  Light curves of the accreting white dwarf pulsator GW Librae spanning a 7.5
month period in 2017 were obtained as part of the Next Generation Transit
Survey. This data set comprises 787 hours of photometry from 148 clear nights,
allowing the behaviour of the long (hours) and short period (20min) modulation
signals to be tracked from night to night over a much longer observing baseline
than has been previously achieved. The long period modulations intermittently
detected in previous observations of GW Lib are found to be a persistent
feature, evolving between states with periods ~83min and 2-4h on time-scales of
several days. The 20min signal is found to have a broadly stable amplitude and
frequency for the duration of the campaign, but the previously noted phase
instability is confirmed. Ultraviolet observations obtained with the Cosmic
Origin Spectrograph onboard the Hubble Space Telescope constrain the
ultraviolet-to-optical flux ratio to ~5 for the 4h modulation, and <=1 for the
20min period, with caveats introduced by non-simultaneous observations. These
results add further observational evidence that these enigmatic signals must
originate from the white dwarf, highlighting our continued gap in theoretical
understanding of the mechanisms that drive them.
