Source sizes and energy partition from RHESSI imaging and spectroscopy Alexander Warmuth Astrophysikalisches Institut Potsdam
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