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

EPTA collaboration; InPTA Collaboration

doi:10.1051/0004-6361/202346844

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

EPTA collaboration, InPTA Collaboration

Physics and Astronomy

Research output: Contribution to journal › Article › peer-review

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Abstract

We present the results of the search for an isotropic stochastic gravitational wave background (GWB) at nanohertz frequencies using the second data release of the European Pulsar Timing Array (EPTA) for 25 millisecond pulsars and a combination with the first data release of the Indian Pulsar Timing Array (InPTA). A robust GWB detection is conditioned upon resolving the Hellings-Downs angular pattern in the pairwise crosscorrelation of the pulsar timing residuals. Additionally, the GWB is expected to yield the same (common) spectrum of temporal correlations across pulsars, which is used as a null hypothesis in the GWB search. Such a common-spectrum process has already been observed in pulsar timing data. We analysed (i) the full 24.7-year EPTA data set, (ii) its 10.3-year subset based on modern observing systems, (iii) the combination of the full data set with the first data release of the InPTA for ten commonly timed millisecond pulsars, and (iv) the combination of the 10.3-year subset with the InPTA data. These combinations allowed us to probe the contributions of instrumental noise and interstellar propagation effects. With the full data set, we find marginal evidence for a GWB, with a Bayes factor of four and a false alarm probability of 4%. With the 10.3-year subset, we report evidence for a GWB, with a Bayes factor of 60 and a false alarm probability of about 0.1% (≳ 3σ significance). The addition of the InPTA data yields results that are broadly consistent with the EPTA-only data sets, with the benefit of better noise modelling. Analyses were performed with different data processing pipelines to test the consistency of the results from independent software packages. The latest EPTA data from new generation observing systems show non-negligible evidence for the GWB. At the same time, the inferred spectrum is rather uncertain and in mild tension with the common signal measured in the full data set. However, if the spectral index is fixed at 13/3, the two data sets give a similar amplitude of (2.5±0.7)×10⁻¹⁵ at a reference frequency of 1 yr⁻¹ . Further investigation of these issues is required for reliable astrophysical interpretations of this signal. By continuing our detection efforts as part of the International Pulsar Timing Array (IPTA), we expect to be able to improve the measurement of spatial correlations and better characterise this signal in the coming years.

Original language	English
Article number	A50
Number of pages	22
Journal	Astronomy and Astrophysics
Volume	678
DOIs	https://doi.org/10.1051/0004-6361/202346844
Publication status	Published - 3 Oct 2023

Bibliographical note

Acknowledgments:
The European Pulsar Timing Array (EPTA) is a collaboration between European and partner institutes, namely ASTRON (NL), INAF/Osservatorio di Cagliari (IT), Max-Planck-Institut für Radioastronomie (GER), Nançay/Paris Observatory (FRA), the University of Manchester (UK), the University of Birmingham (UK), the University of East Anglia (UK), the University of Bielefeld (GER), the University of Paris (FRA), the University of Milan-Bicocca (IT), the Foundation for Research and Technology, Hellas (GR), and Peking University (CHN), with the aim to provide high-precision pulsar timing to work towards the direct detection of low-frequency gravitational waves. An Advanced Grant of the European Research Council allowed to implement the Large European Array for Pulsars (LEAP) under Grant Agreement Number 227947 (PI M. Kramer). The EPTA is part of the International Pulsar Timing Array (IPTA); we thank our IPTA colleagues for their support and help with this paper and the external Detection Committee members for their work on the Detection Checklist. Part of this work is based on observations with the 100-m telescope of the Max-Planck-Institut für Radioastronomie (MPIfR) at Effelsberg in Germany. Pulsar research at the Jodrell Bank Centre for Astrophysics and the observations using the Lovell Telescope are supported by a Consolidated Grant (ST/T000414/1) from the UK’s Science and Technology Facilities Council (STFC). ICN is also supported by the STFC doctoral training grant ST/T506291/1. The Nançay radio Observatory is operated by the Paris Observatory, associated with the French Centre National de la Recherche Scientifique (CNRS), and partially supported by the Region Centre in France. We acknowledge financial support from “Programme National de Cosmologie and Galaxies” (PNCG), and “Programme National Hautes Energies” (PNHE) funded by CNRS/INSU-IN2P3-INP, CEA and CNES, France. We acknowledge financial support from Agence Nationale de la Recherche (ANR-18-CE31-0015), France. The Westerbork Synthesis Radio Telescope is operated by the Netherlands Institute for Radio Astronomy (ASTRON) with support from the Netherlands Foundation for Scientific Research (NWO). The Sardinia Radio Telescope (SRT) is funded by the Department of University and Research (MIUR), the Italian Space Agency (ASI), and the Autonomous Region of Sardinia (RAS) and is operated as a National Facility by the National Institute for Astrophysics (INAF). The work is supported by the National SKA programme of China (2020SKA0120100), Max-Planck Partner Group, NSFC 11690024, CAS Cultivation Project for FAST Scientific. This work is also supported as part of the “LEGACY” MPG-CAS collaboration on low-frequency gravitational wave astronomy. JA acknowledges support from the European Commission (Grant Agreement number: 101094354). JA and SCha were partially supported by the Stavros Niarchos Foundation (SNF) and the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the 2nd Call of the “Science and Society – Action Always strive for excellence – Theodoros Papazoglou” (Project Number: 01431). AC acknowledges support from the Paris Région Île-de-France. AC, AF, ASe, ASa, EB, DI, GMS, MBo acknowledge financial support provided under the European Union’s H2020 ERC Consolidator Grant “Binary Massive Black Hole Astrophysics” (B Massive, Grant Agreement: 818691). GD, KLi, RK and MK acknowledge support from European Research Council (ERC) Synergy Grant “BlackHoleCam”, Grant Agreement Number 610058. This work is supported by the ERC Advanced Grant “LEAP”, Grant Agreement Number 227947 (PI M. Kramer). AV and PRB are supported by the UK’s Science and Technology Facilities Council (STFC; grant ST/W000946/1). AV also acknowledges the support of the Royal Society and Wolfson Foundation. JPWV acknowledges support by the Deutsche Forschungsgemeinschaft (DFG) through thew Heisenberg programme (Project No. 433075039) and by the NSF through AccelNet award #2114721. NKP is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Projektnummer PO 2758/1–1, through the Walter–Benjamin programme. ASa thanks the Alexander von Humboldt foundation in Germany for a Humboldt fellowship for postdoctoral researchers. APo, DP and MBu acknowledge support from the research grant “iPeska” (P.I. Andrea Possenti) funded under the INAF national call Prin-SKA/CTA approved with the Presidential Decree 70/2016 (Italy). RNC acknowledges financial support from the Special Account for Research Funds of the Hellenic Open University (ELKE-HOU) under the research programme “GRAVPUL” (K.E.-80383/grant agreement 319/10-10-2022: PI N. A. B. Gizani). EvdW, CGB and GHJ acknowledge support from the Dutch National Science Agenda, NWA Startimpuls – 400.17.608. BG is supported by the Italian Ministry of Education, University and Research within the PRIN 2017 Research Program Framework, n. 2017SYRTCN. LS acknowledges the use of the HPC system Cobra at the Max Planck Computing and Data Facility. The Indian Pulsar Timing Array (InPTA) is an Indo-Japanese collaboration that routinely employs TIFR’s upgraded Giant Metrewave Radio Telescope for monitoring a set of IPTA pulsars. BCJ, YG, YM, SD, AG and PR acknowledge the support of the Department of Atomic Energy, Government of India, under Project Identification # RTI 4002. BCJ, YG and YM acknowledge support of the Department of Atomic Energy, Government of India, under project No. 12-R&D-TFR-5.02-0700 while SD, AG and PR acknowledge support of the Department of Atomic Energy, Government of India, under project no. 12-R&D-TFR-5.02-0200. KT is partially supported by JSPS KAKENHI Grant Numbers 20H00180, 21H01130, and 21H04467, Bilateral Joint Research Projects of JSPS, and the ISM Cooperative Research Program (2021-ISMCRP-2017). AS is supported by the NANOGrav NSF Physics Frontiers Center (awards #1430284 and 2020265). AKP is supported by CSIR fellowship Grant number 09/0079(15784)/2022-EMR-I. SH is supported by JSPS KAKENHI Grant Number 20J20509. KN is supported by the Birla Institute of Technology & Science Institute fellowship. AmS is supported by 0CSIR fellowship Grant number 09/1001(12656)/2021-EMR-I and T-641 (DST-ICPS). TK is partially supported by the JSPS Overseas Challenge Program for Young Researchers. We acknowledge the National Supercomputing Mission (NSM) for providing computing resources of ‘PARAM Ganga’ at the Indian Institute of Technology Roorkee as well as ‘PARAM Seva’ at IIT Hyderabad, which is implemented by C-DAC and supported by the Ministry of Electronics and Information Technology (MeitY) and Department of Science and Technology (DST), Government of India. DD acknowledges the support from the Department of Atomic Energy, Government of India through Apex Project – Advance Research and Education in Mathematical Sciences at IMSc. The work presented here is a culmination of many years of data analysis as well as software and instrument development. In particular, we thank Drs. N. D’Amico, P. C. C. Freire, R. van Haasteren, C. Jordan, K. Lazaridis, P. Lazarus, L. Lentati, O. Löhmer and R. Smits for their past contributions. We also thank Dr. N. Wex for supporting the calculations of the galactic acceleration as well as the related discussions. The EPTA is also grateful to staff at its observatories and telescopes who have made the continued observations possible. Author contributions: The European Pulsar Timing Array: JA, SB, ASBN, CGB, ABe, MBo, EB, PRB, MBu, RNC, AC, DJC, SCha, SChe, IC, GD, MF, RDF, AF, JRG, BG, EG, JMG, LG, YJG, HH, FI, DIV, JJan, JJaw, GHJ, AJ, RK, EFK, MJK, MK, MAK, KLa, KJL, KLi, YL, AGL, JWM, RAM, MBM, ICN, APa, BBPP, DP, APe, NKP, APo, HQL, ASa, SAS, ASe, GS, LS, RS, BWS, SCS, GT, CT, EvdW, AV, VVK, JPWV, JW, LW and ZW. The EPTA is a multi-decade effort and all authors have contributed through conceptualisation, funding acquisition, data-curation, methodology, software and hardware developments as well as (aspects of) the continued running of the observational campaigns, which includes writing and proofreading observing proposals, evaluating observations and observing systems, mentoring students, developing science cases. All authors also helped in (aspects of) verification of the data, analysis and results as well as in finalising the paper draft. Specific contributions from individual EPTA members are listed in the CRediT (https://credit.niso.org/) format below. The Indian Pulsar Timing Array: PA, SA, MB, ABa, SDa, DD, SDe, NDB, CD, YG, SH, BCJ, FK, DK, TK, NK, MAK, YM, KN, AKP, TP, PR, JS, ASr, MS, ASu, KT and PT. InPTA members contributed in uGMRT observations and data reduction to create the InPTA data set which is employed while assembling the DR2full+ and DR2new+ data sets. Additionally, InPTA members contributed to GWB search efforts with DR2full+ and DR2new+ data sets and their interpretations. Further, they provided quantitative comparisons of GWB posteriors that arise from these data sets and multiple pipelines. For this work specifically, SChen and YJG equally share the correspondence of the paper. CRediT statement: Conceptualisation: AC, APa, APe, APo, ASe, AV, BG, CT, GMS, GT, IC, JA, JPWV, JWM, KJL, KLi, MK. Methodology: AC, APa, ASe, AV, DJC, GMS, JWM, KJL, KLi, LS, MK, SChe. Software: AC, AJ, APa, APe, GD, GMS, KJL, KLi, MJK, RK, SChe, VVK. Validation: AC, APa, ASe, AV, BG, GMS, HQL, JPWV, JWM, KLi, LS, SChe, YJG. Formal Analysis: AC, APa, ASe, AV, BG, EvdW, GMS, HQL, JWM, KLi, LS, MF, NKP, PRB, SChe, YJG. Investigation: APa, APo, ASe, AV, BWS, CGB, DJC, DP, GMS, JWM, KLi, LS, MBM, MBu, MF, PRB, RK, SB, SChe, YJG. Resources: AC, APa, APe, APo, ASe, AV, BWS, GHJ, GMS, GT, IC, JPWV, JWM, KJL, KLi, LG, LS, MJK, MK, RK. Data Curation: AC, AJ, APa, BWS, CGB, DJC, DP, EvdW, GMS, JA, JWM, KLi, MBM, MJK, MK, RK, SChe. Writing - Original Draft: AC, APa, BG, DJC, GMS, JA, KLi, SB, SChe, YJG. Writing - Review & Editing: AC, AF, APa, APo, ASe, AV, BG, DJC, EB, EFK, GMS, GT, JA, JPWV, JWM, KLi, LS, MBo, MK, NKP, PRB, SChe, VVK, YJG. Visualisation: APa, BG, GMS, KLi, MF, PRB, SChe. Supervision: APo, ASe, AV, BWS, CGB, DJC, EFK, GHJ, GMS, GT, JPWV, KJL, MK, SB. Project Administration: APo, ASe, AV, BWS, CGB, CT, GHJ, GMS, GT, JPWV, JWM, LG, MK, SChe. Funding Acquisition: APe, APo, ASe, AV, BWS, GHJ, GT, IC, JA, LG, MJK, MK, SB.

Keywords

gravitational waves
methods:data analysis
pulsars:general

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10.1051/0004-6361/202346844Licence: Creative Commons: Attribution (CC BY)

AntoniadisJ2023secondFinal published version, 2.06 MBLicence: Creative Commons: Attribution (CC BY)

Astrophysics at the University of Birmingham - Consolidated grant 2022-2025
Moore, C. & Vecchio, A.
SCIENCE & TECHNOLOGY FACILITIES COUNCIL
1/04/22 → 31/03/25
Project: Research Councils

Cite this

@article{745dcb8fad824beb9a1bb8f6cc460eb0,

title = "The second data release from the European Pulsar Timing Array: III. Search for gravitational wave signals",

abstract = "We present the results of the search for an isotropic stochastic gravitational wave background (GWB) at nanohertz frequencies using the second data release of the European Pulsar Timing Array (EPTA) for 25 millisecond pulsars and a combination with the first data release of the Indian Pulsar Timing Array (InPTA). A robust GWB detection is conditioned upon resolving the Hellings-Downs angular pattern in the pairwise crosscorrelation of the pulsar timing residuals. Additionally, the GWB is expected to yield the same (common) spectrum of temporal correlations across pulsars, which is used as a null hypothesis in the GWB search. Such a common-spectrum process has already been observed in pulsar timing data. We analysed (i) the full 24.7-year EPTA data set, (ii) its 10.3-year subset based on modern observing systems, (iii) the combination of the full data set with the first data release of the InPTA for ten commonly timed millisecond pulsars, and (iv) the combination of the 10.3-year subset with the InPTA data. These combinations allowed us to probe the contributions of instrumental noise and interstellar propagation effects. With the full data set, we find marginal evidence for a GWB, with a Bayes factor of four and a false alarm probability of 4%. With the 10.3-year subset, we report evidence for a GWB, with a Bayes factor of 60 and a false alarm probability of about 0.1% (≳ 3σ significance). The addition of the InPTA data yields results that are broadly consistent with the EPTA-only data sets, with the benefit of better noise modelling. Analyses were performed with different data processing pipelines to test the consistency of the results from independent software packages. The latest EPTA data from new generation observing systems show non-negligible evidence for the GWB. At the same time, the inferred spectrum is rather uncertain and in mild tension with the common signal measured in the full data set. However, if the spectral index is fixed at 13/3, the two data sets give a similar amplitude of (2.5±0.7)×10−15 at a reference frequency of 1 yr−1 . Further investigation of these issues is required for reliable astrophysical interpretations of this signal. By continuing our detection efforts as part of the International Pulsar Timing Array (IPTA), we expect to be able to improve the measurement of spatial correlations and better characterise this signal in the coming years. ",

keywords = "gravitational waves, methods:data analysis, pulsars:general",

author = "{EPTA collaboration} and {InPTA Collaboration} and J. Antoniadis and P. Arumugam and S. Arumugam and S. Babak and M. Bagchi and Nielsen, {A. -S. Bak} and Bassa, {C. G.} and A. Bathula and A. Berthereau and M. Bonetti and E. Bortolas and Brook, {P. R.} and M. Burgay and Caballero, {R. N.} and A. Chalumeau and Champion, {D. J.} and S. Chanlaridis and S. Chen and I. Cognard and S. Dandapat and D. Deb and S. Desai and G. Desvignes and N. Dhanda-Batra and C. Dwivedi and M. Falxa and Ferdman, {R. D.} and A. Franchini and Gair, {J. R.} and B. Goncharov and A. Gopakumar and E. Graikou and Grie{\ss}meier, {J. -M.} and L. Guillemot and Guo, {Y. J.} and Y. Gupta and S. Hisano and H. Hu and F. Iraci and D. Izquierdo-Villalba and J. Jang and J. Jawor and Janssen, {G. H.} and A. Jessner and Joshi, {B. C.} and F. Kareem and R. Karuppusamy and Keane, {E. F.} and Keith, {M. J.} and A. Vecchio",

note = "Acknowledgments: The European Pulsar Timing Array (EPTA) is a collaboration between European and partner institutes, namely ASTRON (NL), INAF/Osservatorio di Cagliari (IT), Max-Planck-Institut f{\"u}r Radioastronomie (GER), Nan{\c c}ay/Paris Observatory (FRA), the University of Manchester (UK), the University of Birmingham (UK), the University of East Anglia (UK), the University of Bielefeld (GER), the University of Paris (FRA), the University of Milan-Bicocca (IT), the Foundation for Research and Technology, Hellas (GR), and Peking University (CHN), with the aim to provide high-precision pulsar timing to work towards the direct detection of low-frequency gravitational waves. An Advanced Grant of the European Research Council allowed to implement the Large European Array for Pulsars (LEAP) under Grant Agreement Number 227947 (PI M. Kramer). The EPTA is part of the International Pulsar Timing Array (IPTA); we thank our IPTA colleagues for their support and help with this paper and the external Detection Committee members for their work on the Detection Checklist. Part of this work is based on observations with the 100-m telescope of the Max-Planck-Institut f{\"u}r Radioastronomie (MPIfR) at Effelsberg in Germany. Pulsar research at the Jodrell Bank Centre for Astrophysics and the observations using the Lovell Telescope are supported by a Consolidated Grant (ST/T000414/1) from the UK{\textquoteright}s Science and Technology Facilities Council (STFC). ICN is also supported by the STFC doctoral training grant ST/T506291/1. The Nan{\c c}ay radio Observatory is operated by the Paris Observatory, associated with the French Centre National de la Recherche Scientifique (CNRS), and partially supported by the Region Centre in France. We acknowledge financial support from “Programme National de Cosmologie and Galaxies” (PNCG), and “Programme National Hautes Energies” (PNHE) funded by CNRS/INSU-IN2P3-INP, CEA and CNES, France. We acknowledge financial support from Agence Nationale de la Recherche (ANR-18-CE31-0015), France. The Westerbork Synthesis Radio Telescope is operated by the Netherlands Institute for Radio Astronomy (ASTRON) with support from the Netherlands Foundation for Scientific Research (NWO). The Sardinia Radio Telescope (SRT) is funded by the Department of University and Research (MIUR), the Italian Space Agency (ASI), and the Autonomous Region of Sardinia (RAS) and is operated as a National Facility by the National Institute for Astrophysics (INAF). The work is supported by the National SKA programme of China (2020SKA0120100), Max-Planck Partner Group, NSFC 11690024, CAS Cultivation Project for FAST Scientific. This work is also supported as part of the “LEGACY” MPG-CAS collaboration on low-frequency gravitational wave astronomy. JA acknowledges support from the European Commission (Grant Agreement number: 101094354). JA and SCha were partially supported by the Stavros Niarchos Foundation (SNF) and the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the 2nd Call of the “Science and Society – Action Always strive for excellence – Theodoros Papazoglou” (Project Number: 01431). AC acknowledges support from the Paris R{\'e}gion {\^I}le-de-France. AC, AF, ASe, ASa, EB, DI, GMS, MBo acknowledge financial support provided under the European Union{\textquoteright}s H2020 ERC Consolidator Grant “Binary Massive Black Hole Astrophysics” (B Massive, Grant Agreement: 818691). GD, KLi, RK and MK acknowledge support from European Research Council (ERC) Synergy Grant “BlackHoleCam”, Grant Agreement Number 610058. This work is supported by the ERC Advanced Grant “LEAP”, Grant Agreement Number 227947 (PI M. Kramer). AV and PRB are supported by the UK{\textquoteright}s Science and Technology Facilities Council (STFC; grant ST/W000946/1). AV also acknowledges the support of the Royal Society and Wolfson Foundation. JPWV acknowledges support by the Deutsche Forschungsgemeinschaft (DFG) through thew Heisenberg programme (Project No. 433075039) and by the NSF through AccelNet award #2114721. NKP is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Projektnummer PO 2758/1–1, through the Walter–Benjamin programme. ASa thanks the Alexander von Humboldt foundation in Germany for a Humboldt fellowship for postdoctoral researchers. APo, DP and MBu acknowledge support from the research grant “iPeska” (P.I. Andrea Possenti) funded under the INAF national call Prin-SKA/CTA approved with the Presidential Decree 70/2016 (Italy). RNC acknowledges financial support from the Special Account for Research Funds of the Hellenic Open University (ELKE-HOU) under the research programme “GRAVPUL” (K.E.-80383/grant agreement 319/10-10-2022: PI N. A. B. Gizani). EvdW, CGB and GHJ acknowledge support from the Dutch National Science Agenda, NWA Startimpuls – 400.17.608. BG is supported by the Italian Ministry of Education, University and Research within the PRIN 2017 Research Program Framework, n. 2017SYRTCN. LS acknowledges the use of the HPC system Cobra at the Max Planck Computing and Data Facility. The Indian Pulsar Timing Array (InPTA) is an Indo-Japanese collaboration that routinely employs TIFR{\textquoteright}s upgraded Giant Metrewave Radio Telescope for monitoring a set of IPTA pulsars. BCJ, YG, YM, SD, AG and PR acknowledge the support of the Department of Atomic Energy, Government of India, under Project Identification # RTI 4002. BCJ, YG and YM acknowledge support of the Department of Atomic Energy, Government of India, under project No. 12-R&D-TFR-5.02-0700 while SD, AG and PR acknowledge support of the Department of Atomic Energy, Government of India, under project no. 12-R&D-TFR-5.02-0200. KT is partially supported by JSPS KAKENHI Grant Numbers 20H00180, 21H01130, and 21H04467, Bilateral Joint Research Projects of JSPS, and the ISM Cooperative Research Program (2021-ISMCRP-2017). AS is supported by the NANOGrav NSF Physics Frontiers Center (awards #1430284 and 2020265). AKP is supported by CSIR fellowship Grant number 09/0079(15784)/2022-EMR-I. SH is supported by JSPS KAKENHI Grant Number 20J20509. KN is supported by the Birla Institute of Technology & Science Institute fellowship. AmS is supported by 0CSIR fellowship Grant number 09/1001(12656)/2021-EMR-I and T-641 (DST-ICPS). TK is partially supported by the JSPS Overseas Challenge Program for Young Researchers. We acknowledge the National Supercomputing Mission (NSM) for providing computing resources of {\textquoteleft}PARAM Ganga{\textquoteright} at the Indian Institute of Technology Roorkee as well as {\textquoteleft}PARAM Seva{\textquoteright} at IIT Hyderabad, which is implemented by C-DAC and supported by the Ministry of Electronics and Information Technology (MeitY) and Department of Science and Technology (DST), Government of India. DD acknowledges the support from the Department of Atomic Energy, Government of India through Apex Project – Advance Research and Education in Mathematical Sciences at IMSc. The work presented here is a culmination of many years of data analysis as well as software and instrument development. In particular, we thank Drs. N. D{\textquoteright}Amico, P. C. C. Freire, R. van Haasteren, C. Jordan, K. Lazaridis, P. Lazarus, L. Lentati, O. L{\"o}hmer and R. Smits for their past contributions. We also thank Dr. N. Wex for supporting the calculations of the galactic acceleration as well as the related discussions. The EPTA is also grateful to staff at its observatories and telescopes who have made the continued observations possible. Author contributions: The European Pulsar Timing Array: JA, SB, ASBN, CGB, ABe, MBo, EB, PRB, MBu, RNC, AC, DJC, SCha, SChe, IC, GD, MF, RDF, AF, JRG, BG, EG, JMG, LG, YJG, HH, FI, DIV, JJan, JJaw, GHJ, AJ, RK, EFK, MJK, MK, MAK, KLa, KJL, KLi, YL, AGL, JWM, RAM, MBM, ICN, APa, BBPP, DP, APe, NKP, APo, HQL, ASa, SAS, ASe, GS, LS, RS, BWS, SCS, GT, CT, EvdW, AV, VVK, JPWV, JW, LW and ZW. The EPTA is a multi-decade effort and all authors have contributed through conceptualisation, funding acquisition, data-curation, methodology, software and hardware developments as well as (aspects of) the continued running of the observational campaigns, which includes writing and proofreading observing proposals, evaluating observations and observing systems, mentoring students, developing science cases. All authors also helped in (aspects of) verification of the data, analysis and results as well as in finalising the paper draft. Specific contributions from individual EPTA members are listed in the CRediT (https://credit.niso.org/) format below. The Indian Pulsar Timing Array: PA, SA, MB, ABa, SDa, DD, SDe, NDB, CD, YG, SH, BCJ, FK, DK, TK, NK, MAK, YM, KN, AKP, TP, PR, JS, ASr, MS, ASu, KT and PT. InPTA members contributed in uGMRT observations and data reduction to create the InPTA data set which is employed while assembling the DR2full+ and DR2new+ data sets. Additionally, InPTA members contributed to GWB search efforts with DR2full+ and DR2new+ data sets and their interpretations. Further, they provided quantitative comparisons of GWB posteriors that arise from these data sets and multiple pipelines. For this work specifically, SChen and YJG equally share the correspondence of the paper. CRediT statement: Conceptualisation: AC, APa, APe, APo, ASe, AV, BG, CT, GMS, GT, IC, JA, JPWV, JWM, KJL, KLi, MK. Methodology: AC, APa, ASe, AV, DJC, GMS, JWM, KJL, KLi, LS, MK, SChe. Software: AC, AJ, APa, APe, GD, GMS, KJL, KLi, MJK, RK, SChe, VVK. Validation: AC, APa, ASe, AV, BG, GMS, HQL, JPWV, JWM, KLi, LS, SChe, YJG. Formal Analysis: AC, APa, ASe, AV, BG, EvdW, GMS, HQL, JWM, KLi, LS, MF, NKP, PRB, SChe, YJG. Investigation: APa, APo, ASe, AV, BWS, CGB, DJC, DP, GMS, JWM, KLi, LS, MBM, MBu, MF, PRB, RK, SB, SChe, YJG. Resources: AC, APa, APe, APo, ASe, AV, BWS, GHJ, GMS, GT, IC, JPWV, JWM, KJL, KLi, LG, LS, MJK, MK, RK. Data Curation: AC, AJ, APa, BWS, CGB, DJC, DP, EvdW, GMS, JA, JWM, KLi, MBM, MJK, MK, RK, SChe. Writing - Original Draft: AC, APa, BG, DJC, GMS, JA, KLi, SB, SChe, YJG. Writing - Review & Editing: AC, AF, APa, APo, ASe, AV, BG, DJC, EB, EFK, GMS, GT, JA, JPWV, JWM, KLi, LS, MBo, MK, NKP, PRB, SChe, VVK, YJG. Visualisation: APa, BG, GMS, KLi, MF, PRB, SChe. Supervision: APo, ASe, AV, BWS, CGB, DJC, EFK, GHJ, GMS, GT, JPWV, KJL, MK, SB. Project Administration: APo, ASe, AV, BWS, CGB, CT, GHJ, GMS, GT, JPWV, JWM, LG, MK, SChe. Funding Acquisition: APe, APo, ASe, AV, BWS, GHJ, GT, IC, JA, LG, MJK, MK, SB.",

year = "2023",

month = oct,

day = "3",

doi = "10.1051/0004-6361/202346844",

language = "English",

volume = "678",

journal = "Astronomy and Astrophysics",

issn = "0004-6361",

publisher = "EDP Sciences",

}

TY - JOUR

T1 - The second data release from the European Pulsar Timing Array

T2 - III. Search for gravitational wave signals

AU - EPTA collaboration

AU - InPTA Collaboration

AU - Antoniadis, J.

AU - Arumugam, P.

AU - Arumugam, S.

AU - Babak, S.

AU - Bagchi, M.

AU - Nielsen, A. -S. Bak

AU - Bassa, C. G.

AU - Bathula, A.

AU - Berthereau, A.

AU - Bonetti, M.

AU - Bortolas, E.

AU - Brook, P. R.

AU - Burgay, M.

AU - Caballero, R. N.

AU - Chalumeau, A.

AU - Champion, D. J.

AU - Chanlaridis, S.

AU - Chen, S.

AU - Cognard, I.

AU - Dandapat, S.

AU - Deb, D.

AU - Desai, S.

AU - Desvignes, G.

AU - Dhanda-Batra, N.

AU - Dwivedi, C.

AU - Falxa, M.

AU - Ferdman, R. D.

AU - Franchini, A.

AU - Gair, J. R.

AU - Goncharov, B.

AU - Gopakumar, A.

AU - Graikou, E.

AU - Grießmeier, J. -M.

AU - Guillemot, L.

AU - Guo, Y. J.

AU - Gupta, Y.

AU - Hisano, S.

AU - Hu, H.

AU - Iraci, F.

AU - Izquierdo-Villalba, D.

AU - Jang, J.

AU - Jawor, J.

AU - Janssen, G. H.

AU - Jessner, A.

AU - Joshi, B. C.

AU - Kareem, F.

AU - Karuppusamy, R.

AU - Keane, E. F.

AU - Keith, M. J.

AU - Vecchio, A.

N1 - Acknowledgments: The European Pulsar Timing Array (EPTA) is a collaboration between European and partner institutes, namely ASTRON (NL), INAF/Osservatorio di Cagliari (IT), Max-Planck-Institut für Radioastronomie (GER), Nançay/Paris Observatory (FRA), the University of Manchester (UK), the University of Birmingham (UK), the University of East Anglia (UK), the University of Bielefeld (GER), the University of Paris (FRA), the University of Milan-Bicocca (IT), the Foundation for Research and Technology, Hellas (GR), and Peking University (CHN), with the aim to provide high-precision pulsar timing to work towards the direct detection of low-frequency gravitational waves. An Advanced Grant of the European Research Council allowed to implement the Large European Array for Pulsars (LEAP) under Grant Agreement Number 227947 (PI M. Kramer). The EPTA is part of the International Pulsar Timing Array (IPTA); we thank our IPTA colleagues for their support and help with this paper and the external Detection Committee members for their work on the Detection Checklist. Part of this work is based on observations with the 100-m telescope of the Max-Planck-Institut für Radioastronomie (MPIfR) at Effelsberg in Germany. Pulsar research at the Jodrell Bank Centre for Astrophysics and the observations using the Lovell Telescope are supported by a Consolidated Grant (ST/T000414/1) from the UK’s Science and Technology Facilities Council (STFC). ICN is also supported by the STFC doctoral training grant ST/T506291/1. The Nançay radio Observatory is operated by the Paris Observatory, associated with the French Centre National de la Recherche Scientifique (CNRS), and partially supported by the Region Centre in France. We acknowledge financial support from “Programme National de Cosmologie and Galaxies” (PNCG), and “Programme National Hautes Energies” (PNHE) funded by CNRS/INSU-IN2P3-INP, CEA and CNES, France. We acknowledge financial support from Agence Nationale de la Recherche (ANR-18-CE31-0015), France. The Westerbork Synthesis Radio Telescope is operated by the Netherlands Institute for Radio Astronomy (ASTRON) with support from the Netherlands Foundation for Scientific Research (NWO). The Sardinia Radio Telescope (SRT) is funded by the Department of University and Research (MIUR), the Italian Space Agency (ASI), and the Autonomous Region of Sardinia (RAS) and is operated as a National Facility by the National Institute for Astrophysics (INAF). The work is supported by the National SKA programme of China (2020SKA0120100), Max-Planck Partner Group, NSFC 11690024, CAS Cultivation Project for FAST Scientific. This work is also supported as part of the “LEGACY” MPG-CAS collaboration on low-frequency gravitational wave astronomy. JA acknowledges support from the European Commission (Grant Agreement number: 101094354). JA and SCha were partially supported by the Stavros Niarchos Foundation (SNF) and the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the 2nd Call of the “Science and Society – Action Always strive for excellence – Theodoros Papazoglou” (Project Number: 01431). AC acknowledges support from the Paris Région Île-de-France. AC, AF, ASe, ASa, EB, DI, GMS, MBo acknowledge financial support provided under the European Union’s H2020 ERC Consolidator Grant “Binary Massive Black Hole Astrophysics” (B Massive, Grant Agreement: 818691). GD, KLi, RK and MK acknowledge support from European Research Council (ERC) Synergy Grant “BlackHoleCam”, Grant Agreement Number 610058. This work is supported by the ERC Advanced Grant “LEAP”, Grant Agreement Number 227947 (PI M. Kramer). AV and PRB are supported by the UK’s Science and Technology Facilities Council (STFC; grant ST/W000946/1). AV also acknowledges the support of the Royal Society and Wolfson Foundation. JPWV acknowledges support by the Deutsche Forschungsgemeinschaft (DFG) through thew Heisenberg programme (Project No. 433075039) and by the NSF through AccelNet award #2114721. NKP is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) – Projektnummer PO 2758/1–1, through the Walter–Benjamin programme. ASa thanks the Alexander von Humboldt foundation in Germany for a Humboldt fellowship for postdoctoral researchers. APo, DP and MBu acknowledge support from the research grant “iPeska” (P.I. Andrea Possenti) funded under the INAF national call Prin-SKA/CTA approved with the Presidential Decree 70/2016 (Italy). RNC acknowledges financial support from the Special Account for Research Funds of the Hellenic Open University (ELKE-HOU) under the research programme “GRAVPUL” (K.E.-80383/grant agreement 319/10-10-2022: PI N. A. B. Gizani). EvdW, CGB and GHJ acknowledge support from the Dutch National Science Agenda, NWA Startimpuls – 400.17.608. BG is supported by the Italian Ministry of Education, University and Research within the PRIN 2017 Research Program Framework, n. 2017SYRTCN. LS acknowledges the use of the HPC system Cobra at the Max Planck Computing and Data Facility. The Indian Pulsar Timing Array (InPTA) is an Indo-Japanese collaboration that routinely employs TIFR’s upgraded Giant Metrewave Radio Telescope for monitoring a set of IPTA pulsars. BCJ, YG, YM, SD, AG and PR acknowledge the support of the Department of Atomic Energy, Government of India, under Project Identification # RTI 4002. BCJ, YG and YM acknowledge support of the Department of Atomic Energy, Government of India, under project No. 12-R&D-TFR-5.02-0700 while SD, AG and PR acknowledge support of the Department of Atomic Energy, Government of India, under project no. 12-R&D-TFR-5.02-0200. KT is partially supported by JSPS KAKENHI Grant Numbers 20H00180, 21H01130, and 21H04467, Bilateral Joint Research Projects of JSPS, and the ISM Cooperative Research Program (2021-ISMCRP-2017). AS is supported by the NANOGrav NSF Physics Frontiers Center (awards #1430284 and 2020265). AKP is supported by CSIR fellowship Grant number 09/0079(15784)/2022-EMR-I. SH is supported by JSPS KAKENHI Grant Number 20J20509. KN is supported by the Birla Institute of Technology & Science Institute fellowship. AmS is supported by 0CSIR fellowship Grant number 09/1001(12656)/2021-EMR-I and T-641 (DST-ICPS). TK is partially supported by the JSPS Overseas Challenge Program for Young Researchers. We acknowledge the National Supercomputing Mission (NSM) for providing computing resources of ‘PARAM Ganga’ at the Indian Institute of Technology Roorkee as well as ‘PARAM Seva’ at IIT Hyderabad, which is implemented by C-DAC and supported by the Ministry of Electronics and Information Technology (MeitY) and Department of Science and Technology (DST), Government of India. DD acknowledges the support from the Department of Atomic Energy, Government of India through Apex Project – Advance Research and Education in Mathematical Sciences at IMSc. The work presented here is a culmination of many years of data analysis as well as software and instrument development. In particular, we thank Drs. N. D’Amico, P. C. C. Freire, R. van Haasteren, C. Jordan, K. Lazaridis, P. Lazarus, L. Lentati, O. Löhmer and R. Smits for their past contributions. We also thank Dr. N. Wex for supporting the calculations of the galactic acceleration as well as the related discussions. The EPTA is also grateful to staff at its observatories and telescopes who have made the continued observations possible. Author contributions: The European Pulsar Timing Array: JA, SB, ASBN, CGB, ABe, MBo, EB, PRB, MBu, RNC, AC, DJC, SCha, SChe, IC, GD, MF, RDF, AF, JRG, BG, EG, JMG, LG, YJG, HH, FI, DIV, JJan, JJaw, GHJ, AJ, RK, EFK, MJK, MK, MAK, KLa, KJL, KLi, YL, AGL, JWM, RAM, MBM, ICN, APa, BBPP, DP, APe, NKP, APo, HQL, ASa, SAS, ASe, GS, LS, RS, BWS, SCS, GT, CT, EvdW, AV, VVK, JPWV, JW, LW and ZW. The EPTA is a multi-decade effort and all authors have contributed through conceptualisation, funding acquisition, data-curation, methodology, software and hardware developments as well as (aspects of) the continued running of the observational campaigns, which includes writing and proofreading observing proposals, evaluating observations and observing systems, mentoring students, developing science cases. All authors also helped in (aspects of) verification of the data, analysis and results as well as in finalising the paper draft. Specific contributions from individual EPTA members are listed in the CRediT (https://credit.niso.org/) format below. The Indian Pulsar Timing Array: PA, SA, MB, ABa, SDa, DD, SDe, NDB, CD, YG, SH, BCJ, FK, DK, TK, NK, MAK, YM, KN, AKP, TP, PR, JS, ASr, MS, ASu, KT and PT. InPTA members contributed in uGMRT observations and data reduction to create the InPTA data set which is employed while assembling the DR2full+ and DR2new+ data sets. Additionally, InPTA members contributed to GWB search efforts with DR2full+ and DR2new+ data sets and their interpretations. Further, they provided quantitative comparisons of GWB posteriors that arise from these data sets and multiple pipelines. For this work specifically, SChen and YJG equally share the correspondence of the paper. CRediT statement: Conceptualisation: AC, APa, APe, APo, ASe, AV, BG, CT, GMS, GT, IC, JA, JPWV, JWM, KJL, KLi, MK. Methodology: AC, APa, ASe, AV, DJC, GMS, JWM, KJL, KLi, LS, MK, SChe. Software: AC, AJ, APa, APe, GD, GMS, KJL, KLi, MJK, RK, SChe, VVK. Validation: AC, APa, ASe, AV, BG, GMS, HQL, JPWV, JWM, KLi, LS, SChe, YJG. Formal Analysis: AC, APa, ASe, AV, BG, EvdW, GMS, HQL, JWM, KLi, LS, MF, NKP, PRB, SChe, YJG. Investigation: APa, APo, ASe, AV, BWS, CGB, DJC, DP, GMS, JWM, KLi, LS, MBM, MBu, MF, PRB, RK, SB, SChe, YJG. Resources: AC, APa, APe, APo, ASe, AV, BWS, GHJ, GMS, GT, IC, JPWV, JWM, KJL, KLi, LG, LS, MJK, MK, RK. Data Curation: AC, AJ, APa, BWS, CGB, DJC, DP, EvdW, GMS, JA, JWM, KLi, MBM, MJK, MK, RK, SChe. Writing - Original Draft: AC, APa, BG, DJC, GMS, JA, KLi, SB, SChe, YJG. Writing - Review & Editing: AC, AF, APa, APo, ASe, AV, BG, DJC, EB, EFK, GMS, GT, JA, JPWV, JWM, KLi, LS, MBo, MK, NKP, PRB, SChe, VVK, YJG. Visualisation: APa, BG, GMS, KLi, MF, PRB, SChe. Supervision: APo, ASe, AV, BWS, CGB, DJC, EFK, GHJ, GMS, GT, JPWV, KJL, MK, SB. Project Administration: APo, ASe, AV, BWS, CGB, CT, GHJ, GMS, GT, JPWV, JWM, LG, MK, SChe. Funding Acquisition: APe, APo, ASe, AV, BWS, GHJ, GT, IC, JA, LG, MJK, MK, SB.

PY - 2023/10/3

Y1 - 2023/10/3

N2 - We present the results of the search for an isotropic stochastic gravitational wave background (GWB) at nanohertz frequencies using the second data release of the European Pulsar Timing Array (EPTA) for 25 millisecond pulsars and a combination with the first data release of the Indian Pulsar Timing Array (InPTA). A robust GWB detection is conditioned upon resolving the Hellings-Downs angular pattern in the pairwise crosscorrelation of the pulsar timing residuals. Additionally, the GWB is expected to yield the same (common) spectrum of temporal correlations across pulsars, which is used as a null hypothesis in the GWB search. Such a common-spectrum process has already been observed in pulsar timing data. We analysed (i) the full 24.7-year EPTA data set, (ii) its 10.3-year subset based on modern observing systems, (iii) the combination of the full data set with the first data release of the InPTA for ten commonly timed millisecond pulsars, and (iv) the combination of the 10.3-year subset with the InPTA data. These combinations allowed us to probe the contributions of instrumental noise and interstellar propagation effects. With the full data set, we find marginal evidence for a GWB, with a Bayes factor of four and a false alarm probability of 4%. With the 10.3-year subset, we report evidence for a GWB, with a Bayes factor of 60 and a false alarm probability of about 0.1% (≳ 3σ significance). The addition of the InPTA data yields results that are broadly consistent with the EPTA-only data sets, with the benefit of better noise modelling. Analyses were performed with different data processing pipelines to test the consistency of the results from independent software packages. The latest EPTA data from new generation observing systems show non-negligible evidence for the GWB. At the same time, the inferred spectrum is rather uncertain and in mild tension with the common signal measured in the full data set. However, if the spectral index is fixed at 13/3, the two data sets give a similar amplitude of (2.5±0.7)×10−15 at a reference frequency of 1 yr−1 . Further investigation of these issues is required for reliable astrophysical interpretations of this signal. By continuing our detection efforts as part of the International Pulsar Timing Array (IPTA), we expect to be able to improve the measurement of spatial correlations and better characterise this signal in the coming years.

AB - We present the results of the search for an isotropic stochastic gravitational wave background (GWB) at nanohertz frequencies using the second data release of the European Pulsar Timing Array (EPTA) for 25 millisecond pulsars and a combination with the first data release of the Indian Pulsar Timing Array (InPTA). A robust GWB detection is conditioned upon resolving the Hellings-Downs angular pattern in the pairwise crosscorrelation of the pulsar timing residuals. Additionally, the GWB is expected to yield the same (common) spectrum of temporal correlations across pulsars, which is used as a null hypothesis in the GWB search. Such a common-spectrum process has already been observed in pulsar timing data. We analysed (i) the full 24.7-year EPTA data set, (ii) its 10.3-year subset based on modern observing systems, (iii) the combination of the full data set with the first data release of the InPTA for ten commonly timed millisecond pulsars, and (iv) the combination of the 10.3-year subset with the InPTA data. These combinations allowed us to probe the contributions of instrumental noise and interstellar propagation effects. With the full data set, we find marginal evidence for a GWB, with a Bayes factor of four and a false alarm probability of 4%. With the 10.3-year subset, we report evidence for a GWB, with a Bayes factor of 60 and a false alarm probability of about 0.1% (≳ 3σ significance). The addition of the InPTA data yields results that are broadly consistent with the EPTA-only data sets, with the benefit of better noise modelling. Analyses were performed with different data processing pipelines to test the consistency of the results from independent software packages. The latest EPTA data from new generation observing systems show non-negligible evidence for the GWB. At the same time, the inferred spectrum is rather uncertain and in mild tension with the common signal measured in the full data set. However, if the spectral index is fixed at 13/3, the two data sets give a similar amplitude of (2.5±0.7)×10−15 at a reference frequency of 1 yr−1 . Further investigation of these issues is required for reliable astrophysical interpretations of this signal. By continuing our detection efforts as part of the International Pulsar Timing Array (IPTA), we expect to be able to improve the measurement of spatial correlations and better characterise this signal in the coming years.

KW - gravitational waves

KW - methods:data analysis

KW - pulsars:general

U2 - 10.1051/0004-6361/202346844

DO - 10.1051/0004-6361/202346844

M3 - Article

SN - 0004-6361

VL - 678

JO - Astronomy and Astrophysics

JF - Astronomy and Astrophysics

M1 - A50

ER -

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

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Astrophysics at the University of Birmingham - Consolidated grant 2022-2025

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