calcium-rich gap transient

A calcium-rich gap transient (or calcium-rich supernova) is an observed transient rich in calcium spectral lines, that (generally?) falls in the gap in luminosity between a nova and supernova, Their spectra are similar to Type I b or Type I c supernovae, but both core-collapse and Type Ia classifications have problems. They often appear away from the galaxy center, even beyond the apparent host galaxy's border. One idea is they reside in nearby ultra-faint dwarf galaxies. Another is that they occur in binary stars affected by a previous supernova that gave them unusual characteristics causing the spectral differences as well as giving them a velocity kick to explain their position.