Miriam, Hunter, Andy A subset of blip glitches appear to be due to a glitch in the ETMY L2 coil driver chain. We measured the transfer function from the ETMY L2 MASTER channel to the NOISEMON channel (specifically, for the LR quadrant). We used this to subtract the drive signal out of the noisemon, so what remains would be any glitches in the coil drive chain itself (and not just feedback from DARM). The subtraction works very well as seen in plot 1, with the noise floor a factor of 100 below the signal from about 4 to 800 Hz. We identified some blip glitches from Feb 11 and 12 as well as Mar 6 and 7. Some of the Omega scans of the raw noisemon signals look suspicious, so we performed the subtraction. The noisemons seem to have an analog saturation limit at +/- 22,000 counts, so we looked for cases where the noisemon signal is clearly below this. In some cases, there was nothing seen in the noisemon after subtraction, or what remained was small and seemed like it might be due to a soft saturation or nonlinearity in the noisemon. However we have identified at least three times where there is a strong residual. These are the second through fourth plots. We now plan to automate this process to look at many more blip and check all test mass L2 coils in all quadrants.
In case someone wants to know, the times we report here are:
1170833873.5
1170934017
1170975288.38
I have noticed similarly caused glitches on the 10th March, in particular for the highest SNR Omicron glitch for the day:
Looking at the OmegaScan of this glitch in H(t) and then the highest SNR coincident channels which are all the quadrants of H1:SUS-ETMY_L2_NOISEMON:
Hi Borja,
could you point us to the link to those omega scans? I would like to see the time series plots to check if the noisemon channels are saturating (we saw that sometimes they look like that in the spectrogram when it saturates).
I am also going to look into the blip glitches I got for March 10 to see if I find more of those (although I won't have glitches with such a high SNR like the one you posted).
Thanks!
Hi Miriam,
The above OmegaScan can be found here
Also I noticed that yesterday the highest New SNR glitch for the whole day reported by PyCBC live 'Short' is of this type as well. The OmegaScan for this one can be found here.
Hope if helps!
Hi Miriam, Borja,
While following up on a GraceDB trigger, I looked at several glitches from March 1 which seem to match those that Borja posted. The omegascans are here, in case these are also of interest to you.
Hi,
Borja, in the first omega scan you sent, the noisemon channels are indeed saturated. In that case it is difficult to tell apart if that is the reason for the spectrogram looking like that or if indeed it might be a glitch in the coil drive. Once Andy has a more final version of his code, we can check on that. In the second omega scan, the noisemon channels look just like the blip glitch looks in the calib_strain channel, which means the blip was probably already in the DARM loop before and the noisemon channels are just hearing it. Notice also that, besides the PyCBC_Live 'short', we have a version of PyCBC_Live that is dedicated specifically to find blip glitches (see aLog 34257), so at some point we will be looking into times coming from there (I will keep in mind to look into the March 10 list).
Paul, those omega scans do not quite look like what we are looking for. We did look into some blip glitches where the noisemon channels looked like what you sent and we did not find any evidence for glitches in the coil drive. But thanks for your omega scans, I will be checking those times when Andy has a final version of the subtraction code.