Noise budget for the NANOGrav pulsar timing array

The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) recently reported on the presence of a time-correlated stochastic signal across the pulsars in our 12.5-year dataset. While we detect a common spectral process consistent with that expected from supermassive binary black holes, spatial correlations (Hellings-Downs correlations) between the pulsars have not been detected and are necessary in order to claim detection of a gravitational wave background (GWB). As NANOGrav prepares for a GWB search in the 15-year dataset we have undertaken a full accounting of the noise in individual pulsars. The standard noise model in our pulsars consists of a white noise model together with a power-law red noise model, i.e., time-correlated noise with more power in lower frequencies. This full noise budget of our phenomenological model compares the noise power spectral density in our noise models to the spectral characteristics of the common spectral process detected in the NANOGrav 12.5-year analysis.