Gravitational Lens System as a Long Baseline Detector of Extremely Low Frequency Primordial Gravitational Wave

The effect of extremely low frequency primordial gravitational wave with arbitrary direction of propagation on a non-aligned gravitational lens system is investigated. From the point of view of real astrophysical lens model, singular isothermal sphere lens model is adopted in the gravitational lens system. The results show that, under the perturbation from extremely low frequency primordial gravitational wave, time delay in the gravitational lens system could strongly deviate from that deduced from theoretical model. This means that the strongly deviate time delay could be the imprint of extremely low frequency primordial gravitational wave on gravitational lens system, indicating that gravitational lens system could be used as a long baseline detector to detect extremely low frequency primordial gravitational wave.