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RHESSI observations of LDE flares – extremely long persisting HXR sources Mrozek, T., Kołomański, S., Bąk-Stęślicka, U. Astronomical Institute University of Wrocław. Questions. How long? Spatial scale Where?. After the maximum of the flare; not during the impulsive phase.

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RHESSI observations of LDE flares –

extremely long persisting HXR sources

Mrozek, T., Kołomański, S., Bąk-Stęślicka, U.

Astronomical Institute

University of Wrocław


Questions

How long?

Spatial scale

Where?

After the maximum of the

flare; not during the impulsive

phase


YOHKOH results - SXR

Kołomański, S., 2007:

>6h duration

>3 orbits of YOHKOH

starting from

the maximum

of the flare


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


YOHKOH results - HXR

HXR emission in the L channel (14-23 keV) was observed up to 40 minutes

after 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 found

with the use of GOES

lightcurves

~ 50 which last longer

than 3 hours in

RHESSI observations

30 July 2005

X1.3

>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 – 11:40

Grids: 3,4,5,6,8,9

Pixel 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 hours

  • after the maximum)

  • why we can’t obtain images?


Method

Because of

the size

of sources?

grid

number

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 keV

Blue 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 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?


7 Nov 2003

B4.7

S29W90

30-40 degrees behind

the limb



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-thermal or hot components.


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