MG15 - Talk detail

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The opto - acoustical GW detector OGRAN was presented in early papers It is a combination of the acoustical resonance bar (with the central axial tunnel) coupled with the long (2 m) optical FP cavity composed by mirrors attached to the bar ends.. A new quality of such construction is given as: (a) a more complex structure of signal response, containing separately acoustical and optical parts, and (b) a possibility to get sensitivity at the level of bar thermal noise due to the small back action of optical read out. At present the full scale setup is installed into underground facilities of BNO INR RAS and goes through the commissioning phase and test engineering series. Perspective of the next development is associated with a cryogenic version of the opto-acoustical bar tested on a pilot model having a final goal sensitivity h~10^{-21} Hz^{−1/2}. The main goal of the OGRAN detector is an operation in a deep underground of the Baksan Neutrino Observatory in parallel with Baksan Underground Scintillator Telescope (BUST) involved in the collapse searching program through the neutrino events. The BUST plus OGRAN compose the nu-gw couple for two channel registration of rare events - star collapses in the Galaxy and close environment ~ 100 Kpc The presentation contains the detail description of the new GW detector as well as proposed algorithm of joint search for nu-gw correlation.

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A new test of the gravitational redshift effect, was conducted with the RadioAstron satellite, which has been in a highly eccentric orbit around the Earth for several years. We probed the flow of time on board, which varies while RadioAstron (RA) passes through the varying gravitational potential of the Earth, by recording the spacecraft’s downlink signal, which is synchronized to its ultra-stable on-board H-maser, at the ground radio telescopes. The experiment requires us to extract the tiny gravitational redshift signal from the mixture of a number of much larger effects, including those of the nonrelativistic Doppler frequency shift, signal propagation through the Earth’s troposphere and ionosphere, higher-order kinematic effects of special relativity, Earth tides, and various instrumental effects. In order to perform the offline filtering of those effects we developed several algorithms adapted to operational modes RA spacecraft, A total of 17 successful experiments were performed while the on-board H-maser was operational. Preliminary analysis of the data from two experiments gives us a fractional accuracy of the gravitational redshift test of at least 2 . 10^{-4}, which is comparable to that obtained by Gravity Probe A. In this talk we discuss our data analysis algorithms and present arguments in favor of the experiment uncertainty currently being dominated by that of the ionosphere frequency shift. Also we formulate prospects for improving the achieved accuracy further.

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