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

Science  05 Sep 2014:
Vol. 345, Issue 6201, pp. 1162-1165
DOI: 10.1126/science.1254738

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Surprise found by γ-ray metal detector

Astronomers commonly use type-Ia supernovae as standard distance measurement tools, though the physics of these bright sources are not fully understood. One product of the thermonuclear explosion is 56Ni, which probably lies at the heart of the supernova cloud. Diehl et al. detected the gamma-ray emission from 56Ni in SN2014J much earlier than expected, only about 20 days after the initial explosion. This early exposure suggests both an asymmetric event and the production of 56Ni farther out in the ejecta than predicted. These sources will help astronomers measure distances far beyond where supernovae have been studied.

Science, this issue p. 1162

Abstract

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.

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