Long-rising Type II supernovae resembling supernova 1987A - I. A comparative study through scaling relations

With the aim of improving our knowledge about their nature, we conduct a comparative study on a sample of long-rising Type II supernovae (SNe) resembling SN 1987A. To do so, we deduce various scaling relations from different analytic models of H-rich SNe, discussing their robustness and feasibility. Then, we use the best relations in terms of accuracy to infer the SN progenitor's physical properties at the explosion for the selected sample of SN 1987A-like objects, deriving energies of ∼0.5-15 foe, radii of ∼0.2-100 × 1012 cm, and ejected masses of ∼15-55 M⊙. Although the sample may be too small to draw any final conclusion, these results suggest that (i) SN 1987A-like objects have parameters at explosion covering a wide range of values; (ii) the main parameter determining their distribution is the explosion energy; and (iii) a high-mass (≳ 30 M⊙) and high-energy (≳ 10 foe) tail of events, linked to extended progenitors with radii at explosion ∼1013-1014 cm, challenge standard theories of neutrino-driven core-collapse and stellar evolution. We also find a correlation between the amount of 56Ni in the ejecta of the SN 1987A-like objects and the spectrophotometric features of the SN at maximum, which may represent a tool for estimating the amount of 56Ni in the SN ejecta without having information on the tail luminosity.