NANOGrav Constraints on Gravitational Wave Bursts with Memory

TL;DR

This paper reports on a search for gravitational wave memory signals using five years of NANOGrav pulsar data, developing new methods to improve detection speed, but finds no evidence of such signals, setting upper limits on their occurrence rate.

Contribution

The study introduces novel techniques for faster searches of gravitational wave bursts with memory in pulsar timing data and provides the first constraints on their event rates.

Findings

No evidence for gravitational wave bursts with memory was detected.

Upper limits were set on the rate of BWMs with amplitudes above 10^{-13}.

Sensitivity allows detection of supermassive black hole mergers within 30 Mpc in optimal directions.

Abstract

Among efforts to detect gravitational radiation, pulsar timing arrays are uniquely poised to detect "memory" signatures, permanent perturbations in spacetime from highly energetic astrophysical events such as mergers of supermassive black hole binaries. The North American Nanohertz Observatory for Gravitational Waves (NANOGrav) observes dozens of the most stable millisecond pulsars using the Arecibo and Green Bank radio telescopes in an effort to study, among other things, gravitational wave memory. We herein present the results of a search for gravitational wave bursts with memory (BWMs) using the first five years of NANOGrav observations. We develop original methods for dramatically speeding up searches for BWM signals. In the directions of the sky where our sensitivity to BWMs is best, we would detect mergers of binaries with reduced masses of $10^9$ $M_\odot$ out to distances of 30 Mpc; such massive mergers in the Virgo cluster would be marginally detectable. We find no evidence for BWMs. However, with our non-detection, we set upper limits on the rate at which BWMs of various amplitudes could have occurred during the time spanned by our data--e.g., BWMs with amplitudes greater than $10^{-13}$ must occur at a rate less than 1.5 yr$^{-1}$.