A massive, energetic model for the luminous transitional Type Ib/IIb SN 2020cpg

ABSTRACT Using a combined spectral and light-curve modelling approach, we fit massive energetic explosion model to the luminous Type Ib/IIb SN 2020cpg. This has an ejected mass of ∼(7 ± 2) M⊙ with final energy ∼(6 1) × 1051 erg MNi = 0.27 0.05 M⊙. The early spectra are hot blue weak He i lines, complicated Hα region suggested be multicomponent feature. Modelling required ∼0.08 H at velocities >11 000 km s−1 total ∼1.0 >9500 above CO-rich ejecta. ratio kinetic 0.85$_{-0.3}^{+0.5}$ foe M⊙−1. high luminosity results in broadened line that is blended Si ii, C i, which led initial classification 2020cpg as Ib. We instead classify bright transitional event between Ib IIb classes. Comparing our parameters stellar evolution models, progenitor 25–30 M⊙, i.e. stripped most hydrogen shell some helium prior collapse produces core comparable mass. excess 56Ni production compared objects similar may suggest evidence additional sources such failed GRB or magnetar injection, smaller remnant