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arXiv · 2209.04463

SN 2020jgb: A Peculiar Type Ia Supernova Triggered by a Helium-Shell Detonation in a Star-Forming Galaxy

Chang Liu·Adam A. Miller·Abigail Polin·Anya E. Nugent·Kishalay De·Peter E. Nugent·Steve Schulze·Avishay Gal-Yam·Christoffer Fremling·Shreya Anand·Igor Andreoni·Peter Blanchard·Thomas G. Brink·Suhail Dhawan·Alexei V. Filippenko·Kate Maguire·Tassilo Schweyer·Huei Sears·Yashvi Sharma·Matthew J. Graham·Steven L. Groom·David Hale·Mansi M. Kasliwal·Frank J. Masci·Josiah Purdum·Benjamin Racine·Jesper Sollerman·Shrinivas R. Kulkarni
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Abstract

The detonation of a thin ($\lesssim$$0.03\,\mathrm{M_\odot}$) helium shell (He-shell) atop a $\sim$$1\,\mathrm{M_\odot}$ white dwarf (WD) is a promising mechanism to explain normal Type Ia supernovae (SNe Ia), while thicker He-shells and less massive WDs may explain some recently observed peculiar SNe Ia. We present observations of SN 2020jgb, a peculiar SN Ia discovered by the Zwicky Transient Facility (ZTF). Near maximum light, SN 2020jgb is slightly subluminous (ZTF $g$-band absolute magnitude $M_g$ between $-18.2$ and $-18.7$ mag depending on the amount of host galaxy extinction) and shows an unusually red color ($g_\mathrm{ZTF}-r_\mathrm{ZTF}$ between 0.4 and 0.2 mag) due to strong line-blanketing blueward of $\sim$5000 $Å$. These properties resemble those of SN 2018byg, a peculiar SN Ia consistent with a thick He-shell double detonation (DDet) SN. Using detailed radiative transfer models, we show that the optical spectroscopic and photometric evolution of SN 2020jgb are broadly consistent with a $\sim$$0.95\,\mathrm{M_\odot}$ (C/O core + He-shell; up to $\sim$$1.00\,\mathrm{M_\odot}$ depending on the total host extinction) progenitor ignited by a thick ($\sim$$0.13\,\mathrm{M_\odot}$) He-shell. We detect a prominent absorption feature at $\sim$1 $μ\mathrm{m}$ in the near-infrared (NIR) spectrum of SN 2020jgb, which could originate from unburnt helium in the outermost ejecta. While the sample size is limited, similar 1 $μ\mathrm{m}$ features have been detected in all the thick He-shell DDet candidates with NIR spectra obtained to date. SN 2020jgb is also the first subluminous, thick He-shell DDet SN discovered in a star-forming galaxy, indisputably showing that He-shell DDet objects occur in both star-forming and passive galaxies, consistent with the normal SN Ia population.

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Chang Liu, Adam A. Miller, Abigail Polin, Anya E. Nugent, Kishalay De, Peter E. Nugent, Steve Schulze, Avishay Gal-Yam, Christoffer Fremling, Shreya Anand, Igor Andreoni, Peter Blanchard, Thomas G. Brink, Suhail Dhawan, Alexei V. Filippenko, Kate Maguire, Tassilo Schweyer, Huei Sears, Yashvi Sharma, Matthew J. Graham, Steven L. Groom, David Hale, Mansi M. Kasliwal, Frank J. Masci, Josiah Purdum, Benjamin Racine, Jesper Sollerman, Shrinivas R. Kulkarni. 2023-04-09. SN 2020jgb: A Peculiar Type Ia Supernova Triggered by a Helium-Shell Detonation in a Star-Forming Galaxy. https://doi.org/10.3847/1538-4357%2Facbb5e

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