Solar Neutron Events of 2003 October-November

During the period when the Sun was intensely active in 2003 October-November, two remarkable solar neutron events were observed by the ground-based neutron monitors. On 2003 October 28, in association with an X17.2 large flare, solar neutrons were detected with high statistical significance (6.4 σ) by the neutron monitor at Tsumeb, Namibia. On 2003 November 4, in association with an X28-class flare, relativistic solar neutrons were observed by the neutron monitors at Haleakala in Hawaii and Mexico City and by the solar neutron telescope at Mauna Kea in Hawaii simultaneously. Clear excesses were observed at the same time by these detectors, with the significance calculated as 7.5 σ for Haleakala and 5.2 σ for Mexico City. The detector on board the INTEGRAL satellite observed a high flux of hard X-rays and γ-rays at the same time in these events. By using the time profiles of the γ-ray lines, we can explain the time profile of the neutron monitor. It appears that neutrons were produced at the same time as the γ-ray emission.