Virgo Logbook

I calculated the projection of the ambient magnetic contribution to Hrec, following the magnetic noise injections performed at CEB on July 1. In the first plot I show the coherence between Hrec and the 3 magnetometers channels, in corrispondence of the injected lines. Some of them don't produce enough signal in Hrec, so the projection is calculated only at the frequencies in which the coherence has a value higher than 0.5, in order to assess reliability. The projection is shown in the second plot for the 3 magnetometers, superposed to a nominal quiet time Hrec (slightly before the beginning of the injections). The projection was calculated by doing the product of the transfer function (between Hrec and mag) and the ambient magnetic spectrum seen by magnetometers at the same quiet time.

From this preliminary analysis it seems that the magnetic noise level is particularly high and near the sensitivity curve. In order to confirm it, We have to perform other injection studies and assess the reliability of the data processing technique. During last weeks We have done the same injections at NEB and WEB but the coherence was not high enough to perform a reliable projection. Now that we have improved the ITF sensitivity, it could be usefull to repeat injections at least at one of the end buildings. Efforts to understand this magnetic noise budget are on the agenda of these days.