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Observation and Interpretation of Energetic Neutral Hydrogen Atoms from the December 5, 2006 Solar EventWe report the first observations of energetic neutral atoms (ENAs) from a solar flare/coronal mass ejection event. The observations were made during the December 5, 2006 X9 solar flare, located at E79, by the Low Energy Telescopes (LETs) on the STEREO A and B spacecraft. Within 1-2 hours of the flare onset, both LETs observed a sudden burst of 1.6 to 15 MeV protons arriving hours before the onset of the main solar energetic particle (SEP) event at Earth. More than 70% of these particles arrived from a longitude within +-10 degrees of the Sun. The derived emission profile at the Sun lasted for more than an hour and had a profile remarkably similar to the GOES soft X-ray profile. The observed arrival directions and energy spectrum argue strongly that the particle events <5 MeV were due to energetic neutral hydrogen atoms that were stripped of their electrons upon entering the LET sensor. To our knowledge, this is the first reported observation of ENA emission from a solar flare/coronal mass ejection. We discuss possible origins for the production of ENAs in solar events, including charge-transfer reactions involving both flare and shock-accelerated protons. Assuming isotropic emission, we find that ~2 x 10E28 ENAs escaped from the Sun in the upper hemisphere. Based on the 2.2 MeV gamma-ray emission observed by RHESSI in this event, and using measured and theoretical cross sections, we estimate that ~3 x 10E31 ENAs with 1.8 - 5 MeV could be produced by protons accelerated in the flare. CME-driven shock acceleration is also a possible ENA source, but unfortunately there were no CME observations available from this event. Taking into account ENA losses, we conclude that the observed ENAs were most likely produced in the high corona at heliocentric distances 1.6 solar radii.
Document ID
Document Type
Conference Paper
Mewaldt, R. A. (California Inst. of Tech. Pasadena, CA, United States)
Leske, R. A. (California Inst. of Tech. Pasadena, CA, United States)
Stone, E. C. (California Inst. of Tech. Pasadena, CA, United States)
Barghouty, A. F. (NASA Marshall Space Flight Center Huntsville, AL, United States)
Shih, A. Y. (California Univ. Berkeley, CA, United States)
von Rosenvinge, T. T. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Labrador, A. W. (California Inst. of Tech. Pasadena, CA, United States)
Cohen, C. M. S. (California Inst. of Tech. Pasadena, CA, United States)
Cummings, A. C. (California Inst. of Tech. Pasadena, CA, United States)
Cummings, A. C. (Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Date Acquired
August 24, 2013
Publication Date
July 7, 2009
Subject Category
Report/Patent Number
Meeting Information
31st International Cosmic Ray Conference (ICRC)(Lodz)
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