Kavli Affiliate: Kejia Lee
| First 5 Authors: Siyuan Chen, Heng Xu, Yanjun Guo, Bojun Wang, R. Nicolas Caballero
| Summary:
The Chinese Pulsar Timing Array (CPTA) has collected observations from 57
millisecond pulsars using the Five-hundred-meter Aperture Spherical Radio
Telescope (FAST) for close to three years, for the purpose of searching for
gravitational waves (GWs). To robustly search for ultra-low-frequency GWs,
pulsar timing arrays (PTAs) need to use models to describe the noise from the
individual pulsars. We report on the results from the single pulsar noise
analysis of the CPTA data release I (DR1). Conventionally, power laws in the
frequency domain are used to describe pulsar red noise and dispersion
measurement (DM) variations over time. Employing Bayesian methods, we found the
choice of number and range of frequency bins with the highest evidence for each
pulsar individually. A comparison between a dataset using DM piecewise measured
(DMX) values and a power-law Gaussian process to describe the DM variations
shows strong Bayesian evidence in favour of the power-law model. Furthermore,
we demonstrate that the constraints obtained from four independent software
packages are very consistent with each other. The short time span of the CPTA
DR1, paired with the large sensitivity of FAST, has proved to be a challenge
for the conventional noise model using a power law. This mainly shows in the
difficulty to separate different noise terms due to their covariances with each
other. Nineteen pulsars are found to display covariances between the short-term
white noise and long-term red and DM noise. With future CPTA datasets, we
expect that the degeneracy can be broken. Finally, we compared the CPTA DR1
results against the noise properties found by other PTA collaborations. While
we can see broad agreement, there is some tension between different PTA
datasets for some of the overlapping pulsars. This could be due to the
differences in the methods and frequency range compared to the other PTAs.
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