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RHESSI observations of LDE flares – extremely long persisting HXR sources

RHESSI observations of LDE flares – extremely long persisting HXR sources Mrozek, T., Kołomański, S., Bąk-Stęślicka, U. Astronomical Institute University of Wrocław. At last!. YOHKOH results - SXR. Long Duration Event (LDE) Long Duration Flare (LDF) Long Duration Arcade Flare (LDAF)

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RHESSI observations of LDE flares – extremely long persisting HXR sources

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  1. RHESSI observations of LDE flares – extremely long persisting HXR sources Mrozek, T., Kołomański, S., Bąk-Stęślicka, U. Astronomical Institute University of Wrocław

  2. At last!

  3. YOHKOH results - SXR Long Duration Event (LDE) Long Duration Flare (LDF) Long Duration Arcade Flare (LDAF) Kołomański, S., 2007: > 6h duration > 3 orbits of YOHKOH starting from the maximum of the flare

  4. YOHKOH results - SXR Different sources observed at the same time suggest that the energy reales takes place in different places Typical size of the SXR source (LDE case): 1.0-1.5x104 km

  5. YOHKOH results - HXR 1 2 2 1 HXR emission in the L channel (14-23 keV) was observed up to 40 minutes after the maximum of the flare.

  6. YOHKOH results - HXR Rise phase – coronal and footpoint sources Decay phase - HXR source observed 40 minutes after the maximum of the flare. It is 10 times longer than characteristic cooling time of such source – indirect proof for the energy release long after the maximum of the flare.

  7. RHESSI & LDEs - motivation Better spatial resolution – more detailed investigation of sources Better sensitivity - weak, coronal sources could be detected long after the maximum of the flare Better energy resolution – more detailed analysis of LDEs spectra

  8. Difficulties • Main difficulties: • pile-up • attenuators • orbital background

  9. RHESSI & LDE Feb. 2002 – Feb. 2008 ~ 160 LDE flares found with the use of GOES lightcurves ~ 50 which last longer than 3 hours in RHESSI observations (6-12 keV) 30 July 2005 X1.3 >10 h

  10. Method • 2-minutes intervals: • attenuators out • outside the radiation belts • far from the SAA • Thus, for 10 hours • decay we have only • few time intervals • for imaging and • spectroscopy

  11. Method Images: Time interval: 11:38 – 11:40 Grids: 3,4,5,6,8,9 Pixel size: 1”

  12. Method Images: Time interval: 11:38 – 11:40 Grids: 3,4,5,6,8,9 Pixel size: 1” 4-6 keV 10-12 keV 15-23 keV

  13. Method • The signal in the 12-25 keV • interval is observed • (11:40 UT – 6 hours • after the maximum) • why we can’t obtain images?

  14. Method • The signal in the 12-25 keV • interval is observed • (11:40 UT – 6 hours • after the maximum) • why we can’t obtain images? Because of the actual size of the source? – let’s look at the single-detector images

  15. Method grid number The size of sources changes When the diameter of the source is larger than the FWHM of given grid then the modulation vanishes and the source is no longer observed with this grid. For this reason we have to choose grids in more flexible way time

  16. Method As the result we obtain well resolved sources. Time interval: 11:38 – 11:40 Grids #: 8,9 Algorithm: PIXON Energy ranges [keV]: 5-6, 7-8, 9-10, 11-12, 12-14, 15-23 FWHM of the grid #8 is about 100 arc sec

  17. 30 July 2005 - images Comparison with EIT 195 Å RHESSI images reconstructed with the use of PIXON method Red contours – 6-7 keV Blue contours – 15-25 keV 6 hours after the maximum of the flare What is the nature of this source?

  18. 30 July 2005 - spectra double thermal EM: 9.3x1047cm-3, T: 9.3 MK EM: 6.4x1045cm-3, T: 20 MK

  19. 30 July 2005 - spectra thermal + thin target EM: 7.7x1047cm-3, T: 9.9 MK δBB: 7.4, EB: 100 keV, δAB: 20, Ecut: 11.2 keV

  20. 30 July 2005 - spectra thermal + thick target EM: 7.3x1047cm-3, T: 10.0 MK Fe: 3.4x1034 s-1, δBB: 12.2, EB: 600 keV, δAB: 6.0, Ecut: 13.9 keV

  21. 30 July 2005 - spectra thermal + broken power-law EM: 6.5x1047cm-3, T: 10.0 MK γ BB: 1.7, EB: 12.0 keV, γAB: 10.0

  22. 30 July 2005 Having the temperature, emission measure, size and height we were able to estimate the energy balance. To balance the thermal and conductive losses we need a heating of the order of 1 erg s-1cm-3 (1028 erg s-1 from the whole volume) Typical size of the long persisting HXR source is of the order of 104 km

  23. Models, models… Jakimiec, J., et al. 1998 The existence of the turbulent (highly tangled) magnetic field in the loop-top source could keep up the energy release for long time due to small reconnections inside the structure. It explains the spatial correlation between the thermal and non-thermal/hot sources observed in the late phase of LDEs Sweet, P. A. 1958 Emergence of the new flux is the main driver in this model. This idea was recently resurrected by Uchida et al. (1999) and Hirose et al. (2001) Shibata 1995 The main driver of the whole process is the eruption of the filament The several hours long energy release cannot be explained with this scenario.

  24. Conclusions LDEs are well observed by RHESSI. The analysis is complicated due to attenuators, radiation belts, SAA, but not impossible. HXR sources (above 15 keV) are visible even 6 hours after the maximum of the flare. Long-lasting HXR sources are located above structures observed in the EUV range. Observed sources are large and grows with time. The spectral analysis of the sources suggests that there are at least two components present. One is the hot (about 10 MK) and the second is a very hot (20 MK) or steep non-thermal component. The observed features imply the existence of the energy release process which lasts several hours.

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