Limits on Supernova-Associated Fe60/Al26 Nucleosynthesis Ratios from Accelerator Mass Spectrom

Abstract

We searched for the presence of 26 Al in deep-sea sediments as a signature of supernova influx. Our data show an exponential dependence of 26 Al with the sample age that is fully compatible with radioactive decay of terrigenic 26 Al. The same set of samples demonstrated a clear supernova 60 Fe signal between 1.7 and 3.2 Myr ago. Combining our 26 Al data with the recently reported 60 Fe data results in a lower limit of 0.18 +0.15 −0.08 for the local interstellar 60 Fe/ 26 Al isotope ratio. It compares to most of the ratios deduced from nucleosynthesis models and is within the range of the observed average galactic 60 Fe/ 26 Al flux ratio of (0.15±0.05). The radionuclides 26 Al (t 1/2 =0.717±0.017 Myr [1]) 1 and 60 Fe (t 1/2 =2.61±0.04 Myr [2-4]) are key isotopes for 2 understanding nucleosynthesis in our galaxy. Both were 3 present in the early solar system, as evidenced by an ex-4 cess of their decay-products in meteorites [5, 6]. Today, 5 the decay of live 26 Al and 60 Fe is observed in the interstel-6 lar medium (ISM) through their associated characteristic 7 γ-rays [7, 8]. 8 Significant amounts (3-10 %) of 26 Al and 60 Fe are 9 freshly synthesized and ejected into the ISM by (su-10 per) asymptotic giant branch-(S)AGB-stars in the 11 mass range of ∼5-9 M ⊙ [9, 10]. However, the major frac-12 tion is thought to be released by massive stars (9 M ⊙) 13 that explode as core-collapse supernovae (CCSNe) [11-14 13]. Electron-capture (EC)SNe (∼7-11 M ⊙) produce 15 60 Fe, but negligible 26 Al during explosive nucleosynthesis 16 [10, 14]. Additionally, stellar winds of Wolf-Rayet (WR) 17 stars with masses >40 M ⊙ , which also end their lives as 18 SNe, have been proposed as major sources for the galac-19 tic 26 Al inventory [15, 16], while they are not believed to 20 contribute significant amounts of 60 Fe [13, 17]. Hence, 21 the observed ISM distribution of 26 Al and 60 Fe combines 22 a mixture of different stellar sources, with a galactic av-23 eraged 60 Fe/ 26 Al γ-ray flux ratio of (0.15±0.05) [8]. 24 Freshly produced radionuclides from supernova (SN) 25 explosions can be transported over large interstellar dis-26 tances. Material ejected from nearby SNe can enter our 27 solar system and cross the Earth's orbit, potentially leav-28 ing traces of the ejecta in terrestrial archives [18, 19]. 29 Indeed, the radionuclide 60 Fe has been identified in ter-30 restrial [20-24] and lunar samples [25]. The detection of 31 SN-associated 60 Fe deposited about 2-3 Myr ago provides 32 an opportunity to determine the specific SN-associated 33 26 Al/ 60 Fe ratio, disentangling it from the observed galac-34 tic average ratio. 35 Here, we present for the first time a detailed 26 Al time 36 profile and combine this data with the previously mea-37 sured SN-associated 60 Fe data from the same deep-sea 38 sediments [22] to derive the 60 Fe/ 26 Al ratio associated 39 with the recent and local SN events. First, we esti-40 mate whether SN-associated 26 Al is within the detection 41 limit of accelerator mass spectrometry (AMS) using an 42 60 ...

Gamma-Ray Emission of 60Fe and 26Al Radioactivity in Our Galaxy

“…From the consistent analysis approach, with identical data selections, response, and background treatments, we minimise biases or systematics, and obtain a result for the 60 Fe / 26 Al flux ratio of (18.4 ± 4.2) % based on the exponential disk grid maps. This large-scale galactic value is consistent with a local measurement from deposits of material on Earth (Feige et al 2018). Since we do not know the real sky distribution of 60 Fe in the Galaxy, the derived 60 Fe / 26 Al flux ratio will depend on the sky distribution tracers.…”

60Fe in core-collapse supernovae and prospects for X-ray and gamma-ray detection in supernova remnants

“…Wang et al's 0.148 ± 0.06). Recent measurements (Feige et al 2018) further determined a lower limit for the 60 Fe/ 26 Al ratio in the local interstellar medium of 0.18 +0.15 −0.08 by analyzing these SLRs in deep-sea sediments. This measurement agrees well with gamma-ray flux measurements.…”

Stochastic Chemical Evolution of Radioactive Isotopes with a Monte Carlo Approach

“…There are several potential applications of our results to the interpretation of the abundances of now-extinct SLRs that were present in the early Solar System (ESS) 4.6 Gyr ago, as well as the abundances of SLRs deposited in samples from the Earth (Wallner et al 2015(Wallner et al , 2016Feige et al 2018), the Moon (Fimiani et al 2016), and present in cosmic rays (Binns et al 2016 Figure 9. Zoom-in of one arbitrary Monte Carlo realization for τ /γ = 0.2 to visualize our method to calculate the probabilities for M radio to carry the signature of only one event (shown in Figure 10).…”

“…Radioactive nuclei with half-lives of the order of a few tens to a few hundreds Myr (short-lived radionuclides, SLRs hereafter) are one of the most promising tools to investigate a variety of current astrophysical topics including ongoing stellar nucleosynthesis (Diehl 2018), the properties of different rapid neutron-capture (r) process sites (Hotokezaka et al 2015), the physics of the interstellar medium (ISM) (Krause et al 2018) and of the local bubble (Feige et al 2018), the formation of the Solar System (Lugaro et al 2018), and the thermo-mechanical evolution of protoplanets (Lichtenberg et al 2019). The peculiarity of radioactive nuclei is that they decay into a daughter nucleus with a characteristic timescale determined by their half-life.…”