The NANOGrav 11-year Data Set: High-precision Timing of 45 Millisecond Pulsars

TLDR

The data enable constraints on the gravitational‑wave background, as demonstrated in a companion study. This work presents 11‑year high‑precision timing of 45 millisecond pulsars to detect and characterize low‑frequency gravitational waves. The pulsars were observed monthly (weekly for six) with Arecibo and the Green Bank Telescope from 327 MHz to 2.3 GHz, with multi‑frequency epochs to model dispersion, and the authors processed the data, calculated TOAs, removed outliers, and fitted comprehensive timing models including spin, astrometric, orbital, dispersion, pulse‑profile evolution, and noise parameters. The timing solutions yield three new parallaxes, two new Shapiro delays, two new orbital‑period‑variation measurements, and reveal significant red noise in 11 pulsars with smaller spectral indices than typical non‑recycled pulsars, hinting at a distinct origin.

Abstract

Abstract We present high-precision timing data over time spans of up to 11 years for 45 millisecond pulsars observed as part of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) project, aimed at detecting and characterizing low-frequency gravitational waves. The pulsars were observed with the Arecibo Observatory and/or the Green Bank Telescope at frequencies ranging from 327 MHz to 2.3 GHz. Most pulsars were observed with approximately monthly cadence, and six high-timing-precision pulsars were observed weekly. All were observed at widely separated frequencies at each observing epoch in order to fit for time-variable dispersion delays. We describe our methods for data processing, time-of-arrival (TOA) calculation, and the implementation of a new, automated method for removing outlier TOAs. We fit a timing model for each pulsar that includes spin, astrometric, and (for binary pulsars) orbital parameters; time-variable dispersion delays; and parameters that quantify pulse-profile evolution with frequency. The timing solutions provide three new parallax measurements, two new Shapiro delay measurements, and two new measurements of significant orbital-period variations. We fit models that characterize sources of noise for each pulsar. We find that 11 pulsars show significant red noise, with generally smaller spectral indices than typically measured for non-recycled pulsars, possibly suggesting a different origin. A companion paper uses these data to constrain the strength of the gravitational-wave background.