The NANOGrav Nine-year Data Set: Observations, Arrival Time Measurements, and Analysis of 37 Millisecond Pulsars

TL;DR

This paper reports nine years of high-precision timing data for 37 millisecond pulsars, detailing observational methods, data analysis, and evidence of low-frequency timing noise, laying groundwork for gravitational wave detection.

Contribution

It introduces novel measurement techniques and comprehensive analysis methods for pulsar timing data, enhancing the precision needed for gravitational wave searches.

Findings

Detection of low-frequency timing noise in 10 pulsars

Identification of interstellar medium effects in timing noise

High-precision timing data spanning nine years

Abstract

We present high-precision timing observations spanning up to nine years for 37 millisecond pulsars monitored with the Green Bank and Arecibo radio telescopes as part of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) project. We describe the observational and instrumental setups used to collect the data, and methodology applied for calculating pulse times of arrival; these include novel methods for measuring instrumental offsets and characterizing low signal-to-noise ratio timing results. The time of arrival data are fit to a physical timing model for each source, including terms that characterize time-variable dispersion measure and frequency-dependent pulse shape evolution. In conjunction with the timing model fit, we have performed a Bayesian analysis of a parameterized timing noise model for each source, and detect evidence for excess low-frequency, or "red," timing noise in 10 of the pulsars. For 5 of these cases this is likely due to interstellar medium propagation effects rather than intrisic spin variations. Subsequent papers in this series will present further analysis of this data set aimed at detecting or limiting the presence of nanohertz-frequency gravitational wave signals.