Tom Dent, Derek Davis

We noted that at the start of the observing segment beginning May 07 2024 02:14:08 (GPS 1399083266) there was broadband excess noise for the first few minutes of the segment. This issue appears to be due to the line subtraction issues that injected broadband excess noise. We don't the cause of the line subtraction malfunction. 

Spectrograms and spectra of the H1:GDS-CALIB_STRAIN and H1:GDS-CALIB_STRAIN_NOLINES channel shows that the excess noise was introduced during the line subtraction as the broadband noise is not present in the data before line subtraction:

• H1:GDS-CALIB_STRAIN spectrogram - spectra
• H1:GDS-CALIB_STRAIN_NOLINES spectrogram - spectra

It has been previously noted that it is common for the line subtraction to "turn on" up to a few minutes into an observing segment (see alog 72239) but this is the first time that we had noted this type of broadband excess noise being injected. 

Due to the severity of the excess noise, the impacted time period (1399083266 - 1399083406) will need to be CAT1 vetoed.  This includes a few seconds where there was no excess broadband noise but calibration lines were not subtracted.