Abstract We have studied the influence of the density of the annihilation region on the positronium continuum. A relation between the ratio 3γ/2γ and the density is explicitly given, with which one can derive directly from the observed 3γ/2γ the density where the annihilation occurs. A unique solution may be found from the observed width of the 0.511 MeV line. We applied the method to three flares observed by GRS/SMM. It is shown that due to the measuring uncertainties in the 0.511 MeV line width, we cannot distinguish a chromospheric source from a coronal source, though both accurately localized. To improve the measuring accuracy of the 0.511 MeV line and the ratio 3γ/2γ will be an important step for a better understanding of the annihilation process in solar flares.
Keywords Sun: flares --- Sun: X-rays, gamma-rays
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