The rise and fall of an extraordinary Ca-rich transient - The discovery of ATLAS19dqr/SN 2019bkc

S. J. Prentice, K. Maguire, A. Flörs, S. Taubenberger, C. Inserra, C. Frohmaier, T. W. Chen, J. P. Anderson, C. Ashall, P. Clark, M. Fraser, L. Galbany, A. Gal-Yam, M. Gromadzki, C. P. Gutiérrez, P. A. James, P. G. Jonker, E. Kankare, G. Leloudas, M. R. MageeP. A. Mazzali, M. Nicholl, M. Pursiainen, K. Skillen, S. J. Smartt, K. W. Smith, C. Vogl, D. R. Young

Research output: Contribution to journalJournal articleResearchpeer-review

Abstract

This work presents the observations and analysis of ATLAS19dqr/SN 2019bkc, an extraordinary rapidly evolving transient event located in an isolated environment, tens of kpc from any likely host. Its light curves rise to maximum light in 5 − 6 d and then display an decline of Δm15 ∼ 5 mag. With such a pronounced decay, it has one of the most rapidly evolving light curves known for a stellar explosion. The early spectra show similarities to normal and “ultra-stripped” type Ic SNe but the early nebular phase spectra, reached just over two weeks after explosion, display prominent calcium lines, marking SN 2019bkc as a Ca-rich transient. The Ca emission lines at this phase show an unprecedented and unexplained blueshift of 10 000 - 12 000 km s−1. Modelling of the light curve and the early spectra suggests that the transient had a low ejecta mass of 0.2 − 0.4 M⊙ and a low kinetic energy of (2 − 5) x 1050 erg, giving a specific kinetic energy Ek/Mej around unity. The origin of this event cannot be unambiguously defined. While the abundance distribution used to model the spectra marginally favours a progenitor of white dwarf origin through the tentative identification of Ar n, the specific kinetic energy, which is defined by the explosion mechanism, is found to be more similar to an ultra-stripped core-collapse events. SN 2019bkc adds to the diverse range of physical properties shown by Ca-rich events.
Original languageEnglish
Article numberA186
JournalAstronomy & Astrophysics
Volume635
Number of pages17
ISSN0004-6361
DOIs
Publication statusPublished - 2020

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