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Session: Stars, Planets and the Interstellar Medium

Name: Dr. Georgios Dimitriadis (Trinity College Dublin)
Coauthors: No coauthors were included.
Type: Oral
Title: The mass puzzle of "Super-Chandrasekhar" SNe Ia
Abstract:

For a long time there was general consensus that Type Ia Supernovae (SNe Ia) originate from Carbon-Oxygen White Dwarfs (CO WDs) that explode at the very latest when approaching what is known as the Chandrasekhar-mass stability limit (~1.4 solar masses). This fundamental property of the degenerate matter denotes the mass where the degeneracy pressure of the relativistic electron gas loses against the self-gravity of the WD, leading to a collapse. This theoretical paradigm was challenged with the discovery of the prototype SN 2003fg, a transient with enormous luminosity, broad light curve and low kinetic energy, implying a "Super-Chandrasekhar" (SC) mass progenitor. High-cadence and/or untargeted transient surveys performed in recent years have started to discover more members of this intriguing SN Ia subclass, allowing for sample studies while additionally revealing an intrinsic diversity in the population. However, the initial question remains: Do these peculiar events trully result from a SC scenario or alternative channels need to be invoked? What kind of binary configurations and explosion mechanisms can simultaneously explain their main properties and their intrinsic diversity? And, finally, are there observables that can act as a smoking gun for pointing to the correct answer? In this talk, I will focus on two recent SC SNe Ia, 2020esm and 2021zny, that were discovered particularly early and were densely monitored with a variety of ground- and space-based facilities. I will present their main photometric and spectroscopic properties, being similar to the siblings of their subclass, and highlight their unique characteristics: A nearly pure carbon/oxygen atmosphere during the first days after the explosion of SN 2020esm and a flux excess for the first ~ 1.5 days and prominent oxygen emission lines at nebular epochs of SN 2021zny. All our observations are in accordance with a progenitor system of two CO WDs that undergo a merger event, with the disrupted secondary WD ejecting carbon-rich circumstellar material prior to the primary WD detonation. Finally, I will conclude with a preview of ongoing peculiar SNe Ia studies, including SC SNe Ia, that may shed additional light on the nature of these enigmatic events.