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

Kishalay DeCahill Center for Astrophysics, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA; [email protected]M. M. KasliwalCahill Center for Astrophysics, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA; [email protected]Abigail PolinDepartment of Astronomy, University of California, Berkeley, CA, 94720-3411, USAP. NugentDepartment of Astronomy, University of California, Berkeley, CA, 94720-3411, USALars BildstenDepartment of Physics, University of California, Santa Barbara, CA 93106, USAScott M. AdamsCahill Center for Astrophysics, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA; [email protected]E. BellmDIRAC Institute, Department of Astronomy, University of Washington, 3910 15th Avenue NE, Seattle, WA 98195, USANadia BlagorodnovaCahill Center for Astrophysics, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA; [email protected]Kevin B. BurdgeCahill Center for Astrophysics, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA; [email protected]Christopher CannellaCahill Center for Astrophysics, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA; [email protected]S. Bradley CenkoAstrophysics Science Division, NASA Goddard Space Flight Center, Mail Code 661, Greenbelt, MD 20771, USARichard G. DekanyCaltech Optical Observatories, California Institute of Technology, Pasadena, CA 91125, USAMichael FeeneyCaltech Optical Observatories, California Institute of Technology, Pasadena, CA 91125, USADavid HaleCaltech Optical Observatories, California Institute of Technology, Pasadena, CA 91125, USAC. FremlingCahill Center for Astrophysics, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA; [email protected]M. J. GrahamCahill Center for Astrophysics, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA; [email protected]A. Y. Q. HoCahill Center for Astrophysics, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA; [email protected]J. E. JencsonCahill Center for Astrophysics, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA; [email protected]S. R. KulkarniCahill Center for Astrophysics, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USA; [email protected]Russ R. LaherIPAC, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USAFrank J. MasciIPAC, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USAAdam A. MillerCenter for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Department of Physics and Astronomy, Northwestern University, 2145 Sheridan Road, Evanston, IL 60208, USAMaria T. PattersonCity University of SeattleU. D. RebbapragadaJet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USAReed RiddleCaltech Optical Observatories, California Institute of Technology, Pasadena, CA 91125, USADavid L. ShupeIPAC, California Institute of Technology, 1200 East California Boulevard, Pasadena, CA 91125, USARoger M. SmithCaltech Optical Observatories, California Institute of Technology, Pasadena, CA 91125, USA

2019en

ABI

Аннотация

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 ) 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.

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DOI: 10.3847/2041-8213/ab0aec

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