Ansel Neunzert, Kiet Pham

Two comb structures continue to be present in the first 300 Hz. These contaminate many spectral bins, and are currently "most wanted" for CW data quality. Both of these have been noted before; this is an update about their recent changes and clues from DetChar investigations.

~1.6611 Hz comb with a peaked structure around 280 Hz: recently returned

• Example plot 2023 March 19 (shown in yellow triangles) [fig1]
• Example plot 2023 January 7 (shown in blue squares) [fig2]

Relevant previous alogs

• Investigating H1 narrow spectral artifacts: Nov 2022 - mid-Jan 2023
• Combs below 300 Hz in November / early December H1 data

History

• Present as far back as Nov 11 2022. Seems to be persistently present Nov, Dec, and January.
• Disappeared some time between Feb 8 2023 and Feb 17 2023. No data was available in this gap, which prevents pinpointing the date. It then returned on March 18th, during a time when we fortunately had plenty of before/after data. Here are some spectra demonstrating the change. Dates correspond to UTC days:
  • 17th [fig3]
  • 18th [fig4]
  • 19th [fig5]

Known witness channels (same as previously noted): H1:ASC-OMC_A_PIT_OUT_DQ, H1:ASC-OMC_A_YAW_OUT_DQ, H1:ASC-OMC_B_PIT_OUT_DQ , H1:ASC-OMC_B_YAW_OUT_DQ .

Additional notes

• Kiet ran STAMP-PEM to look for additional coherences in the region of this comb. A lot of GS13 channels show up. However, this comb is not actually seen in high resolution spectra of the same channels. It's possible that STAMP-PEM, which computes lower resolution spectra than Fscans but searches over a wider range of channels, is picking up on some broader noise artifact that exists in the same frequency range.
• This reminded me that Derek, Robert, Louis and I did some digging with vaguely similar results back in February. Unfortunately this didn't get posted to the alog, but a post is being drafted which will be available soon! A very brief summary of the parts relevant to lines: we had started out trying to track this 1.6611 Hz comb with the 280 Hz peak. Derek noticed faint glitching around 280 Hz which was mirrored at 35.4 Hz. Since we were a dead end with the 280 Hz noise, we started following up some coherence shown by bruco at 35.4 Hz with a HAM6_SUSPOINT channel. However, we didn't find additional evidence linking the 280 Hz and 35.4 Hz noise. At that time were prevented from running high-resolution Fscan spectra due to condor issues, but we didn't see an identifiable comb-like structure in the 280 Hz region in the SUSPOINT channel. I'd guess that our February investigations and the recent STAMP-PEM results are both seeing a broader noise artifact that happens to be in the same spectral region as the 280 Hz noise.

~4.9842 Hz comb and related ~9.47-8 Hz combs: recently worsened

• Example plot 2023 March 24 [fig6]

Relevant previous alogs

• Investigating H1 narrow spectral artifacts: Nov 2022 - mid-Jan 2023

History

• Started around 2022 December 8. Exact date not completely clear due to data availability.
• Appears to have gotten worse recently, around 2023 March 24. Here are two example spectra showing the change (similar number of SFTs available both days):
  • March 21 (7 SFTs) [fig7]
  • March 24 (8 SFTs) [fig8]
• A series of near-9.47 Hz combs seem to have appeared around the same time, and have a similar shape in the spectrum (variation of height with frequency). Given that they are coherent with the same channels (see below) they are presumably related.

Known witness channels:

• Strongly coherent with numerous GS13 channels, including HAM2 (Z), HAM3 (Y,Z), HAM4 (X,Y,Z), HAM5 (X,Z), HAM6 (X,Z), HAM7 (Z). ~9.47 Hz combs are visible in many of these too. Example: 20230327/H1_ISI-HAM4_BLND_GS13Z_IN1_DQ [fig9]
• Strongly coherent with all the CS magnetometers, as are the ~9.47 Hz combs. Example: 20230328/H1_PEM-CS_MAG_EBAY_SUSRACK_X_DQ  [fig10]

Additional notes

• This comb was found in the GS13 channels unexpectedly while looking for the other (1.6611 Hz) comb based on STAMP-PEM results.