The second data release from the European Pulsar Timing Array
John Antoniadis, P. Arumugam, S. Arumugam, S. Babak, Manjari Bagchi, A.-S. Bak Nielsen, C. Bassa, Adarsh Bathula, A. Berthereau, Matteo Bonetti, Elisa Bortolas, Paul R. Brook, M. Burgay, R. N. Caballero, A. Chalumeau, D. J. Champion, S. Chanlaridis, Siyuan Chen, I. Cognard, Subhajit Dandapat, Debabrata Deb, S. Desai, G. Desvignes, N. Dhanda-Batra, C. Dwivedi, M. Falxa, Irene Ferranti, R. D. Ferdman, Alessia Franchini, J. R. Gair, B. Goncharov, A. Gopakumar, E. Graikou, J.‐M. Grießmeier, L. Guillemot, Y. J. Guo, Yashwant Gupta, Shinnosuke Hisano, H. Hu, F. Iraci, David Izquierdo–Villalba, J. Jang, J. Jawor, G. H. Janssen, A. Jessner, B. C. Joshi, F. Kareem, R. Karuppusamy, E. F. Keane, M. J. Keith, D. Kharbanda, Tomonosuke Kikunaga, Neel Kolhe, M. Kramer, M. A. Krishnakumar, K. Lackeos, K. J. Lee, Y. Liu, Y. Liu, A. G. Lyne, James W. McKee, Yogesh Maan, Robert Main, S. Manzini, M. B. Mickaliger, I. C. Niţu, K. Nobleson, Avinash Kumar Paladi, A. Parthasarathy, Benetge B. P. Perera, D. Perrodin, Antoine Petiteau, N. K. Porayko, A. Possenti, T. Prabu, H. Quelquejay Leclere, Prerna Rana, A. Samajdar, S. A. Sanidas, Alberto Sesana, G. Shaifullah, Jaikhomba Singha, Lorenzo Speri, R. Spiewak, Aman Srivastava, B. W. Stappers, Mayuresh Surnis, S. C. Susarla, Abhimanyu Susobhanan, Keitaro Takahashi, Pratik Tarafdar, G. Theureau, C. Tiburzi, E. van der Wateren, A. Vecchio, V. Venkatraman Krishnan, J. P. W. Verbiest, J. Wang, J. Wang, Ziwei Wu
Abstract
We present the results of a search for continuous gravitational wave signals (CGWs) in the second data release (DR2) of the European Pulsar Timing Array (EPTA) Collaboration. The most significant candidate event from this search has a gravitational wave frequency of 4–5 nHz. Such a signal could be generated by a supermassive black hole binary (SMBHB) in the local Universe. We present the results of a follow-up analysis of this candidate using both Bayesian and frequentist methods. The Bayesian analysis gives a Bayes factor of 4 in favour of the presence of the CGW over a common uncorrelated noise process. In contrast, the frequentist analysis estimates the p-value of the candidate to be < 1%, also assuming the presence of common uncorrelated red noise. However, comparing a model that includes both a CGW and a gravitational wave background (GWB) to a GWB only, the Bayes factor in favour of the CGW model is only 0.7. Therefore, we cannot conclusively determine the origin of the observed feature, nor can we rule it out as a CGW source. We present results of simulations that demonstrate that data containing a weak gravitational wave background can be misinterpreted as data including a CGW and vice versa, providing two plausible explanations for the EPTA DR2 data. Further investigations combining data from all PTA collaborations will be needed to reveal the true origin of this feature.