Red Alert: Massivestars sound warning they are about to go supernova RoyalAstroSoc
Each scenario creates large amounts of optically thick circumstellar gas, which attenuates the flux in the optical by several orders of magnitude. This means that an RSG on the verge of core-collapse would be very red and very faint in the optical, regardless of how or on what time-scale the material was produced.
The much slower build-up of CSM within the ‘superwind’ scenario causes the progenitor to be conspicuously red and faint for many decades preceding SN. This is strongly inconsistent with observations of nearby SNe, which have always appeared to have colours and magnitudes normal for mid- to late-M supergiants.
Therefore, whatever the mechanism for generating this CSM, it must do it on a very rapid time-scale. Specifically, the build-up of the CSM must happen within a year of the core-collapse. The final overarching conclusion we can make from this work is that, shortly before core-collapse, RSGs must undergo some prodigious mass-losing event which radically alters the appearance of the star. Therefore, the signature of an imminent explosion should be a dramatic change in the progenitor stars’ optical – near-IR photometry on time-scales of less than a month. Such a signature should be detectable in the coming era of wide-field short cadence photometry.