RHESSI observations of LDE flares – extremely long persisting HXR sources
Mrozek, T., Kołomański, S., Bąk-Stęślicka, U.
Astronomical InstituteUniversity of Wrocław
Questions
How long?
Spatial scale
Where?
After the maximum of theflare; not during the impulsive phase
YOHKOH results - SXR
Kołomański, S., 2007:
>6h duration
>3 orbits of YOHKOH starting from the maximumof the flare
YOHKOH results - SXR
Different sources observed at the same time suggest that the energy reales takes placein different locations
Typical sizes of the SXR sources are 1.0-1.5x104 km
YOHKOH results - HXR
HXR emission in the L channel (14-23 keV) was observed up to 40 minutesafter the maximum of the flare
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.
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, searching for different types of sources (very hot thermal, non-thermal)
RHESSI & LDE
Feb. 2002 – Feb. 2008
~ 160 LDE flares foundwith the use of GOESlightcurves
~ 50 which last longer than 3 hours in RHESSI observations
30 July 2005X1.3>10 h
Method
2-minutes intervals:
-with attenuators out
- outside the radiation belts
- far from the SAA
Thus, for 10 hours decay we have only three time intervals for imaging and spectroscopy (for this flare, in other cases we can have up to 9-10 intervals)
Method
Images:
Time interval: 11:38 – 11:40Grids: 3,4,5,6,8,9Pixel size: 1”
4-6 keV 10-12 keV 15-23 keV
Method
The signal in the 12-25 keV interval is observed (11:40 UT – 6 hoursafter the maximum) - why we can’t obtain images?
Method
Because of the size of sources?
gridnumber
time
Method
We have to choose detectors in more flexible way – sources are large, but the result is realiable
30 July 2005 - images
Comparison with EIT 195 Å
RHESSI images reconstructed with the use of PIXON method
Red contours – 6-7 keVBlue contours – 15-25 keV
6 hours after the maximum of the flare
30 July 2005 - spectra
double thermal
30 July 2005 - spectra
thermal + thin target
30 July 2005 - spectra
thermal + thick target
30 July 2005 - spectra
thermal + broken power-law
30 July 2005
How long?
HXR emission in 15-25 keV is observed 6 hours after the maximum - we need an energyrelease existing for such long time
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)
Spatial scale:
the order of 104 km
Where?
7 Nov 2003
B4.7S29W90
30-40 degrees behind the limb
Extremely weak
Conclusions
LDEs are observed by RHESSI however the analysis is very complicated due to attenuators, radiation belts, SAA and other
HXR sources (above 15 keV) are visible even 6 hours after the maximum of the flare.
Long-lasting HXR sources are located above structures seen in different wavelengths andhave large sizes.
For long-lasting HXR sources located far above the solar limb we do not detect significantnon-thermal or hot components.
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