The NANOGrav 11 yr Data Set: Limits on Gravitational Wave Memory
The mergers of supermassive black hole binaries (SMBHBs) promise to be incredible sources of gravitational waves (GWs). While the oscillatory part of the merger gravitational waveform will be outside the frequency sensitivity range of pulsar timing arrays, the nonoscillatory GW memory effect is detectable. Further, any burst of GWs will produce GW memory, making memory a useful probe of unmodeled exotic sources and new physics. We searched the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) 11 yr data set for GW memory. This data set is sensitive to very low-frequency GWs of ~3 to 400 nHz (periods of ~11 yr–1 month). Finding no evidence for GWs, we placed limits on the strain amplitude of GW memory events during the observation period. We then used the strain upper limits to place limits on the rate of GW memory causing events. At a strain of 2.5 × 10⁻¹⁴, corresponding to the median upper limit as a function of source sky position, we set a limit on the rate of GW memory events at <0.4 yr⁻¹. That strain corresponds to an SMBHB merger with reduced mass of ηM ~ 2 × 10¹⁰ M_⊙ and inclination of ι = π/3 at a distance of 1 Gpc. As a test of our analysis, we analyzed the NANOGrav 9 yr data set as well. This analysis found an anomolous signal, which does not appear in the 11 yr data set. This signal is not a GW, and its origin remains unknown.
© 2020 The American Astronomical Society. Received 2019 October 17; revised 2019 December 6; accepted 2019 December 8; published 2020 January 23. Author contributions. This document is the result of more than a decade of work by the entire NANOGrav collaboration. We acknowledge specific contributions below. Z.A., K.C., P.B.D., M.E.D., T.D., J.A.E., E.C.F., R.D.F., E.F., P.A.G., G.J., M.L.J., M.T.L., L.L., D.R.L., R.S.L., M.A.M., C.N., D.J.N., T.T.P., S.M.R., P.S.R., R.S., I.H.S., K.S., J.K.S., and W.Z. developed the 11 yr data set. P.T.B. led this analysis and coordinated the paper writing. J.A.E. and P.T.B. implemented the search algorithms in enterprise. P.T.B. and K.I. performed the data analysis. K.A., A.M.H., and N.S.P. conducted preliminary search pipeline testing. D.R.M., J.A.E., S.R.T., and R.vH. performed an initial analysis of the 9 yr data set including an investigation of the anomolous signal. K.I. and S.B.S. contributed to the astrophysical interpretation. The NANOGrav project receives support from National Science Foundation (NSF) Physics Frontier Center award #1430284. NANOGrav research at UBC is supported by an NSERC Discovery Grant and Discovery Accelerator Supplement and by the Canadian Institute for Advanced Research. Portions of this research were carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. P.T.B. acknowledges support from the West Virginia University Center for Gravitational Waves and Cosmology. M.V. and J.S. acknowledge support from the JPL RTD program. S.R.T. was partially supported by an appointment to the NASA Postdoctoral Program at the Jet Propulsion Laboratory, administered by Oak Ridge Associated Universities through a contract with NASA. J.A.E. was partially supported by NASA through Einstein Fellowship grants PF4-150120. S.B.S. and C.A.W. were supported by NSF award #1815664. W.W.Z. is supported by the Chinese Academy of Science Pioneer Hundred Talents Program, the Strategic Priority Research Program of the Chinese Academy of Sciences grant No. XDB23000000, the National Natural Science Foundation of China grant No. 11690024, and by the Astronomical Big Data Joint Research Center, cofounded by the National Astronomical Observatories, Chinese Academy of Sciences and the Alibaba Cloud. Portions of this work performed at NRL are supported by the Chief of Naval Research. The Flatiron Institute is supported by the Simons Foundation. We are grateful for computational resources provided by the Leonard E. Parker Center for Gravitation, Cosmology and Astrophysics at the University of Wisconsin-Milwaukee, which is supported by NSF grants 0923409 and 1626190. Data for this project were collected using the facilities of the Green Bank Observatory and the Arecibo Observatory. The National Radio Astronomy Observatory and Green Bank Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc. The Arecibo Observatory is a facility of the National Science Foundation operated under cooperative agreement by the University of Central Florida in alliance with Yang Enterprises, Inc. and Universidad Metropolitana.
Submitted - 1911.08488.pdf
Published - Aggarwal_2020_ApJ_889_38.pdf