Wide-band timing noise in pulsar timing arrays

The evolution of pulsar pulse profiles with observing frequency and the time-variable dispersion measure (DM) induced by turbulent interstellar-medium (ISM) fluctuations limit the sensitivity of pulsar timing arrays (PTAs) to nanohertz gravitational waves. A global trend in PTA development is the deployment of ultra-wideband (UWB) receivers and backends, together with two-dimensional (2D) template profiles in pulsar timing analysis. This study reviews the current status of broadband PTA observations worldwide and the fundamental characteristics of broadband timing noise in millisecond pulsars (MSPs). A major breakthrough in broadband timing lies in the use of 2D profile templates, which enables the simultaneous measurement of time of arrival (TOA) and DM, effectively addressing the frequency-dependent biases inherent in traditional narrowband timing. Applying the 2D-template method to real PTA data reduces the number of TOAs to about 1/30 of the original, significantly lowering computational complexity; for pulsars with high DM and other environmental effects, the timing precision improves by 10%–15%. PTA broadband observations also demonstrate advantages in DM precision (down to ∼ 10^-5 mathrmpc cm^-3 and red-noise mitigation. By accurately modeling the frequency evolution of pulse profiles and ISM-induced noise, broadband timing provides a methodological foundation for low-frequency, high-precision timing with next-generation PTA facilities such as the Square Kilometre Array (SKA), playing a critical role in the detection of nanohertz gravitational-wave signals.