Gamma-Ray and High-Energy-Neutron Measurements on CORONAS-F during the Solar Flare of28October2003

The solar flare of 28 October 2003 (X17.2/4B) was recorded by the SONG instrument onboard the CORONAS-F satellite. Adescription of the SONG instrument, its in-orbit operation and the principal data reduction methods used to derive the flare gamma-ray properties are presented. Appreciable gamma-ray emission was observed in the 0.2-300MeV energy range. Several time intervals were identified which showed major changes in the intensity and spectral shape of the flare gamma-ray emission. The primary bremsstrahlung proves to be extended to 90MeV and dominates during 11:02:11-11:03:50 UT time interval, i.e. at the beginning of the flare impulsive phase. Afterwards, the SONG response was consistent with detection of the pion-decay gamma emission. Asharp increase in the pion-decay-generated gamma-ray emission was observed at 11:03:51 plus or minus 2s UT, implying a substantial change in the spectrum of accelerated ions, which testified the appearance of protons with energies of >300MeV on the Sun. This emission lasted at least 8-9min until the end of our measurements. The ion acceleration to high energies was also proved by the detection of neutrons with energies >500MeV. It was found that the most efficient acceleration of high-energy protons coincides in time with the highest rate of the magnetic-flux change rate. The maximum gamma-ray flux at 100MeV was 1.110 super(-2)photonscm super(-2)s super(-1) MeV super(-1), exceeding all the fluxes that have ever been recorded.