The NANOGrav 11-year Data Set: High-precision timing of 45 Millisecond Pulsars (1801.01837v3)

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, with six high--timing-precision pulsars observed weekly, and 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, if necessary, binary parameters, in addition to time-variable dispersion delays and parameters that quantify pulse-profile evolution with frequency. The new timing solutions provide three new parallax measurements, two new Shapiro delay measurements, and two new measurements of large 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. Future papers will use these data to constrain or detect the signatures of gravitational-wave signals.

• The paper details high-precision timing of 45 millisecond pulsars over 11 years, advancing gravitational wave detection techniques.
• It utilizes advanced data collection and automated outlier removal methods to enhance pulsar timing models and astrometric measurements.
• The analysis identifies significant red noise and reports new parallax and Shapiro delay measurements, deepening our understanding of pulsar dynamics.

An Analysis of the NANOGrav 11-Year Data Set on Millisecond Pulsar Timing

This paper presents the results from the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) 11-year data set, which includes high-precision timing measurements of 45 millisecond pulsars. The objective of the NANOGrav collaboration is to detect low-frequency gravitational waves with periods of several years, using millisecond pulsars as natural detectors. These findings are crucial as they expand our understanding of gravitational waves in the nanohertz frequency band and further explore pulsar timing methodologies.

Key Findings and Methodologies

1. Data Collection and Processing:
   • Observations were conducted using the Arecibo Observatory and the Green Bank Telescope, with frequencies ranging from 327 MHz to 2.3 GHz.
   • The data spans up to 11 years, enhancing the precision of timing models. Pulsars were observed monthly, with six of them being observed weekly for increased precision.
2. Gravitational Wave Detection:
   • The research aims to detect gravitational waves generated by cosmic events, such as supermassive black hole mergers, within the nanohertz frequency band.
   • By refining and analyzing the timing data from multiple pulsars, the researchers can identify correlated time variations indicative of gravitational waves.
3. Data Analysis:
   • Timing models were enhanced to include spin, astrometric, and orbital parameters, along with accounting for time-variable dispersion delays.
   • Three additional parallax measurements and two Shapiro delay measurements were reported, contributing further to astrometric precision and binary pulsar analysis.
   • The authors employed a new automated method for removing outlier time-of-arrivals (TOAs), improving the reliability of data.
4. Noise Characteristics and Astrometric Measurements:
   • Eleven pulsars exhibited significant red noise, with different spectral indices than those typically associated with non-recycled pulsars, suggesting alternative origins of this noise.
   • An analysis yielded 20 significant timing parallax measurements, including three first instances for specific pulsars, aiding the estimation of distances and spatial distribution of these cosmic objects.
5. Binary Pulsar Analysis:
   • The paper details intricate assessments of binary pulsars, calculating pulsar and companion masses, orbital variations, and secular changes in Keplerian parameters. These calculations are vital for understanding pulsar evolution and testing theories of general relativity.

Implications and Future Directions

The data set's extension and refinement significantly contribute to pulsar timing precision and gravitational wave research. High-precision pulsar timing arrays such as NANOGrav are indispensable for extending our understanding of gravitational waves and testing fundamental physics laws, such as general relativity. The continual enhancement of data analysis techniques, detection of timing noise, and pulsar timing models elevate the sensitivity of gravitational wave detection.

Furthermore, the paper's findings amplify expectations for gravitational wave detections via this novel approach within the next few years. As more pulsars are added to the array, and as the timing baseline extends, the sensitivity and likelihood of gravitational wave detection are anticipated to rise. A robust detection could lead to breakthroughs in astrophysics, providing insights into massive cosmic events.

Overall, the NANOGrav 11-year data set underscores the potential of pulsar timing arrays as tools for gravitational wave astronomy and their role in advancing astrophysical research. This data-rich approach continues to unravel the mysteries of the universe, holding promise for future discoveries.