The optical properties of three Type II supernovae: 2014cx, 2014cy, and 2015cz

We present the photometric and spectroscopic analysis of three Type II SNe: 2014cx, 2014cy and 2015cz. SN 2014cx is a conventional Type IIP with shallow slope (0.2mag/50d) and an atypical short plateau (∼86 d). SNe 2014cy and 2015cz show relatively large decline rates (0.88 and 1.64mag/50d, 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 M50 V ,14cx =−16.6± 0.4mag, M 50 V ,14cy =−16.5± 0.2mag and M50 V ,15cz =−17.4± 0.3mag. A relatively broad range of 56Ni masses is ejected in these explosions (0.027-0.070M ). The spectra shows the classical evolution of Type II SNe, dominated by a blue continuum with broad H lines at early phases and narrower metal lines with PCygni profiles during the plateau. High velocity H i features are identified in the plateau spectra of SN 2014cx at 11600 km s−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 radii for the three objects within errors (478, 507 and 608R for SNe 2014cx, 2014cy and 2015cz, respectively) and a range of ejecta masses (15.0, 22.2 and 18.7M for SNe 2014cx, 2014cy and 2015cz), and a modest range of explosion energies (3.3 6.0 foe where 1 foe = 1051 erg).