Early 56Ni decay γ-rays from SN2014J suggest an unusual explosion


Detection of a nickel line in the Supernova SN2014J, some two weeks after the explosion. The position of the signal agrees within the measurement error with the position of the supernova (indicated by the cross). Picture from MPE press release.

Type Ia supernovae result from binary systems that include a carbon-oxygen white dwarf, and these thermonuclear explosions typically produce 0.5 solar masses
of radioactive 56Ni. The 56Ni is commonly believed to be buried deeply in the expanding supernova cloud. Surprisingly, in SN2014J we detected the lines at 158 and 812 keV from 56Ni decay (half-life 6.1 days) earlier than the expected several-week time scale, only ~20 days after the explosion, and with flux levels corresponding to roughly 10% of the total expected amount of 56Ni. Some mechanism must break the spherical symmetry of the supernova, and at the same time create a major amount of 56Ni at the outskirts. A plausible explanation is that a belt of helium from the companion star is accreted by the white dwarf, where this material explodes and then triggers the supernova event.

Paper published in Science, Volume 345, Issue 6201, pp. 1162-1165 (2014), full text available at http://de.arxiv.org/abs/1407.3061Press release at the Max Planck Institute for Extraterrestrial Physics.