Source sizes and energy partition from RHESSI

imaging and spectroscopy

Alexander Warmuth

Astrophysikalisches Institut Potsdam

Thermal vs. nonthermal energy content

• What is the energy partition (thermal vs. nonthermal) in solar flares?

• How do these quantities change with flare importance?

• Consequences of energy partition:is it consistent with the standard picture (heating by nonthermal electron beams driving evaporation)?

• Parameters from HXR spectral fits: - emission measure- temperature

• Parameters from HXR imaging: - thermal source area thermal volume (direct)

- footpoint area- footpoint separation thermal energy:

Thermal component:

thermal volume (indirect)

VEMTkE bth 3

• Parameters from HXR spectral fits: - total injected electron flux above low-energy cutoff nonthermal energy

Nonthermal component:

• 18 flares (from C5.5 to X17.2)

• Time series of HXR spectral fits:- VTH + THICK- corrected for decimation, albedo & pile-up physical parameters

• Time series of HXR images: - images at thermal energies: thermal areas

- images at nonthermal energies: footpoint areas & sep. geometric parameters

Method

HXR spectroscopy: Spectral time series

Area measurements

Imaging algorithms used:• CLEAN uniform weighting• CLEAN natural weighting• MEM_NJIT• VIS_FWD

Area measurements:• CLEAN: gaussian fit to sources, FWHM, quadratic subtraction of CLEAN beam• MEM_NJIT: area inside 50% contour• VIS_FWD: area directly obtained from fit

Volumes:• direct: Vdir = 4 /3 Ath3/2

• indirect: Vind = AFP * l

Time series of an M-class flare:FWHM, area & volume

CLEAN uniform VIS_FWDCLEAN natural MEM_NJIT

Thermal volumes – direct & indirect method (cotemporal)

Thermal and nonthermal total energies

• Radiative losses:after Cox & Tucker (1969)

• Conductive losses:approximation by Veronig et al. (2005)

Losses from the thermal plasma

TEMPrad ~

lTAP FPcond /~ 2/7

Radiative & conductive losses vs. nontherm. energy

Losses

• Conductive losses on the order of 1E32 erg in large flares

• But: simple model may be not applicable

• However:from SORCE observations:total radiative energy in 2003 Oct 28 flare: 4E32 erg(Kopp et al. (2004), Woods et al. (2004), Emslie et al. (2005))

• are high conductive losses real after all?

Conclusions

• using several imaging algorithms gives error estimation on source areas & volumes

• good correlation between thermal & nonthermal energies

• strong radiative and conductive losses

• consistent with total radiated energy

• conduction could heat dense lower atmosphere which radiates in UV & WL

• Consequence: either low cutoff energy of nonthermal electrons or additional heating mechanisms