Open AccessEvidence for extended acceleration of solar flare ions from 1–8 MeV solar neutrons detected with the MESSENGER Neutron Spectrometer
Author(s) -
Feldman William C.,
Lawrence David J.,
Goldsten John O.,
Gold Robert E.,
Baker Daniel N.,
Haggerty Dennis K.,
Ho George C.,
Krucker Säm,
Lin Robert P.,
Mewaldt Richard A.,
Murphy Ronald J.,
Nittler Larry R.,
Rhodes Edgar A.,
Slavin James A.,
Solomon Sean C.,
Starr Richard D.,
Vilas Faith,
Vourlidas Angelos
Publication year - 2010
Publication title -
journal of geophysical research: space physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.67
H-Index - 298
eISSN - 2156-2202
pISSN - 0148-0227
DOI - 10.1029/2009ja014535
Subject(s) - physics , coronal mass ejection , solar flare , neutron , neutron monitor , solar energetic particles , spectrometer , astrophysics , flare , particle acceleration , nuclear physics , solar wind , electron , plasma , optics
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.