The transitional yype Ibn/IIn SN 2022pda, with pre-explosion outbursts and a double-peaked light curve

We report the results of a photometric and spectroscopic follow-up campaign of the unusual interacting supernova (SN) 2022pda. Precursor variability lasting ∼100 days is observed before the explosion. The SN light curve has a double-peak shape. It reached a first maximum of Mr = −19.6 ± 0.2 mag, followed by an initial 2 month decline and a second, broad peak lasting about 6 months. The early spectra show a blue continuum with dominant H and He emission lines. A high-resolution pre-maximum spectrum shows that the profile of the He i λ 5876 line consists of a moderately narrow (∼1900 km s−1) P Cygni absorption superposed on a broader (∼3300 km s−1) component. In the blue region, several spectral features are identified, including C iii/N iii/O ii blends. Two broad bumps at 4600–5200 Å and 6400–6800 Å regions reveal a complex profile, which are likely due to blends of H, He, and other emission lines. Late-time spectra are still dominated by prominent and broad H and He lines in emission. Shock-driven model fits to the bolometric light curve suggest that the SN is powered by interaction with a massive CSM with enhanced mass-loss rates ∼5 M⊙yr−1, expelled during two events that occurred ∼1 and ∼0.2 yr before the explosion. The overall SN evolution indicates that SN 2022pda is a transitional event between an H-rich SN IIn (SN 2009ip-like) and an He-rich SN Ibn. Our findings suggest that the progenitor was likely a luminous blue variable transitioning towards a Wolf–Rayet stage.