SN 2008ax

SN 2008ax was a helium-rich type Ib core-collapse supernova in the interacting galaxy NGC 4490. It was independently detected on 3 March 2008 by LOSS and 4 March by Koichi Itagaki. The site had been monitored six hours before discovery, thus constraining the time of the explosion breakout. It was the third-brightest supernova of 2008. The brightness in the B-band peaked about 20 days after the explosion. X-ray emissions were detected from the event, which are most likely the result of shock heating from the supernova ejecta and circumstellar material.

Images of the source location made using the Hubble Space Telescope in 2011 and 2013 were used to identify the progenitor. If it was a single star, the images are compatible with a supergiant star with a class of B to mid-A type. However, this is not favored by models which indicate the progenitor had a relatively low mass of 4–$5 Solar mass$ and extended hydrogen-rich atmosphere with a radius of 30–$40 Solar radius$. An alternative, more plausible model suggests the progenitor was part of an interacting binary system where much of the atmosphere was lost through mass transfer to the companion.