X-ray observations of solar active regions from OSO-5

Observations of solar active regions by a grazing incidence X-ray telescope on board OSO-5 are reported. The evolution of the hot, coronal components of active regions have been studied during successive rotations across the solar disc. In particular, it is found that the X-ray emission is very dependent on the photospheric magnetic field. Models of active regions are constructed as a function of the underlying magnetic field.