SN 2018hna: Adding a piece to the puzzles of the explosion of blue supergiants

Abstract

We present extensive optical/ultraviolet observations and modelling analysis for the nearby SN 1987A-like peculiar Type II supernova (SN) 2018hna. Both photometry and spectroscopy covered phases extending to >500 days after the explosion, making it one of the best-observed SN II of this subtype. SN 2018hna is obviously bluer than SN 1987A during the photospheric phase, suggesting higher photospheric temperature, which may account for weaker Ba ii λ6142 lines in its spectra. Analysis of early-time temperature evolution suggests a radius of ∼45 R⊙ for the progenitor of SN 2018hna, consistent with a blue supergiant (BSG). By fitting the bolometric light curve with hydrodynamical models, we find that SN 2018hna has an ejecta mass of ∼(13.7–17.7) M⊙, a kinetic energy of ∼ (1.0–1.2) × 1051 erg, and a 56Ni mass of about 0.05 M⊙. Moreover, based on standard stellar evolution and the oxygen mass (0.44–0.73 M⊙) deduced from nebular [O i] lines, the progenitor of SN 2018hna is expected to have an initial main-sequence mass <16 M⊙. In principle, such a relatively low-mass star cannot end as a BSG just before core-collapse, except some unique mechanisms are involved, such as rapid rotation, restricted semiconvection, etc. On the other hand, binary scenario may be more favourable, like in the case of SN 1987A. While the much lower oxygen mass inferred for SN 2018hna may imply that its progenitor system also had much lower initial masses than that of SN 1987A.

Probing Diversity of Type II Supernovae with the Chinese Space Station Telescope

“…The rapid initial decline of the bolometric light curve indicated a relatively compact progenitor, while the long rise to the second peak is mainly powered by slower diffusion of radioactive decay energy [92]. Several objects with similar long-rising light curves have since been identified and classified as 87A-like objects [93][94][95][96][97][98]. Most of the 87A-like events appear in slightly low-metallicity environments [99].…”

Long-rising Type II Supernovae in the Zwicky Transient Facility Census of the Local Universe

“…SN 2018hna occurred 43 5 from its host galaxy UGC 07534 at z = 0.0024, corresponding to a physical separation of ≈2 kpc. Additional photometry and more detailed analysis of this SN can be found in Singh et al (2019) and Xiang et al (2023).…”

“…SN 2018hna is the only previously published long-rising SN II in our sample, so we refer to the more complete optical spectral sequences published by Singh et al (2019) and Xiang et al (2023). In this work, we present only the four SEDM spectra obtained as part of regular ZTF classification and follow-up programs.…”

“…This long rise is broadly considered characteristic of 1987A-like SNe because it is well-explained by a compact BSG progenitor-much of the initial explosion energy is spent adiabatically expanding the compact star (Arnett et al 1989;Kleiser et al 2011;Taddia et al 2013). Other long-rising SNe II found since 1987 include: SN 1998A (Pastorello et al 2005); SN 2000cb (Kleiser et al 2011);SN 2004ek, SN 2004em, and SN 2005ci (Taddia et al 2016; SN 2006V and SN 2006au (Taddia et al 2012; SN 2009E (Pastorello et al 2012); SN 2009mw (Takáts et al 2016); PTF09gpn, PTF12gcx, and PTF12kso (Taddia et al 2016); SN 2018hna (Singh et al 2019;Xiang et al 2023); SN Refsdal (Rodney et al 2016); OGLE-2014-SN-073 (Terreran et al 2017); and DES16C3cje (Gutiérrez et al 2020). Additionally, SN 1909A and1982F are also 1987A-like events (Pastorello et al 2012;Taddia et al 2013), but have limited data coverage.…”