QUIET-TIME INTERPLANETARY ∼2-20 keV SUPERHALO ELECTRONS AT SOLAR MINIMUM

被引:94
作者
Wang, Linghua [1 ,2 ]
Lin, Robert P. [2 ,3 ,4 ]
Salem, Chadi [2 ]
Pulupa, Marc [2 ]
Larson, Davin E. [2 ]
Yoon, Peter H. [4 ,5 ]
Luhmann, Janet G. [2 ]
机构
[1] Peking Univ, Dept Geophys, Beijing 100871, Peoples R China
[2] Univ Calif Berkeley, Space Sci Lab, Berkeley, CA 94720 USA
[3] Univ Calif Berkeley, Dept Phys, Berkeley, CA 94720 USA
[4] Kyung Hee Univ, Sch Space Res, Yongin, Gyeonggi, South Korea
[5] Univ Maryland, IPST, College Pk, MD 20742 USA
基金
美国国家科学基金会;
关键词
acceleration of particles; solar wind; Sun: particle emission; RHESSI MICROFLARE STATISTICS; SUPRATHERMAL TAILS; WIND; STEREO; PLASMA; ACCELERATION; SPECTRUM; HALO;
D O I
10.1088/2041-8205/753/1/L23
中图分类号
P1 [天文学];
学科分类号
0704 ;
摘要
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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页数:6
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