The link between the Local Bubble and radioisotopic signatures on Earth

The link between the Local Bubble and radioisotopic signatures on Earth

Feige, J.; Breitschwerdt, D.; Wallner, A.; Schulreich, M. M.; Dettbarn, C.; Fifield, K.; Fuchs, B.; Merchel, S.; Rugel, G.; Steier, P.; Tims, S.; Winkler, S. R.; Golser, R.

The terrestrial 2-3 Myr old 60Fe signal has been probed to be a global phenomenon [1]. Even lunar samples show an 60Fe excess pointing towards a recent injection into the solar system [2]. The most likely sources are stellar explosions within a moving group that passed the solar neighborhood, and whose surviving members are now in the Sco-Cen association [3]. We have traced the trajectories of those stars back in time and, by analyzing the uncertainties of the stellar positions, calculated the most probable explosion sites of the perished stars. By determining their masses and explosion times, we found a sequence of supernovae starting 13 Myr ago. We used analytical and numerical methods to generate the Local Superbubble, as well as its neighboring Loop I Superbubble, and link its formation to the 60Fe signature. Similar calculations with 26Al show only a marginal signal due to its shorter half-life and the broad extension of the supernova signal of ~1.5 Myr. Recent AMS measurements of 26Al contents in four deep-sea sediment cores from the Indian Ocean confirm this result. The data show an exponential decrease towards larger depths as expected from atmospherically-produced 26Al. This terrestrial concentration overwhelms a possible signature from nearby supernovae. With 60Fe data determined from the sediment samples [1] lower limits of 60Fe/26Al ratios were calculated. These are in line with gamma-line flux ratios from SPI/INTEGRAL data in the interstellar medium [4].
[1] A. Wallner et al., this conference.
[2] L. Fimiani et al., in Proceedings of the Lunar and Planetary Science Conference, Texas, 2014, p. 1778.
[3] B. Fuchs et al., MNRAS 373, 993 (2006).
[4] W. Wang, Proceedings of the International Astronomical Union, China, 2008, p. 333.

Keywords: accelerator mass spectrometry; AMS; supernova

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