V. Rudenko (SAI MSU), N. Bartel (York U.), L. Gurvits (JIVE), K. Belousov (ASC), M. Bietenholz (HartRAO), A. Biriukov (ASC), W. Cannon (York U.), G. Cimo

1
Probing the Gravitational Redshift Effect with
the RadioAstron satellite
Astro Space Center of the Lebedev Physical
Institute (Russia) Lavochkin Scientific and
Production Association (Russia) Sternberg
Astronomical Institute (Russia) Keldysh Institute
for Applied Mathematics (Russia) York University
(Canada) Joint Institute for VLBI in Europe (the
Netherlands) University of California in
Santa-Barbara (USA) Hartebeesthoek Radio
Observatory (South Africa)
V. Rudenko (SAI MSU), N. Bartel (York U.), L.
Gurvits (JIVE), K. Belousov (ASC), M. Bietenholz
(HartRAO), A. Biriukov (ASC), W. Cannon (York
U.), G. Cimo (JIVE), A. Fionov (SAI MSU), A.
Gusev (SAI MSU), C. Gwinn (UCSB), D. Duev
(JIVE), M. Johnson (UCSB), V. Kauts (ASC), G.
Kopelyansky (ASC), A. Kovalenko (PRAO), V.
Kulagin (SAI MSU), D. Litvinov (SAI MSU), G.
Molera (JIVE), S. Pogrebenko (JIVE), N. Porayko
(SAI MSU), S. Sazankov (ASC), A. Skripkin
(Comcon), V. Soglasnov (ASC), K. Sokolovsky (ASC)
Rencontre de Moriond, 2128 March 2015
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• Einstein obtained the gravitational redshift
  formula in 1906 considering the equivalence of
  homogeneous gravity field and inertia
  (accelerated reference system)
• a test of the grav. redshift effect is a test of
  the EP measurement of the free fall
  acceleration of a photon
• RS astro test with Sirius B (W. Adams, 1925)
  light from massive stars arrives with decreased
  frequency

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• EP fundamental basis of GR
• GR postulates ? equivalence of gravity and
  inertia
• UFF for test bodies ( 10-12 10-13 )
• UGR for photons ( 10-4 )
• LLI for physical laws ( 10-4 )
• PPN parameters

curvature ? 1 10-5 light-time delay light deflection
nonlinearity ? 1 10-4 perihelion shift red shift in 2nd order
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GP-A , 1976
Df/fDt/tgh/c210-9
h104km
?vmin 6 cm/s
(Df/f)H?10-13
0,01
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(No Transcript)
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(P/Q) ?2 (R/S) 1(N/M)2 -1/2 ? 0

• Online compensation
• Doppler shift
• - atmospheric shift

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Gravitational red shift experiment with SRT
Radioastron
increase sensitivity due to the measurement
repetition 10-4 ? 10-5
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(No Transcript)
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RadioAstron orbit
Moon ? highly evolving orbit Period 8 10
day GRS modulation 0.410-10 5.810-10
9.410-11 6.410-10
1,000 80,000 km
6.810-10
280,000 350,000 km
Orbit determination accuracy Position 100 m
radio, 10 cm SLR Velocity 1 mm/s
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Green Bank tracking station (USA)
Radio links 8.4 GHz down (tone) 15 GHz down
(data) 7.2 GHz up (tone) S-band TC
Pushchino tracking station (Russia)
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Effelsberg (Germany)
Yebes (Spain)
Svetloe (Russia)
GBT (USA)
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VCH-1010 Hydrogen maser frequency standard of
the space radio telescope RadioAstron
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Allan deviation stochastic and systematic

log ?y(?)
log ?
 
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VCH-1010 (RadioAstron) vs. VLG-10 (GP-A)
Allan deviation s(t)
Averaging time t, s
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(No Transcript)
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Frequency method clock motion
,
orbit
meteo data model
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1st-order Doppler effect 8.4 GHz link
Frequency, Hz
Distance, 103 km
Date (January 2014)
1st-order Doppler
geocentric distance
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Gravitational redshift and 2nd-order Doppler
effect 8.4 GHz link
Frequency, Hz
Distance, 103 km
Date (January 2014)
2nd-order Doppler
geocentric distance
gravitational redshift
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GRAVITATIONAL REDSHIFT EXPERIMENT WITH THE SRT
RADIOASTRON
Contributions to the total frequency shift of the
8.4 GHz signal. Puschino TS, Oct 2012
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GRAVITATIONAL REDSHIFT EXPERIMENT WITH THE SRT
RADIOASTRON
Residual frequency of the 8.4 GHz signal.
Puschino TS, Oct 2012
geocentric distance
residual frequency
Distance, 103 km
Frequency, Hz
Date (October)
Agreement between theory and experiment 3
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Gravity Probe A (1976)
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RadioAstron radio links operating modes
1-way H-Maser mode
2-way Coherent mode
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RadioAstron radio links operating modes
Mixed Semi-Coherent mode
Biriukov et al. 2014, Astron. Rep. 58, N.11, p.
783
software processing
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SRT RADIOASTRON ON-BOARD HARDWARE
SYNCHRONIZATION SEMI-COHERENT MODE
Spectrum of the 15 GHz signal, transmitted data
is noise-like
Normalized spectral power density, dB
Frequency, Hz
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Semi-Coherent Test-2 ? incompatibility with
astronomy
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SRT RadioAstron on-board hardware
synchronization Semi-coherent mode
Spectrum of the 15 GHz signal Test-2 mode
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2015/02/15 Onsala, 8.4 GHz, 2-way Recorded signal
spectrum
Normalized power (log scale)
Frequency, Hz
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2015/02/15 Onsala, 8.4 GHz, 2-way Signal phase
Phase, rad
Session time, s
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2015/02/15 Onsala, 8.4 GHz, 2-way Stopped-phase
signal spectrum
Normalized power (log scale)
?f ? 0.001 Hz
Frequency, Hz
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SRT RADIOASTRON ON-BOARD HARDWARE
SYNCHRONIZATION SEMI-COHERENT MODE
Select components of the 15 GHz signal
spectrum 31 Aug 2014, Puschino TS, 082000 UTC,
mode Test-2 18 MHz
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Number of observing telescopes near perigee in
2016
Geocentric distance, 103 km
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Number of observing telescopes near perigee in
2016
Geocentric distance, 103 km
10 experiments at lt10,000 km distance and
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Experiment accuracy
Signal frequency instability at 1000 s 1 ? 1014 to 2 ? 1014 )
Systematic errors space and ground clock drift over 1 experiment uncertainties due to orbit determination errors 2 ? 1015 2 ? 1015
DU/c2 variation 2 ? 1010 to 4 ? 1010
Experiment accuracy (15 sessions 11 hr, 2 telescopes on average) 2 ? 105
) Work in progress
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Gravitational redshift tests
Mission Launch/ status Frequency standard Achieved/ planned accuracy
Gravity Probe A 1976 completed H-maser 1.410-4
RadioAstron 2011 active H-maser 210-5
ACES 2016 Cs-fountain H-maser 210-6
STE-Quest 2026 ? 210-8
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Thanks for attention