SN 2018hna: 1987A-like supernova with a signature of shock breakout

Abstract

High-cadence ultraviolet, optical, and near-infrared photometric and low-resolution spectroscopic observations of the peculiar Type II supernova (SN) 2018hna are presented. The early-phase multiband light curves (LCs) exhibit the adiabatic cooling envelope emission following the shock breakout up to ~ 14 days from the explosion. SN 2018hna has a rise time of ~ 88 days in the V band, similar to SN 1987A. A 56Ni mass of ~0.087 ± 0.004 M ⊙ is inferred for SN 2018hna from its bolometric LC. Hydrodynamical modeling of the cooling phase suggests a progenitor with a radius ~50 R ⊙, a mass of ~14–20 M ⊙, and an explosion energy of ~1.7–2.9 × 1051 erg. The smaller inferred radius of the progenitor than a standard red supergiant is indicative of a blue supergiant progenitor of SN 2018hna. A subsolar metallicity (~0.3 Z ⊙) is inferred for the host galaxy UGC 07534, concurrent with the low-metallicity environments of 1987A-like events.