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Detection of high-energy solar neutrons and protons by ground level detectors on April 15, 2001 |
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| Authors: | Y Muraki Y Matsubara S Masuda S Sakakibara T Sako K Watanabe R Bütikofer EO Flückiger A Chilingarian G Hovsepyan F Kakimoto T Terasawa Y Tsunesada H Tokuno A Velarde P Evenson J Poirier T Sakai |
| Institution: | aSolar-Terrestrial Environment Laboratory, Nagoya University, Furo-cho, Chikusa, Nagoya 464-8601, Japan bPhysikalisches Institut, University of Bern, Bern, CH-3012 Bern, Switzerland cYerevan Physics Institute, Yerevan, AM-375036, Armenia dDepartment of Physics, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan eInstituto Investigaciones Fisicas, Universidad Mayor de San Andres, La Paz, Casilla 8635, Bolivia fBartol Research Institute, University of Delaware, Newark, DE 19716, USA gDepartment of Physics, University of Notre Dame, Notre Dame, IN 46556, USA hCollege of Industrial Technologies, Nihon University, Narashino 275-0005, Japan iSpace Sciences Laboratory, University of California, Berkeley, 7 Gauss Way 7450, Berkeley, CA 94720, USA |
| Abstract: | In association with the large solar flare of April 15, 2001, the Chacaltaya neutron monitor observed a 3.6σ enhancement of the counting rate between 13:51 and 14:15 UT. Since the enhancement was observed beginning 11 min before the GLE, solar neutrons must be involved in this enhancement. The integral energy spectrum of solar neutrons can be expressed by a simple power law in energy with the index γ=-3.0±1.0. On the other hand, an integral energy spectrum of solar protons has been obtained in the energy range between 650 MeV and 12 GeV. The spectrum can also be expressed by a power law with the power index γ=-2.75±0.15. The flux of solar protons observed at Chacaltaya (at  12 GeV) was already one order less than the flux of the galactic cosmic rays. It may be the first simultaneous observation of the energy spectra of both high-energy protons and neutrons. Comparing the Yohkoh soft X-ray telescope images with the observed particle time profiles, an interesting picture of the particle acceleration mechanism has been deduced. |
| Keywords: | Solar neutron and proton Neutron telescope Neutron monitor Easter event Solar cosmic rays |
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