A thermonuclear supernova interacting with hydrogen- and helium-deficient circumstellar material

Tsalapatas, K. and Sollerman, J. and Chiba, R. and Kool, E. and Johansson, J. and Rosswog, S. and Schulze, S. and Moriya, T. J. and Andreoni, I. and Brink, T. G. and Chen, T. X. and Covarrubias, S. and De, K. and Dimitriadis, G. and Filippenko, A. V. and Fremling, C. and Gangopadhyay, A. and Maguire, K. and Mo, G. and Sharma, Y. and Sravan, N. and Terwel, J. H. and Yang, Y. (2025) A thermonuclear supernova interacting with hydrogen- and helium-deficient circumstellar material. Astronomy and Astrophysics, 704: A135. ISSN 0004-6361

Abstract

Identifying the progenitors of thermonuclear supernovae (Type Ia supernovae; SNe Ia) remains a key objective in contemporary astronomy. The rare sub-class of SNe Ia-CSM that interacts with circumstellar material (CSM) allows for studies of the progenitor’s environment before explosion, and generally favours single-degenerate progenitor channels. The case of SN Ia-CSM PTF11kx clearly connected thermonuclear explosions with hydrogen-rich CSM-interacting events, and the more recent SN 2020eyj connected SNe Ia with helium-rich companion progenitors. Both of these objects displayed delayed CSM interaction which established their thermonuclear nature. Here we present a study of SN 2020aeuh, a Type Ia-CSM with delayed interaction. We analyse photometric and spectroscopic data that monitor the evolution of SN 2020aeuh and compare its properties with those of peculiar SNe Ia and core-collapse SNe. At early times, the evolution of SN 2020aeuh resembles a slightly overluminous SN Ia. Later, the interaction-dominated spectra develop the same pseudocontinuum seen in Type Ia-CSM PTF11kx and SN 2020eyj. However, the later-time spectra of SN 2020aeuh lack hydrogen and helium narrow lines. Instead, a few narrow lines could be attributed to carbon and oxygen. We fit the pseudobolometric light curve with a CSM-interaction model, yielding a CSM mass of 1 − 2 M ⊙ . We propose that SN 2020aeuh was a Type Ia supernova that eventually interacted with a dense medium that was deficient in both hydrogen and helium. Whereas previous SNe Ia-CSM constitute our best evidence of non-degenerate companion progenitors, the CSM around SN 2020aeuh is more difficult to understand. We include a hydrodynamical simulation for a double-degenerate dynamical collision to showcase that such a progenitor scenario could produce significant amounts of hydrogen-poor CSM, although likely not as much as the inferred CSM mass around SN 2020aeuh. It is clear that SN 2020aeuh challenges current models of stellar evolution leading up to a SN Ia explosion.