Abstract
Abstract When galaxies merge, the supermassive black holes in their centers may form binaries and emit low-frequency gravitational radiation in the process. In this paper, we consider the galaxy 3C 66B, which was used as the target of the first multimessenger search for gravitational waves. Due to the observed periodicities present in the photometric and astrometric data of the source, it has been theorized to contain a supermassive black hole binary. Its apparent 1.05-year orbital period would place the gravitational-wave emission directly in the pulsar timing band. Since the first pulsar timing array study of 3C 66B, revised models of the source have been published, and timing array sensitivities and techniques have improved dramatically. With these advances, we further constrain the chirp mass of the potential supermassive black hole binary in 3C 66B to less than (1.65 ± 0.02) × 109 M ⊙ using data from the NANOGrav 11-year data set. This upper limit provides a factor of 1.6 improvement over previous limits and a factor of 4.3 over the first search done. Nevertheless, the most recent orbital model for the source is still consistent with our limit from pulsar timing array data. In addition, we are able to quantify the improvement made by the inclusion of source properties gleaned from electromagnetic data over “blind” pulsar timing array searches. With these methods, it is apparent that it is not necessary to obtain exact a priori knowledge of the period of a binary to gain meaningful astrophysical inferences.
Highlights
Continuous gravitational waves (GWs), defined by single-source cyclic GW emission, are expected to arise from the supermassive black hole binaries (SMBHBs) that form during a galaxy merger
When a SMBHB evolves such that it emits GWs in the microhertz to nanohertz GW band, a sufficiently massive and/or nearby SMBHB may be detectable by pulsar timing arrays (PTAs; e.g., Aggarwal et al 2019)
The results discussed can be reproduced, and the MarkovChain Monte Carlo (MCMC) data examined, using code provided for the reader’s convenience
Summary
Continuous gravitational waves (GWs), defined by single-source cyclic GW emission, are expected to arise from the supermassive black hole binaries (SMBHBs) that form during a galaxy merger. When a SMBHB evolves such that it emits GWs in the microhertz to nanohertz GW band (orbital periods of weeks to several decades), a sufficiently massive and/or nearby SMBHB may be detectable by pulsar timing arrays (PTAs; e.g., Aggarwal et al 2019) (hereafter A19). Most works that do target limits on specific sources using electromagnetic information have used smaller data sets consisting of a single pulsar with as a periodogram approach (Jenet et al 2004; Feng et al 2019), or have been derived from the stochastic GW background (Zhu et al 2019) rather than the full GW analysis pipeline. We have combined these methods in the first search of this type, where we used the entire NANOGrav array of pulsars and full GW search analysis, while incorporating electromagnetic data to conduct a more informed search for GWs from our test source, 3C66B
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