CAREER: Multimessenger Astrophysics with Pulsar Timing Arrays in the Detection Era

The recent announcement by the North American Nanohertz Observatory for Gravitational Waves (NANOGrav) and pulsar timing array (PTA) collaborations around the world of evidence for a gravitational wave background (GWB) demonstrates that PTAs are moving into an unprecedented sensitivity regime for gravitational wave (GW) signals in the nanohertz frequency range. PTAs can see further back in time than the cosmic microwave background radiation and allow us to survey the population of supermassive binary black holes (SMBBHs) as a stochastic GWB. Detection of the background heralds the coming of individual source detections just when the Vera C. Rubin Observatory and the ten-year Legacy Survey of Space and Time (LSST) are scheduled to begin obtaining consistent and high quality time series data of active galactic nuclei (AGN) --- perfectly timed to coincide with the era of the first single-source detections in the PTA band. GW detections at these frequencies take time and necessitate the use of state-of-the-art data analysis techniques to build custom noise models for individual pulsar data sets in order to enhance the huge investment of the NSF into nanohertz gravitational wave astronomy just as PTAs enter the detection era. As the cosmic symphony of the stochastic GWB becomes more significant in the data, it is now necessary for PTAs to tune these galactic-scale detectors to optimize the ability to also resolve individual SMBBHs. PTAs will arbitrate the SMBBH hypothesis for quasiperiodic light curves in AGN, and this work will maximize the multimessenger detectability space of SMBBH systems by informing PTA and LSST observing strategies in order to ensure the detection of a multimessenger source during the LSST-era. The project includes curriculum development and implementation of a summer workshop in astrophysics-themed data analysis that will foster inspired teaching, stimulate excitement in PTA research, facilitate the learning goals of undergraduate and graduate students, and support the transition of community college students into 4-year schools. The first research goal will be using techniques recently pioneered to transform PTA noise mitigation strategies with the use of custom Bayesian models to gain from the data we already have in hand. Preliminary analyses have shown significant changes in parameter recovery and significance statistics when using these custom models. This work will inform a reconceptualization of the use of detector characterization tools to rethink pulsar observing strategies and the reorganization of these tools for lightweight predictions of single-source detectability of GW candidates from electromagnetic time-domain surveys. Supported by these first two goals will be research to develop the framework and software interface needed to quickly assess AGN for the presence of SMBBHs. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.