  We present time-of-arrival (TOA) measurements and timing models of 47
millisecond pulsars (MSPs) observed from 2004 to 2017 at the Arecibo
Observatory and the Green Bank Telescope by the North American Nanohertz
Observatory for Gravitational Waves (NANOGrav). The observing cadence was three
to four weeks for most pulsars over most of this time span, with weekly
observations of six sources. These data were collected for use in low-frequency
gravitational wave searches and for other astrophysical purposes. 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. A separate set of "wideband" TOAs will be presented in a companion
paper. We detail a number of methodological changes compared to our previous
work which yield a cleaner and more uniformly processed data set. Our timing
models include several new astrometric and binary pulsar measurements,
including previously unpublished values for the parallaxes of PSRs J1832-0836
and J2322+2057, the secular derivatives of the projected semi-major orbital
axes of PSRs J0613-0200 and J2229+2643, and the first detection of the Shapiro
delay in PSR J2145-0750. We report detectable levels of red noise in the time
series for 14 pulsars. As a check on timing model reliability, we investigate
the stability of astrometric parameters across data sets of different lengths.
We report flux density measurements for all pulsars observed. Searches for
stochastic and continuous gravitational waves using these data will be subjects
of forthcoming publications.
