Soft X-ray Fluxes of Major Flares Far Behind the Limb as Estimated Using STEREO EUV Images
Soft X-ray Fluxes of Major Flares Far Behind the Limb as Estimated Using STEREO EUV Images
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DOI：
10.1007/s11207-013-0307-7
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发表时间：
2013-11-01
期刊：
影响因子：
2.8
通讯作者：
Wuelser, J. -P.
中科院分区：
文献类型：
--
作者：
Nitta, N. V.;Aschwanden, M. J.;Wuelser, J. -P.
自 2010 年以来，随着太阳活动的增加，双 STEREO 航天器上的极紫外成像仪 (EUVI) 观测到了许多来自太阳背面的耀斑。我们的目标是通过找到 EUVI 与 GOES X 射线通量的关系，根据 EUVI 数据估计它们的 X 射线峰值通量。由于 192 处存在 Fe xxiv 线，EUVI 195 通道的响应在 15 MK 附近有一个次宽峰，其通量密切跟踪耀斑上升阶段的 X 射线通量。如果耀斑等离子体是等温的，则 EUVI 通量应与 GOES 通量成正比。事实上，耀斑的多热性质和其他因素使 EUVI 观测中 X 射线通量的估计变得复杂。我们通过将 GOES 通量与太阳动力学天文台 (SDO) 上大气成像组件 (AIA) 的高节奏 EUV 数据进行比较来讨论不确定性。我们得出的结论是，EUVI 195 数据可以提供对强烈耀斑（例如，GOES 尺度中的 M4 以上）的 X 射线峰值通量的估计，不确定性较小。最后，我们展示了远离肢体后方区域的强烈耀斑示例，其中一些在 AIA 图像中显示出爆发特征。
With increasing solar activity since 2010, many flares from the backside of the Sun have been observed by the Extreme Ultraviolet Imager (EUVI) on either of the twin STEREO spacecraft. Our objective is to estimate their X-ray peak fluxes from EUVI data by finding a relation of the EUVI with GOES X-ray fluxes. Because of the presence of the Fe xxiv line at 192 , the response of the EUVI 195 channel has a secondary broad peak around 15 MK, and its fluxes closely trace X-ray fluxes during the rise phase of flares. If the flare plasma is isothermal, the EUVI flux should be directly proportional to the GOES flux. In reality, the multithermal nature of the flare and other factors complicate the estimation of the X-ray fluxes from EUVI observations. We discuss the uncertainties, by comparing GOES fluxes with the high cadence EUV data from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). We conclude that the EUVI 195 data can provide estimates of the X-ray peak fluxes of intense flares (e.g., above M4 in the GOES scale) to small uncertainties. Lastly we show examples of intense flares from regions far behind the limb, some of which show eruptive signatures in AIA images.