Transcript Document
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, 21–28 March 2015
• 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
/ / c
2
GM
Rstar c 2
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
GP-A , 1976
f/f=t/t~gh/c2~10-9
vmin~ 6 cm/s
h~104km
(f/f)H10-13
±0,01%
(P/Q) – 2 (R/S)•
•[1+(N/M)2 ] -1/2 0
Online compensation
- Doppler shift
- atmospheric shift
Gravitational red shift experiment with SRT “Radioastron”
increase sensitivity
due to the
measurement
repetition
10^{-4} 10^{-5}
RadioAstron orbit
Moon highly evolving orbit
Period: 8 – 10 day
GRS modulation: 0.4∙10-10 – 5.8∙10-10
Orbit determination accuracy
Position: 100 m radio, 10 cm SLR
Velocity: 1 mm/s
Green Bank tracking station (USA)
Radio links:
8.4 GHz down (tone)
15 GHz down (data)
7.2 GHz up (tone)
S-band T&C
Pushchino tracking station (Russia)
Effelsberg (Germany)
Svetloe (Russia)
Yebes (Spain)
GBT (USA)
VCH-1010
Hydrogen maser frequency standard
of the space radio telescope “RadioAstron”
Allan deviation: stochastic and systematic
log y(t)
log t
Allan deviation (t)
VCH-1010 (RadioAstron) vs. VLG-10 (GP-A)
Averaging time t, s
FREQUENCY METHOD: CLOCK MOTION
,
orbit
meteo data + model
Distance, 103 km
Frequency, Hz
1st-order Doppler effect
8.4 GHz link
Date (January 2014)
geocentric distance
1st-order Doppler
Distance, 103 km
Frequency, Hz
Gravitational redshift and 2nd-order Doppler effect
8.4 GHz link
Date (January 2014)
geocentric distance
2nd-order Doppler
gravitational redshift
GRAVITATIONAL REDSHIFT EXPERIMENT WITH THE SRT “RADIOASTRON”
Contributions to the total frequency shift of the 8.4 GHz signal.
Puschino TS, Oct 2012
GRAVITATIONAL REDSHIFT EXPERIMENT WITH THE SRT “RADIOASTRON”
Residual frequency of the 8.4 GHz signal. Puschino TS, Oct 2012
Distance, 103 km
Frequency, Hz
geocentric distance
residual frequency
Date (October)
AGREEMENT BETWEEN THEORY AND EXPERIMENT: 3%
Gravity Probe A (1976)
RadioAstron radio links operating modes
1-way “H-Maser” mode
2-way “Coherent” mode
RadioAstron radio links operating modes
Mixed “Semi-Coherent” mode
Biriukov et al. 2014, Astron. Rep. 58, N.11, p. 783
software
processing
SRT RADIOASTRON ON-BOARD HARDWARE SYNCHRONIZATION: “SEMI-COHERENT” MODE
Normalized spectral power density, dB
Spectrum of the 15 GHz signal,
transmitted data is noise-like
Frequency, Hz
“Semi-Coherent” + “Test-2” incompatibility with astronomy
SRT RADIOASTRON ON-BOARD HARDWARE SYNCHRONIZATION:
“SEMI-COHERENT” MODE
Spectrum of the 15 GHz signal
“Test-2” mode
Normalized power (log scale)
2015/02/15 Onsala, 8.4 GHz, 2-way
Recorded signal spectrum
Frequency, Hz
Phase, rad
2015/02/15 Onsala, 8.4 GHz, 2-way
Signal phase
Session time, s
2015/02/15 Onsala, 8.4 GHz, 2-way
Stopped-phase signal spectrum
Normalized power (log scale)
f 0.001 Hz
Frequency, Hz
SRT RADIOASTRON ON-BOARD HARDWARE SYNCHRONIZATION: “SEMI-COHERENT” MODE
Select components of the 15 GHz signal spectrum
31 Aug 2014, Puschino TS, 08:20:00 UTC, mode: “Test-2” 18 MHz
Geocentric distance, 103 km
Number of observing telescopes near perigee in 2016
Geocentric distance, 103 km
Number of observing telescopes near perigee in 2016
~10 experiments at <10,000 km distance and
Experiment accuracy
Signal frequency instability at 1000 s
1 10–14 to 2 10–14
*)
Systematic errors:
space and ground clock drift over 1 experiment
2 10–15
uncertainties due to orbit determination errors
2 10–15
U/c2 variation
2 10–10 to 4 10–10
Experiment accuracy
2 10–5
(15 sessions 1+1 hr, 2 telescopes on average)
*) Work in progress
GRAVITATIONAL REDSHIFT TESTS
Launch/
status
Frequency
standard
Achieved/
planned
accuracy
1976
completed
H-maser
1.4∙10-4
RadioAstron
2011
active
H-maser
2∙10-5
ACES
2016
Cs-fountain +
H-maser
2∙10-6
≥ 2026
?
2∙10-8
Mission
Gravity Probe A
STE-Quest
Thanks for attention