Piernicola suggested that the step glitches we have could be what in the past was called payload glitches. Following entries from that logbook at first sight these are different, as the one example of spectrum of payload glitch had a 1/f^2.5 spectral shape instead of something between 1/f and 1/f^0.5 that the step glitches have. However, checking if some high frequency mode is excited by the step glitches is a good idea. That idea is also linked to earlier issues of that kind back in 2008.

Looking at (5-10) step glitches from June 21, all of them have an associated glitch at high frequency. Figure 1-4 shows a couple of example of normalized spectrograms of SDB2_B1_PD1_Audio_100KHz. Each time I have selected the frequency range when the largest increase in spectrum compared to the median was present. These are 4 different glitches, each time centered at 64s in the time series. In some

As a control I have checked one random time, and one 25 minute glitch time, and in neither of them there was a glitch above 10kHz.

Figure 5, For some of the step glitches I could also find a glitch at 7814Hz at the same time, but not for all step glitches. 7814Hz is the drum mode frequency of the WE mirror. 

It would be interesting to check on a larger sample of step glitches whether all have a glitch at high frequency (between 10kHz and 30kHz) at the same time, and which fraction of them have a glitch at the WE drum mode frequency (7815Hz). It would be also interesting to check the much smaller number of step glitches in late April / early May, if those had also the same property. The drum mode in April/May may be different by a few Hz, as it was a different mirror suspended at the same time.

This makes it probable that the step glitches are due to the WE mirror settling, for exampl with some kind of curing or drying process in the mirror ears. These would be after the suspension fiber, so not necessarily filtered by the pendulum. The more systematic study of which frequencies are excited (in particular how often the drum mode we know is excited) would allow to confirm that. If confirmed, then the only solution is to wait for the glitches to slowly reduce in rate, as they have been doing for the past two weeks.

Back in 2008 the exponential decay in the glitch rate had a e-folding time scale of 2 weeks. That would be the same order of magnitude as the decreased observed over the last two weeks.

/users/mwas/detchar/hoftGlitch_20250620/arches.m