The Most Rapidly-Declining Type I Supernova 2019bkc/ATLAS19dqr. (arXiv:1905.02205v1 [astro-ph.HE])

The Most Rapidly-Declining Type I Supernova 2019bkc/ATLAS19dqr. (arXiv:1905.02205v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Chen_P/0/1/0/all/0/1">Ping Chen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dong_S/0/1/0/all/0/1">Subo Dong</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Stritzinger_M/0/1/0/all/0/1">M. D. Stritzinger</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Holmbo_S/0/1/0/all/0/1">Simon Holmbo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Strader_J/0/1/0/all/0/1">Jay Strader</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kochanek_C/0/1/0/all/0/1">C. S. Kochanek</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Peng_E/0/1/0/all/0/1">Eric W. Peng</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Benetti_S/0/1/0/all/0/1">S. Benetti</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bersier_D/0/1/0/all/0/1">D. Bersier</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Brownsberger_S/0/1/0/all/0/1">Sasha Brownsberger</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Buckley_D/0/1/0/all/0/1">David A. H. Buckley</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gromadzki_M/0/1/0/all/0/1">Mariusz Gromadzki</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Moran_S/0/1/0/all/0/1">Shane Moran</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pastorello_A/0/1/0/all/0/1">A. Pastorello</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Aydi_E/0/1/0/all/0/1">Elias Aydi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bose_S/0/1/0/all/0/1">Subhash Bose</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Connor_T/0/1/0/all/0/1">Thomas Connor</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Elias_Rosa_N/0/1/0/all/0/1">N. Elias-Rosa</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+French_K/0/1/0/all/0/1">K. Decker French</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Holoien_T/0/1/0/all/0/1">Thomas W.-S. Holoien</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mattila_S/0/1/0/all/0/1">Seppo Mattila</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shappee_B/0/1/0/all/0/1">B. J. Shappee</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Stark_A/0/1/0/all/0/1">Antony A. Stark</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Swihart_S/0/1/0/all/0/1">Samuel J. Swihart</a>

We report observations of the hydrogen- and helium-deficient supernova (SN)
2019bkc/ATLAS19dqr. With B- and r-band decline between peak and 10 days post
peak of Delta m_10(B) = 4.9+/-0.1 mag and Delta m_10(r) = 4.1+/-0.1 mag,
respectively, SN 2019bkc is the most rapidly-declining Type I SN discovered so
far. The light curves and spectra of SN 2019bkc show some unprecedented
characteristics compared to known SNe, while its closest matches are the
rapidly-declining SN 2005ek and SN 2010X. SN 2019bkc appears ‘hostless’, with
no identifiable host galaxy near its location, although it may be associated
with the galaxy cluster MKW1 at z=0.02. SN 2019bkc poses a challenge for
existing models of fast-evolving SNe.

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