ZTF 18aaqeasu (SN2018byg): A Massive Helium-shell Double Detonation on a Sub-Chandrasekhar-mass White Dwarf

Kishalay De, Mansi M. Kasliwal, Abigail Polin, Peter E. Nugent, Lars Bildsten, Scott M. Adams, Eric C. Bellm, Nadia Blagorodnova, Kevin B. Burdge, Christopher Cannella, S. Bradley Cenko, Richard G. Dekany, Michael Feeney, David Hale, U. Christoffer Fremling, Matthew J. Graham, Anna Y.Q. Ho, Jacob E. Jencson, S. R. Kulkarni, Russ R. LaherFrank J. Masci, Adam A. Miller, Maria T. Patterson, Umaa Rebbapragada, Reed L. Riddle, David L. Shupe, Roger M. Smith

Research output: Contribution to journalArticlepeer-review

32 Scopus citations

Abstract

The detonation of a helium shell on a white dwarf (WD) has been proposed as a possible explosion triggering mechanism for SNe Ia. Here, we report ZTF 18aaqeasu (SN 2018byg/ATLAS 18pqq), a peculiar Type I supernova, consistent with being a helium-shell double-detonation. With a rise time of ≈18 days from explosion, the transient reached a peak absolute magnitude of M R ≈ -18.2 mag, exhibiting a light curve akin to sub-luminous SN 1991bg-like SNe Ia, albeit with an unusually steep increase in brightness within a week from explosion. Spectra taken near peak light exhibit prominent Si absorption features together with an unusually red color (g - r ≈ 2 mag) arising from nearly complete line blanketing of flux blueward of 5000 . This behavior is unlike any previously observed thermonuclear transient. Nebular phase spectra taken at and after ≈30 days from peak light reveal evidence of a thermonuclear detonation event dominated by Fe-group nucleosynthesis. We show that the peculiar properties of ZTF 18aaqeasu are consistent with the detonation of a massive (≈0.15 ) helium shell on a sub-Chandrasekhar mass (≈0.75 ) WD after including mixing of ≈0.2 of material in the outer ejecta. These observations provide evidence of a likely rare class of thermonuclear supernovae arising from detonations of massive helium shells.

Original languageEnglish (US)
Article numberL18
JournalAstrophysical Journal Letters
Volume873
Issue number2
DOIs
StatePublished - 2019

Keywords

  • supernovae: general
  • supernovae: individual (SN2018byg)
  • surveys
  • white dwarfs Supporting material: data behind figures

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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