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Published January 1, 2020 | Version v1
Journal article Open

SN 2019ein: New Insights into the Similarities and Diversity among High-velocity Type Ia Supernovae

Creators

  • 1. Kyoto Univ, Dept Astron, Sakyo Ku, Kyoto 6068502, Japan
  • 2. Kyoto Univ, Okayama Observ, 3037-5 Honjo,Kamogata Cho, Okayama 7190232, Japan
  • 3. Tokyo Inst Technol, Dept Phys, Meguro Ku, 2-12-1 Ookayama, Tokyo 1528551, Japan
  • 4. Natl Astron Observ Japan, Ishigakijima Astron Observ, 1024-1 Arakawa, Ishigaki, Okinawa 9070024, Japan
  • 5. Hiroshima Univ, Dept Phys Sci, Kagamiyama 1-3-1, Higashihiroshima 7398526, Japan
  • 6. Univ Tokyo, Inst Adv Study, Kavli Inst Phys & Math Universe WPI, 5-1-5 Kashiwanoha, Kashiwa, Chiba 2778583, Japan
  • 7. Univ Hyogo, Ctr Astron, Nishi Harima Astron Observ, 407-2 Nishigaichi,Sayo Cho, Sayo, Hyogo 6795313, Japan
  • 8. Natl Astron Observ Japan, NINS, Okayama Branch Off, Subaru Telescope, Okayama 7190232, Japan

Description

We present optical observations of the Type Ia supernova (SN) 2019ein, starting two days after the estimated explosion date. The spectra and light curves show that SN 2019ein belongs to a high-velocity (HV) and broad-line group with a relatively rapid decline in the light curves (Delta m(15)(B) = 1.36 0.02 mag) and a short rise time (15.37 0.55 days). The Si ii lambda 6355 velocity, associated with a photospheric component but not with a detached high-velocity feature, reached similar to 20,000 km s(-1) 12 days before the B-band maximum. The line velocity, however, decreased very rapidly and smoothly toward maximum light, to similar to 13,000 km s(-1), which is relatively low among HV SNe. This indicates that the speed of the spectral evolution of HV SNe Ia is correlated with not only the velocity at maximum light, but also the light-curve decline rate, as is the case for normal-velocity (NV) SNe Ia. Spectral synthesis modeling shows that the outermost layer at >17,000 km s(-1) is well described by an O-Ne-C burning layer extending to at least 25,000 km s(-1), and there is no unburnt carbon below 30,000 km s(-1); these properties are largely consistent with the delayed detonation scenario and are shared with the prototypical HV SN 2002bo despite the large difference in Delta m(15)(B). This structure is strikingly different from that derived for the well-studied NV SN 2011fe. We suggest that the relation between the mass of Ni-56 (or Delta m(15)) and the extent of the O-Ne-C burning layer provides an important constraint on the explosion mechanism(s) of HV and NV SNe.

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