The NANOGrav 15 Yr Data Set: Removing Pulsars One by One from the Pulsar Timing Array

TL;DR

This paper examines the internal consistency of the NANOGrav 15-year pulsar timing data by sequentially removing pulsars and analyzing the impact on the gravitational wave background signal, confirming the signal's robustness against such removal.

Contribution

It introduces a novel pulsar removal analysis method to test the internal consistency of gravitational wave signals in pulsar timing arrays, supported by synthetic data comparisons.

Findings

Signal strength remains consistent when pulsars are removed sequentially.

No inconsistencies found between real and simulated data regarding the gravitational wave background.

Methodology enhances tools for future pulsar timing array analyses.

Abstract

Evidence has emerged for a stochastic signal correlated among 67 pulsars within the 15-year pulsar-timing data set compiled by the NANOGrav collaboration. Similar signals have been found in data from the European, Indian, Parkes, and Chinese PTAs. This signal has been interpreted as indicative of the presence of a nanohertz stochastic gravitational wave background. To explore the internal consistency of this result we investigate how the recovered signal strength changes as we remove the pulsars one by one from the data set. We calculate the signal strength using the (noise-marginalized) optimal statistic, a frequentist metric designed to measure correlated excess power in the residuals of the arrival times of the radio pulses. We identify several features emerging from this analysis that were initially unexpected. The significance of these features, however, can only be assessed by comparing the real data to synthetic data sets. After conducting identical analyses on simulated data sets, we do not find anything inconsistent with the presence of a stochastic gravitational wave background in the NANOGrav 15-year data. The methodologies developed here can offer additional tools for application to future, more sensitive data sets. While this analysis provides an internal consistency check of the NANOGrav results, it does not eliminate the necessity for additional investigations that could identify potential systematics or uncover unmodeled physical phenomena in the data.