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

March 2019 • 2019ApJ...873L..18D

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

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 {M}) helium shell on a sub-Chandrasekhar mass (≈0.75 {M}) WD after including mixing of ≈0.2 {M} 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.


IPAC Authors

Frank Masci

Senior Scientist

Dave Shupe

Senior Scientist