On temporal variation of the 0.511 MeV line in a solar flare

The time profile of the 0.511 MeV line flux for the flare of 16 December 19 88 is studied. Differing from previous conclusions, we found that a fixed s pectral index cannot fit the observations. It is shown that a good fit can be realized if the spectral index varies with time. But the same good fit c an be also obtained if the conversion factor of positrons to the 0.511 MeV photons changes with time. At present it is very difficult to say which sit uation is more practical.