期刊
ASTROPHYSICAL JOURNAL LETTERS
卷 753, 期 1, 页码 -出版社
IOP PUBLISHING LTD
DOI: 10.1088/2041-8205/753/1/L23
关键词
acceleration of particles; solar wind; Sun: particle emission
资金
- NASA [NAS5-03131, NNX10AQ31G]
- WCU [R31-10016]
- Korean Ministry of Education, Science and Technology
- NSF [AGS0940985]
- Directorate For Geosciences
- Div Atmospheric & Geospace Sciences [0940985] Funding Source: National Science Foundation
- Directorate For Geosciences
- Div Atmospheric & Geospace Sciences [0962726] Funding Source: National Science Foundation
- NASA [NNX10AQ31G, 126570] Funding Source: Federal RePORTER
We present a statistical survey of similar to 2-20 keV superhalo electrons in the solar wind measured by the SupraThermal Electron instrument on board the two STEREO spacecraft during quiet-time periods from 2007 March through 2009 March at solar minimum. The observed superhalo electrons have a nearly isotropic angular distribution and a power-law spectrum, f proportional to v(-gamma), with. ranging from gamma to 8.7, with nearly half between 6.5 and 7.5, and an average index of 6.69 +/- 0.90. The observed power-law spectrum varies significantly on a spatial scale of greater than or similar to 0.1 AU and a temporal scale of greater than or similar to several days. The integrated density of quiet-time superhalo electrons at 2-20 keV ranges from similar to 10(-8) cm(-3) to 10(-6) cm(-3), about 10(-9)-10(-6) of the solar wind density, and, as well as the power-law spectrum, shows no correlation with solar wind proton density, velocity, or temperature. The density of superhalo electrons appears to show a solar-cycle variation at solar minimum, while the power-law spectral index gamma has no solar-cycle variation. These quiet-time superhalo electrons are present even in the absence of any solar activity-e. g., active regions, flares or microflares, type III radio bursts, etc.-suggesting that they may be accelerated by processes such as resonant wave-particle interactions in the interplanetary medium, or possibly by nonthermal processes related to the acceleration of the solar wind such as nanoflares, or by acceleration at the CIR forward shocks.
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