RHESSI microflare statistics.: I.: Flare-finding and frequency distributions
RHESSI microflare statistics.: I.: Flare-finding and frequency distributions
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DOI：
10.1086/529011
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发表时间：
2008-04-20
影响因子：
4.9
通讯作者：
Lin, R. P.
中科院分区：
文献类型：
--
作者：
Christe, S.;Hannah, I. G.;Lin, R. P.
本文首次对RHESSI在2002年3月至2007年3月期间观测到的所有X射线微耀斑进行了深入的统计调查，总共有25,705个事件，比以前的研究大了一个数量级。这些微耀斑是使用一种新的耀斑发现算法发现的，该算法设计用于在RHESSI的全灵敏度可用时搜索6-12 keV的计数率，以找到最小的事件。峰值和总计数率连同峰值和微耀斑质心位置处的计数光谱一起自动获得沿着。我们的微耀斑震级低于GOES C级，平均GOES A级（扣除背景）。它们被发现只发生在活动区域，而不是在“安静”的太阳中，并且类似于大型耀斑。月平均微耀斑速率随太阳活动周期而变化，在活跃期和平静期，微耀斑速率分别为每天90次至5次。大多数耀斑被发现是脉冲的（74%），上升时间短于衰减时间。平均耀斑持续时间与6分钟相似，耀斑发现算法设定的最短时间为1分钟。在3-6、6-12和12-25 keV的能带中的峰值计数率的频率分布可以由幂律分布表示，其负幂律指数分别为1.50 +/- 0.03、1.51 +/- 0.03和1.58 +/- 0.02。我们发现，这些幂律指数作为时间的函数是恒定的。单个事件的X射线光子谱可以近似为幂律谱[dJ/d（hv）类似于（hv）（-gamma）]。使用10-15和15-20 keV之间的光子通量的比率，我们发现4 < gamma < 12，平均值为7.4。基于这些值，计算非热功率。微耀斑的发生频率随能量释放率的变化符合幂律，指数为-1.7 +/-0.1。我们估计，在五年的观测中，与微耀斑相关的加速电子（> 10 keV）沉积在活动区的总能量通量平均低于1026 erg s（-1）。
We present the first in-depth statistical survey of all X-ray microflares observed by RHESSI between 2002 March and 2007 March, a total of 25,705 events, an order of magnitude larger then previous studies. These microflares were found using a new flare-finding algorithm designed to search the 6-12 keV count rate when RHESSI's full sensitivity was available in order to find the smallest events. The peak and total count rate are automatically obtained along with count spectra at the peak and the microflare centroid position. Our microflare magnitudes are below GOES C class, on average GOES A class (background subtracted). They are found to occur only in active regions, not in the "quiet'' Sun, and are similar to large flares. The monthly average microflaring rate is found to vary with the solar cycle and ranges from 90 to 5 flares a day during active and quiet times, respectively. Most flares are found to be impulsive (74%), with rise times shorter than decay times. The mean flare duration is similar to 6 minutes with a 1 minute minimum set by the flare-finding algorithm. The frequency distributions of the peak count rate in the energy bands, 3-6, 6-12, and 12-25 keV, can be represented by power-law distributions with a negative power-law index of 1.50 +/- 0.03, 1.51 +/- 0.03, and 1.58 +/- 0.02, respectively. We find that these power-law indices are constant as a function of time. The X-ray photon spectra for individual events can be approximated with a power-law spectrum [dJ/d(hv) similar to (hv)(-gamma)]. Using the ratio of photon fluxes between 10-15 and 15-20 keV, we find 4 < gamma < 12, with an average of 7.4. Based on these values, the nonthermal power is calculated. The microflare occurrence frequency varies with the rate of energy release consistent with a power law with an exponent of -1.7 +/- 0.1. We estimate the total energy flux deposited in active regions by microflare-associated accelerated electrons (> 10 keV) over the five years of observations to be, on average, below 1026 erg s(-1).