Improved determination of γ by VLBI

Aims. This study revisits the estimate of the post-Newtonian relativistic parameter γ reported previously. We use (i) improved geophysical and astronomical modeling in the analysis software package, and (ii) a higher number of observations, a large part of which come from a relatively small number of VLBA experiments at 8 GHz.Methods. We analyzed more than seven million group delays measured by very long baseline interferometry between August 1979 and August 2010. The parameter γ was least squares fitted to delays as a global parameter over the entire observational time period.Results. The most complete solution of this study yielded γ  = 0.99992 ± 0.00012, whereas it was 0.99984 ± 0.00015 in our 2009 paper. The item (i), which is recognized as important for geodesy and reference frame realization, provides estimates of  |γ  − 1|  that are smaller than 10-4 . As expected, the formal error in γ decreases when additional sessions are processed. In particular, we demonstrate that the inclusion of more than 1.7 million observations from the VLBA (mainly from the RDV and VLBA calibrator survey experiments) in the analysis decreases the formal error in the estimate of γ by about 15% with respect to our previous determination.