Flares observed by the normal incidence X-ray telescope on 1989 September 11

Abstract

We report observations of two solar flares seen in soft X-rays during a sounding rocket flight of the Normal Incidence X-ray Telescope (NIXT) payload on 1989 September 11. The rocket was launched at the onset of a two-ribbon event which reached a maximum intensity of C5 (GOES classification) slightly before the start of our X-ray observations. The flare in X-rays consists primarily of a single bright loop crossing the neutral line and having its footpoints at the southern ends of the ribbons; this loop accounts for more than two-thirds of the emission and is shown to have an electron density of ∼6 × 1010 cm-3 at a temperature of ∼6 × 106 K. However, within the remainder of each of the flare ribbons, we also observe complicated coronal structure which although energetically less important is clearly interacting with the main flare loop. A second event in an active region at the limb began during the flight: its most striking feature is a strong correlation with Hα images taken at the same time, which indicates the coexistence of chromospheric and coronal temperature material in close proximity. We give possible interpretations of this phenomenon as either a sheath of X-ray emitting material surrounding the Hα ejection or as an admixture of hot and cool magnetic flux tubes, each ejecting the material which they contain.