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

TL;DR

This paper establishes upper limits on gravitational waves from supermassive black-hole binaries in the microhertz range using FAST pulsar timing data, extending the frequency coverage beyond traditional PTA bands.

Contribution

It presents the first constraints on microhertz gravitational waves using FAST data, focusing on a less explored frequency band and specific pulsar observations.

Findings

Sky-average 95% upper limit at 1μHz is 1.26×10⁻¹²

Directional upper limit towards PSR J1713+5307 is 4.77×10⁻¹³

Demonstrates feasibility of using FAST for microhertz GW searches

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 $\mu$Hz GW frequency band between $10^{-7}$ and $3\times10^{-6}$ 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 $\mu$Hz band coverage. Our sky-average continuous source upper limit at the 95% confidence level at 1$\mu$Hz is 1.26$\times10^{-12}$, while the same limit in the direction of the pulsar is 4.77$\times10^{-13}$.