Trans- Iron Galactic Element Recorder

1. Measurement of the Relative Abundances of the Ultra-Heavy Galactic Cosmic-Rays (30Z40) with TIGER Washington University in St. Louis B.F. Rauch, W.R. Binns, J.R. Cummings, M.H. Israel, J.T. Link, L.M. Scott California Institute of Technology S. Geier, R.A. Mewaldt, S.M Schindler, E.C. Stone Goddard Space Flight Center L.M. Barbier, J.W. Mitchell, G.A. de Nolfo, R.E. Streitmatter University of Minnesota C.J. Waddington Trans- Iron Galactic Element Recorder This work supported by NASA under grant NNG05WC04G.

2. Outline of Talk • Discussion of TIGER science objectives • Overview of previous experimental results • Description of TIGER instrument and flights • Present preliminary TIGER results • Present preliminary comparison of results with GCR source models • Discussion of work in progress • Conclusions

3. TIGER Science Objectives • Measure a direct sample of matter from the birthplace of Galactic Cosmic Rays (GCRs) • Measure elemental abundances and energy spectra • Use measured elemental abundances to: • Compare Ultra-Heavy (UH) GCR abundances with source models • Measure the Co/Ni elemental abundance ratio in the 300 MeV/nuc to 10 GeV/nuc range • Search for spectral features in Fe spectrum that would be expected from nearby microquasars

4. GCR Source Models • There is a broad consensus that GCRs are accelerated by SN shocks. • The question we are seeking to answer with the UH data is the nature of the material that is accelerated. • The rare UH elemental abundances can help select between these models.

5. Current Models • Warm stellar atmospheres?—FIP fractionation: preferential acceleration of more easily ionized elements. (Cassé & Gorre, 1978) • Cold ISM (dust and gas)?—Volatility fractionation: atoms sputtering off of accelerated dust grains (Meyer, Drury & Ellison, 1997) • OB associations (superbubbles)?-No current predictions for UH abundances (Higdon & Lingenfelter, 2003)

6. Cosmic Ray Source: Cold dust or hot stellar atmospheres Most Low-FIP elements are non-Volatile. Of the handful of elements that break this association several are rare elements with Z>30 including 31Ga, 32Ge, 37Rb. Adopted from Meyer, Drury, Ellison 1998.

7. Results from Previous Experiments • Left Figure is the chare histogram from HEAO-HNE (Sep. 1979 – Jan. 1981), which resolved only even-odd pairs in this range (Binns et al. 1983) • Right Figure is the charge histogram from Ariel 6 (June 1979 - Feb. 1982), which also had limited resolution (Fowler et al. 1987)

8. Most Recent Results • Left Figure is ACE/CRIS isotopic data colleted over 17 months (George et al. 1999) • Right Figure compares existing experimental data in the 30  Z  34 range with solar system and propagated solar system abundances (George et al. 1999)

9. 2001-2002 2003-2004

10. Flight Trajectories Dec 21, 2001 – Jan 21, 2002 Dec 17, 2003 – Jan 4, 2004

11. Altitude Profiles Dec 17, 2003 – Jan 4, 2004 Dec 21, 2001 – Jan 21, 2002 130 120 110 Average: 118,800 ft (36,210 m), Average pressure: 5.5 mbar, 372,977 resolved Fe events Average: 127,800 ft (38,950 m), Average pressure: 4.1 mbar, 245,436 resolved Fe events

12. Crossplots Ni Fe Cr Zn Ni Ti Ca Fe Cr Ti Ca C0 has 2.5 GeV/nuc Energy threshold Note that for most of the iron and lower charges, only about 1/5th of the events have been plotted to prevent saturation of the charge contours. Aerogel Cherenkov Scintillators (S1 + S2) Acrylic Cherenkov Acrylic Cherenkov

13. 2001 TIGER Data • 2001 dataset analyzed previously by Link, et al. • Note change in scale at Z = 29 Fe Zn Ti Cr Ga Ge Se Ni Kr Sr

14. Combined 2001 and 2003 Data • 2001 dataset analyzed previously by Link, et al. • Note change in scale at Z = 29 • 2003 dataset analysis still preliminary

15. Combined 2001 and 2003 Data Fe • 2001 dataset analyzed previously by Link, et al. • Note change in scale at Z = 29 • 2003 dataset analysis still preliminary Zn Ti Cr Ga Ge Se Ni Sr Kr

16. Volatility or FIP Fractionation • Volatility model does seem to fit best, except at 31Ga which agrees with FIP and disagrees with Volatility at the 2.5  level • However, 32Ge agrees with Volatility and disagrees with FIP at the 7  level. • Is disagreement with Volatility just statistics? • Or does it indicate that the source material does not have a simple solar-system composition? Zn Ga Ge Se Br Kr Rb Sr Zr As Y

17. Expected accumulated statistics for 50 days of ~10 times larger instrument. Assumes data points will fall exactly as expected in volatility model.

18. Work in Progress • Implementing improved charge assignments in the lower energy regime (300 MeV/nuc-2.5 GeV/nuc) using a model of scintillator light output (BTV model) • Optimizing interaction cuts for UH and lower charge regions • Propagation of abundances from balloon altitudes to the top of the atmosphere for: • Direct comparison with previous abundance measurements (Ariel-6, HEAO-3, ACE-CRIS) • More direct comparison with relative abundances from GCR source models • Possible propagation of abundances back to Galactic source

19. Conclusions • We have demonstrated that TIGER has achieved the excellent resolution required to resolve UH nuclei • The clear peaks that we observe for 30Zn, 31Ga, 32Ge, and 34Se represent the best measurements made to-date for these elements • The data agree best with a volatility model which would indicate a cold dust/gas origin of GCRs • However, 31Ga agrees best with the FIP model, but is only ~ 2.5 from volatility • If the real origin of GCRs is superbubbles, then FIP and Volatility model abundances may not be the right comparison • Clearly,additional data would place better constraints on models • An instrument with a larger collecting power (x10) is needed to make major advances in measuring the UH abundances