Optimal filters for the construction of the ensemble pulsar time

An algorithm of the ensemble pulsar time based on the optimal Wiener filtration method has been constructed. This algorithm allows the separation of the contributions to the post-fit pulsar timing residuals of the atomic clock and the pulsar itself. Filters were designed using the cross- and auto-covariance functions of the timing residuals. The method has been applied to the timing data of millisecond pulsars PSR B1855+09 and B1937+21 and allowed the filtering out of the atomic-scale component from the pulsar data. Direct comparison of the terrestrial time TT(BIPM06) and the ensemble pulsar time PTens revealed that the fractional instability of TT(BIPM06)-PTens is equal to sigma(z) = (0.8 +/- 1.9) x 10(-15). Based on the sigma(z) statistics of TT(BIPM06)-PTens, a new limit of the energy density of the gravitational wave background was calculated to be equal to Omega(g)h(2) similar to 3 x 10(-9).