PyCBC analysts, Thomas Dent, Andrew Lundgren
Investigation of some unusual and loud CBC triggers led to identifying a new set of glitches which occur a few times a day, looking like one or two cycles of extremely high-frequency scattering arches in the strain channel. One very clear example is this omega scan (26th Jan) - see particularly LSC-REFL_A_LF_OUT_DQ and IMC-IM4_TRANS_YAW spectrograms for the scattering structure. (Hence the possible name SPINOSAURUS, for which try Googling.)
The cause is a really strong transient excitation at around 30Hz (aka 'thud') hitting the central station, seen in many accelerometer, seismometer, HEPI, ISI and SUS channels. We made some sound files from a selection of these channels :
- PEM-CS_SEIS_LVEA_VERTEX_Z (sped up by factor 4)
- PEM-CS_ACC_OPLEV_ITMY_X (sped up by factor 4)
- PEM-CS_ACC_BEAMTUBE_MCTUBE_Y (sped up by factor 2)
PEM microphones, interestingly, don't pick up the disturbance in most cases - so probably it is coming through the ground.
Note that the OPLEV accelerometer shows ringing at ~60-something Hz.
Working hypothesis is that the thud is exciting some resonance/relative motion of the input optics which is causing light to be reflected off places where it shouldn't be ..
The frequency of the arches (~34 per second) would indicate that whatever is causing scattering has a motion frequency of about 17Hz (see eg https://ldvw.ligo.caltech.edu/ldvw/view?act=getImg&imgId=154054 as well as the omega scan above).
Maybe someone at the site could recognize what this is from listening to the .wav files?
A set of omega scans of similar events on 26th Jan (identified by thresholding on ISI-GND_STS_HAM2_Y) can be found at https://ldas-jobs.ligo-wa.caltech.edu/~tdent/wdq/isi_ham2/
Wow that is pretty loud, seems like it is even seen (though just barely) on seismometers clear out at EY with about the right propagation delay for air or ground propagation in this band (about 300 m/s). Like a small quake near the corner station or something really heavy, like the front loader, going over a big bump or setting its shovel down hard. Are other similar events during working hours and also seen at EY or EX?
It's hard to spot any pattern in the GPS times. As far as I have checked the disturbances are always much stronger in CS/LVEA than in end station (if seen at all in EX/EY ..).
More times can be found at https://ldas-jobs.ligo-wa.caltech.edu/~tdent/wdq/isi_ham2/jan23/ https://ldas-jobs.ligo-wa.caltech.edu/~tdent/wdq/isi_ham2/jan24/
Hveto investigations have uncovered a bunch more times - some are definitely not in working hours, eg https://ldas-jobs.ligo-wa.caltech.edu/~tjmassin/hveto/O2Ac-HPI-HAM2/scans/1169549195.98/ (02:46 local) https://ldas-jobs.ligo-wa.caltech.edu/~tjmassin/hveto/O2Ab-HPI-HAM2/scans/1168330222.84/ (00:10 local)
Here's a plot which may be helpful as to the times of disturbances in CS showing the great majority of occurrences on the 23rd, 26th-27th and early on 28th Jan (all times UTC). This ought to be correlated with local happenings.
The ISI-GND HAM2 channel also has loud triggers at times where there are no strain triggers as the ifo was not observing. The main times I see are approximately (UTC time)
Jan 22 : hours 13, 18 21-22
Jan 23 : hours 0-1, 20
Jan 24 : hours 0, 1, 3-6, 10, 18-23
Jan 25 : hours 21-22
Jan 26 : hours 17-19, 21-22
Jan 27 : hours 1-3, 5-6, 10, 15-17, 19, 21, 23
Jan 28 : hours 9-10
Jan 29 : hours 19-20
Jan 30 : hours 17, 19-20
Hmm. Maybe this shows a predominance of times around hour 19-20-21 UTC i.e. 11-12-13 PST. Lunchtime?? And what was special about the 24th and 27th ..
Is this maybe snow falling off the buildings? The temps started going above the teens on the 18th or so and started staying near freezing by the 24th. Fil reported seeing a chunk he thought could be ~200 lbs fall.
Ice Cracking On Roofs?
In addition to ice/snow falls mentioned by Jim, thought I'd mention audible bumps I heard from the Control Room during some snowy evenings a few weeks ago (alog33199)....Beverly Berger emailed me suggesting this could be ice cracking on the roof. We currently do not have tons of snow on the roofs, but there are some drifts which might be on the order of a 1' tall.
MSR Door Slams?
After hearing the audio files from Thomas' alog, I was sensitive to the noise this morning. Because of this, thought I'd note some times this morning when I heard a noise similar to Thomas' audio, and this noise was the door slamming when people were entering the MSR (Mass Storage Room adjacent to the Control Room & there were a pile of boxes which the door would hit when opened...I have since slid them out of the way). Realize this isn't as big of a force as what Robert mentions or the snow falls, but just thought I'd note some times when they were in/out of the room this morning:
I took a brief look at the times in Corey's previous 'bumps in the night' report, I think I managed to deduce correctly that it refers to UTC times on Jan 13. Out of these I could only find glitches corresponding to the times 5:32:50 and 6:09:14. There were also some loud triggers in the ISI-GND HAM2 channel on Jan 13, but only one corresponded in time with Corey's bumps: 1168320724 (05:31:46).
The 6:09 glitch seems to be a false alarm, a very loud blip glitch at 06:09:10 (see https://ldas-jobs.ligo-wa.caltech.edu/~tdent/wdq/H1_1168322968/) with very little visible in aux channels. The glitch would be visible on the control room glitchgram and/or range plot but is not associated with PEM-CS_SEIS or ISI-GND HAM2 disturbances.
The 5:32:50 glitch was identified as a 'PSL glitch' some time ago - however, it also appears to be a spinosaurus! So, a loud enough spinosaurus will also appear in the PSL.
Evidence : Very loud in PEM-CS_SEIS_LVEA_VERTEX channels (https://ldvw.ligo.caltech.edu/ldvw/view?act=getImg&imgId=155306) and characteristic sail shape in IMC-IM4 (https://ldvw.ligo.caltech.edu/ldvw/view?act=getImg&imgId=155301).
The DetChar SEI/Ground BLRMS Y summary page tab has a good witness channel, see the 'HAM2' trace in this plot for the 13th - ie if you want to know 'was it a spinosaurus' check for a spike in HAM2.
Here is another weird-audio-band-disturbance-in-CS event (or series of events!) from Jan 24th ~17:00 UTC :
https://ldas-jobs.ligo-wa.caltech.edu/~tdent/detchar/o2/PEM-CS_ACC_LVEAFLOOR_HAM1_Z-1169312457.wav
Could be someone walking up to a piece of the instrument, dropping or shifting some heavy object then going away .. ??
Omega scan: https://ldas-jobs.ligo-wa.caltech.edu/~tdent/wdq/psl_iss/1169312457.3/
The time mentioned in the last entry turns out to have been a scheduled Tuesday maintenance where people were indeed in the LVEA doing work (and the ifo was not observing, though locked).