2. EARTH GRAVITY FIELD VARIATIONS MEASURED BY THE FREE MASS INTERFEROMETER.

1. V.N.Rudenko, A.V.Gusev.
2. V.N.Rudenko & VIRGO team

1. A new approach in the gravitational wave experiment is considered. In addition to the old method of searching for coincident reaction of two separated gravitational antennae it was proposed to seek perturbations of the gravitational detector noise background correlated with astrophysical events uch as neutrino and gamma ray bursts registered by correspondent detectors. The reason of this pproach lies in understanding that last stages of stellar evolution such as a binary coalescence, supernova explosion, collapse, traditionally considered as gravitational burst sources, should be accompanied also neutrino and very likely gamma radiation.  It means in general that a detection of neutrino or gamma ray bursts defines time marks around which one might hope to find also gravitational detector exitations. An advantage of this method consists first of all in a remarkable reduction of the observational time interval and second in a potentional opportunity to accumulate week gravitational signals. A list of desirable events at present can be provided by four world neutrino telescops and cosmic CGRO and BepoSAX satellites. In this situation  one has to formulate an joint optimal data processing algorithm for gravitational detector output with parallel records of neutrino and gamma ray observatories. A simple searching for coincidences is insufficient due to an inevitable unknown time deay between events of different nature but mainly due to a deficit of gravitational and neutrino detector sensitivity. It has to be done according to the optimal filtration theory taking into account available information of noise and conceivable model of signal. Some versions of such optimal algorithms are presented in this report. Its efficiency is demonstrated in reanalysis of the old data concerning the phenomenon of neutrino-gravity correlation registered during of SN1987A explosion. Modifications associated with the gamma-gravity correlations are also presented.

2. A new development of the idea of parallel monitoring of the low frequency Earth gravity field variations in the process of free mass antenna operation is presented. The analysis is carried out in application to the specific mirror's suspension having place in the Virgo project (Virgo perattenuator) which admitts an exploring of the alignment circuits for to pick up a geophysical information. Geophysical signals and noises are analysed in detailes as well as instrumental slow drifts and fluctuations. Some simple computer simulation are performed to illustrate possible effects and a manner of operation. Results are compared with possibilities of conventional geophysical devices