Origin of the FUV continuum excess and emission features

Determine whether a partially stripped progenitor, an asymmetric or clumped ejecta structure, or an unusually high ejecta temperature can explain both the rest-frame far-ultraviolet continuum excess and the possible far-ultraviolet emission features observed in SN 2025wny.

Background

SN 2025wny exhibits possible C II, Hα, and He I signatures at approximately 57 days after peak, lacks the clear O II absorption complex expected at its inferred temperatures, and shows a persistent far-ultraviolet continuum excess with possible emission features. The paper considers several interpretations, including a partially stripped progenitor, asymmetric or clumped ejecta, and temperatures too high for O II formation.

The authors explicitly state that it is unresolved whether any of these interpretations can account for the far-ultraviolet behavior. Resolving this issue is important for identifying the progenitor structure and the physical origin of the unusual late-time spectral energy distribution.

References

It is unclear whether these interpretations can explain the rest-frame FUV continuum excess or possible FUV emission features, especially with the high inferred photospheric temperatures ($T\gtrsim 16{,}000$ K; Figure 1).

— Follow-up of SN 2025wny II: Superluminous Supernova Physics at Cosmic Noon  (2608.28415 - Li et al., 28 Aug 2026) in Section 6.2, “Implications of C II, Hα, and He I signatures”