The height structure of solar active regions at X-ray wavelengths as deduced from OSO-8 limb crossing observations

Twenty limb crossing light curves of solar active region emission in the 1–4 keV energy band have been constructed from data gathered by the Lockheed Mapping X-Ray Heliometer experiment on OSO-8. These light curves indicate that 50% of the observed counts arise from heights below 20 000 km and 90% from heights below 57 000 km. The best fit is obtained for a model in which the emission density increases steadily down to the lowest observable levels, but the possibility of a small emission free gap at the base cannot be ruled out. On the average, the temperature of the plasma appears to be slightly higher at the base of a region than in its upper levels.