Interstellar medium (ISM) monitoring of NANOGrav pulsars

The NANOGrav project´s goal is to make a direct detection of gravitational waves taking advantage of the extraordinary rotational stability of millisecond pulsars. The project has identified 80 pulsars for regular timing over the next 10-20 years. The fantastic timing precision at the level of 100 ns necessary for detection of gravitational waves imposes strict requirements on understanding and correcting for systematic errors at the same precision level. A major source of systematic error has been identified as the changing interstellar medium density, which manifests itself in the dispersion correction applied to each observation. In this presentation we describe a new program to monitor a subset of NANOGrav pulsars using a large radio telescope in Goldstone, CA. The wideband capability of this instrument combined with excellent sensitivity provides an opportunity to develop and maintain a long-term precision monitoring program of interstellar plasma along the lines of sight to these pulsars.