AAS 201st Meeting, January, 2003
Session 101. Cosmology and Gravitation
Oral, Wednesday, January 8, 2003, 10:00-11:30am, 612

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[101.07] Measuring the Speed of Propagation of Gravity

S. Kopeikin (University of Missouri-Columbia), E.B. Fomalont (NRAO)

On 2002 Sep 08, the position of the bright quasar, J0842+1835, was deflected by the gravitational field of Jupiter as it passed within 3.7' of the quasar line-of-site. General relativity predicts that moving celestial objects like Jupiter deflect light differently than that by a static mass. We have estimated that the first-order gravitational deflection term is \approx 1000~\muarcsec directed radially away from Jupiter. The second order (dynamic) term is associated with the motion of Jupiter, and depends on the ratio of its orbital speed with the speed of propagation of gravity from Jupiter, cg. The expected deflection difference between cg=\infty and cg=c (the speed of light) is \approx 50~\muarcsec in the direction of motion of Jupiter. In order to measure the deflection of the quasar's apparent position, we observed with the VLBA + Effelsberg at 8.4 GHz on five days: 2002 Sep 04, 07, 08, 09, 12. For ten hours on each day, one minute scans were alternated among J0842+1835, J0839+1802 (0.8\circ SW), and J0854+2006 (3.3\circ NE) to measure the precise separation of the quasars as a function of time. By observing for five days, we can remove the effects of variable source structure and determine realistic error estimates. By observing with two calibrators on either side of J0842+1835, we can remove most of the tropospheric and instrumental instabilities. We hope to achieve a positional sensitivity of about 10~\muarcsec on Sep 08, and anticipate the results that gravity propagates with the same speed as light.

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Bulletin of the American Astronomical Society, 34, #4
© 2002. The American Astronomical Soceity.