Thermal and nonthermal contributions to the solar flare

X-ray flux

B. Dennis & K. Phillips NASA/GSFC, USA

J. & B. Sylwester SRC, Poland

R. Schwartz & K. Tolbert SSAI/GSFC, USA

The RHESSI Team

Separating Thermal & Nonthermal

• Temporal - gradual vs. impulsive

• Spatial - coronal vs. footpoint

• Spectral - exponential vs. power-law

• Spectral – iron-line complexes- always thermal!!!?

Thermal Spectra from Chianti (v. 4.2)Coronal Abundances (Fe & Ni 4 x photospheric)

Iron-line Complexes

Peak Energies• Function of temperature• Complicated by RHESSI gain change with rate)

Equivalent Widths (line-to-continuum ratio)• Function of temperature and iron abundance

Flux Ratio• Function of temperature alone• Caspi, Krucker, & Lin - poster E2.3-0013-04

Fe complex at ~6.7 keV (1.9 Å)Fe/Ni complex at ~8 keV (1.6 Å)

Fe-line Energy vs. Temperature

Fe-line Equivalent Width vs. T

Chianti – coronal abundancesMazzotta ionization fractions

Mewe – coronal abundancesArnand & Raymond ionization fractions

Chianti – photospheric abundances

26 April 2003 Flare Time Profile

A0 A1 A3 A1 A0

All Detectors

▬ 3 - 6 keV

▬ 6 – 12 keV

▬ 12 – 25 keV

▬ 25 – 50 keV

Time for spectrum

RHESSI Count-rate Spectrum

RESIK, RHESSI, and GOES Spectra

RESIK 1st Order

RHESSI

GOES

26 April 2002, 03:00 UT

RESIK and RHESSI Flare Spectra

▬ RESIK 3rd order

Δ RHESSI Data

▬ RHESSI best-fit spectrum

Fe-line fluxes(photons cm-2 s-1)

RESIK: 9.2 x 104

RHESSI: 6.1 x 104

26 April 2002, 03:03:12 – 03:05:32 UT

Photon Energy in keV

Flu

x in

ph

oton

s s-1

cm

-2 k

eV-1

Equivalent Width vs. Temperature

Chianti prediction

4x photospheric iron abundance

Attenuator States

+ A0 - early rise

o A1 - peak

□ A3 - 1st peak

● A1 - decay

x A0 - late decay

Equivalent Width vs. Temperature

Chianti prediction

4x photospheric iron abundance

Attenuator States

+ A0 - early rise

o A1 - peak

□ A3 - 1st & 2nd peaks

● A1 - decay

x A0 - late decay

Equivalent Width vs. Temperature

1T + 3G

2T + 3G

Attenuator States

+ A0 - early rise

o A1 - peak

□ A3 - 1st & 2nd peaks

● A1 - decay

x A0 - late decay

Conclusions

• Fe/H abundance ~4 x photospheric– Supports coronal origin of flare plasma

(Feldman et al., ApJ, 609, 439, 2004)

• Temperature determination needs work– Chianti Fe/Ni-line fluxes in error?– RHESSI sensitivity vs. energy– RESIK sensitivity & fluorescence levels– Multi-temperature analysis

THERMAL AND NONTHERMAL CONTRIBUTIONS TO THE SOLAR FLARE X-RAY FLUX

AbstractThe relative thermal and nonthermal contributions to the total energy budget of a solar flare are being determined through analysis of RHESSI X-ray imaging and spectral observations in the energy range from ~5 to ~50 keV. The classic ways of differentiating between the thermal and nonthermal components – exponential vs. power-law spectra, impulsive vs. gradually varying flux, compact vs. extended sources – can now be combined for individual flares. In addition, RHESSI’s sensitivity down to ~4 keV and energy resolution of ~1 keV FWHM allow the intensities and equivalent widths of the complex of highly ionized iron lines at ~6.7 keV and the complex of highly ionized iron and nickel lines at ~8 keV to be measured as a function of time. Using the spectral line and continuum intensities from the Chianti (version 4.2) atomic code, the thermal component of the total flare emission can be more reliably separated from the nonthermal component in the measured X-ray spectrum (Phillips, ApJ 2004, in press). The abundance of iron can also be determined from RHESSI line-to-continuum measurements as a function of time during larger flares. Results will be shown of the intensity and equivalent widths of these line complexes for several flares and the temperatures, emission measures, and iron abundances derived from them. Comparisons will be made with 6.7-keV Fe-line fluxes measured with the RESIK bent crystal spectrometer on the Coronas-F spacecraft operating in third order during the peak times of three flares (2002 May 31 at 00:12 UT, 2002 December 2 at 19:26 UT, and 2003 April 26 at 03:00 UT). During the rise and decay of these flares, RESIK was operating in first order allowing the continuum flux to be measured between 2.9 and 3.7 keV for comparison with RHESSI fluxes at its low-energy end.

IntroductionRHESSI 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 (1995) 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.

ReferencesMewe, 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, K. P.; Landi, E.; Mason, H. E.; Monsignori Fossi, B. C.; Young, P. R., “CHIANTI - an atomic database for emission lines” A & A Supplement series, 125, 149-173, 1997.

26 April 2003 Time Profile

A0 A1 A3 A1 A0

RHESSI Spectra

Thin Shutters In (A1)

Detector #4

1-minute accumulations

RHESSI Count-rate Spectrum

RHESSI Count Spectrum26 April 2003

RHESSI Photon Spectrum26 April 2003