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GRS Measurement

By A. Cacciani

Frascati, March 21th 2006

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Introduction

• GRS … one of the three classical tests of General Relativity

• … so far it has been tested only to the first order in m/r,

• THAT IS, no test for the Einstein field eqn

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Theoretical background for gravity

In general

where

222222 rr

2tt

2 d sin rd rdrgdt gd ϕθ−θ−−=τ

K

K

r

m21g

r

m)(2

r

m21g

rr

2

tt

+⎟⎠⎞

⎜⎝⎛γ+=

+⎟⎠⎞

⎜⎝⎛αγ−β+⎟

⎠⎞

⎜⎝⎛α−=

with α, β, γ constants. Einstein puts them all = 1.

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• GRS depends only on gtt.• A large mass is needed to increase the expected

signal• Also, it should be at rest or perfectly known relative

velocity: • The Sun is the only choise. • To the first order, for the Sun:

Δν/ν is 633 m/s Doppler equivalent , that is 10-6 the speed of light.

• The second order adds another term 10- 4 smaller, that is, a signal of about 1 mm/s Doppler equivalent.

Theoretical background for gravity

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Competing instruments

Masers, radio,..

• They have enough stability ( claimed 10-14 )

• But they need to be launched in orbits around the Sun

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Competing instruments

Our instrument: the MOF

• It is already proven to the level of 10-12 • It does not need to be launched around

the Sun, • We are looking at the SOLAR SPECTRUM • Previous measurements (not MOF) of the

Solar GRS did not go better than few % (LoPresto et al. - 1991)

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MISURA DEL GRS SOLARE

by:

Alessandro Cacciani

Runa BriguglioUniversity of Rome “LA SAPIENZA”, Italy

 

Fabrizio MassaINFN sez. Di Roma

 

Paolo RapexExternal collaborator

 

James LoPrestoEdinboro University of Pennsylvania, USA

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8,00E-01

8,50E-01

9,00E-01

9,50E-01

1,00E+00

1,05E+00

1,10E+00

1,15E+00

1,20E+00

1,25E+00

1,30E+00

1,E-15 1,E-13 1,E-11 1,E-09 1,E-07 1,E-05 1,E-03 1,E-01 1,E+01

A sensitive test of Fundamental Physics,

especially General Relativity • Previous results:

Pound & al.1960:Effetto Mossbauer

Vessot & al. 1980:Maser

Lo Presto 1991:GRS

Snider 1971:GRS

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How to improve?Instrumental progress such as MOF Technology

•Two narrow bands trasmission filter: FWHM= 50 mA, tuned on a Solar Line

•Intrinsic stability

•High efficiency (30%)

•Photon-shot noise limited

•Image detector

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In order to reach this sensitivity, a comparison between the solar MOF signals from two satellites, one near the Earth and the other close to the Sun, will cancel all the unwanted effects, but the GRS alone. The second order signal is in the range of a mm/s (Doppler equivalent), well within the capability of our MOF.

Real test of General Relativity requires time dilation effect at a second order

10-5-10-6 times the first order effect.On the sun we expect a second order effect of

10-5-10-6 x 636 m/s 1mm/s

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Typical Doppler image with MOF

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Doppler signal on the solar

equator

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Preliminary Results

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Human Resource Activity

A.Cacciani (70%)

1) General Supervisor2) External contacts3) Cell fabrication a) Lab set up b) Fabrication c) Test4) Observations

F. Massa  (70%)

5) Data Acquisition Software Developm. a) Design b) Test6) Observations

R. Briguglio  (70%)

7) Instrument set up, test and maintenance8) Observations

P. Rapex 

(50%)

9) Data reduction Software a) Analysis b) Test and implementations c) Final results production10) Electronic design support a) Cell heaters b) CCD synchronization