The aspherical explosions of the 03fg-like Type Ia supernovae 2021zny and 2022ilv revealed by polarimetry

Abstract

A peculiar subtype of Type Ia supernovae (SNe), 03fg-like (super-Chandrasekhar) SNe, show different observational properties from prototypical Type Ia SNe, typically having high luminosity at the light-curve peak, low expansion velocities, and strong carbon features. The origin of this class of Type Ia SNe has been actively debated. Recent nebular-phase infrared observations of the 03fg-like Type Ia SN 2022pul using the James Webb Space Telescope revealed large-scale asymmetries in the ejecta and the presence of the strong [Ne II] line at 12.81 $\mu$m, suggesting a violent merger of two white dwarfs as its origin. Polarimetry is another powerful tool to study overall ejecta asymmetries of spatially-unresolved SNe. Here, we aim to check the universality of the violent merger scenario as the origin of the 03fg-like Type Ia SNe, by studying their explosion geometries using polarimetry. In this letter, we present imaging-polarimetric observations of the two 03fg-like Type Ia SNe 2021zny and 2022ilv. SNe 2021zny and 2022ilv show high intrinsic polarization ($\sim 1$ % -$\sim 2$ %), which might be composed of multiple components with different polarization angles. This indicates that they have complex aspherical structures in their ejecta, supporting the violent merger scenario for their origin. Our observations provide the first clear evidence from polarimetry for such aspherical structures.

6 pages, 4 figures, submitted to A&A Letters

References in corpus (17)

• The type Ia supernova SNLS-03D3bb from a super-Chandrasekhar-mass white dwarf star
• Spectropolarimetry of Supernovae
• The Luminous and Carbon-Rich Supernova 2006gz: A Double Degenerate Merger?
• New mass limit for white dwarfs: super-Chandrasekhar type Ia supernova as a new standard candle
• Progenitors of type Ia supernovae
• Off-center explosions of Chandrasekhar-mass white dwarfs: an explanation of super-bright type Ia supernovae?
• Spectral modelling of the "Super-Chandra" Type Ia SN 2009dc - testing a 2 M_sun white dwarf explosion model and alternatives
• Discovery of the Fastest Early Optical Emission from Overluminous SN Ia 2020hvf: A Thermonuclear Explosion within a Dense Circumstellar Environment
• Predicting polarization signatures for double-detonation and delayed-detonation models of Type Ia supernovae
• Carnegie Supernova Project: The First Homogeneous Sample of "Super-Chandrasekhar Mass"/2003fg-like Type Ia Supernova
• Type Ia supernovae within dense carbon-oxygen rich envelopes: a model for 'Super-Chandrasekhar' explosions?
• SN 2021zny: an early flux excess combined with late-time oxygen emission suggests a double white dwarf merger event
• The luminous type Ia supernova 2022ilv and its early excess emission
• Ground-based and JWST Observations of SN 2022pul: II. Evidence from Nebular Spectroscopy for a Violent Merger in a Peculiar Type-Ia Supernova
• Nebular spectra from Type Ia supernova explosion models compared to JWST observations of SN 2021aefx
• Initial Flash and Spectral Formation of Type Ia Supernovae with An Envelope: Applications to Over-luminous SNe Ia
• The Effects of Circumstellar Dust Scattering on the Light Curves and Polarizations of Type Ia Supernovae

Cited by in corpus (3)

• The Ultraviolet Spectra of 2003fg-like Type Ia Supernovae
• $R_V$ from multi-waveband galaxy polarimetry in supernovae vicinity
• The Type Ia Supernova 2021hem: A 2003fg-like Event in an Apparently Hostless Environment