The NANOGrav 15-year Data Set: Observations and Timing of 68 Millisecond Pulsars (2306.16217v1)

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.

• The paper presents a 15-year dataset of 68 millisecond pulsars, significantly advancing pulsar timing precision and gravitational wave detection.
• It details improved timing methodologies using Python-based processing pipelines and tools such as PSRCHIVE and PINT for accurate TOA measurements.
• The analysis identifies red noise in 23 pulsars, bolstering the pulsar timing array's sensitivity to nHz-frequency gravitational waves.

An Overview of the NANOGrav 15-year Data Set: Observations and Timing of 68 Millisecond Pulsars

The publication titled "The NANOGrav 15-year Data Set: Observations and Timing of 68 Millisecond Pulsars" provides a detailed account of the dataset acquired by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) over a 15-year period. This dataset marks the fifth public release from NANOGrav and represents a substantial enhancement over previous datasets due to its extensive observational baseline and increased number of monitored millisecond pulsars (MSPs). In this article, the NANOGrav collaboration elaborates on their methodologies, data processing techniques, and the implications of their findings related to gravitational wave detection.

Data Collection and Observations

The dataset encompasses observations of 68 MSPs using facilities such as the Arecibo Observatory, the Green Bank Telescope (GBT), and the Very Large Array (VLA). The latest data release spans nearly 16 years for many pulsars, with observations conducted in a frequency range of 327 MHz to 3 GHz. The experiment adheres to a monthly cadence at Arecibo and a roughly four-week cadence at the GBT and VLA. The selection of newly added MSPs was based on their potential contribution to pulsar timing array (PTA) analyses, taking into account their timing precision and astrophysical significance.

Data Processing and Timing Models

Advancements have been made in the data processing pipeline, with a particular focus on improving timing precision through new methodologies. The pipeline, which now incorporates Python-based timing software, was designed to handle both "narrowband" and "wideband" time-of-arrival (TOA) measurements, with significant procedural updates to enhance TOA data quality. The processing and analysis utilize software packages such as PSRCHIVE and PINT for data reduction and timing measurements, respectively.

The construction of timing models includes various parameters such as pulsar spin, astrometry, and binary system characteristics, utilizing models appropriate for different orbital characteristics. Systematic $F$-statistic tests determine the inclusion of additional parameters to ensure model accuracy and robustness.

Noise Analysis and Newly Detected Parameters

The data set facilitates the detection and analysis of red noise and white noise parameters. Through comprehensive Bayesian methods, NANOGrav addresses noise characteristics specific to different backend-receiver combinations, ensuring that the models account for temporal correlations and frequency-dependent effects in TOA data. A significant finding of the paper is the identification of detectable levels of red noise in the time series of 23 pulsars.

Implications for Gravitational Wave Detection

The NANOGrav 15-year dataset represents a significant stride toward the detection and analysis of nHz-frequency gravitational waves. This dataset's implications are vast, offering potential insights into the stochastic gravitational-wave background (GWB), which could indicate the presence of cosmic phenomena such as merging supermassive black holes. The increase in the number of MSPs observed bolsters the sensitivity of the PTA, providing a more comprehensive framework for gravitational wave investigations.

Future Prospects

The paper paves the way for further data collection and analysis efforts, as increasing the MSP sample size remains a central goal for enhancing gravitational wave detection capabilities. Additionally, the collaborative efforts between NANOGrav, the European PTA, the Parkes PTA, and the Indian PTA through the International Pulsar Timing Array (IPTA) promise combined data releases that will undoubtedly amplify our understanding of the universe's gravitational wave landscape.

In conclusion, the "NANOGrav 15-year Data Set" paper represents a significant contribution to the field of gravitational wave astronomy, underscoring the importance of long-term, high-precision pulsar timing observations and the continuous evolution of analytical methodologies driving forward the quest for gravitational wave discovery.