Quarter-res, animated GIF movie (1 Mbyte)
Quarter-res, MPEG movie (150 kbyte)
Half-res, animated GIF movie (1.3 Mbyte)
Half-res, MPEG movie (150 kbyte)
Notice in the half-resolution movie the material which seems to be "re-directed" towards the south (downwards), so that it can escape towards the bottom-righthand corner. Also note the appearance of some loops to the righthand side (also in half-res, but barely discernible in quarter-res) which seem to initially retract downwards before subsequently expanding outwards. Are these merely illusions, due to limited temporal and spatial resolution? Or are these real physical motions? We suspect the latter, but it's too early to know for sure.
Click them image to link to NASA's solar flare theory pages, where bremsstrahlung
radiation and many other aspect of flare theory are explained.
Yohkoh HXT observes photons between 14 and 93keV. Photons above 20keV, if generated by a hot plasma, would correspond to a temperature of hundreds of millions of degrees, and most of the time we don't expect these temperatures to be present. We think instead that this emission is also bremsstrahlung radiation but generated by electrons accelerated to close to the speed of light, which stream out of the flare acceleration site, through the solar plasma, emitting as they go. So when we see hard X-ray emission, we are see where these accelerated particles are, and may be able to deduce where they came from.
Most hard X-rays are emitted from the lower regions of the atmosphere, where the density is high and the emission strong. But the Masuda sources are high up in the corona, above the location of the soft X-ray flare loops. This is just what is seen in our 26-October-99 event.
The two images above are from the early phase of the flare. The left-hand image is an overlay of the contours of the HXT Lo channel emission (14-23keV) on the SXT loops. The Lo channel emission is kind of amorphous, and mostly just maps the SXT emission. The right-hand image shows the contours of the HXT M1 channel (23-33keV) on the same SXT image and is resolved into 3 bright sources. One looks like a loop footpoint, as it is inside the limb of the Sun. Another is around the bright kernel of the SXT flare loop, but may also be another footpoint. But the furthest right source appears above the strongest SXT emission. This, we think, is a `Masuda' source. Notice that it appears near the site where blobs of material are observed to be ejected in the SXT movies. Could this be significant?
There have been many explanations for these above-the-loop HXR sources.
Some people think that they are in fact caused by super-hot plasma
at a temperature of 200 million Kelvin. Others think that they are generated
by trapped, accelerated particles. Perhaps this flare will tell us more?
David McKenzie <firstname.lastname@example.org>
Lyndsay Fletcher <email@example.com>
October 29, 1999