Starting form 9:30 UTC, for two hours some data have been acquired with SR TY misaligned in many steps, up to the usual 2 urad which sets the DCP below 200 Hz. The aligned state with SR TY in loop has been recovered at 11:35 UTC.
An interesting comparison can be done with old data taken with an intermediate SR TY misalignment. Fig 1 shows the comparison when the DCP is about 270 Hz: the mystery noise is clearly lower. Fig 2 shows that the working point is quite similar, according to the DCP and the optical gain; now the dark fringe is much darker.
As we know, in the past the mystery noise was lower with a higher misalignement (fig3); now, going further with the misalignament the curve does not change in the region where the mystery noise is supposed to be limiting (fig 4). To be noticed that there is still an improvement of the dark fringe when the DCP is pushed down (fig 5).
A rough estimation of the noise components (fig 6) says that a pessimistic estimation of the thermal noise (0.7e-23 @ 100 Hz) is almost sufficient to explain the curve.
