Probing Ion Acceleration by Observing Gamma Rays

from Solar FlaresAlbert Y. Shih1

NASA Advisor: Brian R. Dennis2

Faculty Advisor: Robert P. Lin1

1 Department of Physics and Space Sciences Laboratory, UC Berkeley, Berkeley, CA2 4 NASA Goddard Space Flight Center, Greenbelt, MD

Flare

electrons

protons, alphas, heavy ions

neutrons

bremsstrahlung

nuclear de-excitation, positron annihilation

neutron-capture Sun

Gamma rays

Thermalizationtime delay of ~ 100 secondsspatial separation of < 1 arcsec

n (cm-3)

1011

1012

1013

1014

1015

A RHESSI gamma-ray spectrum

Model components

positron annihilation

neutron-capture

bremsstrahlung

nuclearde-excitation

total model

What can be done?

• Line energies– Angular distribution of accelerated ions

• Line fluxes– Ambient elemental abundances– Shape of the acceleration spectrum

• Line shapes– Accelerated elemental abundances– Temperature, density, etc.

Temporal Variability Analysis00:27:20–00:32:56 UT 00:32:56–00:43:20 UT

Low-FIP: Fe , Mg , Si

High-FIP: Ne , C , O

Temporal Variability Results2002 July 23 2003 October 28 2003 November 2

0.29±0.08 0.80±0.14

Low-FIP/high-FIP ratiosLow-FIP/high-FIP ratios

0.36±0.05 0.74±0.20

Protons vs. thermal emission

Region not fully investigated

Protons vs. high-energy electrons

Direct proportionality

After selection cuts

Future Work

• Modeling work to explore the scientific implications of these observations

• Searches for radioactive material persisting after flares

• Designs for future instruments to extend the observations of the signatures of ion acceleration to both lower and higher energies