Ionospheric effects of solar flares. II. The flare spectrum below 10 Å deduced from satellite observations

Abstract

The spectral distribution and its time development for X-rays below 10 Å during solar flares are deduced from the measurements of integrated flux levels by satellite-borne detectors in the 0.5–3 Å and 1–8 Å bands. An exponential distribution and a power law distribution are considered, as well as a composite spectrum with two different electron temperatures in the bands 0.5-3 Å and 3–8 Å. Analysis of X-ray response for selected flare events gave spectral temperatures of about (1-3)×10⁷°K for λ < 3 Å and about (8–10)×10⁶°K for λ > 3 Å. The power law representation gave a distribution of λ^m, with m having values between 1–2 at the peak of the flare. Gradual changes in spectral temperatures are shown for some events.