Improved determination of gamma by VLBI

Sébastien Lambert (1, 2, 3) , Christophe Le Poncin-Laffite (1, 2, 3)

1 SYRTE - Systèmes de Référence Temps Espace
2 Systèmes de référence célestes
3 Théorie et métrologie

Aims: This study revisits the estimate of the post-Newtonian relativistic parameter gamma 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 gamma 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 gamma = 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 |gamma - 1| that are smaller than 10^-4. As expected, the formal error in gamma 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 gamma by about 15% with respect to our previous determination.

Domaines: Astrophysique [astro-ph]

Sébastien Lambert, Christophe Le Poncin-Laffite. Improved determination of gamma by VLBI. Astronomy and Astrophysics - A&A, 2011, 529, pp.70. ⟨10.1051/0004-6361/201016370⟩. ⟨hal-03785812⟩