Optical photometry & sp. of type IIn SN2021qqp

Its unusual light curve is marked by a long precursor for ~300d, a rapid increase in brightness for ~60d, and then a sharp increase of ~1.6mag in only a few days to a first peak of Mr~-19.5mag. The light curve then declines rapidly until it rebrightens to a second distinct peak of Mr~-17.3mag centered at ~335d after the first peak.

The spectra are dominated by Balmer lines with a complex morphology, including a narrow component with a width of ~1300km/s (first peak) and ~2500km/s (second peak) that we associate with the circumstellar medium (CSM) and a P Cygni component with an absorption velocity of ~8500km/s (first peak) and ~5600km/s (second peak) that we associate with the SN-CSM interaction shell. Using the luminosity and velocity evolution, we construct a flexible analytical model, finding two significant mass-loss episodes with peak mass loss rates of ~10 and ~5M_{sun}_/yr about 0.8 and 2yr before explosion, respectively, with a total CSM mass of ~2-4M_{sun}_.