SuperTIGER Abundances of Galactic Cosmic Rays for the Atomic Number (Z) Interval 30 to 56

Abstract

Iron Galactic Element Recorder) is a long-duration-balloon instrument that completed its first Antarctic flight during the 2012-2013 austral summer, spending 55 days at an average float altitude of 125,000 feet. SuperTIGER measured the relative abundances of Galactic cosmic-ray (GCR) nuclei with high statistical precision and well resolved individual element peaks from 10 Ne to 40 Zr. SuperTIGER also made exploratory measurements of the relative abundances up to 56 Ba. Although the statistics are low for elements heavier than 40 Zr, we present preliminary relative abundance measurements of charges = 41 − 56 with individual element resolution. GCR measurements up to 40 Zr support a source acceleration model where supernovae in OB associations preferentially accelerate refractory elements that are more readily embedded in interstellar dust grains than volatiles. In addition, injection into the GCR for both refractory and volatile elements appears to follow a charge dependence consistent with their grain sputtering cross sections. Our preliminary measurements of the = 41 − 56 range suggest the existence of an alternative GCR source or acceleration model for > 40 elements. We report progress in refining this interesting result.

Rapporteur Talk: Cosmic Ray Direct

“…Here, we will highlight two contributions that have applied and updated this kind of reasoning to modern data. At this ICRC, the SuperTIGER collaboration presented new results on their measurements of the abundance of heavy elements up to = 56 [43]. Previously, the TIGER experiment had confirmed the split between refractory and volatiles as suggested by Ellison, Drury and Meyer.…”

Galactic cosmic rays: direct measurements, status and perspectives

“…Ultraheavy nuclei offer a complementary view of the high-energy universe, with an origin to be understood in terms of r-process reactions in supernovae or binary neutron star mergers. [32]. The abundances are normalized to a model assuming an 80% solar system contribution mixed with a 20% massive star material contribution.…”

“…Ultraheavy nuclei, beyond iron, offer a very different view of the high-energy universe as they do not primarily originate in stellar nucleosynthesis, but instead must be formed in a neutron capture rprocess occurring either during a supernova explosion or during the merger of two neutron stars. The SuperTIGER balloon experiment [32] has accumulated an impressive series of heavy element populations thanks to a long Antarctic exposure and a large geometric factor. This is illustrated in Fig.…”

“…Figure 7. CR abundance distribution as a function of atomic number as measured by SuperTIGER[32]. The abundances are normalized to a model assuming an 80% solar system contribution mixed with a 20% massive star material contribution.…”

Future radioisotope measurements to clarify the origin of deep-ocean 244Pu

“…A nearby r-process event would mainly produce stable isotopes, which would be difficult to identify in deposits on the Earth or Moon, but might be detectable among the cosmic rays. Indeed, SuperTIGER measurements of cosmic-ray elemental composition have recently reported [32,33] that elements with 42 ≤ Z ≤ 54 show anomalously high abundances. These heavy elements exceed the levels of a mix of 80% solar-system abundances with a 20% admixture of supernova winds and ejecta that fits lower-mass cosmicray species.…”