Sheila, Jennie W
We have some a series of peaks inthe DARM spectrum from 25-34 Hz, some of which have broad shoulders, which have been with us for a long time but are now more prominent due to improvements in low frequency sensitivity.
I took a 2mHz resolution spectrum from a time with good range last night (165 Mpc). I tried searching all of these frequencies on the alog but found none of them.
| frequency (Hz) | |
| 25.223 | |
| 26.475 | maybe BS roll mode (0.3 Hz off) Jennie found HAM6 channels in Gabriele's BRUCO from last night around 26.5 Hz. This frequency shifted since March 31st when it was at 26.512 Hz. Jim found these peaks in HAM6 GS13s and HPI L4Cs, and sees them when the IFO is locked and unlocked. He also sees that the frequency of this line shifted slightly since March 31st in the seismic sensors, as in DARM |
| 27.418 | HSTS bounce modes could be candidates (these look closest): SRM, SR2, PR2, MC1, MC2 Jim also sees this in HAM6 GS13s and L4Cs. |
| 27.504 | SR2/SRM bounce modes are closest |
| 27.707 | SR3 bounce? |
| 28.217 | PR3 bounce BRUCO shows coherence with PRCL, which |
| 29.000 | suspicously close to exactly 29 Hz, Jim also sees this in HAM6 GS13s and L4Cs. |
| 29.971 | |
| 32.301 | broad shoulder, dramatic change with PRCL offset |
| 33.334 | |
| 33.428 | |
| 33.639 | PR2 coherence |
| 33.639 | |
| 33.513 | |
| 35.712 | |
| 40.938 | HSTS and HLTS roll modes, PR2 and MC2 are closest. 40.938*0.6666 is 27.291 Hz, not lining up exactly with any of the above. (see similar discussion here: 21696) |
In the resonances wiki there is a ERM mode listed at 25.6281 (calculated not measured). There is a BS roll mode (R3) calculated as 25.9175 Hz with a link to 49643, which suggests it is 26.06 Hz
Jennie searched Gabriele's Bruco from last night, and found that there are PRCL coherences for some of these peaks. I retook the 2mHz spectra for a comparison of the times before and after the PRCL offset was first tuned, you can toggle between this and this screenshot to see the difference. Since this PRCL offset was first put in, we have changed the BS camera spot position which brought back the board PRCL coherence this offset was getting rid of (76814). The PRCL offset did seem to reduce the broad noise in DARM around these peaks, as you can see in the third attachment with with more binning.
Here's a similar effort from a few weeks ago: 76505
Interestingly, some of the peaks appear to have moved:
25.194 to 25.225 Hz
26.536 to 26.477 Hz
27.041 Hz is gone
29.500 Hz is gone
33.591 to 33.642 Hz
35.221 to 35.400 Hz
39.800 Hz is gone
