The second data release from the European Pulsar Timing Array

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-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; 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 Leclere; 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 Krishnan; J. P. W. Verbiest; J. Wang; L. Wang; Z. Wu

doi:10.1051/0004-6361/202348568

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Volume 690 (October 2024)

A&A, 690 (2024) A118

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Issue		A&A Volume 690, October 2024


Article Number		A118
Number of page(s)		14
Section		Astrophysical processes
DOI		https://doi.org/10.1051/0004-6361/202348568
Published online		03 October 2024

A&A, 690, A118 (2024)

V. Search for continuous gravitational wave signals

EPTA Collaboration and InPTA Collaboration
J. Antoniadis¹^,2, P. Arumugam³, S. Arumugam⁴, S. Babak⁵, M. Bagchi⁶^,7, A.-S. Bak Nielsen²^,8, C. G. Bassa⁹, A. Bathula¹⁰, A. Berthereau¹¹^,12, M. Bonetti¹³^,14^,15, E. Bortolas¹³^,14^,15, P. R. Brook¹⁶, M. Burgay¹⁷, R. N. Caballero¹⁸, A. Chalumeau¹³, D. J. Champion², S. Chanlaridis¹, S. Chen¹⁹, I. Cognard¹¹^,12, S. Dandapat²⁰, D. Deb⁶, S. Desai²¹, G. Desvignes², N. Dhanda-Batra²², C. Dwivedi²³, M. Falxa⁵^,11^,⋆, I. Ferranti¹³^,5, R. D. Ferdman²⁴, A. Franchini¹³^,14, J. R. Gair²⁵, B. Goncharov²⁶^,27, A. Gopakumar²⁰, E. Graikou², J.-M. Grießmeier¹¹^,12, L. Guillemot¹¹^,12, Y. J. Guo², Y. Gupta²⁸, S. Hisano²⁹, H. Hu², F. Iraci³⁰^,17, D. Izquierdo-Villalba¹³^,14, J. Jang², J. Jawor², G. H. Janssen⁹^,31, A. Jessner², B. C. Joshi²⁸^,3, F. Kareem³²^,33, R. Karuppusamy², E. F. Keane³⁴, M. J. Keith³⁵, D. Kharbanda²¹, T. Kikunaga²⁹, N. Kolhe³⁶, M. Kramer²^,35, M. A. Krishnakumar²^,8, K. Lackeos², K. J. Lee³⁷^,38, K. Liu², Y. Liu³⁸^,8, A. G. Lyne³⁵, J. W. McKee³⁹^,40, Y. Maan²⁸, R. A. Main², S. Manzini¹³^,5, M. B. Mickaliger³⁵, I. C. Niţu³⁵, K. Nobleson⁴¹, A. K. Paladi⁴², A. Parthasarathy², B. B. P. Perera⁴³, D. Perrodin¹⁷, A. Petiteau⁴⁴^,5, N. K. Porayko¹³^,2, A. Possenti¹⁷, T. Prabu⁴⁵, H. Quelquejay Leclere⁵, P. Rana²⁰, A. Samajdar⁴⁶, S. A. Sanidas³⁵, A. Sesana¹³^,14^,15, G. Shaifullah¹³^,14^,17, J. Singha³, L. Speri²⁵, R. Spiewak³⁵, A. Srivastava²¹, B. W. Stappers³⁵, M. Surnis⁴⁷, S. C. Susarla⁴⁸, A. Susobhanan⁴⁹, K. Takahashi⁵⁰^,51, P. Tarafdar⁶, G. Theureau¹¹^,12^,52, C. Tiburzi¹⁷, E. van der Wateren⁹^,31, A. Vecchio¹⁶, V. Venkatraman Krishnan², J. P. W. Verbiest⁵³^,8^,2, J. Wang⁸^,54^,55, L. Wang³⁵ and Z. Wu³⁸^,8

¹ Institute of Astrophysics, FORTH, N. Plastira 100, 70013 Heraklion, Greece
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
³ Department of Physics, Indian Institute of Technology Roorkee, Roorkee-247667, India
⁴ Department of Electrical Engineering, IIT Hyderabad, Kandi, Telangana 502284, India
⁵ Université Paris Cité, CNRS, Astroparticule et Cosmologie, 75013 Paris, France
e-mail: lorenzo.speri@aei.mpg.de
⁶ The Institute of Mathematical Sciences, C. I. T. Campus, Taramani, Chennai 600113, India
⁷ Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400094, India
⁸ Fakultät für Physik, Universität Bielefeld, Postfach 100131, 33501 Bielefeld, Germany
⁹ ASTRON, Netherlands Institute for Radio Astronomy, Oude Hoogeveensedijk 4, 7991 PD Dwingeloo, The Netherlands
¹⁰ Department of Physical Sciences, Indian Institute of Science Education and Research, Mohali, Punjab 140306, India
¹¹ Laboratoire de Physique et Chimie de l’Environnement et de l’Espace, Université d’Orléans / CNRS, 45071 Orléans Cedex 02, France
¹² Observatoire Radioastronomique de Nançay, Observatoire de Paris, Université PSL, Université d’Orléans, CNRS, 18330 Nançay, France
¹³ Dipartimento di Fisica “G. Occhialini”, Universitá degli Studi di Milano-Bicocca, Piazza della Scienza 3, 20126 Milano, Italy
¹⁴ INFN, Sezione di Milano-Bicocca, Piazza della Scienza 3, 20126 Milano, Italy
¹⁵ INAF – Osservatorio Astronomico di Brera, via Brera 20, 20121 Milano, Italy
¹⁶ Institute for Gravitational Wave Astronomy and School of Physics and Astronomy, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
¹⁷ INAF – Osservatorio Astronomico di Cagliari, via della Scienza 5, 09047 Selargius (CA), Italy
¹⁸ Hellenic Open University, School of Science and Technology, 26335 Patras, Greece
¹⁹ Kavli Institute for Astronomy and Astrophysics, Peking University, Beijing 100871, PR China
²⁰ Department of Astronomy and Astrophysics, Tata Institute of Fundamental Research, Homi Bhabha Road, Navy Nagar, Colaba, Mumbai 400005, India
²¹ Department of Physics, IIT Hyderabad, Kandi, Telangana 502284, India
²² Department of Physics and Astrophysics, University of Delhi, Delhi 110007, India
²³ Department of Earth and Space Sciences, Indian Institute of Space Science and Technology, Valiamala, Thiruvananthapuram, Kerala 695547, India
²⁴ School of Physics, Faculty of Science, University of East Anglia, Norwich NR4 7TJ, UK
²⁵ Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Am Mühlenberg 1, 14476 Potsdam, Germany
e-mail: lorenzo.speri@aei.mpg.de
²⁶ Gran Sasso Science Institute (GSSI), 67100 L’Aquila, Italy
²⁷ INFN, Laboratori Nazionali del Gran Sasso, 67100 Assergi, Italy
²⁸ National Centre for Radio Astrophysics, Pune University Campus, Pune 411007, India
²⁹ Kumamoto University, Graduate School of Science and Technology, Kumamoto 860-8555, Japan
³⁰ Universitá di Cagliari, Dipartimento di Fisica, S.P. Monserrato-Sestu Km 0, 700 - 09042 Monserrato (CA), Italy
³¹ Department of Astrophysics/IMAPP, Radboud University Nijmegen, P.O. Box 9010 6500 GL Nijmegen, The Netherlands
³² Department of Physical Sciences,Indian Institute of Science Education and Research Kolkata, Mohanpur 741246, India
³³ Center of Excellence in Space Sciences India, Indian Institute of Science Education and Research Kolkata, Kolkata 741246, India
³⁴ School of Physics, Trinity College Dublin, College Green, Dublin 2 D02 PN40, Ireland
³⁵ Jodrell Bank Centre for Astrophysics, Department of Physics and Astronomy, University of Manchester, Manchester M13 9PL, UK
³⁶ Department of Physics, St. Xavier’s College (Autonomous), Mumbai 400001, India
³⁷ Department of Astronomy, School of Physics, Peking University, Beijing 100871, PR China
³⁸ National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, PR China
³⁹ E.A. Milne Centre for Astrophysics, University of Hull, Cottingham Road, Kingston-upon-Hull HU6 7RX, UK
⁴⁰ Centre of Excellence for Data Science, Artificial Intelligence and Modelling (DAIM), University of Hull, Cottingham Road, Kingston-upon-Hull HU6 7RX, UK
⁴¹ Department of Physics, BITS Pilani Hyderabad Campus, Hyderabad, 500078 Telangana, India
⁴² Joint Astronomy Programme, Indian Institute of Science, Bengaluru, Karnataka 560012, India
⁴³ Arecibo Observatory, HC3 Box 53995, Arecibo PR 00612, USA
⁴⁴ IRFU, CEA, Université Paris-Saclay, 91191 Gif-sur-Yvette, France
⁴⁵ Raman Research Institute India, Bengaluru, Karnataka 560080, India
⁴⁶ Institut für Physik und Astronomie, Universität Potsdam, Haus 28, Karl-Liebknecht-Str. 24/25, 14476 Potsdam, Germany
⁴⁷ Department of Physics, IISER Bhopal, Bhopal Bypass Road, Bhauri, Bhopal, 462066 Madhya Pradesh, India
⁴⁸ Ollscoil na Gaillimhe – University of Galway, University Road, Galway H91 TK33, Ireland
⁴⁹ Center for Gravitation, Cosmology, and Astrophysics, University of Wisconsin-Milwaukee, Milwaukee, WI 53211, USA
⁵⁰ Division of Natural Science, Faculty of Advanced Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan
⁵¹ International Research Organization for Advanced Science and Technology, Kumamoto University, 2-39-1 Kurokami, Kumamoto 860-8555, Japan
⁵² Laboratoire Univers et Théories LUTh, Observatoire de Paris, Université PSL, CNRS, Université de Paris, 92190 Meudon, France
⁵³ Florida Space Institute, University of Central Florida, 12354 Research Parkway, Partnership 1 Building, Suite 214, Orlando, 32826-0650 FL, USA
⁵⁴ Ruhr University Bochum, Faculty of Physics and Astronomy, Astronomical Institute (AIRUB), 44780 Bochum, Germany
⁵⁵ Advanced Institute of Natural Sciences, Beijing Normal University, Zhuhai 519087, China

Received: 11 November 2023
Accepted: 24 June 2024

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.

Key words: gravitational waves / methods: data analysis / pulsars: general

^⋆

Corresponding authors; stas@apc.in2p3.fr, falxa@apc.in2p3.fr, lorenzo.speri@aei.mpg.de.

Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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