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RHESSI observations of LDE flares extremely
long persisting HXR sources Mrozek, T.,
Kolomanski, S., Bak-Steslicka, U. Astronomical
Institute University of Wroclaw
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Questions
How long? Spatial scale Where?
After the maximum of the flare not during the
impulsive phase
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YOHKOH results - SXR
Kolomanski, S., 2007 gt6h duration gt3 orbits of
YOHKOH starting from the maximum of the flare
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YOHKOH results - SXR
Different sources observed at the same time
suggest that the energy reales takes place in
different locations Typical sizes of the SXR
sources are 1.0-1.5x104 km
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YOHKOH results - HXR
HXR emission in the L channel (14-23 keV) was
observed up to 40 minutes after the maximum of
the flare
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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.
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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)
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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 30 July 2005 X1.3 gt10 h
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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)

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Method
Images Time interval 1138 1140 Grids
3,4,5,6,8,9 Pixel size 1
4-6 keV
10-12 keV
15-23 keV
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Method

• The signal in the
• 12-25 keV interval
• is observed
• (1140 UT 6 hours
• after the maximum)
• why we cant obtain images?

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Method
Because of the size of sources?
grid number
time
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Method
We have to choose detectors in more flexible way
sources are large, but the result is realiable
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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
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30 July 2005 - spectra
double thermal
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30 July 2005 - spectra
thermal thin target
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30 July 2005 - spectra
thermal thick target
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30 July 2005 - spectra
thermal broken power-law
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30 July 2005
How long? HXR emission in 15-25 keV is observed
6 hours after the maximum - we need an
energy release 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?
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7 Nov 2003
B4.7 S29W90 30-40 degrees behind the limb
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Extremely weak
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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 and have large sizes. For
long-lasting HXR sources located far above the
solar limb we do not detect significant non-therma
l or hot components.