The gravitational redshift monitored with RadioAstron from near Earth up to 350,000 kmстатья
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Аннотация:We report on our efforts to test the Einstein Equivalence Principle by measuring
the gravitational redshift with the VLBI spacecraft RadioAstron, in an eccentric orbit around Earth with geocentric distances as small as ~ 7,000 km and up to 350,000 km. The spacecraft and its ground stations are each equipped with stable hydrogen maser frequency standards and measurements were obtained at both 8.4 and 15 GHz between 2012 and 2017. Over the course of the ~ 9 d orbit, the gravitational redshift varies between 6.8 10^{-10} and 0.6 10^{-10}. Since the frequency ofset between the masers cannot be measured independently of the absolute gravitational redshift, only the variation of the observed gravitational redshift was used in this analysis. We obtain a preliminary measurement of the fractional deviation of the gravitational redshift from prediction of 0.016 (+-) 0.003stat (+-)0.030syst with the
systematic uncertainty being dominated by the error in accounting for the non-relativistic Doppler shift. This result is consistent with zero within the uncertainties. For the first time, the gravitational redshift has been probed over such large distances in the vicinity of Earth. About three orders of magnitude more accurate measurements are perhaps possible with RadioAstron using dedicated interleaved observations combining uplink and downlink modes of operation.