2021MNRAS.504.1009D

We present the photometric and spectroscopic analysis of three Type II supernovae (SNe): 2014cx, 2014cy, and 2015cz. SN 2014cx is a conventional Type IIP with shallow slope (0.2 mag/50 d) and an atypical short plateau (∼86 d). SNe 2014cy and 2015cz show relatively large decline rates (0.88 and 1.64 mag/50 d, respectively) at early times before settling to the plateau phase, unlike the canonical Type IIP/L SN light curves. All of them are normal luminosity SN II with an absolute magnitude at mid-plateau of M_V,14 cx_⁵⁰=-16.6 ±0.4 mag, M_V,14 cy_⁵⁰=-16.5 ±0.2 mag, and M_V,15 cz_⁵⁰=-17.4 ±0.3 mag. A relatively broad range of ⁵⁶Ni masses is ejected in these explosions (0.027-0.070 M_☉). The spectra shows the classical evolution of SNe II, dominated by a blue continuum with broad H lines at early phases and narrower metal lines with P Cygni profiles during the plateau. High-velocity H I features are identified in the plateau spectra of SN 2014cx at 11 600 kms ^–1, possibly a sign of ejecta-circumstellar interaction. The spectra of SN 2014cy exhibit strong absorption profile of H I similar to normal luminosity events whereas strong metal lines akin to sub-luminous SNe. The analytical modelling of the bolometric light curve of the three events yields similar progenitor radii within errors (478, 507, and 660 R _☉ for SNe 2014cx, 2014cy, and 2015cz, respectively), a range of ejecta masses (15.0, 22.2, and 20.6 M _☉ for SNe 2014cx, 2014cy, and 2015cz), and a modest range of explosion energies (3.3-7.2 foe where 1 foe=10 ⁵¹erg).