We have investigated the occurrence and correlation of specific states of the ISC_LOCK and INIT_ALIGN during O4a. We downloaded minute averaged data for these channels, taking the minimum for ISC_LOCK and the mean for INIT_ALIGN for every minute. The total number of minutes in O4a has been 341’281, we report the amount of time spent in each state as a percentage of the total time.

The left panel on the first plot shows the percentage of time spent in each ISC_LOCK states, while the right panel excludes the time spent in the ‘Low noise’ state.

We then looked into detail at the states occupied while the ISC_LOCK was in ‘prep’, ‘initial alignment’ or ‘als’ which make up the biggest contribution when we do not consider the ‘Low Noise’ state, i.e. when the detector is down.

The third plot shows the percentage of time out of the total time spent in ‘prep’ states for each of the sub-states.

The fourth plot shows the same for the ‘als’ states. It is interesting to notice that the total time spent in the state “Locking_arms_green” for O4a has been ~10 days, this includes the ISC_LOCK state 12 and the INIT_ALIGN state 8 while in the ISC_LOCK state 7 (Initial alignment).

In the fifth plot we show the percentage of time for each INIT_ALIGN state when the ISC_LOCK is on ‘Initial_alignment’ computed over the total time spent in this state. One can note that the most common states are ‘Locking_green_arms’, ‘SRC_aligning’, ‘Prc_aligning’ and ‘Init_align_complete’. The total time spent in this latter stage over the course of O4a is 12.5 hours. The last plot is an histogram of the occurrences of the consecutive minutes spent in the ‘init_align_complete’ status by INIT_ALIGN. The mean consecutive time spent in this state is 31 minutes. The outlier at 278 minutes corresponds to 3 am to 7 am on the 22^nd September 2023.