1. SN 2018zd: an unusual stellar explosion as part of the diverse Type II Supernova landscape
- Author
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András Pál, F. Huang, Łukasz Wyrzykowski, A. Ordasi, Ádám Sódor, T. G. Brink, R. Szakats, Attila Bódi, G. Zsidi, L. Kriskovics, Jujia Zhang, Alexei V. Filippenko, Vinkó József, J. M. Derkacy, K. Vida, G. Csörnyei, O. Hanyecz, Cs. Kalup, Jun Mo, P. Mikołajczyk, Hanna Sai, X. Zhang, Réka Könyves-Tóth, B. Ignácz, E. Baron, Huijuan Wang, Qian Zhai, Xiaofeng Wang, Krisztián Sárneczky, WeiKang Zheng, Liming Rui, and Tianmeng Zhang more...
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High Energy Astrophysical Phenomena (astro-ph.HE) ,Physics ,010308 nuclear & particles physics ,Electron capture ,Star (game theory) ,FOS: Physical sciences ,Flux ,Astronomy and Astrophysics ,Astrophysics ,Type II supernova ,Light curve ,01 natural sciences ,Spectral line ,13. Climate action ,Space and Planetary Science ,0103 physical sciences ,Asymptotic giant branch ,Astrophysics - High Energy Astrophysical Phenomena ,Ejecta ,010303 astronomy & astrophysics - Abstract
We present extensive observations of SN 2018zd covering the first $\sim450$\,d after the explosion. This SN shows a possible shock-breakout signal $\sim3.6$\,hr after the explosion in the unfiltered light curve, and prominent flash-ionisation spectral features within the first week. The unusual photospheric temperature rise (rapidly from $\sim 12,000$\,K to above 18,000\,K) within the earliest few days suggests that the ejecta were continuously heated. Both the significant temperature rise and the flash spectral features can be explained with the interaction of the SN ejecta with the massive stellar wind ($0.18^{+0.05}_{-0.10}\, \rm M_{\odot}$), which accounts for the luminous peak ($L_{\rm max} = [1.36\pm 0.63] \times 10^{43}\, \rm erg\,s^{-1}$) of SN 2018zd. The luminous peak and low expansion velocity ($v \approx 3300$ km s$^{-1}$) make SN 2018zd to be like a member of the LLEV (luminous SNe II with low expansion velocities) events originated due to circumstellar interaction. The relatively fast post-peak decline allows a classification of SN 2018zd as a transition event morphologically linking SNe~IIP and SNe~IIL. In the radioactive-decay phase, SN 2018zd experienced a significant flux drop and behaved more like a low-luminosity SN~IIP both spectroscopically and photometrically. This contrast indicates that circumstellar interaction plays a vital role in modifying the observed light curves of SNe~II. Comparing nebular-phase spectra with model predictions suggests that SN 2018zd arose from a star of $\sim 12\,\rm M_{\odot}$. Given the relatively small amount of $^{56}$Ni ($0.013 - 0.035 \rm M_{\odot}$), the massive stellar wind, and the faint X-ray radiation, the progenitor of SN 2018zd could be a massive asymptotic giant branch star which collapsed owing to electron capture., Accepted for publication in MNRAS, 20 pages, 11 figures more...
- Published
- 2020
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