for an isotropic stochastic gravitational wave background. After deriving the expressions that reconstruct these noises from the timing data, we estimate the gravitational wave sensitivity of our proposed processing technique to single-source signals to be at least one order of magnitude higher than that achievable by directly processing the timing data from an equal-size array. These noises are the dominant sources of correlated timing fluctuations in the lower-part ( ≈ 10 − 9 − 10 − 8 Hz) of the gravitational wave band accessible by pulsar timing experiments. We propose a data processing technique to cancel monopole and dipole noise sources (such as clock and ephemeris noises, respectively) in pulsar timing array searches for gravitational radiation.

Ephemeris free