Presentation #335.09 in the session “The Next Decade Of Nanohertz Gravitational-wave Astrophysics with Pulsar-Timing Arrays”.
Nearly all galaxies contain supermassive black holes, and when these galaxies merge, they can form supermassive black hole binaries. As they progress towards merger, these binaries emit strong nanohertz gravitational waves (GWs). Pulsar timing arrays (PTAs) such as the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) have performed high cadence observations that span many years to detect GWs in this low-frequency regime. The recently released NANOGrav 12.5-year data set contains timing data of 47 millisecond pulsars, 45 of which are used for GW analyses. This data set is NANOGrav’s most sensitive to date, and has already yielded promising results in searches for the stochastic GW background (GWB). The stochastic GW background signal is a combination of many SMBH binaries that cannot be individually detected, but whose total combined signal can be found in the data as a common noise process. Now, we will search the data for GWs from individual SMBH binaries, which can be modeled as single sources that stand out from the background noise. In the absence of a detection, we will place stringent 95% upper limits on the strength of gravitational waves across the nanohertz band. We will also explore the necessary methods to appropriately search for continuous GWs alongside a common red process, which will be crucial for the detection of individual sources, as the GWB is expected to dominate.