Measurement of the Relative Abundances of the Ultra-Heavy

Galactic Cosmic-Rays (30Z40) 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-IronGalacticElementRecorder

This work supported by NASA under grant NNG05WC04G.

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

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

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.

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)

Adopted from Meyer, Drury, Ellison 1998.

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.

Cosmic Ray Source: Cold dust or hot stellar atmospheres

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)

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)

Aerogel Cherenkov (C0)

Acrylic Cherenkov (C1)

PMT

Fiber Hodo

S2

Aerogel Radiator

S4

Fiber Hodo

TIGER INSTRUMENT CROSS-SECTION

117 cm

S1

S3

55 c

m

2001-2002 2003-2004

Flight TrajectoriesDec 21, 2001 – Jan 21, 2002 Dec 17, 2003 – Jan 4, 2004

Dec 21, 2001 – Jan 21, 2002Dec 17, 2003 – Jan 4, 2004

110

130

120

Altitude Profiles

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

Ni

Fe

CaTi

Cr

Zn

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.

Fe

Ni

C0 has 2.5 GeV/nuc Energy threshold

Ca

Cr

Ti

Acrylic Cherenkov

Aer

ogel

Che

renk

ov

Acrylic Cherenkov

Sci

ntil

lato

rs (

S1

+ S

2)Crossplots

2001 TIGER Data

2001 dataset analyzed previously by Link, et al.

Note change in scale at Z = 29

Ti Cr

Fe

Ni

Zn

GaGe Se Kr Sr

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

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

Ti Cr

Fe

Ni

Zn

Ga Ge Se

Kr Sr

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

As

Se Br Kr Rb Sr

Y

Zr

Assumes data points will fall exactlyas expected in volatility model.

Expected accumulated statistics for 50 days of ~10 times larger instrument.

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

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