N. Vilmer and G. Trottet
DASOP/LPSH , Observatoire de Paris, section d, Astrophysique de Meudon, 92195-Meudon Cedex, France
Gamma-ray line emission (GRL) provides a unique information
on ions accelerated during flares. While the bombardment of ambient nuclei
by accelerated protons or alpha particles produce narrow GRL deexcitation
lines, the inverse reactions in which accelerated C or heavier nuclei collide
with ambient H or He produce broad lines. Both types of GRL emission have
been observed in flares, but the analysis of broad lines has been performed
so far on less events. Such a study was done for the behind the limb flare
of 1 June 1991 observed by PHEBUS/GRANAT in which the thick target chromospheric
part of the emission usually predominant in other flares was occulted.
A strong coronal contribution was deduced (Barat et al, 1994) and effects
due to the partial trapping of energetic particles are expected due to
the different energy loss rates encountered by the different ion species
(see Ramaty et al., 1997) and by the bremsstrahlung radiating electrons.
Trap plus precipitation models in which the emission is a combination of
radiation from trapped particles and particles precipitating into denser
regions of the atmosphere have been previously developed for electrons
and protons and applied to a few hard X-ray (HXR) and GRL line flares (e.g.
Hulot et al, 1992). In this contribution, we extend the previous model
to include the heavy ions and investigate the relative timing expected
for narrow and broad GRL lines. We examine the conditions on the particle
injection and radiation allowing to observe such an effect and evaluate
the expected time dependence of the different GRL fluence ratio. The results
of the model are discussed in the context of the 1 June 1991 event. Finally,
we shall briefly discuss the potential application of such a model to the
HESSI observations.
References:
Barat C., Trottet G., Vilmer N., et al., 1994 ApJ(Letters) 425, L109
Hulot E., Vilmer N., Chupp E.L., Dennis, B.R. Kane, S.R. 1992, Astronomy Astrophysics 256, 273
Ramaty R., Mandzhavidze N., Barat C., Trottet G., 1997 ApJ 479, 458