Supernova impostor

Supernova impostors are stellar explosions that appear at first to be a type of supernova but do not destroy their progenitor stars. As such, they should be considered to be a class of extra-powerful novae. They are also known as Type V supernovae, Eta Carinae analogs, and giant eruptions of luminous blue variables LBV.

Appearance, origin and mass loss

Supernova impostors appear as remarkably faint supernovae of spectral type IIn, those which have hydrogen in their spectrum and narrow spectral lines indicating relatively low gas speeds. These impostors exceed their pre-outburst states by several magnitudes, with typical peak absolute visual magnitudes of −11 to −14. The trigger mechanism of these outbursts remains unexplained, though it is thought to be caused by violating the classical Eddington luminosity limit, initiating severe mass loss. If the ratio of radiated energy to kinetic energy is near unity, as in Eta Carinae, then we might expect an ejected mass of about 0.16 solar masses.

Examples

Possible examples of supernova impostors include the 1843 eruption of Eta Carinae, P Cygni, SN 1961V, SN 1954J, SN 1997bs and SN 2008S in NGC 6946, where detections of the surviving progenitor stars are claimed.

One supernova impostor that made news after the fact was the one observed on Oct. 20, 2004 in galaxy UGC 4904 by Japanese amateur astronomer Koichi Itagaki. This LBV star blew itself up just two years later on Oct. 11, 2006 as supernova SN 2006jc.