TY - JOUR

T1 - A Carbon/Oxygen-dominated Atmosphere Days after Explosion for the "Super-Chandrasekhar" Type Ia SN 2020esm

AU - Dimitriadis, Georgios

AU - Foley, Ryan J.

AU - Arendse, Nikki

AU - Coulter, David A.

AU - Jacobson-Galan, Wynn

AU - Siebert, Matthew R.

AU - Izzo, Luca

AU - Jones, David O.

AU - Kilpatrick, Charles D.

AU - Pan, Yen-Chen

AU - Taggart, Kirsty

AU - Auchettl, Katie

AU - Gall, Christa

AU - Hjorth, Jens

AU - Kasen, Daniel

AU - Piro, Anthony L.

AU - Raimundo, Sandra

AU - Ramirez-Ruiz, Enrico

AU - Rest, Armin

AU - Swift, Jonathan J.

AU - Woosley, Stan E.

PY - 2022/3/1

Y1 - 2022/3/1

N2 - Seeing pristine material from the donor star in a type Ia supernova (SN Ia) explosion can reveal the nature of the binary system. In this paper, we present photometric and spectroscopic observations of SN 2020esm, one of the best-studied SNe of the class of "super-Chandrasekhar" SNe Ia (SC SNe Ia), with data obtained 12 to +360 days relative to peak brightness, obtained from a variety of ground- and space-based telescopes. Initially misclassified as a type II supernova, SN 2020esm peaked at M-B = -19.9 mag, declined slowly (Delta m(15)(B) = 0.92 mag), and had particularly blue UV and optical colors at early times. Photometrically and spectroscopically, SN 2020esm evolved similarly to other SC SNe Ia, showing the usual low ejecta velocities, weak intermediate-mass elements, and the enhanced fading at late times, but its early spectra are unique. Our first few spectra (corresponding to a phase of greater than or similar to 10 days before peak) reveal a nearly pure carbon/oxygen atmosphere during the first days after explosion. This composition can only be produced by pristine material, relatively unaffected by nuclear burning. The lack of H and He may further indicate that SN 2020esm is the outcome of the merger of two carbon/oxygen white dwarfs. Modeling its bolometric light curve, we find an Ni-56 mass of 1.23(-0.14)(+0.14) M-circle dot and an ejecta mass of 1.75(-0.20)(+0.32)M(circle dot), in excess of the Chandrasekhar mass. Finally, we discuss possible progenitor systems and explosion mechanisms of SN 2020esm and, in general, the SC SNe Ia class.

AB - Seeing pristine material from the donor star in a type Ia supernova (SN Ia) explosion can reveal the nature of the binary system. In this paper, we present photometric and spectroscopic observations of SN 2020esm, one of the best-studied SNe of the class of "super-Chandrasekhar" SNe Ia (SC SNe Ia), with data obtained 12 to +360 days relative to peak brightness, obtained from a variety of ground- and space-based telescopes. Initially misclassified as a type II supernova, SN 2020esm peaked at M-B = -19.9 mag, declined slowly (Delta m(15)(B) = 0.92 mag), and had particularly blue UV and optical colors at early times. Photometrically and spectroscopically, SN 2020esm evolved similarly to other SC SNe Ia, showing the usual low ejecta velocities, weak intermediate-mass elements, and the enhanced fading at late times, but its early spectra are unique. Our first few spectra (corresponding to a phase of greater than or similar to 10 days before peak) reveal a nearly pure carbon/oxygen atmosphere during the first days after explosion. This composition can only be produced by pristine material, relatively unaffected by nuclear burning. The lack of H and He may further indicate that SN 2020esm is the outcome of the merger of two carbon/oxygen white dwarfs. Modeling its bolometric light curve, we find an Ni-56 mass of 1.23(-0.14)(+0.14) M-circle dot and an ejecta mass of 1.75(-0.20)(+0.32)M(circle dot), in excess of the Chandrasekhar mass. Finally, we discuss possible progenitor systems and explosion mechanisms of SN 2020esm and, in general, the SC SNe Ia class.

KW - WHITE-DWARFS

KW - LIGHT CURVES

KW - THERMONUCLEAR EXPLOSIONS

KW - OPTICAL-SPECTRA

KW - MASS

KW - EVOLUTION

KW - DISTANCE

KW - PROJECT

KW - 2011FE

KW - SAMPLE

U2 - 10.3847/1538-4357/ac4780

DO - 10.3847/1538-4357/ac4780

M3 - Journal article

VL - 927

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 1

M1 - 78

ER -