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Coronal hard X-ray sources

Coronal hard X-ray sources. The corona is tenuous and bremsstrahlung is inefficient => it should be dark in hard X-rays Nevertheless several clear observations of coronal sources >20 keV have been reported. The first clear evidence?. Coronal hard X-ray source from

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Coronal hard X-ray sources

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  1. Coronal hard X-ray sources • The corona is tenuous and bremsstrahlung is inefficient => it should be dark in hard X-rays • Nevertheless several clear observations of coronal sources >20 keV have been reported

  2. The first clear evidence? Coronal hard X-ray source from a limb-occulted flare in 1969 (Frost & Dennis, 1971). Note: • Coronal height ~30,000 km • Impulsive phase evident • X-ray spectrum ~hn-2 in later extended phase Review by Cliver et al., ApJ 305, 920 (1986)

  3. Coronal sources of hard X-rays? • Late non-thermal sources (radio type IV?) • Masuda “above-the-loop-top” hard X-rays • Direct emission from escaping electrons (counterpart of Type III bursts) • Coronal thick targets • Early-phase hard spectrum sources (e.g. July 23 2002)

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