Relativistic neutrons were observed by the neutron monitors at Mt. Chacaltaya and Mexico City and by the solar neutron telescopes at Chacaltaya and Mt. Sierra Negra in association with an X17.0 flare on 2005 September 7. The neutron signal continued for more than 20 min with high statistical significance. Intense emissions of γ-rays were also registered by INTEGRAL, and during the decay phase by RHESSI. We analyzed these data using the solar-flare magnetic-loop transport and interaction model of Hua et al. [Hua, X.-M., Kozlovsky, B., Lingenfelter, R.E. et al. Angular and energy-dependent neutron emission from solar flare magnetic loops, Astrophys. J. Suppl. Ser. 140, 563-579, 2002], and found that the model could successfully fit the data with intermediate values of loop magnetic convergence and pitch-angle scattering parameters. These results indicate that solar neutrons were produced at the same time as the γ-ray line emission and that ions were continuously accelerated at the emission site.
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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.