Searching for the Nano-Hertz Stochastic Gravitational Wave Background with the Chinese Pulsar Timing Array Data Release I

TLDR

Observing and timing millisecond pulsars with high rotational stability enables the direct detection of gravitational waves through spatial correlations in their times‑of‑arrival. This article outlines the forthcoming CPTA Data Release 1 papers and anticipates that future International Pulsar Timing Array analyses and subsequent CPTA releases will better test the nHz gravitational‑wave background. The Chinese Pulsar Timing Array conducts observations with Chinese radio telescopes, notably the Five‑hundred‑meter Aperture Spherical radio Telescope, to monitor millisecond pulsars for gravitational‑wave signatures. Statistical analysis of CPTA DR1 data reveals a correlated signal with amplitude log A_c = –14.4 (+1.0/–2.8) for spectral index α ∈ [–1.8, 1.5] and 4.6σ evidence for the Hellings‑Downs correlation near 14 nHz.

Abstract

Observing and timing a group of millisecond pulsars (MSPs) with high rotational stability enables the direct detection of gravitational waves (GWs). The GW signals can be identified from the spatial correlations encoded in the times-of-arrival of widely spaced pulsar-pairs. The Chinese Pulsar Timing Array (CPTA) is a collaboration aiming at the direct GW detection with observations carried out using Chinese radio telescopes. This short article serves as a `table of contents' for a forthcoming series of papers related to the CPTA Data Release 1 (CPTA DR1) which uses observations from the Five-hundred-meter Aperture Spherical radio Telescope (FAST). Here, after summarizing the time span and accuracy of CPTA DR1, we report the key results of our statistical inference finding a correlated signal with amplitude $\log A_{\rm c}= -14.4 \,^{+1.0}_{-2.8}$ for spectral index in the range of $\alpha\in [-1.8, 1.5]$ assuming a GW background (GWB) induced quadrupolar correlation. The search for the Hellings-Downs (HD) correlation curve is also presented, where some evidence for the HD correlation has been found that a 4.6-$\sigma$ statistical significance is achieved using the discrete frequency method around the frequency of 14 nHz. We expect that the future International Pulsar Timing Array data analysis and the next CPTA data release will be more sensitive to the nHz GWB, which could verify the current results.