Chromospheric magnetic field and density structure measurements using hard X-rays in a flaring coronal loop

No doubt a blitheringly simple cartoon, but one that illustrates an interesting application of the hard X-ray data and an important attempt to bring models and data together. The observational claim is that the harder X-rays come from down deeper in the atmosphere, thus tending to confirm the thick-target model. This would be great if true, but it is a very difficult measurement because of systematic effects in the interpretation of RHESSI imaging. The ballooning-out of the field in the low corona would naturally be expected in any static field extrapolation, since the sources of the field lie below the photosphere. Unfortunately this canopy-like expansion it has never been observed directly in terms of actual observable geometry, and so model-dependent inferences such as those presented here are the best we can do. Please refer also to the Isobe cartoon for an additional complication.