Comparing Recent Pulsar Timing Array Results on the Nanohertz Stochastic Gravitational-wave Background

Creators: Agazie, G.; Antoniadis, J.; Anumarlapudi, A.; Archibald, A. M.; Arumugam, P.; Arumugam, S.; Arzoumanian, Z.; Askew, J.; Babak, S.; Bagchi, M.; Bailes, M.; Nielsen, A.-S. Bak; Baker, P. T.; Bassa, C. G.; Bathula, A.; Bécsy, B.; Berthereau, A.; Bhat, N. D. R.; Blecha, L.; Bonetti, M.; Bortolas, E.; Brazier, A.; Brook, P. R.; Burgay, M.; Burke-Spolaor, S.; Burnette, R.; Caballero, R. N.; Cameron, A.; Case, R.; Chalumeau, A.; Champion, D. J.; Chanlaridis, S.; Charisi, M.; Chatterjee, S.; Chatziioannou, K.¹; Cheeseboro, B. D.; Chen, S.; Chen, Z.-C.; Cognard, I.; Cohen, T.; Coles, W. A.; Cordes, J. M.; Cornish, N. J.; Crawford, F.; Cromartie, H. T.; Crowter, K.; Curyło, M.; Cutler, C. J.; Dai, S.; Dandapat, S.; Deb, D.; DeCesar, M. E.; DeGan, D.; Demorest, P. B.; Deng, H.; Desai, S.; Desvignes, G.; Dey, L.; Dhanda-Batra, N.; Di Marco, V.; Dolch, T.; Drachler, B.; Dwivedi, C.; Ellis, J. A.; Falxa, M.; Feng, Y.; Ferdman, R. D.; Ferrara, E. C.; Fiore, W.; Fonseca, E.; Franchini, A.; Freedman, G. E.; Gair, J. R.; Garver-Daniels, N.; Gentile, P. A.; Gersbach, K. A.; Glaser, J.; Good, D. C.; Goncharov, B.; Gopakumar, A.; Graikou, E.; Griessmeier, J.-M.; Guillemot, L.; Gültekin, K.; Guo, Y. J.; Gupta, Y.; Grunthal, K.; Hazboun, J. S.; Hisano, S.; Hobbs, G. B.; Hourihane, S.; Hu, H.; Iraci, F.; Islo, K.; Izquierdo-Villalba, D.; Jang, J.; Jawor, J.; Janssen, G. H.; Jennings, R. J.; Jessner, A.; Johnson, A. D.; Jones, M. L.; Joshi, B. C.; Kaiser, A. R.; Kaplan, D. L.; Kapur, A.; Kareem, F.; Karuppusamy, R.; Keane, E. F.; Keith, M. J.; Kelley, L. Z.; Kerr, M.; Key, J. S.; Kharbanda, D.; Kikunaga, T.; Klein, T. C.; Kolhe, N.; Kramer, M.; Krishnakumar, M. A.; Kulkarni, A.; Laal, N.; Lackeos, K.; Lam, M. T.; Lamb, W. G.; Larsen, B. B.; Lazio, T. J. W.; Lee, K. J.; Levin, Y.; Lewandowska, N.; Littenberg, T. B.; Liu, K.; Liu, T.; Liu, Y.; Lommen, A.; Lorimer, D. R.; Lower, M. E.; Luo, J.; Luo, R.; Lynch, R. S.; Lyne, A. G.; Ma, C.-P.; Maan, Y.; Madison, D. R.; Main, R. A.; Manchester, R. N.; Mandow, R.; Mattson, M. A.; McEwen, A.; McKee, J. W.; McLaughlin, M. A.; McMann, N.; Meyers, B. W.; Meyers, P. M.; Mickaliger, M. B.; Miles, M.; Mingarelli, C. M. F.; Mitridate, A.; Natarajan, P.; Nathan, R. S.; Ng, C.; Nice, D. J.; Niţu, I. C.; Nobleson, K.; Ocker, S. K.; Olum, K. D.; Osłowski, S.; Paladi, A. K.; Parthasarathy, A.; Pennucci, T. T.; Perera, B. B. P.; Perrodin, D.; Petiteau, A.; Petrov, P.; Pol, N. S.; Porayko, N. K.; Possenti, A.; Prabu, T.; Leclere, H. Quelquejay; Radovan, H. A.; Rana, P.; Ransom, S. M.; Ray, P. S.; Reardon, D. J.; Rogers, A. F.; Romano, J. D.; Russell, C. J.; Samajdar, A.; Sanidas, S. A.; Sardesai, S. C.; Schmiedekamp, A.; Schmiedekamp, C.; Schmitz, K.; Schult, L.; Sesana, A.; Shaifullah, G.; Shannon, R. M.; Shapiro-Albert, B. J.; Siemens, X.; Simon, J.; Singha, J.; Siwek, M. S.; Speri, L.; Spiewak, R.; Srivastava, A.; Stairs, I. H.; Stappers, B. W.; Stinebring, D. R.; Stovall, K.; Sun, J. P.; Surnis, M.; Susarla, S. C.; Susobhanan, A.; Swiggum, J. K.; Takahashi, K.; Tarafdar, P.; Taylor, J.; Taylor, S. R.; Theureau, G.; Thrane, E.; Thyagarajan, N.; Tiburzi, C.; Toomey, L.; Turner, J. E.; Unal, C.; Vallisneri, M.¹; van der Wateren, E.; van Haasteren, R.; Vecchio, A.; Venkatraman Krishnan, V.; Verbiest, J. P. W.; Vigeland, S. J.; Wahl, H. M.; Wang, S.; Wang, Q.; Witt, C. A.; Wang, J.; Wang, L.; Wayt, K. E.; Wu, Z.; Young, O.; Zhang, L.; Zhang, S.; Zhu, X.-J.; Zic, A.; International Pulsar Timing Array Collaboration

1. California Institute of Technology

Abstract

The Australian, Chinese, European, Indian, and North American pulsar timing array (PTA) collaborations recently reported, at varying levels, evidence for the presence of a nanohertz gravitational-wave background (GWB). Given that each PTA made different choices in modeling their data, we perform a comparison of the GWB and individual pulsar noise parameters across the results reported from the PTAs that constitute the International Pulsar Timing Array (IPTA). We show that despite making different modeling choices, there is no significant difference in the GWB parameters that are measured by the different PTAs, agreeing within 1σ. The pulsar noise parameters are also consistent between different PTAs for the majority of the pulsars included in these analyses. We bridge the differences in modeling choices by adopting a standardized noise model for all pulsars and PTAs, finding that under this model there is a reduction in the tension in the pulsar noise parameters. As part of this reanalysis, we "extended" each PTA's data set by adding extra pulsars that were not timed by that PTA. Under these extensions, we find better constraints on the GWB amplitude and a higher signal-to-noise ratio for the Hellings–Downs correlations. These extensions serve as a prelude to the benefits offered by a full combination of data across all pulsars in the IPTA, i.e., the IPTA's Data Release 3, which will involve not just adding in additional pulsars but also including data from all three PTAs where any given pulsar is timed by more than a single PTA.

Copyright and License

© 2024. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Acknowledgement

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 toward the direct detection of low-frequency GWs. 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. The NANOGrav collaboration receives support from National Science Foundation (NSF) Physics Frontiers Center award Nos. 1430284 and 2020265, the Gordon and Betty Moore Foundation, NSF AccelNet award No. 2114721, an NSERC Discovery Grant, and CIFAR. Part of this research was undertaken as part of the Australian Research Council (ARC) Centre of Excellence for Gravitational Wave Discovery (OzGrav) under grant CE170100004.

An Advanced Grant of the European Research Council allowed us to implement the Large European Array for Pulsars (LEAP) under grant agreement No. 227947 (PI M. Kramer). 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). 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 Arecibo Observatory is a facility of the NSF operated under cooperative agreement (AST-1744119) by the University of Central Florida (UCF) in alliance with Universidad Ana G. Méndez (UAGM) and Yang Enterprises (YEI), Inc. The Green Bank Observatory is a facility of the NSF operated under cooperative agreement by Associated Universities, Inc. The National Radio Astronomy Observatory is a facility of the NSF operated under cooperative agreement by Associated Universities, Inc. Murriyang, the Parkes 64 m radio telescope, is part of the Australia Telescope National Facility (https://ror.org/05qajvd42), which is funded by the Australian Government for operation as a National Facility managed by CSIRO. We acknowledge the Wiradjuri People as the Traditional Owners of the Observatory site.

This work made use of the OzSTAR national facility at Swinburne University of Technology. OzSTAR is funded by Swinburne University of Technology and the National Collaborative Research Infrastructure Strategy (NCRIS). This work was conducted in part using the resources of the Advanced Computing Center for Research and Education (ACCRE) at Vanderbilt University, Nashville, TN. This work used resources of the IN2P3 Computing Center (CC-IN2P3—Lyon/Villeurbanne—France) funded by the Centre National de la Recherche Scientifique.

The work is supported by the National SKA program 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 GW astronomy. J.A. acknowledges support from the European Commission (grant agreement No. 101094354). J.A. and S.Chan. were partially supported by the Stavros Niarchos Foundation (SNF) and the Hellenic Foundation for Research and Innovation (HFRI) under the 2nd Call of the "Science and Society—Action Always strive for excellence—Theodoros Papazoglou" (project No. 01431). A.Ch. acknowledges support from the Paris Île-de-France Region. A.Ch., A.F., A.Se., A.Sa., E.B., D.I., G.M.S., and M.Bo. acknowledge financial support provided under the European Union's H2020 ERC Consolidator Grant "Binary Massive Black Hole Astrophysics" (B Massive, grant agreement No. 818691). G.D., K.Li., R.K., and M.Kr. acknowledge support from European Research Council (ERC) Synergy grant "BlackHoleCam," grant agreement No. 610058. I.C.N. is supported by the STFC doctoral training grant ST/T506291/1. A.V. and P.R.B. are supported by the UK's Science and Technology Facilities Council (STFC; grant ST/W000946/1). A.V. also acknowledges the support of the Royal Society and Wolfson Foundation. N.K.P. is funded by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation)—Projektnummer PO 2758/1-1, through the Walter-Benjamin program. A.Sa. thanks the Alexander von Humboldt foundation in Germany for a Humboldt fellowship for postdoctoral researchers. A.Po., D.P., and M.Bu. acknowledge support from both 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) and the INAF Large Grant 2022 "GCjewels" (P.I. Andrea Possenti) approved with the Presidential Decree 30/2022. R.N.C. acknowledges financial support from the Special Account for Research Funds of the Hellenic Open University (ELKE-HOU) under the research program "GRAVPUL" (K.E.-80383/grant agreement 319/10-10-2022; PI N. A. B. Gizani). E.v.d.W., C.G.B., and G.H.J. acknowledge support from the Dutch National Science Agenda, NWA Startimpuls—400.17.608. B.G. is supported by the Italian Ministry of Education, University and Research within the PRIN 2017 Research Program Framework, No. 2017SYRTCN.

B.C.J. acknowledges the support from the Raja Ramanna Chair fellowship of the Department of Atomic Energy, Government of India (grant 3/3401 Atomic Energy Research 00 004 Research and Development 27 02 31 1002//2/2023/RRC/R&D-II/13886). B.C.J., Y.G., Y.M., S.Dan., A.G., and P.R. acknowledge the support of the Department of Atomic Energy, Government of India, under Project Identification No. RTI 4002. B.C.J., Y.G., and Y.M. acknowledge the support of the Department of Atomic Energy, Government of India, under project No. 12-R&D-TFR-5.02-0700, while S.D., A.G., and P.R. acknowledge the support of the Department of Atomic Energy, Government of India, under project No. 12-R&D-TFR-5.02-0200. K.T. is partially supported by JSPS KAKENHI grant Nos. 20H00180, 21H01130, and 21H04467; Bilateral Joint Research Projects of JSPS; and the ISM Cooperative Research Program (2021-ISMCRP-2017). A.K.P. is supported by CSIR fellowship grant No. 09/0079(15784)/2022-EMR-I. S.H. is supported by JSPS KAKENHI grant No. 20J20509. K.N. is supported by the Birla Institute of Technology & Science Institute fellowship. Am.S. is supported by CSIR fellowship grant No. 09/1001(12656)/2021-EMR-I and T-641 (DST-ICPS). T.K. is partially supported by the JSPS Overseas Challenge Program for Young Researchers. D.Deb. acknowledges the support from the Department of Atomic Energy, Government of India through Apex Project—Advance Research and Education in Mathematical Sciences at IMSc. J.S. acknowledges funding from the South African Research Chairs Initiative of the Department of Science and Technology and the National Research Foundation of South Africa.

L.B. acknowledges support from the National Science Foundation under award AST-1909933 and from the Research Corporation for Science Advancement under Cottrell Scholar Award No. 27553. S.B. gratefully acknowledges the support of a Sloan Fellowship and the support of NSF under award No. 1815664. The work of R.B., R.C., D.D., N.La., X.S., J.P.S., and J.T. is partly supported by the George and Hannah Bolinger Memorial Fund in the College of Science at Oregon State University. M.C., P.P., and S.R.T. acknowledge support from NSF AST-2007993. M.C. and N.S.P. were supported by the Vanderbilt Initiative in Data Intensive Astrophysics (VIDA) Fellowship. K.Ch., A.D.J., and M.V. acknowledge support from the Caltech and Jet Propulsion Laboratory President's and Director's Research and Development Fund. K.Ch. and A.D.J. acknowledge support from the Sloan Foundation. Support for this work was provided by the NSF through the Grote Reber Fellowship Program administered by Associated Universities, Inc./National Radio Astronomy Observatory. Support for HTC is provided by NASA through the NASA Hubble Fellowship Program grant No. HST-HF2-51453.001 awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555. K.Cr. is supported by a UBC Four Year Fellowship (6456). M.E.D. acknowledges support from the Naval Research Laboratory by NASA under contract S-15633Y. T.D. and M.T.L. are supported by an NSF Astronomy and Astrophysics Grant (AAG) award No. 2009468. E.C.F. is supported by NASA under award No. 80GSFC21M0002. G.E.F., S.C.S., and S.J.V. are supported by NSF award PHY2011772. K.A.G. and S.R.T. acknowledge support from NSF CAREER award No. 2146016. The Flatiron Institute is supported by the Simons Foundation. S.H. is supported by the National Science Foundation Graduate Research Fellowship under grant No. DGE-1745301. N.La. acknowledges the support from the Larry W. Martin and Joyce B. O'Neill Endowed Fellowship in the College of Science at Oregon State University. Part of this research was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration (80NM0018D0004). D.R.L. and M.A.Mc. are supported by NSF No. 1458952. M.A.Mc. is supported by NSF No. 2009425. C.M.F.M. was supported in part by the National Science Foundation under grant Nos. NSF PHY-1748958 and AST-2106552. A.Mi. is supported by the Deutsche Forschungsgemeinschaft under Germany's Excellence Strategy—EXC 2121 Quantum Universe—390833306. P.N. acknowledges support from the BHI, funded by grants from the John Templeton Foundation and the Gordon and Betty Moore Foundation. The Dunlap Institute is funded by an endowment established by the David Dunlap family and the University of Toronto. K.D.O. was supported in part by NSF grant No. 2207267. T.T.P. acknowledges support from the Extragalactic Astrophysics Research Group at Eötvös Loránd University, funded by the Eötvös Loránd Research Network (ELKH), which was used during the development of this research. S.M.R. and I.H.S. are CIFAR Fellows. Portions of this work performed at NRL were supported by ONR 6.1 basic research funding. J.D.R. also acknowledges support from start-up funds from Texas Tech University. J.S. is supported by an NSF Astronomy and Astrophysics Postdoctoral Fellowship under award AST-2202388 and acknowledges previous support by the NSF under award 1847938. C.U. acknowledges support from BGU (Kreitman fellowship) and the Council for Higher Education and Israel Academy of Sciences and Humanities (Excellence fellowship). C.A.W. acknowledges support from CIERA, the Adler Planetarium, and the Brinson Foundation through a CIERA-Adler postdoctoral fellowship. O.Y. is supported by the National Science Foundation Graduate Research Fellowship under grant No. DGE2139292.

R.M.S. acknowledges support through ARC Future Fellowship FT190100155. S.Da. is the recipient of an Australian Research Council Discovery Early Career Award (DE210101738) funded by the Australian Government. Y.L. acknowledges support of the Simons Investigator grant 827103.

Contributions

An alphabetical-order author list was used for this paper to recognize the vast extent of the time and effort by many people that went into this project. All authors contributed to the activities of the IPTA collaboration leading to the work presented here and reviewed the text and figures prior to the paper's submission. This project was organized as part of the Gravitational Wave Analysis Working Group of the IPTA by P.T.B., A.Ch., and N.S.P.

S.Dan. and P.T.B. led the GW comparisons, with contributions from L.D., S.De., and A.G. A.Ch. led the noise comparisons, with contributions from B.B.L., S.Dan., C.D., F.K., D.Deb., and C.M.F.M. G.S. led the GW sensitivity analysis, with contributions from K.Gr., N.K.P., J.S.H., and K.E.W. K.A.G., L.Sch., and N.S.P. performed the factorized likelihood and optimal statistic analyses. W.G.L. performed the free spectral refitting. J.S.H. and K.E.W. developed and performed the fully extended optimal statistic analysis. P.T.B., A.Ch., N.S.P., S.Dan., K.A.G., L.Sch., W.G.L., B.C.J., and G.S. wrote the text and generated figures.

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