The second data release from the European Pulsar Timing Array IV. Search for continuous gravitational wave signals

• DOI: 10.48550/arxiv.2306.16226
• Publication Date: 2024-10-01
• Authors: J. Antoniadis; P. Arumugam; S. Arumugam; S. Babak; M. Bagchi; A.-S. Bak Nielsen; C. G. Bassa; A. Bathula; A. Berthereau; M. Bonetti; E. Bortolas; P. R. Brook; M. Burgay; R. N. Caballero; A. Chalumeau; D. J. Champion; S. Chanlaridis; S. Chen; I. Cognard; S. Dandapat; D. Deb; S. Desai; G. Desvignes; N. Dhanda-Batra; C. Dwivedi; M. Falxa; I. Ferranti; R. D. Ferdman; A. Franchini; J. R. Gair; B. Goncharov; A. Gopakumar; E. Graikou; J.-M. Grießmeier; L. Guillemot; Y. J. Guo; Y. Gupta; S. Hisano; H. Hu; F. Iraci; D. Izquierdo-Vill...; J. Jang; J. Jawor; G. H. Janssen; A. Jessner; B. C. Joshi; F. Kareem; R. Karuppusamy; E. F. Keane; M. J. Keith; D. Kharbanda; T. Kikunaga; N. Kolhe; M. Kramer; M. A. Krishnakumar; K. Lackeos; K. J. Lee; K. Liu; Y. Liu; A. G. Lyne; J. W. McKee; Y. Maan; R. A. Main; S. Manzini; M. B. Mickaliger; I. C. Niţu; K. Nobleson; A. K. Paladi; A. Parthasarathy; B. B. P. Perera; D. Perrodin; A. Petiteau; N. K. Porayko; A. Possenti; T. Prabu; H. Quelquejay Lec...; P. Rana; A. Samajdar; S. A. Sanidas; A. Sesana; G. Shaifullah; J. Singha; L. Speri; R. Spiewak; A. Srivastava; B. W. Stappers; M. Surnis; S. C. Susarla; A. Susobhanan; K. Takahashi; P. Tarafdar; G. Theureau; C. Tiburzi; E. van der Wateren; A. Vecchio; V. Venkatraman Kr...; J. P. W. Verbiest; J. Wang; L. Wang; Z. Wu
• Keywords: High Energy Astrophysical Phenomena (astro-ph.HE); Astrophysics - High Energy Astrophysical Phenomena; Astrophysics - Cosmology and Nongalactic Astrophysics; Astrophysics - Astrophysics of Galaxies; General Relativity and Quantum Cosmology; Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astronomy; 115; FOS: Physical sciences; General Relativity and Quantum Cosmology (gr-qc); Astrophysics - Astrophysics of Galaxies; 01 natural sciences; General Relativity and Quantum Cosmology; Astrophysics of Galaxies (astro-ph.GA); 0103 physical sciences; [PHYS.GRQC]Physics [physics]/General Relativity and Quantum Cosmology [gr-qc]; gravitational waves / methods: data analysis / pulsars: general; [PHYS.ASTR]Physics [physics]/Astrophysics [astro-ph]; Astrophysics - High Energy Astrophysical Phenomena; Astrophysics - Cosmology and Nongalactic Astrophysics

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.