Emission from circumstellar interaction in normal Type II supernovae

Optical Observations of Core-Collapse Supernovae

“…Observations at radio [59] and Xray [60] wavelengths revealed that the ejecta are interacting with relatively dense circumstellar material [61], probably ejected from the system during the course of its pre-SN evolution. Optical evidence for this interaction also began emerging at τ > ∼ 10 months: the Hα emission line grew in relative prominence, and by τ ≈ 14 months it had become the dominant line in the spectrum [53,62,63], consistent with models [31]. Its profile was very broad (FWHM ≈ 17,000 km s −1 ; Figure 8) and had a relatively flat top, but with prominent peaks and valleys whose likely origin is Rayleigh-Taylor instabilities in the cool, dense shell of gas behind the reverse shock [64].…”

Moderately luminous Type II supernovae

“…The Hα and Hβ still show a dominant emission component with an absorption component comparable with those of other SNe II at the same phase. Nevertheless, the absorption profiles display flat, blue shoulders, possibly an evidence of a residual interaction of the SN ejecta with the CSM (see Chevalier 1982;Chevalier & Fransson 1994). For this reason, the 27d spectrum may represent the rare snapshot of the spectral transition from a type IIn to a normal, non-interacting type II SN.…”

Classification of Supernovae

“…The interaction of the fast ejecta with the slowly expanding CSM generates a forward shock in the CSM and a reverse shock in the ejecta. The shocked material emits energetic radiation whose characteristics strongly depend on the density of both the CSM and the ejecta, and on the properties of the shock [30]. Thus the great diversity of observed SNIIn can provide clues to the different history of the mass-loss in the late evolution of progenitors.…”