The International Pulsar Timing Array (IPTA) recently completed its analysis of their most recent official data release, known as Data Release 2. This consisted of precision timing data from 65 millisecond pulsars, combined from separate datasets of the European Pulsar Timing Array (EPTA), the North American Nanohertz-frequency Gravitational Waves Observatory (NANOGrav), and the Parkes Pulsar Timing Array (PPTA). It found very strong evidence for a spectrally similar low-frequency signal in many of the pulsars. The characteristics of this signal are in broad agreement with spectral models of an astrophysical gravitational-wave (GW) background from a population of supermassive binary black holes. However, no evidence has been found for the distinctive pattern of cross-correlations between pulsars that would identify GWs as the origin of this low-frequency signal. These results, synthesized from older PTA datasets, corroborate what has been more recently found by NANOGrav, PPTA, and EPTA in their most recent data releases. Whether or not this spectrally similar low-frequency signal is correlated between pulsars in accordance with a GW background is something that will be resolved with further data collection, expanded arrays of monitored pulsars, and continued analyses. By combining the data and efforts of PTA collaborations, the IPTA can naturally achieve these aims, and is currently working to answer this question.
Below, we include links to the recently published results from the three individual PTAs’ data sets:
- The NANOGrav 12.5-year Data Set: Search For An Isotropic Stochastic Gravitational-Wave Background, The Astrophysical Journal Letters, Volume 905, Number 2 (2020), arXiv:2009.0449
- On the Evidence for a Common-spectrum Process in the Search for the Nanohertz Gravitational-wave Background with the Parkes Pulsar Timing Array, The Astrophysical Journal Letters, Volume 917, Issue 2 (2021), arXiv:2107.12112
- Common-red-signal analysis with 24-yr high-precision timing of the European Pulsar Timing Array: inferences in the stochastic gravitational-wave background search, Monthly Notices of the Royal Astronomical Society, Volume 508, Issue 4 (2021), arXiv:2110.13184