Departamento de Fisica Espacial, Instituto de Geofisica, UNAM, Ciudad Universitaria, Delegacion de Coyoacan,Codigo Postal 04510, Mexico, D.F.MEXICO

Gamma ray lines (GRL) during the solar proton event (SPE) of September 29, 1989 originated at solar longitudes of 25-30 degrees from the flare site. Although a CME-driven shock has been proposed as the most plausible mechanism to account for the accelerated particles responsible for the gamma rays, no generally accepted explanation exists at present. On the other hand, in 1991, at least three long duration GRL events (June 4, 11, and 15) were observed at several satellites. Likewise, none of the models put forward to explain these events are convincing. For example, prolonged particle acceleration during the late stage of the flare of June 15, 1991 can not account for accompanying microwave emission which is oscillatory in nature, at least in this particular event. In our opinion, this kind of events should be considered in the framework of a new concept of multiple acceleration in the extended coronal structures. In this paper, we mainly make a comparison of the observational situations characterizing these peculiar events. A plausible mechanism is based on stochastic acceleration by hydromagnetic turbulence in the magnetic field during its post-flare restoration. This sustained (but episodic or multiple) acceleration must involve precipitation of accelerated particles in a loss cone configuration. The interaction of these particles with the chromospheric or subcoronal material would produce an extended long lasting GRL event; escaping particle population forms a long duration SPE in space.