Searching for continuous gravitational waves in the Parkes Pulsar Timing Array data release 3

We present results from an all-sky search for continuous gravitational waves from individual supermassive binary black holes using the third data release of the Parkes Pulsar Timing Array (PPTA). Even though we recover a common-spectrum stochastic process, potentially induced by a nanohertz gravitational-wave background, we find no evidence of continuous waves. Therefore, we place upper limits on the gravitational-wave strain amplitude: in the most sensitive frequency range around 10 nHz, we obtain a sky-averaged 95% credibility upper limit of ≈ 7 × 10⁻¹⁵. Our search is sensitive to supermassive binary black holes with a chirp mass of ≥10⁹ M_⊙ up to a luminosity distance of 50 Mpc for our least sensitive sky direction and 200 Mpc for the most sensitive direction. This work provides at least 4 times better sensitivity in the 1–200 nHz frequency band than our last search based on the PPTA’s first data release. We expect that PPTA will continue to play a key role in detecting continuous gravitational waves in the exciting era of nanohertz gravitational-wave astronomy.