Resolving the explosion of supernova 2023ixf in Messier 101 within its\n complex circumstellar environment

Observing a supernova explosion shortly after it occurs can reveal important\ninformation about the physics of stellar explosions and the nature of the\nprogenitor stars of supernovae (SNe). When a star with a well-defined edge\nexplodes in vacuum, the first photons to escape from its surface appear as a\nbrief shock-breakout flare. The duration of this flare can extend to at most a\nfew hours even for nonspherical breakouts from supergiant stars, after which\nthe explosion ejecta should expand and cool. Alternatively, for stars exploding\nwithin a distribution of sufficiently dense optically thick circumstellar\nmaterial, the first photons escape from the material beyond the stellar edge,\nand the duration of the initial flare can extend to several days, during which\nthe escaping emission indicates photospheric heating. The difficulty in\ndetecting SN explosions promptly after the event has so far limited data\nregarding supergiant stellar explosions mostly to serendipitous observations\nthat, owing to the lack of ultraviolet (UV) data, were unable to determine\nwhether the early emission is heating or cooling, and hence the nature of the\nearly explosion event. Here, we report observations of SN 2023ixf in the nearby\ngalaxy M101, covering the early days of the event. Using UV spectroscopy from\nthe Hubble Space Telescope (HST) as well as a comprehensive set of additional\nmultiwavelength observations, we trace the photometric and spectroscopic\nevolution of the event and are able to temporally resolve the emergence and\nevolution of the SN emission.\n