Searching for isotropic stochastic gravitational-wave background in the international pulsar timing array second data release

Abstract

We search for isotropic stochastic gravitational-wave background (SGWB) in the International Pulsar Timing Array second data release. By modeling the SGWB as a power-law, we find very strong Bayesian evidence for a common-spectrum process, and further this process has scalar transverse (ST) correlations allowed in general metric theory of gravity as the Bayes factor in favor of the ST-correlated process versus the spatially uncorrelated common-spectrum process is 30 ± 2. The median and the 90% equal-tail amplitudes of ST mode are , or equivalently the energy density parameter per logarithm frequency is , at frequency of 1 year−1. However, we do not find any statistically significant evidence for the tensor transverse (TT) mode and then place the 95% upper limits as , or equivalently , at frequency of 1 year−1.