Exploring Continuous Waves for Pulsar Timing Arrays in a Parameterized Post-Einsteinian Formalism

Pulsar timing arrays have the ability to detect the gravitational waves emitted by supermassive black hole binaries. These gravitational waves carry with them the information of the spacetime surrounding the compact objects, as well as information about the dynamical processes dictating the evolution of the system. As this system is slowly evolving, the gravitational radiation is expected to be seen as a continuous wave emanating from the direction of the sky that the binary system is in. Modified theories of gravity allow for this emission to carry with it additional effects which are not present in general relativity. As there are a number of various theories of gravity, a detailed study for all of their modifications would be a tedious endeavor. Rather than looking at a particular modified theory of gravity, we here discuss a theory-agnostic approach to parameterizing modifications to general relativity. In particular, we investigate the effects of a parameterized post-Einsteinian formalism on a gravitational system emitting continuous waves, similar to those expected from supermassive black hole binaries. Our approach modifies existing code within the enterprise and enterprise_extensions packages to work with pulsar timing data from the NANOGrav collaboration. The goal of this approach is to determine what, if any, limits can be placed on the coupling parameters of the formalism that can aid in constraining modified effects of gravity not present in general relativity.