hinese Pulsar Timing Array Upper Limits on Microhertz Gravitational Waves from Supermassive Black-hole Binaries Using PSR J1713+0747 FAST Data

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, in the context of the Chinese Pulsar Timing Array project. We focus on circular orbits in theHz GW frequency band between 107and 3106Hz. 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 2019 August and 2021 April. A dense observation campaign was carried out in 2020 September to allow for theHz band coverage. Our sky-averaged continuous source upper limit at the 95% confidence level at 1Hz is 1.261012, while the same limit in the direction of the pulsar is 4.771013.