Research On Sensitivity Curve Of Gravitational Wave Background Based On Pulsar Timing Array

One of the main targets of the Pulsar Timing Array(PTA)is to detect the isotropic,stochastic gravitational wave background(GWB).In order to study whether the errors caused by the ephemeris and reference time will affect the detection of GWB,and the extent of the effects,we carried out a study of the gravitational wave background sensi-tivity curve based on pulsar timing,including three research work:study the influence of solar system ephemeris,reference time,number of pulsars and observation duration on gravitational wave sensitivity curve.We first studied and improved the calculation of the integrated sensitivity curve.We found that at the most sensitive frequency band of the PTA,different integration step sizes would cause differences in the sensitivity curve,and an excessive integration step size would overestimate the sensitivity curve.When the value of the integration step is small enough,the integration sensitivity curve will converge to a stable state.For simulated timing data,we first discussed the effect of three different reference atomic time scales on the integrated sensitivity curve in pulsar timing.The results show that when TT(BIPM2018)is selected as the reference time scale,the lowest point ofthe sensitivity curve can reach 1.5 × 10-12,which is about three times higher than when using TT(TAI)time scale.Second,we analyzed the impact of different versions of the DE ephemeris.The lowest point of the sensitivity curve based on DE200 is about 2 × 10-10,which is 2 orders of magnitude worse than the sensitivity curve based on DE405.The results based on DE436 are very close to those based on DE405,and are both around 1.5 × 10-12.For the actual observation data,we selected millisecond pulsars with a time span of more than 10 years from the first data released by the International Pulsar Timing Array(IPTA),and retained the timing residuals of all participating pulsars according to the common observation duration.The weighted root mean square of the obtained timing residuals is used as timing noise to calculate the corresponding noise power spec-tral density,and the signal-to-noise ratio of the two pulsar subsets is calculated using the maximum and low gravitational wave amplitudes allowed by the observation,re-spectively.Observations of more millisecond pulsars have improved the performance of detecting background gravitational waves.In addition,the lowest point of the sen-sitivity curve of the 15-year data set is about 8 × 10-11,which is about an order of magnitude higher than the 10-year data set's ability to detect background gravitational waves.And in the whole observation band,the ability of more pulsars to detect back-ground gravitational wave sources is high.The difference between the sensitivity curves caused by different reference clocks and ephemeris under simulated data is obviously different.Due to the unresolvable red noise in the actual observation data,the errors caused by different reference time and ephemeris are overwhelmed by other noises,but we believe that as the accuracy of timing observation increases,the difference between the sensitivity curve of the observed data caused by the reference clock and ephemeris will become more and more obvious.