Simulations of ⁶⁰Fe entrained in ejecta from a near-Earth supernova Effects of observer motion

Recent studies have shown that live (not decayed) radioactive ⁶⁰Fe is present in deep-ocean samples, Antarctic snow, lunar regolith, and cosmic rays. ⁶⁰Fe represents supernova (SN) ejecta deposited in the Solar system around 3 Myr ago, and recently an earlier pulse ≈7 Myr ago has been found. These data point to one or multiple near-Earth SN explosions that presumably participated in the formation of the Local Bubble. We explore this theory using 3D high-resolution smooth-particle hydrodynamical simulations of isolated SNe with ejecta tracers in a uniform interstellar medium (ISM). The simulation allows us to trace the SN ejecta in gas form and those eject in dust grains that are entrained with the gas. We consider two cases of diffused ejecta: when the ejecta are well-mixed in the shock and when they are not. In the latter case, we find that these ejecta remain far behind the forward shock, limiting the distance to which entrained ejecta can be delivered to ≈100 pc in an ISM with n_H = 0.1 cm^-3 mean hydrogen density. We show that the intensity and the duration of ⁶⁰Fe accretion depend on the ISM density and the trajectory of the Solar system. Furthermore, we show the possibility of reproducing the two observed peaks in ⁶⁰Fe concentration with this model by assuming two linear trajectories for the Solar system with 30-km s^-1 velocity. The fact that we can reproduce the two observed peaks further supports the theory that the ⁶⁰Fe signal was originated from near-Earth SNe.