SN 1986E eight years after outburst: a link to SN 1957D?

We report on the optical recovery of SN~1986E 7.1 and 7.9 years after explosion. The spectra are dominated by broad H$α$ and [O~I] $λλ$6300,6364 emission lines with a minor contribution from [Ca~II] $λλ$7291,7324 and, possibly, [Fe~II] $λ$7155. Compared with the spectra of the other recovered SNII, SN1986E shows strong H$α$ luminosity similar to SN~1979C but, in contrast, weak [O~III] emission. So far, among classified SNe, only type II Linears have been recovered a few years past the explosion. The high optical luminosity of Linear SNII at this phase is most likely related to the interaction of the ejecta with the circumstellar wind which is also expected to produce strong radio emission. Therefore radio observations of the remnant of SN~1986E are worth attempting. The circumstellar interaction model predicts that, in the next decade, the strength of the [O~III]/H$α$ emission rapidly increases and [O~III] $λλ$4959,5007 should eventually dominate the spectrum. We observed this effect in SN~1957D 30 years after explosion which therefore may represent the normal evolution of SNII with a dense circumstellar medium. The details observed in the spectra of both SNe suggest directions for further refinement of the modelling.

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