We detail a number of methodological changes, compared to our previous work, which yield a cleaner and more uniformly processed data set. A separate set of 'wideband' TOAs will be presented in a companion paper. We detail our observational methods and present a set of TOA measurements, based on 'narrowband' analysis, in which many TOAs are calculated within narrow radio-frequency bands for data collected simultaneously across a wide bandwidth. These data were collected for use in low-frequency gravitational wave searches and for other astrophysical purposes.
The observing cadence was three to four weeks for most pulsars over most of this time span, with weekly observations of six sources.
We present time-of-arrival (TOA) measurements and timing models of 47 millisecond pulsars observed from 2004 to 2017 at the Arecibo Observatory and the Green Bank Telescope by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav).
