Early 56Ni decay {\gamma}-rays from SN2014J suggest an unusual explosion

TL;DR

Early detection of 56Ni decay gamma-rays in SN2014J indicates an unusual explosion possibly involving asymmetric ejection of nickel, challenging standard models of supernova nucleosynthesis.

Contribution

This paper reports the first early detection of 56Ni decay gamma-rays in SN2014J, suggesting a novel explosion mechanism involving asymmetric nickel distribution.

Findings

Detected 56Ni gamma-ray lines 20 days after explosion

Observed flux levels indicate ~10% of expected 56Ni

Suggests asymmetric explosion with nickel at supernova outskirts

Abstract

Type-Ia supernovae result from binary systems that include a carbon-oxygen white dwarf, and these thermonuclear explosions typically produce 0.5 M_solar 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 ({\tau}~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.