V. N. Rudenko

Gravitational redshift test with the space radio telescope “RadioAstron”

The space radio telescope “RadioAstron” is equipped with a high performance hydrogen maser frequency standard and thus provides a unique opportunity for a gravitational redshift test. We consider various modes of operation of the on-board scientific equipment and their impact on accuracy of the anticipated experiment. We find that the accuracy of the test is limited by ∼10−2 for the hardware configuration routinely used in radio astronomical observations, which is a consequence of using ballistic data to remove the nonrelativistic Doppler frequency shift from the analyzed signal. On the other hand, the so-called “Semi-coherent” mode of the on-board hardware provides for combining the space and ground maser signals in such a way that the resulting signal carries information about the useful effect but is free from the nonrelativistic Doppler and tropospheric frequency shifts. The proposed compensation scheme, which is different from the one used in the Gravity Probe A experiment, allows for testing the gravitational redshift effect with ∼10−6 accuracy.

A precise system for measuring weak optoacoustic perturbations

The practical implementation of a high-sensitivity measuring system based on an extended Fabry-Perot interferometer, which reacts to small variations of its optical length, is presented. The attained sensitivity is limited by the spectral noise density of optical pumping, which is lower than the resonance spectral density of thermal fluctuations of the interferometer base by one order of magnitude. Structurally, the system is an optoacoustic gravitational antenna without cooling (OGRAN). Extrapolating the results obtained for a pilot model to a large-size variant of the setup fo recasts a sensitivity sufficient for searching for gravitational bursts in the Galaxy and its nearest vicinity (within 100 kpc).

The search for gravitational radiation of non-terrestrial origin

Abstract The results of a new radiation-gravitational experiment are briefly described. Webers effect of “coincident events” exceeding the statistically expected value is not observed on the level ∼ 5 × 10 6 erg/sec. cm 2 for the gravitation energy flux.

An optoacoustical gravitational antenna

An optoacoustical gravitational detector that structurally combines the principles of interferometric and solid-state gravitational antennas is described. A large acoustical resonator, which is matched to a commensurate Fabry-Perot (FP) optical interferometer, serves as the sensitive element for recording changes in the gravitational-field gradient. In a test experiment, the spectral density of recorded spatial deformations (metric variations) was 10−19 Hz−1/2 at a frequency of ∼1.3 kHz within a band of ∼4 Hz, which can be extended by an order of magnitude upon a corresponding increase in the sharpness of the interferometer mirrors. The new antenna is designed for detecting relativistic catastrophes (collapses) in the Galaxy and the nearest vicinity during complex (multichannel) monitoring with neutrino telescopes of the Baksan Neutrino Observatory of the Institute for Nuclear Research, Russian Academy of Sciences.

Probing the gravitational redshift with an Earth-orbiting satellite

We present an approach to testing the gravitational redshift effect using the RadioAstron satellite. The experiment is based on a modification of the Gravity Probe A scheme of nonrelativistic Doppler compensation and benefits from the highly eccentric orbit and ultra-stable atomic hydrogen maser frequency standard of the RadioAstron satellite. Using the presented techniques we expect to reach an accuracy of the gravitational redshift test of order 10^(−5), a magnitude better than that of Gravity Probe A. Data processing is ongoing, our preliminary results agree with the validity of the Einstein Equivalence Principle.

Baksan laser interferometer

A description is given of the construction and technical parameters of a long-base (75m) laser interferometer made at the Shternberg State Astronomical Institute of Moscow State University and introduced into continuous operation in the Northern Caucasus. The purpose of the interferometer is to investigate lithospheric deformations in a wide frequency range (up to 103 Hz). An estimate of the spectral density of deformations has been obtained from the results of observations over a ten-month period.

Analysis of the “Ulitka” noise background as an anti-coincidence filter for the OGRAN gravitational-wave antenna

An analysis of experimental data from the “Ulitka” high-frequency gravitational-gradient meter installed in the underground Baksan Neutrino Observatory of the Russian Academy of Sciences is presented, focusing on the planned use of this instrument as an “anti-coincidence filter” for the OGRAN gravitational-wave antenna. The statistics of the Ulitka noise background over a year’s observing are analyzed, and compared with the background measured earlier when Ulitka was located on the territory of the Sternberg Astronomical Institute in Moscow. A reduction in the rate of occurrence of large nonthermal spikes is noted. We have found associations between earthquakes and excitations of the seismically isolated high-frequency mode of the longitudinal oscillations of Ulitka.

High-frequency gravitational wave detector with electromagnetic-gravitational resonance

In view of the increased interest in high-frequency gravitational wave detectors, we discuss detection of gravitational waves by their action on an electromagnetic wave in a closed waveguide or resonator. The principle of such a detector (proposed earlier by V.B. Braginsky and M.B. Mensky under the name of electromagnetic-gravitational resonance) is sketched, and basic formulas for various shapes of the waveguide are derived. The resonator with parallel mirrors (FP cavity) is considered as a special case. It is shown that the existing interferometric GW antennas may be used for detecting high-frequency gravitational waves.

RadioAstron gravitational redshift experiment : status update

A test of a cornerstone of general relativity, the gravitational redshift effect, is currently being conducted with the RadioAstron spacecraft, which is on a highly eccentric orbit around Earth. Using ground radio telescopes to record the spacecraft signal, synchronized to its ultra-stable on-board H-maser, we can probe the varying flow of time on board with unprecedented accuracy. The observations performed so far, currently being analyzed, have already allowed us to measure the effect with a relative accuracy of

Sensitivity Enhancement of the Gravitational Detector OGRAN

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