Microflare Heating From RHESSI and Hinode Observations

1. Microflare Heating From RHESSI and Hinode Observations Ryan Milligan NASA-GSFC Ryan Milligan NASA/GSFC

2. 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 chromosphericevaporation, 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 Ryan Milligan NASA/GSFC

3. He II Fe XXIV Fe XII 6-12 keV Fe XV SOT Ca II EIS Fe XV XRT Ti_poly Red = downflows Blue = upflows Ryan Milligan NASA/GSFC

4. RHESSI Spectral Analysis • Spectrum taken from 1 minute at flare peak • Corrections for pulse pile-up and gain offset were applied Ryan Milligan NASA/GSFC

5. Gain 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 Ryan Milligan NASA/GSFC

6. Gain 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 Ryan Milligan NASA/GSFC

7. Pileup 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 Ryan Milligan NASA/GSFC

8. Pileup 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 Ryan Milligan NASA/GSFC

9. Spectral Fit Results • Peak temperature of 15±1 MK • No evidence for nonthermal emission • Presence of Fe/Ni feature at 8 keV confirms high-continuum temperature Ryan Milligan NASA/GSFC

10. Feldman et al. (1996) Hannah et al. (2008) Statistics of Flare Temperatures Ryan Milligan NASA/GSFC

11. Klimchuk et al. (2008) EBTEL 0D hydro-code • Models plasma parameters for various forms of injected energy • Peak temp is higher when less energy is used to accelerate electrons Ryan Milligan NASA/GSFC

12. Ryan Milligan NASA/GSFC

13. 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 Ryan Milligan NASA/GSFC

14. 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 Ryan Milligan NASA/GSFC

15. Conclusions • 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 Ryan Milligan NASA/GSFC