ZTF 18aaqeasu (SN 2018byg): A Massive Helium-shell Double Detonation on a Sub-Chandrasekhar Mass White Dwarf. (arXiv:1901.00874v1 [astro-ph.HE])

ZTF 18aaqeasu (SN 2018byg): A Massive Helium-shell Double Detonation on a Sub-Chandrasekhar Mass White Dwarf. (arXiv:1901.00874v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+De_K/0/1/0/all/0/1">Kishalay De</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kasliwal_M/0/1/0/all/0/1">Mansi M. Kasliwal</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Polin_A/0/1/0/all/0/1">Abigail Polin</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nugent_P/0/1/0/all/0/1">Peter E. Nugent</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bildsten_L/0/1/0/all/0/1">Lars Bildsten</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Adams_S/0/1/0/all/0/1">Scott M. Adams</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bellm_E/0/1/0/all/0/1">Eric C. Bellm</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Blagorodnova_N/0/1/0/all/0/1">Nadia Blagorodnova</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Burdge_K/0/1/0/all/0/1">Kevin B. Burdge</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cannella_C/0/1/0/all/0/1">Christopher Cannella</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cenko_S/0/1/0/all/0/1">S. Bradley Cenko</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dekany_R/0/1/0/all/0/1">Richard G. Dekany</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Feeney_M/0/1/0/all/0/1">Michael Feeney</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hale_D/0/1/0/all/0/1">David Hale</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fremling_C/0/1/0/all/0/1">Christoffer Fremling</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Graham_M/0/1/0/all/0/1">Matthew J. Graham</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ho_A/0/1/0/all/0/1">Anna Y. Q. Ho</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jencson_J/0/1/0/all/0/1">Jacob E. Jencson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kulkarni_S/0/1/0/all/0/1">S. R. Kulkarni</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Laher_R/0/1/0/all/0/1">Russ R. Laher</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Masci_F/0/1/0/all/0/1">Frank J. Masci</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Miller_A/0/1/0/all/0/1">Adam A. Miller</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Patterson_M/0/1/0/all/0/1">Maria T. Patterson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rebbapragada_U/0/1/0/all/0/1">Umaa Rebbapragada</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Riddle_R/0/1/0/all/0/1">Reed L. Riddle</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shupe_D/0/1/0/all/0/1">David L. Shupe</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Smith_R/0/1/0/all/0/1">Roger M. Smith</a>

The detonation of a helium shell on a white dwarf has been proposed as a
possible explosion triggering mechanism for Type Ia supernovae. 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 $approx 18$
days from explosion, the transient reached a peak absolute magnitude of $M_R
approx -18.2$ mag, exhibiting a light curve akin to sub-luminous SN
1991bg-like Type Ia supernovae, 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 ($g-r
approx 2$ mag) arising from nearly complete line blanketing of flux blue-wards
of 5000 AA. This behavior is unlike any previously observed thermonuclear
transient. Nebular phase spectra taken at and after $approx 30$ 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 ($approx 0.15$ M$_odot$) helium
shell on a sub-Chandrasekhar mass ($approx 0.75$ M$_odot$) white dwarf after
including mixing of $approx 0.2$ 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.

The detonation of a helium shell on a white dwarf has been proposed as a
possible explosion triggering mechanism for Type Ia supernovae. 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 $approx 18$
days from explosion, the transient reached a peak absolute magnitude of $M_R
approx -18.2$ mag, exhibiting a light curve akin to sub-luminous SN
1991bg-like Type Ia supernovae, 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 ($g-r
approx 2$ mag) arising from nearly complete line blanketing of flux blue-wards
of 5000 AA. This behavior is unlike any previously observed thermonuclear
transient. Nebular phase spectra taken at and after $approx 30$ 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 ($approx 0.15$ M$_odot$) helium
shell on a sub-Chandrasekhar mass ($approx 0.75$ M$_odot$) white dwarf after
including mixing of $approx 0.2$ 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.

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