Feldman, William C. and Lawrence, David J. and Goldsten, John O. and Gold, Robert E. and Baker, Daniel N. and Haggerty, Dennis K. and Ho, George C. and Krucker, Säm and Lin, Robert P. and Mewaldt, Richard A. and Murphy, Ronald J. and Nittler, Larry R. and Rhodes, Edgar A. and Slavin, James A. and Solomon, Sean C. and Starr, Richard D. and Vilas, Faith and Vourlidas, Angelos (2010) Evidence for extended acceleration of solar flare ions from 1–8 MeV solar neutrons detected with the MESSENGER Neutron Spectrometer. Journal of Geophysical Research A, 115 . Art. No. A01102. ISSN 0148-0227 http://resolver.caltech.edu/CaltechAUTHORS:20100216-090807790
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Neutrons produced on the Sun during the M2 flare on 31 December 2007 were observed at 0.48 AU by the MESSENGER Neutron Spectrometer. These observations are the first detection of solar neutrons inside 1 AU. This flare contained multiple acceleration episodes as seen in type III radio bursts. After these bursts ended, both the energetic particle and neutron fluxes decayed smoothly to background with an e-folding decay time of 2.84 h, spanning a 9 h time period. This time is considerably longer than the mean lifetime of a neutron, which indicates that either the observed neutrons were generated in the spacecraft by solar energetic particle protons, or they originated on the Sun. If most of the neutrons came from the Sun, as our simulations of neutron production on the spacecraft show, they must have been continuously produced. A likely explanation of their long duration is that energetic ions were accelerated over an extended time period onto closed magnetic arcades above the corona and then slowly pitch angle–scattered by coronal turbulence into their chromospheric loss cones. Because of their relatively low energy loss in the Neutron Spectrometer (0.5–7.5 MeV), most of these neutrons beta decay to energetic protons and electrons close to the Sun, thereby forming an extended seed population available for further acceleration by subsequent shocks driven by coronal mass ejections in interplanetary space.
|Additional Information:||© 2010 American Geophysical Union. Received 5 June 2009; revised 9 September 2009; accepted 18 September 2009; published 23 January 2010. The MESSENGER mission is supported by the NASA Discovery Program. We are grateful to the entire MESSENGER team for making the mission a success. Special thanks go to Brian Anderson for his essential contributions to the Magnetometer instrument. This work was carried out under the auspices of the Planetary Science Institute, Johns Hopkins University Applied Physics Laboratory, and all of the institutions of the coauthored team. The work at Caltech was supported by NASA under grant NNX-08AI11G, andW. C. Feldman also thanks the Los Alamos National Laboratory for providing an office and access to their library during parts of this project.|
|Group:||Space Radiation Laboratory|
|Subject Keywords:||solar neutrons|
|Official Citation:||Feldman, W. C., et al. (2010), Evidence for extended acceleration of solar flare ions from 1–8 MeV solar neutrons detected with the MESSENGER Neutron Spectrometer, J. Geophys. Res., 115, A01102, doi:10.1029/2009JA014535.|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Tony Diaz|
|Deposited On:||17 Feb 2010 00:23|
|Last Modified:||04 Mar 2013 22:43|
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