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Light curves of the accreting white dwarf pulsator GW Librae spanning a 7.5month period in 2017 were obtained as part of the Next Generation TransitSurvey. This data set comprises 787 hours of photometry from 148 clear nights,allowing the behaviour of the long (hours) and short period (20min) modulationsignals to be tracked from night to night over a much longer observing baselinethan has been previously achieved. The long period modulations intermittentlydetected in previous observations of GW Lib are found to be a persistentfeature, evolving between states with periods ~83min and 2-4h on time-scales ofseveral days. The 20min signal is found to have a broadly stable amplitude andfrequency for the duration of the campaign, but the previously noted phaseinstability is confirmed. Ultraviolet observations obtained with the CosmicOrigin Spectrograph onboard the Hubble Space Telescope constrain theultraviolet-to-optical flux ratio to ~5 for the 4h modulation, and <=1 for the20min period, with caveats introduced by non-simultaneous observations. Theseresults add further observational evidence that these enigmatic signals mustoriginate from the white dwarf, highlighting our continued gap in theoreticalunderstanding of the mechanisms that drive them.

NGTS and HST insights into the long period modulation in GW Librae