Time delays in large and small loop thermal models for hard X-ray bursts

The time histories of the emission at 10, 30, and 100 keV averaged over the loop from small and large loop thermal models of hard X-ray emission are studied. The small (15000 km) loop cases show a characteristic delay in the peak of the 100 keV emission relative to the 30 keV emission of about 1.5 s which should be detectable. The large (47 000 km) loop cases show no delay, but in the case of a continuous energy input, the 30 keV emission has a peak at 9.5 s whereas the 100 keV emission rises monotonically. Again, this difference should be detectable to the extent that it is not washed out by a dominant beam or escaping tail component which is not considered in this paper. A large loop case where only classical and saturated heat conduction are allowed is considered. The 30 keV emission has a peak at 7.5 s whereas the 100 keV emission rises monotonically. The peak temperature reached is 8 × 10⁷ K and the probability of finding examples in the data uncontaminated by a dominant beam or escaping tail component should be considerably higher than in the cases with higher rates of energy input.