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

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

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 ~ 108-1011 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

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

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

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 18-22 keV RHESSI 25-50 keV

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

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

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

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

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

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

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

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