SN 2015bf: A fast declining type II supernova with flash-ionized signatures. Issue 4 (28th May 2021)

• Record Type: Journal Article
• Authors: Lin, Han; Wang, Xiaofeng; Zhang, Jujia; Lin, Weili; Mo, Jun; Filippenko, Alexei V; Zheng, WeiKang; Brown, Peter J; Xiang, Danfeng; Huang, Fang; Cai, Yongzhi; Zhang, Tianmeng; Li, Xue; Rui, Liming; Zhang, Xinghan; Sai, Hanna; Zhao, Xulin; Graham, Melissa L; Shivvers, I; Halevi, G; Yuk, H; Brink, Thomas G
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 505:Issue 4(2021)
• Page Start: 4890
• Page End: 4905
• Publication Date: 2021-05-28
• Subjects: stars: evolution -- supernovae: general -- supernovae: individual: (SN 2015bf); Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stab1550
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: We present optical and ultraviolet photometry, as well as optical spectra, for the type II supernova (SN) 2015bf. Our observations cover the phases from ∼2 to ∼200 d after explosion. The first spectrum is characterized by a blue continuum with a blackbody temperature of ∼24 000 K and flash-ionized emission lines. After about 1 week, the spectra of SN 2015bf evolve like those of a regular SN II. From the luminosity of the narrow emission component of H α, we deduce that the mass-loss rate is larger than ${\sim}3.7\times 10^{-3}\, {\rm M_\odot \, yr^{-1}}$ . The disappearance of the flash features in the first week after explosion indicates that the circumstellar material is confined within ∼6 × 10 14 cm. Thus, we suggest that the progenitor of SN 2015bf experienced violent mass loss shortly before the supernova explosion. The multiband light curves show that SN 2015bf has a high peak luminosity with an absolute visual magnitude MV = −18.11 ± 0.08 mag and a fast post-peak decline with a V -band decay of 1.22 ± 0.09 mag within ∼50 d after maximum light. Moreover, the R -band tail luminosity of SN 2015bf is fainter than that of SNe II with similar peak by 1–2 mag, suggesting a small amount of 56 Ni (${\sim}0.009\, {\rm M_\odot }$ ) synthesized during the explosion. Such a low nickel mass indicates that the progenitor of SN 2015bf could be a super-asymptotic-giant-branch star that collapsed owing to electron capture.