Cycle 24 Meeting, Napa December 2008 Ryan Milligan NASA/GSFC Microflare Heating From RHESSI and...

Ryan MilliganNASA/GSFC

Cycle 24 Meeting, NapaDecember 2008

Microflare Heating From Microflare Heating From RHESSI and Hinode RHESSI and Hinode

ObservationsObservations

Ryan MilliganNASA-GSFC



Energy released during flares…Energy released during flares…• Is divided between:

– Directly heating plasma in the corona at the magnetic reconnection site

– Accelerating electrons out of the thermal distribution

• These in turn drive chromospheric evaporation, filling the loop with high-temperature plasma

This aim of this study is to investigate the mechanism responsible for unusually high-temperatures observed during a microflare using RHESSI and Hinode



SOT Ca II EIS Fe XV XRT Ti_poly

Red = downflowsBlue = upflows

Fe XXIV

6-12 keV

He IIFe XIIFe XV



• Spectrum taken from 1 minute at flare peak

• Corrections for pulse pile-up and gain offset were applied

RHESSI Spectral AnalysisRHESSI Spectral Analysis



Gain offset correctionGain offset correction

• Before the anneal RHESSI calibration was poorly known

• Data could be modified manually by fine-tuning the gain offset

• drm_mod works only for single detector



Pileup correctionPileup correction

• Criteria for pileup– Total counts >104

– Excess emission at ~13 keV (twice the peak at 6.7 keV in A0 state)

• pileup_mod works only for single detector



Pileup correctionPileup correction

• Criteria for pileup:– Total counts >104

– Excess emission at ~13 keV (twice the peak at 6.7 keV in A0 state)

• pileup_mod works only for single detector



• Peak temperature of 15±1 MK

• No evidence for nonthermal emission

• Presence of Fe/Ni feature at 8 keV confirms high-continuum temperature

Spectral Fit ResultsSpectral Fit Results



Hannah et al. (2008)Feldman et al. (1996)

Statistics of Flare TemperaturesStatistics of Flare Temperatures



Klimchuk et al. (2008) Klimchuk et al. (2008) EBTEL 0D hydro-codeEBTEL 0D hydro-code

• Models plasma parameters for various forms of injected energy

• Peak temp is higher when less energy is used to accelerate electrons



If the flow in XRT is real:• Plasma flows left to right

along the loop• Evaporation occurs at X-ray

temperatures• Fe XV redshifts are

“chromospheric condensation” due to the overpressure of rising material

- too hot according to models - requires electron beam

• Blueshifts at right FP are due to the heat flux along the loop



If flow in Fe XV is real:• Plasma flows from right

to left along the loop• Brightening in XRT is

actually a build up of hot material being deposited in the left leg of the loop

• Upflow velocity consistent with evaporation due to thermal conduction



ConclusionsConclusions• Above-average temperature of 15 MK was

observed during a B-class flare• Absence of nonthermal emission plus low-

velocity upflows suggest that direct heating in the corona was responsible– Consistent with recent hydrodynamical model– Evaporation still required to supply material to

corona• Contradicting flow patterns were observed by

EIS and XRT

Cycle 24 Meeting, Napa December 2008 Ryan Milligan NASA/GSFC Microflare Heating From RHESSI and...

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