2022MNRAS.513.4983V

Photometric and spectroscopic data for two Low Luminosity Type IIP Supernovae (LL SNe IIP) 2020cxd and 2021aai are presented. SN 2020cxd was discovered 2 d after explosion at an absolute magnitude of M_r = -14.02 ± 0.21 mag, subsequently settling on a plateau which lasts for ∼120 d. Through the luminosity of the late light curve tail, we infer a synthesized ⁵⁶Ni mass of (1.8 ± 0.5) x 10^–3 M_☉. During the early evolutionary phases, optical spectra show a blue continuum (T \gt 8000 K) with broad Balmer lines displaying a P Cygni profile, while at later phases, Ca II, Fe II, Sc II, and Ba II lines dominate the spectra. Hydrodynamical modelling of the observables yields R ≃575 R_☉ for the progenitor star, with M_ej = 7.5 M_☉ and E ≃0.097 foe emitted during the explosion. This low-energy event originating from a low-mass progenitor star is compatible with both the explosion of a red supergiant (RSG) star and with an Electron Capture Supernova arising from a super asymptotic giant branch star. SN 2021aai reaches a maximum luminosity of M_r = -16.57 ± 0.23 mag (correcting for A_V = 1.92 mag), at the end of its remarkably long plateau (∼140 d). The estimated ⁵⁶Ni mass is (1.4 ± 0.5) x 10^–2 M_☉. The expansion velocities are compatible with those of other LL SNe IIP (few 10³ km s^–1). The physical parameters obtained through hydrodynamical modelling are R ≃575 R_☉, M_ej = 15.5 M_☉, and E = 0.4 foe. SN 2021aai is therefore interpreted as the explosion of an RSG, with properties that bridge the class of LL SNe IIP with standard SN IIP events.