GRS%20Measurement

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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

with a, ß, ? constants. Einstein puts them all
1.
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Theoretical background for gravity

• 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
• ??/? 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.

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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 Briguglio
• University of Rome LA SAPIENZA, Italy
•  
• Fabrizio Massa
• INFN sez. Di Roma
•  
• Paolo Rapex
• External collaborator
•  
• James LoPresto
• Edinboro University of Pennsylvania, USA

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A sensitive test of Fundamental Physics,
especially General Relativity

• Previous results

Snider 1971 GRS
Lo Presto 1991 GRS
Vessot al. 1980 Maser
Pound al. 1960 Effetto Mossbauer
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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

• Image detector

• High efficiency (30)

• Photon-shot noise limited

• Intrinsic stability

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• 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

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.
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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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