The Spectral Reclassification of Nearby (z < 0.02) Type IIn Supernovae

Abstract Type IIn supernovae (SNe IIn) are an enigmatic subclass of SNe that show heterogeneity in their photometric and spectroscopic properties. Complex, multi-component Balmer line profiles are a defining property of SNe IIn. Perhaps owing to the heterogeneity in the SN IIn class, online databases often conflict and hold outdated or erroneous classifications. This is compounded by SN “impostors” and H ii region contamination. We outline a classification scheme based on multi-component H α profiles and apply it to a sample of 115 nearby (redshift z < 0.02) SNe that have held a SN IIn classification on the Open Supernova Catalogue (OSC). We find that 25 of our transients were misclassified as SNe IIn. We also note that there is disagreement between OSC and the Transient Name Server for 51 of the transients.