) Chinese Journal ofAstronomy and Astrophysics Scintillation & Pulsar Timing: Low-level Timing Noise from the

Abstract Many systematic effects need to be removed in order to obtain the highest quality pulsar timing data. Interstellar propagation effects may be reduced by employing coherent dedispersion and observing at 1 GHz or above to avoid strong scattering. However, these techniques may not adequately bring propagation effects below the level of other systematic or random errors in the observation. We show that low-level scattering in a Kolmogorov halo produces time delays that are much larger than normally recognized and are time variable. These may be a significant source of noise in some high precision timing efforts