Chinese Pulsar Timing Array upper limits on microhertz gravitational waves from supermassive black-hole binaries using PSR J1713+0747 FAST data

Abstract

We derive the gravitational-wave (GW) strain upper limits from resolvable supermassive black-hole binaries using the data from the Five-hundred-meter Aperture Spherical radio Telescope (FAST), in the context of the Chinese Pulsar Timing Array project. We focus on circular orbits in the $\hat{I}¼$Hz GW frequency band between $10^{-7}$ and $3\times 10^{-6}$ Hz. This frequency band is higher than the traditional pulsar timing array band and is less explored. We used the data of the millisecond pulsar PSR J1713+5307 observed between August 2019 and April 2021. A dense observation campaign was carried out in September 2020 to allow for the $\hat{I}¼$Hz band coverage. Our sky-average continuous source upper limit at the 95% confidence level at 1$\hat{I}¼$Hz is 1.26$\times 10^{-12}$, while the same limit in the direction of the pulsar is 4.77$\times 10^{-13}$.

Accepted by Research in Astronomy and Astrophysics (RAA)