Time Domain Science with ALMA and the Wideband Sensitivity Upgrade

Time domain astronomy is key to understand astrophysical processes that vary in time. Unfortunately, many of these events are often elusive or difficult to study – either because they are unpredictable on-off events (like neutron star mergers, supernovae, gamma-ray-bursts or some fast radio bursts), or because the time scales are too short (less than a second) or too long (years or more) to be easily observed. There is a wealth of astronomical sources showing variability, from fast-spinning pulsars to evolving stars or tidal disruption events, with enormous differences in their characteristic time scales. In addition, some experiments require a very high timing accuracy, like gravity theory tests with radio pulsars. Offering the community observatories capable to observe in all the different time ranges and with sufficient sensitivity and timing accuracy is challenging. ALMA, with its broad wavelength range and superb sensitivity, is a fundamental instrument for time domain research; in particular because the millimetre window is often less explored in some of these experiments than other wavelengths. In this talk, we will focus on the requirements to enable, improve, or facilitate, time domain science with ALMA and the Wideband Sensitivity Upgrade. We will make some emphasis in the very-fast time domain (fractions of a second to minutes), which is typically the most difficult to access due to more stringent technical requirements.