Summary: Looking over O3 H1 data so far, spectral lines in 1800 s long Fourier transforms continue to be problematic and will be degrade astrophysical results of continuous gravitational wave searches. It would be helpful if commissioning/engineering teams can compare with what the LLO team has done in order to mitigate most spectral contamination.

I'll note that I'm getting greedy because O3 data is already much better for spectral content than O2 data for both detectors (and better broadband sensitivity!). Again, my thanks to the entire team on the progress over O2! When I see how clean of spectral features L1 data appears compared to H1, however, I want both detectors to have equally clean data. I hope some improvements to hardware configuration will mitigate the H1 spectral lines, but this needs attention from boots on the ground at LHO.

Details:
Keith Riles has a very nice week-by-week and running cumulative pages for looking at H1 and L1 spectral data computed from the standard set of 1800 s long, Tukey windowed Short Fourier Transforms--SFTs (see here for H1 and here for L1). 

I want to draw attention in particular to two problematic features that require attention:
1) Below 100 Hz, the prevalence of lines in H1 data is much greater than L1. See attached figure 1 (H1) compared with figure 2 (L1) showing both the most recent week of data and the cumulative O3 data up to now.

2) The behavior of the spectral features is quite dynamic from day to day and week to week. This can be seen, for example, in attached figure 3 showing the ratio of this week's H1 data divided by the cumulative H1 data. Spikes above the mean show an increase in line activity, while spikes dropping below the mean show a decrease in line activity. Every week shows a slightly different figure, meaning the lines and/or coupling is changing with time. Figure 4 shows the L1 data, which is much better behaved, probably because there are so few lines present in the data.

These features are likely going to limit some searches for long duration gravitational wave signals, and may obscure putative signals that could be detectable during O3. With lines present in the data, especially when the lines are dynamic as they appear to be in H1, will require changes to searches and increase the amount of time spent to deal with these artifacts in post-processing. With improvements (as demonstrated by L1), the searches will be more sensitive and can be published more timely.