The NANOGrav 12.5-year Data Set: Search for Gravitational Wave Memory

TL;DR

This study conducted a Bayesian search for gravitational wave memory in 12.5 years of NANOGrav data, found no evidence, and established upper limits on GW memory strain amplitudes across the sky.

Contribution

It provides the first comprehensive upper limits on gravitational wave memory signals using a long-term pulsar timing array dataset.

Findings

No convincing evidence for GW memory signals was found.

Upper limits on strain amplitude are approximately 3.3 x 10^-14.

Upper limits improve over time with continued data collection.

Abstract

We present the results of a Bayesian search for gravitational wave (GW) memory in the NANOGrav 12.5-yr data set. We find no convincing evidence for any gravitational wave memory signals in this data set (Bayes factor = 2.8). As such, we go on to place upper limits on the strain amplitude of GW memory events as a function of sky location and event epoch. These upper limits are computed using a signal model that assumes the existence of a common, spatially uncorrelated red noise in addition to a GW memory signal. The median strain upper limit as a function of sky position is approximately $3.3 \times 10^{-14}$. We also find that there are some differences in the upper limits as a function of sky position centered around PSR J0613$-$0200. This suggests that this pulsar has some excess noise which can be confounded with GW memory. Finally, the upper limits as a function of burst epoch continue to improve at later epochs. This improvement is attributable to the continued growth of the pulsar timing array.