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.