CGRO observations of gamma-ray flares associated with ACE particle events
D.J. Morris, L.M. Kistler, E. Moebius, M.A. Popecki and J. Ryan
Space Science Center, University of New Hampshire, Durham, NH, USA
B. Klecker
Max-Planck-Institut fur extraterrestrische Physik, Garching, Germany
During the period in which the ACE spacecraft has been operating, the Compton
Gamma-Ray Observatory (CGRO) has continued monitoring hard X-ray and gamma-ray
emission from the sun, among other sources. The high-energy photons provide
information about both the electrons, through bremsstrahlung continuum emission,
and nuclei, through nuclear line emission, while they are still near the site
of their acceleration. The question of the common origin of solar photons and
particles is addressed through comparison of the photon observations with
associated ACE events. Among many hard-X ray flares associated with particle
events seen by ACE, three have particularly interesting spectra from the CGRO
Burst and Transient Source Experiment (BATSE). Two, on 4 Nov 1997 and 22 Nov
1998, had very hard continuum spectra up to MeV energies, but no indication of
nuclear lines. The third event, on 28 Nov 1998, shows substantial 511-keV line
emission, above the ever-present instrumental background; this could be due to
the production either of short-lived positron emitters, such as 11C,
or pions.