# Presentation: 161388

## Thermal and Nonthermal Contributions to theFlare X-ray Flux

- Brian R. Dennis1, Kenneth J. H. Phillips1, 2, Richard A. Schwartz1, 3, Anne K. Tolbert1,3, and Hugh S. Hudson4
- 1NASA GSFC, 2NRC Senior Resident Research Associate
- 3SSAI, 4SSL Berkeley

## Introduction

- RHESSI provides high resolution imaging and spectroscopy X-ray observations in the critical energy range from a few keV to a few tens of keV. These observations allow the following classic ways to be used to differentiate between the thermal and nonthermal components of the X-ray flux:
- gradually vs. impulsively varying flux
- exponential vs. power-law spectra,
- extended coronal vs. compact footpoint sources
- RHESSI also detects the iron-line complex at ~6.7 keV (1.9 Å).
- The peak energy is a function of temperature.
- The equivalent width (line-to-continuum ratio) is a function of temperature and iron abundance.
- Mewe (1985/6) and Chianti (1997) give line and continuum spectra as functions of temperature and abundances.
- These predictions are compared with RHESSI measurements for the X-flare on 21 April 2002.
- References
- Mewe, Gronenschild, van den Oord, 1985, (Paper V)  A. & A. Suppl., 62, 197; Mewe, Lemen, and van den Oord, 1986, (Paper VI) A. & A. Suppl., 65, 511
- Mewe, R., Kaastra, J. S., Liedahl, D. A., “Update of MEKA: MEKAL” (http://heasarc.gsfc.nasa.gov/docs/journal/meka6.html) Legacy, Journal of the High Energy Astrophysics Science Archive Research Center (HESARC), NASA GSFC, 6, 16, 1995.
- _[Dere](http://adsabs.harvard.edu/cgi-bin/author_form?author=Dere%2C%20K&db_key=AST)__[, K. P.](http://adsabs.harvard.edu/cgi-bin/author_form?author=Dere%2C%20K&db_key=AST)_; _[Landi](http://adsabs.harvard.edu/cgi-bin/author_form?author=Landi%2C%20E&db_key=AST)__[, E.](http://adsabs.harvard.edu/cgi-bin/author_form?author=Landi%2C%20E&db_key=AST)_; _[Mason, H. E.](http://adsabs.harvard.edu/cgi-bin/author_form?author=Mason%2C%20H&db_key=AST)_; _[Monsignori](http://adsabs.harvard.edu/cgi-bin/author_form?author=Monsignori%20Fossi%2C%20B&db_key=AST)__[ ](http://adsabs.harvard.edu/cgi-bin/author_form?author=Monsignori%20Fossi%2C%20B&db_key=AST)__[Fossi](http://adsabs.harvard.edu/cgi-bin/author_form?author=Monsignori%20Fossi%2C%20B&db_key=AST)__[, B. C.](http://adsabs.harvard.edu/cgi-bin/author_form?author=Monsignori%20Fossi%2C%20B&db_key=AST)_; _[Young, P. R.](http://adsabs.harvard.edu/cgi-bin/author_form?author=Young%2C%20P&db_key=AST)_, “CHIANTI - an atomic database for emission lines” A & A Supplement series, 125, 149-173, 1997.

## X-flare on 21 April 2002

## RHESSI Time History

- Soft X-ray flux (<12 keV) rises gradually suggesting thermal emission.
- Hard X-ray flux (>25 keV) shows impulsive peaks at ~01:16 UT suggesting nonthermal emission.

## RHESSI ContoursWhite:	6 – 12 keVBrown:	12 – 25 keVBlue: 	25 – 50 keV

- TRACE Image1.95 nm

## RHESSI Imaging

- Compact hard X-ray sources (>25 keV) on TRACE ribbons suggest nonthermal emission at loop footpoints.
- Extended soft X-ray source (<25 keV) and diffuse TRACE emission in corona suggest thermal emission at ~20 MK.

## Shutters Out

## RHESSI SpectraThin Shutters In (A1)Detector #41-minute accumulations

- RHESSI SpectraThin Shutters In (A1)Detector #41-minute accumulations

## RHESSI Spectra Thin Shutters (A1)Thin + Thick (A3)Detector #41-minute accumulations

## RHESSI Spectra

- Steep spectra before ~01:00 UT suggest thermal emission.
- Flatter power-law spectrum above ~20 keV at 01:16 UT suggests nonthermal emission.
- Peak at ~6.7 keV (1.9 Å) is the iron-line complex from thermal plasma.
- Peak at ~8 keV is most probably the Fe/Ni complex.
- Peak at ~10.5 keV is most probably caused by K-escape from the germanium detectors.

## Mewe & Chianti Thermal Spectra

## Peak Position of Iron-line Complex

- Energy in keV

## Iron-line ComplexRHESSI Measurements of Peak Energy

## Iron-line Complex - Peak Energy

- Detector-to-detector variations and higher-than-predicted peak energy must be instrument calibration issues.
- Variation of peak energy with time may be related to high detector count rates.
- Reason for sharp rise in peak energy determined from detector #8 after ~01:14 UT is unknown.

## Equivalent Width of Iron-Line Complex

- Mewe_spec(coronal - Meyer 1985)

- Chianti (coronal abundances)

- Chianti (photospheric)

## Iron-line ComplexRHESSI Measurements of Equivalent Width

## Iron-line Complex – Equivalent Width

- Equivalent-width measurements should be relatively independent of detector energy calibration and sensitivity.
- Detector-to-detector differences seem to be related to energy resolution.
- Large differences exist between Mewe (1985/6) and Chianti (1997) predictions.
- Measured equivalent widths are higher than predicted by both Mewe and Chianti, even for coronal abundances (Fe abundance 3 x photospheric).

## Conclusions

- RHESSI can differentiate between thermal and nonthermal emissions.
- Iron-line features are clearly seen in RHESSI spectra.
- Detector response is still preliminary – work in progress.
- Mewe (1985/6) and Chianti (1997) models of the thermal spectra differ in the predicted line intensities.
- GOES temperatures may be inaccurate since they are calculated using the older Mewe spectra.