The NANOGrav 11-year Data Set: Limits on Gravitational Wave Memory
by the NANOGrav Collaboration; corresponding author: Paul T. Baker.
In press with The Astrophysical Journal, arXiv:1911.08488.
The mergers of supermassive black hole binaries (SMBHB) promise to be incredible sources of gravitational waves (GW). While the oscillatory part of the merger gravitational waveform will be outside the frequency sensitivity range of pulsar timing arrays (PTA), the non-oscillatory GW memory effect is detectable. Further, any burst of gravitational waves 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-year data set for GW memory. This data set is sensitive to very low frequencies of ~3 to 400 nHz (periods of ~11 years to 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 × 1014, 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 per year. That strain corresponds to a SMBHB merger with reduced mass of ~2 × 1010 solar masses and inclination of 60° at a distance of 1 Gpc.