Figure 1. In the spectrum there is a new bump at 54.8Hz. It has not been there at the beginning of the year, and it isn't one of the dither lines that I am aware off. It is important to identify what is the origin of it.
The only thing that comes to my mind is the new cover of the EPRB bench. In the past there has been issues with a bump at 63Hz related to SPRB/EPRB, when EPRB was open.
This is a quick look at ENV_EPRB_ACC_Y (I don't know if this is a good witness)
It seems there is no coherence at 54.8 Hz
Maybe there are other sensors to look at.
I've ran an instance of BruCo to find coherence among more than 5000 channels with Hrec_hoft_20000Hz.
The results can be consulted here.
Unfortunately, no safe channel was found to be coherent around the bump frequencies.
The latest list of unsafe and unreliable channels can be consulted here.
Figure 1. Francesco remembered that two years ago we had a line at ~54Hz that had appeared on Aug 2 2024 https://logbook.virgo-gw.eu/virgo/?r=64873
Figure 2 compares the spectrum from Aug 2 in the evening and yesterday. The line we have now is much higher, and a bit broader, and is actually composed of two peaks.
Looking at Samuel's bruco, the smaller peak on the left at 54Hz, seems to be the same as the issue in Aug 2024, as it is coherent with SDB1 suspension accelerometers: https://scientists.virgo-gw.eu/DataAnalysis/DetCharDev/users/salvador/BruCo/Hrec_hoft_1475582418/Sa_OB_BR_LVDT3_500Hz.png, which was also the case of the line in Aug 2024. It would be interesting to look through the logbook how this issue was resolved two years ago, or if it disappeared on its own.
The main bump at 54.8Hz seems to be something else.
