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arXiv · 2402.18299

Origin of broad He II 4686\AA\ emission in early spectra of type IIP supernovae

Nikolai Chugai·Victor Utrobin
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Abstract

We propose a model for the origin of the broad He II 4686A emission in the early spectrum of type II SN~2020jfo. The 4686A line is emitted presumably by dense fragments embedded into a hot gas of the forward shock wave. The fragments are produced as a result of a heavy braking of the dense low-mass shell at the ejecta boundary and a simultaneous Rayleigh-Taylor instability. The temperature of line-emitting fragments is $\approx$5$\times10^4$K. Calculations of ionization and excitation of helium and hydrogen account for the He II 4686A luminosity, the large flux ratio of He II 4686A/H$\alpha$, and a significant optical depth of the 4686A line. We demonstrate that fragments heating by hot electrons behind the forward shock compensates cooling via the HeII 304A emission.

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Nikolai Chugai, Victor Utrobin. 2024-02-28. Origin of broad He II 4686\AA\ emission in early spectra of type IIP supernovae. https://arxiv.org/abs/2402.18299

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