Based on the ion plasma and magnetic field observations of Vega-1 near its closest approach to comet Halley a self-consistent scenario is developed according to which the observed magnetic field topology, the observed burst of ions at energies 200--600 eV, and the observed directional dependence of the flow of these ions leads to the conclusion that these burst-particles are cometary ions which have been accelerated by the process of merging of magnetic field lines of opposite polarity. ¿ American Geophysical Union 1987