TY - JOUR

T1 - SN 2021zny: an early flux excess combined with late-time oxygen emission suggests a double white dwarf merger event

AU - Dimitriadis, Georgios

AU - Maguire, Kate

AU - Karambelkar, Viraj R

AU - Lebron, Ryan J

AU - 畅), Chang Liu (刘

AU - Kozyreva, Alexandra

AU - Miller, Adam A

AU - Ridden-Harper, Ryan

AU - Anderson, Joseph P

AU - Chen, Ting-Wan

AU - Coughlin, Michael

AU - Valle, Massimo Della

AU - Drake, Andrew

AU - Galbany, Lluís

AU - Gromadzki, Mariusz

AU - Groom, Steven L

AU - Gutiérrez, Claudia P

AU - Ihanec, Nada

AU - Inserra, Cosimo

AU - Johansson, Joel

AU - Müller-Bravo, Tomás E

AU - Nicholl, Matt

AU - Polin, Abigail

AU - Rusholme, Ben

AU - Schulze, Steve

AU - Sollerman, Jesper

AU - Srivastav, Shubham

AU - Taggart, Kirsty

AU - Wang, Qinan

AU - 轶), Yi Yang (杨

AU - Young, David R

PY - 2023/5/1

Y1 - 2023/5/1

N2 - We present a photometric and spectroscopic analysis of the ultraluminous and slowly evolving 03fg-like Type Ia SN 2021zny. Our observational campaign starts from ∼5.3 h after explosion (making SN 2021zny one of the earliest observed members of its class), with dense multiwavelength coverage from a variety of ground- and space-based telescopes, and is concluded with a nebular spectrum ∼10 months after peak brightness. SN 2021zny displayed several characteristics of its class, such as the peak brightness (M B = −19.95 mag), the slow decline (Δm 15(B) = 0.62 mag), the blue early-time colours, the low ejecta velocities, and the presence of significant unburned material above the photosphere. However, a flux excess for the first ∼1.5 d after explosion is observed in four photometric bands, making SN 2021zny the third 03fg-like event with this distinct behaviour, while its +313 d spectrum shows prominent [O I] lines, a very unusual characteristic of thermonuclear SNe. The early flux excess can be explained as the outcome of the interaction of the ejecta with ∼ 0.04 M ☉ of H/He-poor circumstellar material at a distance of ∼10 12 cm, while the low ionization state of the late-time spectrum reveals low abundances of stable iron-peak elements. All our observations are in accordance with a progenitor system of two carbon/oxygen white dwarfs that undergo a merger event, with the disrupted white dwarf ejecting carbon-rich circumstellar material prior to the primary white dwarf detonation.

AB - We present a photometric and spectroscopic analysis of the ultraluminous and slowly evolving 03fg-like Type Ia SN 2021zny. Our observational campaign starts from ∼5.3 h after explosion (making SN 2021zny one of the earliest observed members of its class), with dense multiwavelength coverage from a variety of ground- and space-based telescopes, and is concluded with a nebular spectrum ∼10 months after peak brightness. SN 2021zny displayed several characteristics of its class, such as the peak brightness (M B = −19.95 mag), the slow decline (Δm 15(B) = 0.62 mag), the blue early-time colours, the low ejecta velocities, and the presence of significant unburned material above the photosphere. However, a flux excess for the first ∼1.5 d after explosion is observed in four photometric bands, making SN 2021zny the third 03fg-like event with this distinct behaviour, while its +313 d spectrum shows prominent [O I] lines, a very unusual characteristic of thermonuclear SNe. The early flux excess can be explained as the outcome of the interaction of the ejecta with ∼ 0.04 M ☉ of H/He-poor circumstellar material at a distance of ∼10 12 cm, while the low ionization state of the late-time spectrum reveals low abundances of stable iron-peak elements. All our observations are in accordance with a progenitor system of two carbon/oxygen white dwarfs that undergo a merger event, with the disrupted white dwarf ejecting carbon-rich circumstellar material prior to the primary white dwarf detonation.

KW - supernovae: individual: 2021zny

KW - transients: supernovae

U2 - 10.1093/mnras/stad536

DO - 10.1093/mnras/stad536

M3 - Journal article

VL - 521

SP - 1162

EP - 1183

JO - Monthly Notices of the Royal Astronomical Society

JF - Monthly Notices of the Royal Astronomical Society

SN - 0035-8711

IS - 1

ER -