The X-Ray Corona and the Photospheric Magnetic Field

Abstract

Soft X-ray (3–60 Å) photographs of the solar corona have been obtained on four flights of a rocket-borne grazing incidence telescope having a resolution of a few arc seconds. The configuration of the X-ray emitting structures in the corona has been compared to the magnetic field distribution measured by photospheric longitudinal magnetograms. The X-ray structures trace the three dimensional configuration of the magnetic field through the lower corona.Active regions in the corona take the form of tubular structures connecting regions of opposite magnetic polarity within the same or adjacent chromospheric active regions.Higher, larger structures link widely separated active regions into complexes of activity covering substantial fractions of the disk. The complexes are separated by areas of low average field in the photosphere. Interconnections across the solar equator appear to originate over areas of preceding polarity.Enhanced X-ray emission is observed, outside the active belt, over areas of enhanced general magnetic field. Bright point-like X-ray features are observed above bipolar areas in the general coronal field.Two, probably related, classes of X-ray features are associated with points of high field gradient along the longitudinal magnetic, ‘neutral line’. Both in the non-flaring active region and in flares the brightest emission is observed from one or more small line sources (at our present resolution). In flares this can account for a substantial fraction of the total soft X-ray emission of the flare.