Finding Supermassive Black Hole Binary Mergers in Pulsar Timing Array Data
"Pulsar Timing Arrays (PTAs) have the capability to detect gravitational waves (GWs) in the nanohertz frequency regime and the dominant signals searched for in the data are the stochastic gravitational wave background (SGWB) and continuous waves from inspiraling supermassive black hole binaries (SMBHBs). But how do we search for these systems as they enter their final stages and merge?
In this talk, I present a new framework that opens a third observational window for PTAs - the direct search for late-stage inspirals and mergers of SMBHBs, including their nonlinear gravitational-wave memory. We adapt a physically complete waveform model based on numerical relativity surrogates, incorporating both oscillatory components and nonlinear memory. Unlike standard burst-with-memory searches that approximate the signal as an instantaneous step, our model captures the gradual memory buildup and full waveform morphology. Applying this framework to recent European and Parkes PTA data releases, we place upper limits on the mass and distance of the merging binaries. I will discuss the implications for tracking binaries approaching merger, and for enabling future multimessenger follow-up of supermassive black hole coalescences. I will also discuss how information from merger searches can be taken beyond individual-source detection to constrain the underlying SMBHB merger population, combining individual merger signals with information from the SGWB.
Finally, I will discuss possible multiband connections between PTAs and space-based gravitational-wave observatories such as LISA, and ask what complementary information different observations of the same massive black hole merger could provide."
Host: Ludovica Carbone