From Radio to X-Ray: Flares on the dMe Flare Star EV Lacertae
From Radio to X-Ray: Flares on the dMe Flare Star EV Lacertae
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DOI：
10.1086/427275
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发表时间：
2004-11
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影响因子：
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通讯作者：
R. Osten;S. Hawley;J. Allred;C. Johns–Krull;Christine Roark
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作者：
R. Osten;S. Hawley;J. Allred;C. Johns–Krull;Christine Roark
我们在2001年9月对M矮耀斑恒星EV Lacertae进行了为期两天的耀斑观测，利用射电连续谱、光学光度和光谱、紫外光谱和x射线光谱观测的组合来表征这颗活跃的、单一的、晚型恒星耀斑的多波长特性。我们在观测到的每个波长区域都发现了耀斑。从这颗恒星上观测到的一个巨大的射电耀斑直径分别为3.6厘米和6厘米，这是迄今为止在dMe耀斑恒星上观测到的最明亮的回旋同步加速器耀斑。射电耀斑可以被解释为包含了一个大的磁性体积，与恒星盘相当，并包含了被困的电子，这些电子在数小时的时间尺度上衰变。在6 cm处通量增强并伴有高负圆极化发射（πc→-100%），表明在EV Lac的电晕中存在相干发射机制。有许多光学白光耀斑，但没有来自色球的发射在线响应的特征出现。两种小的紫外增强在非热展宽量上有所不同。在整个观测过程中有许多x射线耀斑发生，对未分散光子和光栅事件的分析显示没有丰度变化的证据。在一些耀斑期间存在较高的温度；然而，达到的最高温度因耀斑而异。没有证据表明在任何耀斑间隔期间密度会发生变化。在多波长背景下，强烈的射电耀斑的开始与脉冲光学u波段耀斑一致，在1分钟内，但没有x射线响应的特征。当光学耀斑和紫外线耀斑发生时，还有其他的时间间隔，但这些与同期x射线耀斑无关：时间积分光度与瞬时x射线耀斑光度不匹配，正如人们对Neupert效应所期望的那样。我们研究了来自不同波长区域的耀斑产生时间巧合的概率，但发现并非所有的耀斑关联都可以用高耀斑率引起的耀斑叠加来解释。我们警告说，对于像EV Lac这样的高耀斑速率恒星，不要仅仅根据时间相关性来建立多波长耀斑的因果关系。
We present the results of a campaign to observe flares on the M dwarf flare star EV Lacertae over the course of two days in 2001 September, utilizing a combination of radio continuum, optical photometric and spectroscopic, ultraviolet spectroscopic, and X-ray spectroscopic observations to characterize the multiwavelength nature of flares from this active, single, late-type star. We find flares in every wavelength region in which we observed. A large radio flare from the star was observed at both 3.6 and 6 cm and is the most luminous example of a gyrosynchrotron flare yet observed on a dMe flare star. The radio flare can be explained as encompassing a large magnetic volume, comparable to the stellar disk, and involving trapped electrons that decay over timescales of hours. Flux enhancements at 6 cm accompanied by highly negatively circularly polarized emission (πc → -100%) imply that a coherent emission mechanism is operating in the corona of EV Lac. There are numerous optical white-light flares, and yet no signature of emission-line response from the chromosphere appears. Two small ultraviolet enhancements differ in the amount of nonthermal broadening present. There are numerous X-ray flares occurring throughout the observation, and an analysis of undispersed photons and grating events reveals no evidence for abundance variations. Higher temperatures are present during some flares; however, the maximum temperature achieved varies from flare to flare. There is no evidence for density variations during any flare intervals. In the multiwavelength context, the start of the intense radio flare is coincident with an impulsive optical U-band flare, to within 1 minute, and yet there is no signature of an X-ray response. There are other intervals of time when optical flaring and UV flaring is occurring, but these cannot be related to the contemporaneous X-ray flaring: the time-integrated luminosities do not match the instantaneous X-ray flare luminosity, as one would expect for the Neupert effect. We investigate the probability of chance occurrences of flares from disparate wavelength regions producing temporal coincidences but find that not all the flare associations can be explained by a superposition of flares due to a high flaring rate. We caution against making causal associations of multiwavelength flares based solely on temporal correlations for high flaring rate stars such as EV Lac.