The Measurement of the Light Deflection from Jupiter: Experimental Results

We have determined the relativistic light deflection of the quasar J0842+1835 as Jupiter passed within 3.7 on 2002 September 8, by measuring the time delay using the VLBA and Effelsberg radio telescopes at 8.4 GHz. At closest approach, General Relativity (GR) predicts a radial (static) deflection of 1190 μarcsec, and tangential (retarded or dynamic) deflection in the direction of Jupiter’s motion of 51 μarcsec. Our experiment achieved an rms position error of ≤ 10 μarcsec, and measured this retarded deflection to be 0.98± 0.19 (rms error) times that predicted by GR. Comments on the interpretation of this experiment as a measurement of the speed of gravity are given. The increased positional accuracy for this VLBI phase referencing experiment was achieved by using two calibrator sources. Subject headings: gravitation—quasars: individual (QSO J0842+1835)—relativity techniques: interferometric 1. The Gravitational Deflection of Radio Waves by Jupiter Einstein solved the equation of light propagation in the field of a static body, and predicted the deflection of light at the limb of the Sun of 1.75 (Einstein 1916), and this relativistic deflection was measured for the first time in 1919 (Dyson, Eddington & Davidson 1920). The deflection prediction by Einstein was confirmed in a series of other experiments, the most precise of which was made with Very Long Baseline Interferometry (VLBI) (Lebach et al. 1995). Kopeikin ( 2001, 2003a,b) generalized the problem of light propagation in the gravitational field of an arbitrary moving object, and showed that the first order term of the deflection depends on the retarded position of the moving object as defined by the retarded solution of the Einstein wave equations (see also Will ( 2003)). A once-in-a-decade configuration occurred on September 8, 2002 when Jupiter passed within 3.7 of the bright radio quasar J0842+1835. If Jupiter is at an angular distance θ from the quasar, the relativistic time delay, △(τl,m), between two radio telescopes, separated by a distance Bl,m, is △(τl,m) = −(1 + γ) 2GMJ crmJ ×