Modeling the uncertainties of solarsystem ephemerides for robust gravitationalwave searches with pulsar timing arrays
Abstract
The regularity of pulsar emissions becomes apparent once we reference the pulses' times of arrivals to the inertial rest frame of the solar system. It follows that errors in the determination of Earth's position with respect to the solarsystem barycenter can appear as a timecorrelated bias in pulsartiming residual time series, affecting the searches for lowfrequency gravitational waves performed with pulsar timing arrays. Indeed, recent array datasets yield different gravitationalwave background upper limits and detection statistics when analyzed with different solarsystem ephemerides. Crucially, the ephemerides do not generally provide usable error representations. In this article we describe the motivation, construction, and application of a physical model of solarsystem ephemeris uncertainties, which focuses on the degrees of freedom (Jupiter's orbital elements) most relevant to gravitationalwave searches with pulsar timing arrays. This model, BayesEphem, was used to derive ephemerisrobust results in NANOGrav's 11yr stochasticbackground search, and it provides a foundation for future searches by NANOGrav and other consortia. The analysis and simulations reported here suggest that ephemeris modeling reduces the gravitationalwave sensitivity of the 11yr dataset; and that this degeneracy will vanish with improved ephemerides and with the longer pulsar timing datasets that will become available in the near future.
 Publication:

arXiv eprints
 Pub Date:
 January 2020
 arXiv:
 arXiv:2001.00595
 Bibcode:
 2020arXiv200100595V
 Keywords:

 Astrophysics  High Energy Astrophysical Phenomena;
 Astrophysics  Instrumentation and Methods for Astrophysics;
 General Relativity and Quantum Cosmology
 EPrint:
 Fixed typo in author list. Code that supports all calculations and figures is available at github.com/nanograv/11yr_stochastic_analysis/tree/master/bayesephem