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.