1. Marina Battaglia, FHNW Säm Krucker, FHNW/UC Berkeley
Direct imaging and spectroscopy of flare accelerated electron beams with STIX
Marina Battaglia, FHNW
Säm Krucker, FHNW/UC Berkeley

2. Context → Soft X-ray sources typically observed from near
Introduction to flares
Solar limb
→ Soft X-ray sources typically observed from near
the top of coronal loops
hard X-ray sources observed from loop footpoints

3. n ~ 108-1011 cm-3 acceleration site acceleration site n > 1012 cm-3
photosphere
faint
HXR emission
THIN target
intense
THICK target
acceleration
site
n > 1012 cm-3
n ~ cm-3
acceleration
site
Photosphere
Chromosphere
Corona →
30-40 keV
4-5 orders of
magnitude!
Normalized X-ray flux
Density [cm-3]
Height [Mm]
Battaglia et al. 2012

4. Current observations of electron beaming
Directivity is expected in flare models
Observations in dm radio wavelengths hint at outgoing
electron beams
2. Occasional hard X-ray observations from the high corona
Methods for determining the anisotropy and the electron
beam strength

5. 1. X-ray and radio observations of decimetric spikes
Temporal association
Phoenix II Spectrogram
RHESSI lightcurve
Battaglia & Benz (2009)

6. Some hard X-ray emission from near the coronal soft X-ray source
Spatial relation
Some hard X-ray emission from
near the coronal soft X-ray source
Radio emission higher up in the
corona
Associated CME
→ Flare related emission and
activity from the high corona
CME
dm radio emission
Battaglia & Benz (2009)
RHESSI 6-12 keV
RHESSI keV
RHESSI keV

7. 2. Special case: HXRs from above the flare site
small soft X-ray emission,
but large HXR burst!
fast (2000 km/s) backside CME.
flare site 40 degrees behind limb.
motion
40o
flare
RHESSI
15-25 keV
Krucker, White, & Lin (2007)
Earth

8. very large source (>200 arcsec) expanding and rising
HXR emission from electrons
in magnetic structures within coronal mass ejections.
300”
speed of CME front ~ 2000 km/s
~400 km/s
~800 km/s

9. 3. Methods for determining the anisotropy and the electron beam strength
Stereoscopic spectroscopy (Li et al. 1994)
X-ray polarisation (Suarez-Garcia et al. 2006)
Use albedo in spectra (Kasparova et al. 2007, Kontar & Brown 2006)
direct photons (up)
Compton backscattered
photons (up)
Corona
Photosphere
hard X-ray source

10. Use albedo signature via measurements of the X-ray source size (Kontar & Jeffrey 2010, Battaglia, Kontar & Hannah 2011)
primary
source
albedo patch
Photosphere
direct photons (up)
Compton backscattered
photons (up)
Corona
Simulated photon map
“True source”
FWHM of forward fitted total flux
Albedo contribution
 deviation from Gaussian
Isotropic
Anisotropic 2:1

11. Direct measurements of upward and downward component using occultation in stereoscopic observations with STIX
Possibility 1: STIX observes the hard
X-ray footpoints
A spectrometer from Earth for which
the footpoints are occulted measures
the HXR from the corona
outward beam
“STIX”
footpoints

12. X Possibility 2: Direct observation of upward component by STIX “STIX”
footpoints
outward beam
“STIX” X
footpoints
earthbound spectrometer

13. Detectability of upward component
STIX background
STIX background
theoretical image
simulated RHESSI image
(10 arcsec resolution)
10 times higher coronal density
Saint-Hilaire et al. 2009
starting height of beam: 20 arcsec  n=3x109 cm-3

14. Conclusions
X-ray observations (spectra and images) are an important diagnostic of flare accelerated electrons
Measuring the downward and upward ratio of flare accelerated electrons is crucial for our understanding of the flare acceleration mechanism
Direct X-ray observations of the signatures of both, downward and upward beam component are difficult due to dynamic range and background
STIX, due to higher sensitivity, should be able to directly image the outward component and, in conjunction with a potential Earth orbiting spectrometer, will be able to perform high resolution stereoscopic observations