Rana, Matt, Evan

Back on 2015-07-20, we accidentally rang up the butterfly mode of the EY test mass. We notched this mode out of the DARM actuation path, so that it is not excited by DARM feedback. Additionally, I installed a bandpass filter in mode 9 of the EY L2 BLRMS monitors so that we could monitor the ringdown of the mode.

We looked at 2 hours of data starting at 2015-07-20 11:01:30 Z. Looking at the DARM spectrum from that time, the frequency of the mode is 6053.805(5) Hz. From the BLRMs, we see a nice ringdown in the amplitude. Fitting an exponential to this ringdown, the time constant is 1300 s. This gives the Q of the mode as 2×10⁷ or so. Uncertainty TBD.