Transcript Document 7281778

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
d  gtt dt  grr dr  r d  r sin  d
2
2
where
2
2
2
2
2
2
2
m
m
g tt  1  2   2(  )   
 r 
 r 
m
g rr  1  2     
 r 
with α, β, γ constants. Einstein puts them all =3 1.
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:
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.
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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:
Vessot & al. 1980:
Maser
Snider 1971:
GRS
Lo Presto 1991:
GRS
1,30E+00
1,25E+00
1,20E+00
1,15E+00
1,10E+00
Pound & al.
1960:
Effetto Mossbauer
1,05E+00
1,00E+00
9,50E-01
9,00E-01
8,50E-01
8,00E-01
1,E-15
1,E-13
1,E-11
1,E-09
1,E-07
1,E-05
1,E-03
1,E-01
81,E+01
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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Human Resource
A.Cacciani
Activity
1) General Supervisor
2) External contacts
3) Cell fabrication
a) Lab set up
b) Fabrication
c) Test
4) Observations
(70%)
F. Massa
5) Data Acquisition Software Developm.
a) Design
b) Test
6) Observations
(70%)
R. Briguglio
7) Instrument set up, test and
maintenance
8) Observations
(70%)
P. Rapex
(50%)
9) Data reduction Software
a) Analysis
b) Test and implementations
c) Final results production
10) Electronic design support
a) Cell heaters
b) CCD synchronization
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