Spectral Analysis and Energy Estimates in M/X Flares using

RHESSI and SXI

Amir Caspi1,2, Säm Krucker2, Robert P. Lin1,2

1 Department of Physics, University of California, Berkeley, CA 947202 Space Sciences Laboratory, University of California, Berkeley, CA 94720

June 19, 2003 AAS/SPD Meeting 2

Why is spectral analysis important?

• Provides estimates of energy in thermal and non-thermal electrons

• Provides clues to heating mechanism(s)

• How does SXI help?– Broad band response in soft X-rays– Sensitive to lower-temperature plasmas– Another estimate of thermal energy

June 19, 2003 AAS/SPD Meeting 3

01/24/2003 M1.9 flare

June 19, 2003 AAS/SPD Meeting 4

Fitting the spectra

Forward modeling - which model/fit is best/proper?

June 19, 2003 AAS/SPD Meeting 5

Thermal + Power Law

- Naïve model, poor fit early on, requires small low-energy cutoff at all times

June 19, 2003 AAS/SPD Meeting 6

2 Thermals + Power Law

- Much better fit early on, but ambiguous at later times; still somewhat incomplete

June 19, 2003 AAS/SPD Meeting 7

Analysis - methods and problems

• Low-T component dominant <15 keV– Iron feature is good measure of thermal component

• Power law dominant >30-35 keV– Spectral index fairly easy to fit, but…

• Low-E cutoff very hard to determine– Power law & High-T component interfere

June 19, 2003 AAS/SPD Meeting 8

• Low-T component dominates thermal energy• High-T should vary smoothly - constraint on fit

Spectral parameters, energies

June 19, 2003 AAS/SPD Meeting 9

Conclusions• Forward modeling gives ambiguous results

– Still provides a reasonable first estimate of energies

• High-T component complicates analysis

•Calculate SXI-derived T, EM time profiles•Continue analysis for variety of flares

–More cases may help determine low-E cutoff

Future Work