The International Pulsar Timing Array: First Data Release (1602.03640v1)

Abstract: The highly stable spin of neutron stars can be exploited for a variety of (astro-)physical investigations. In particular arrays of pulsars with rotational periods of the order of milliseconds can be used to detect correlated signals such as those caused by gravitational waves. Three such "Pulsar Timing Arrays" (PTAs) have been set up around the world over the past decades and collectively form the "International" PTA (IPTA). In this paper, we describe the first joint analysis of the data from the three regional PTAs, i.e. of the first IPTA data set. We describe the available PTA data, the approach presently followed for its combination and suggest improvements for future PTA research. Particular attention is paid to subtle details (such as underestimation of measurement uncertainty and long-period noise) that have often been ignored but which become important in this unprecedentedly large and inhomogeneous data set. We identify and describe in detail several factors that complicate IPTA research and provide recommendations for future pulsar timing efforts. The first IPTA data release presented here (and available online) is used to demonstrate the IPTA's potential of improving upon gravitational-wave limits placed by individual PTAs by a factor of ~2 and provides a 2-sigma limit on the dimensionless amplitude of a stochastic GWB of 1.7x10^{-15} at a frequency of 1 yr^{-1}. This is 1.7 times less constraining than the limit placed by (Shannon et al. 2015), due mostly to the more recent, high-quality data they used.

• The paper provides the first aggregated IPTA dataset from 49 pulsars observed over decades.
• It employs advanced Bayesian analysis and DM variation modeling to address heterogeneity and timing noise.
• The results significantly constrain the stochastic gravitational wave background, setting new benchmarks for future studies.

Overview of "The International Pulsar Timing Array: First Data Release"

The paper "The International Pulsar Timing Array: First Data Release," authored by J.P.W. Verbiest et al., presents a comprehensive analysis of pulsar timing data collated from three major regional Pulsar Timing Arrays (PTAs): the European Pulsar Timing Array (EPTA), the North American Nanohertz Observatory for Gravitational Waves (NANOGrav), and the Parkes Pulsar Timing Array (PPTA). These PTAs collectively form the International Pulsar Timing Array (IPTA), aimed at investigating gravitational waves (GWs) through correlated timing signals in millisecond pulsars (MSPs).

Key Contributions and Methodology

The paper introduces the first data release of the IPTA, which aggregates data from various independent PTAs to form a more extensive and possibly comprehensive pulsar timing dataset. This dataset serves as a prime tool to enhance the detection prospects of low-frequency gravitational waves. The authors discuss the challenges inherent in combining heterogeneous datasets, such as systemic offsets and error estimation, and emphasize the need for meticulous data handling and analysis. For mitigating these challenges, they employ advanced methods for timing residual analysis and source-independent DM variation modeling.

Data Set Description

The IPTA dataset described in the paper includes data from 49 pulsars, observed over varying spans ranging from several years to decades. The authors meticulously document the temporal and frequency coverage of each dataset, ensuring that systemic offsets between different recording systems and telescopes are addressed. The data's heterogeneity is apparent in the inclusion of multiple observatories: the historical datasets have been revitalized and new, high-precision observations have been conducted, spanning a timescale that extends in some cases over three decades.

Results and Findings

A significant finding of the paper is its constructive criticism of the current pulsar timing practices, encouraging a more standardized approach to future data handling. Through their analysis method, utilizing the Bayesian framework of temponest, they manage to obtain refined models of DM variations and time noise, which are essential for accurate pulsar timing models. Among their results, they derive an indicative upper limit on the stochastic GW background's dimensionless amplitude, significantly improving upon the limits set by individual PTA analyses.

Practical Implications

The implications of this paper are two-fold: practically, it sets a new benchmark for handling diverse datasets in pulsar timing for gravitational wave detection, and theoretically, it paves the way toward a more unified approach in the field. By encouraging practices such as including the standard templates used for creating data sets and suggesting the storage of ToAs along with metadata, like integration time and frequency information, the paper provides guidelines that aim to streamline future projects.

Future Prospects and Developments

Looking ahead, with the advancements in survey capabilities and the imminent operation of the Square Kilometre Array (SKA), the IPTA is poised at the brink of a transformative phase in GW astronomy. The expected increase in the number of cataloged millisecond pulsars, combined with refined methodologies for DM and noise correction, positions the IPTA to become a cornerstone in GW detection efforts. The paper underscores the importance of continued improvement in data acquisition and analysis processes to maintain alignment with the expanding scientific and technical frontiers.

Conclusion

This paper not only delivers the first comprehensive data release of the IPTA but also lays groundwork directives and provides insightful critiques that are expected to influence pulsar timing and gravitational wave detection methodologies significantly. It eloquently highlights the synergistic potential of international collaboration in astronomy, particularly in the pursuit of one of modern astronomy's ambitious goals: the direct detection of gravitational waves through pulsar timing arrays.