Kiet, Evan, Anamaria 

We noticed that since August 24th, 2024—following the detector maintenance break in O4b—NonSENS has been consistently injecting noise into the 58–60 Hz band.

The ratio of strain after/before cleaning has been tracked via the DetChar summary pages. Attached to this alog are three examples, taken on August 24th, 2024; December 23rd, 2024; and March 31st, 2025. The peak around 58–60 Hz appears to grow over this period, and and remains present after the O4c commissioning break. 

We’ve also attached the NonSENS noise budget for March 31st, 2025. It shows a peak in the jitter noise at 58–60 Hz, which aligns with the band NonSENS has been injecting noise into, so perhaps it is not subtracting jitter correctly?