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

2019; IOP Publishing; Volume: 873; Issue: 2 Linguagem: Inglês

10.3847/2041-8213/ab0aec

2041-8213

Kishalay De, M. M. Kasliwal, Abigail Polin, P. Nugent, Lars Bildsten, S. M. Adams, Eric C. Bellm, N. Blagorodnova, Kevin B. Burdge, Christopher Cannella, S. B. Cenko, Richard Dekany, Michael Feeney, David Hale, C. Fremling, M. J. Graham, Anna Y. Q. Ho, J. Jencson, S. R. Kulkarni, Russ R. Laher, Frank J. Masci, A. A. Miller, Maria T. Patterson, Umaa Rebbapragada, Reed Riddle, D. L. Shupe, Roger M. Smith,

Pulsars and Gravitational Waves Research

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 Å. 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 <?CDATA ${M}_{\odot }$?> ) helium shell on a sub-Chandrasekhar mass (≈0.75 <?CDATA ${M}_{\odot }$?> ) WD after including mixing of ≈0.2 <?CDATA ${M}_{\odot }$?> 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.