Early 56Ni decay gamma rays from SN2014J suggest an unusual explosion

Type Ia supernovae result from binary systems that include a carbon-oxygen white dwarf, and these thermonuclear explosions typically produce 0.5 solar mass of radioactive ⁵⁶Ni. The ⁵⁶Ni is commonly believed to be buried deeply in the expanding supernova cloud. In SN2014J, we detected the lines at 158 and 812 kiloelectron volts from ⁵⁶Ni decay (time ~8.8 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.