Virgo Logbook

The unlock of this night that also excited the NE suspension seems indeed due to an airplane or helicopter. Fig 1 shows the spectrograms of microphones and seismometers of central and north buildings. As shown by the Doppler-patterns, the UFO first passes at relatively large distance from the central building and passes about 1 minute later at very close distance to the NE.

Fig 2 shows some spectrogram of NE topstage accellerometers. It looks like some resonance of the vertical loop at 27 Hz gets excited, which causes the unlock. The probable culprit might be a Chinook (big double-rotor military transport helicopter). Yesterday morning, I saw one flying close to the WE from my office. This caused a pretty similar, low-frequency spectrogram, see fig 3. Note that in this case, the noise is clearly seen in the microphone. I find it very strange that the microphone of the NE doesnt see anything, see fig 1.