We have successfully detected solar neutrons at ground level in association with the X17.0 solar flare that occurred on 2005 September 7. Observations were made with the solar neutron telescopes and neutron monitors located in Bolivia and Mexico. In this flare, large fluxes of hard X-rays and γ-rays were observed by the GEOTAIL and the INTEGRAL satellites. The INTEGRAL observations include the 4.4 MeV line γ-rays of 12 C. The data suggest that solar neutrons were produced at the same time as these hard electromagnetic radiations. We have however found an apparent discrepancy between the observed and the expected time profiles. This fact suggests a possible extended neutron emission.
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The authors wish to acknowledge the work of our colleagues to manage and maintain the solar neutron telescopes. We also thank the INTEGRAL team, for their support to the mission and guidance in the analysis of the INTEGRAL satellite data. K. Watanabe’s work is supported by the Grant-in-Aid program of the Japan Society for the Promotion of Science Fellows. This work was supported by the Grant-in-Aid for Scientific Research on Priority Area, 11203204, by the Ministry of Education, Culture, Sports, Science, and Technology of Japan, and the Grant-in-Aid for Scientific Research, 16540242 by the Japan Society for the Promotion of Science. This research was partly supported by Nihon University Multidisciplinary Global Research Grant for 2001 and 2002 and DGAPA-UNAM Grant 115303. Finally, we thank Dr. Hugh Hudson for reading this manuscript.