The Influence of Different Solar System Planetary Ephemeris on Pulsar Timing

Abstract

The pulsar timing offers a comprehensive avenue for exploring diverse topics physics and astrophysics. High-precision solar system planetary ephemeris crucial for pulsar timing as it provides the positions and velocities of solar system planets include the Earth. However, it is inevitable that inherent inconsistencies exist in these ephemerides. Differences between various ephemerides can significantly impact pulsar timing and parameter estimations. Currently, pulsar timing highly depend on the JPL DE ephemeris, for instance, the Pulsar Timing Array (PTA) data analysis predominantly utilizes DE436. In this study, we examine inconsistencies across various ephemeris series, including JPL DE, EPM, and INPOP. Notably, discrepancies emerge particularly between the current ephemeris DE436 and the earliest released ephemeris DE200, as well as the most recent ephemerides, e.g. DE440, INPOP21A, and EPM2021. A further detailed analysis of the effects of ephemeris on geometric correction procedures for the conversion of measured topocentric Time of Arrivals (TOAs) is presented in this study. Our researches reveal that variations in the Roemer delays across different ephemerides lead to distinct differences. The timing residuals and the fact that these discrepancies can be readily incorporated into the subsequent pulsar parameters, leading to inconsistent fitting estimates, suggest that the influence of errors in the ephemeris on the timing process might currently be underappreciated.