Supernova-Produced ${}^{53}\mathrm{Mn}$ on Earth

For the time period from 1.5 to 4 Myr before the present we found in deep ocean ferromanganese crusts a ${}^{53}\mathrm{Mn}$ excess concentration in terms of ${}^{53}\mathrm{Mn}/\mathrm{Mn}$ of about $4\times {10}^{-14}$ over that expected for cosmogenic production. We conclude that this ${}^{53}\mathrm{Mn}$ is of supernova origin because it is detected in the same time window, about 2.5 Myr ago, where ${}^{60}\mathrm{Fe}$ has been found earlier. This overabundance confirms the supernova origin of that ${}^{60}\mathrm{Fe}$. For the first time, supernova-formed ${}^{53}\mathrm{Mn}$ has been detected and it is the second positively identified radioisotope from the same supernova. The ratio ${}^{53}\mathrm{Mn}/{}^{60}\mathrm{Fe}$ of about 14 is consistent with that expected for a SN with a $11–25{\mathrm{M}}_{\odot }$ progenitor mass and solar metallicity.

Figure 1

Shows the measured isotope ratios ${}^{53}\mathrm{Mn}/\mathrm{Mn}$ at different depths/ages in the crusts. Top to bottom are for the four crusts from the Pacific: the two from Midway atoll, (29DR-32 and 29DR-45), one from the Donizetti ridge (4DR) and one from Central Pacific (237KD). Error bars for small event numbers were calculated following the prescription of Feldman and Cousins [34]. The $1\sigma$ limits are drawn.

Figure 2

Merged ${}^{53}\mathrm{Mn}/\mathrm{Mn}$ ratios ($C/C_0$) from the different crusts at the time of incorporation. The red curve is the result of a fit of a Gaussian with fixed width $\sigma =0.8\mathrm{Myr}$.