STEREO Observations of Energetic Neutral Atoms during the 5 December 2006 Solar Event

Details STEREO Observations of Energetic Neutral Atoms during the 5 December 2006 Solar Event STEREO Observations of Energetic Neutral Atoms during the 5 December 2006 Solar Event

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsh11a..02m&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #SH11A-02

Physics

7513 Coronal Mass Ejections (2101), 7514 Energetic Particles (2114), 7519 Flares, 7837 Neutral Particles (2151), 7845 Particle Acceleration

Scientific paper

We report the discovery of energetic neutral atoms (ENAs) emitted during the X9 solar event of 5 December 2006. Beginning ~1 hour following the onset of this flare, located at ~E70, the Low Energy Telescopes (LETs) on both STEREO A and B spacecraft observed a sudden increase in the count rate of 1.6 to 15 MeV protons, with a typical velocity-dispersive profile. At this time both STEREO spacecraft were located near Earth and were oriented such that both LETs viewed the Sun directly, and, in combination, covered 360° in heliographic longitude. Particle arrival directions are measured to 7° in longitude. It was found that more than 60% of the 1.6 - 15 MeV protons observed within 3 hours of the flare onset (before the bulk of the solar energetic particles began arriving at Earth) arrived from a longitude within 10° of the Sun. When the arrival time of each of ~100 individual proton events is corrected back to the Sun using the measured kinetic energy, the resulting emission profile is very similar to the GOES soft x-ray profile, and continues for ~1 hour or more. At higher energies, the 13 to 100 MeV proton count rates in the STEREO High Energy Telescopes (HETs), which do not view the Sun directly, showed only a small increase. While the time profile observed by the LETs is consistent with the possibility of neutron-decay protons, both the arrival directions and energy spectrum argue strongly that the majority of the proton events were due to energetic neutral hydrogen atoms that arrived from the solar direction and were stripped in passing through the windows of the LET telescopes. To our knowledge, this is the first reported observation of ENA emission from a solar flare/coronal mass ejection. This talk will present the observations and discuss possible origins for the production of ENAs in a large solar event.

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