Non-magnetic cataclysmic variables which have been observed in outburst at least once are known as novae. They occur suddenly and unexpectedly, showing a dramatic rise in luminosity (up to 19 magnitudes!) over a period of only hours or days.
The name originates from the Latin nova stella for new star, which is exactly what early astronomers thought they were seeing. Distinguished from supernovae as a separate class of object in the 1930s, they are now classified as either classical novae, recurrent novae or dwarf novae depending on their outburst properties.