Radiocarbon Production by the Gamma-Ray Component of Supernova Explosions

Abstract

We selected SN1006, the brightest and closest to Earth of all supernovas historically observed, for a study of 14C production by e-,e+-bremsstrahlung cascades initiated by hard y rays (>10 MeV) from that event. During the cascade, bremsstrahlung energies eventually fall within a giant (n,y), (n,2y) cross-section, peaking at 23 MeV and approaching effectively zero below 10 MeV and above 40 MeV. The neutrons are absorbed primarily in the reaction 14N(n,p)14C. Cellulose from single-year tree rings from AD 1003 to AD 1020 was measured to determine Delta-14C. Three years after the first visual observation of SN1006, Delta-14C rose and remained above pre-AD 1009 values until AD 1018. Comparison of the 7 years before AD 1009 with the 9 years following show an average increase of 6.1 +/1.6 (s.d.) per mil (significant at the 99.6% confidence level). Such a pulse of 14C requires a total production of neutrons of 17.1 x 10^7 n cm-2e, implying an input of 11.3 x 10^4 ergs cm-2e y-ray energy. This requires the total supernova y-ray energy (>10 MeV) to have been 1 x 10^50 ergs.