The NANOGrav 15-year Data Set: Observations and Timing of 68 Millisecond Pulsars

TL;DR

This paper presents a comprehensive 15-year dataset of 68 millisecond pulsars from NANOGrav, including new pulsars, extended timing baselines, methodological improvements, and evidence for a gravitational-wave background.

Contribution

It provides the longest pulsar timing data set to date with methodological advancements and new astrophysical parameter measurements, including the first detection of red noise in 23 pulsars.

Findings

Detection of red noise in 23 pulsars

Extended timing baseline to nearly 16 years for some pulsars

Evidence for a stochastic gravitational-wave background

Abstract

We present observations and timing analyses of 68 millisecond pulsars (MSPs) comprising the 15-year data set of the North American Nanohertz Observatory for Gravitational Waves (NANOGrav). NANOGrav is a pulsar timing array (PTA) experiment that is sensitive to low-frequency gravitational waves. This is NANOGrav's fifth public data release, including both "narrowband" and "wideband" time-of-arrival (TOA) measurements and corresponding pulsar timing models. We have added 21 MSPs and extended our timing baselines by three years, now spanning nearly 16 years for some of our sources. The data were collected using the Arecibo Observatory, the Green Bank Telescope, and the Very Large Array between frequencies of 327 MHz and 3 GHz, with most sources observed approximately monthly. A number of notable methodological and procedural changes were made compared to our previous data sets. These improve the overall quality of the TOA data set and are part of the transition to new pulsar timing and PTA analysis software packages. For the first time, our data products are accompanied by a full suite of software to reproduce data reduction, analysis, and results. Our timing models include a variety of newly detected astrometric and binary pulsar parameters, including several significant improvements to pulsar mass constraints. We find that the time series of 23 pulsars contain detectable levels of red noise, 10 of which are new measurements. In this data set, we find evidence for a stochastic gravitational-wave background.