Robert, Evan, Anamaria

The peaks in DARM around 280, 550, 850 aand 1100 are coherent with the CS_EBAY_LSCRACK magnetometer. (The power lines are marked separately)

This has been seen before in March, but at the time they went away, even though the magnetometer spectra did not change. The coupling must be highly variable. At the time we had moved the fan power to a completely different power system in the hope that the mechanism was through the shared power of the fans and IO chassis (which acquires DARM).

However, it seems they have returned sometime around May 1st (a Wednesday), and have been in DARM since then, still variable but there nonetheless.
We should check if there were any relevant changes around that time to give us a clue about the coupling mechanism.

GregM recently added the magnetometer to the fscan pages, but it might be nice to go back and recreate the coherences over all of O3.
See example attached from this link: https://ldas-jobs.ligo-wa.caltech.edu/~pulsar/fscan/H1/daily/H1Fscan_coherence/fscanNavigation.html

We would like to ask DetChar to look into the behavior of this coupling and its effect on DARM.