来自鲸鱼座UV的微弱偏振耀斑的154 MHz探测
154 MHz detection of faint, polarized flares from UV Ceti
摘要：
我们已经发现了四个耀斑的紫外鲸鱼座在154兆赫使用默奇森宽场阵列。耀斑的通量密度在10- 65毫焦耳--比文献中大多数耀斑在这些频率下的通量密度弱100倍--并且只在偏振中被探测到。圆极化部分在3 $σ$置信度下被限制为$>27$ %，并且两个耀斑表现出极性反转。我们认为，这些耀斑周期性地发生在一个时间尺度上一致的紫外鲸鱼座的旋转周期。在观测到的最亮耀斑期间，我们还检测到偏振分数为$>18$ %的显著线性偏振。平均6分钟，10 MHz频率箱的数据，我们发现，这些耀斑的通量密度不改变超过30 MHz带宽的默奇森宽场阵列，但我们不能排除更精细的时间-频率结构。使用测量的流量密度的耀斑，我们估计亮度温度之间的$(10^{13}-10^{14})\,$ K，指示的相干发射机制。亮度温度和偏振特性表明电子回旋脉塞机制。我们还计算了耀斑速率给出我们的四个观测到的耀斑，并比较它们的耀斑速率为一组M矮星与已知的100- 200 MHz的耀斑。我们的测量是第一次在100-200 MHz的强度为$<100$ mJy的耀斑。
英文摘要：
We have detected four flares from UV Ceti at 154 MHz using the Murchison Widefield Array. The flares have flux densities between 10--65 mJy --- a factor of 100 fainter than most flares in the literature at these frequencies --- and are only detected in polarization. The circular polarized fractions are limited to $>27$% at 3$σ$ confidence and two of the flares exhibit polarity reversal. We suggest that these flares occur periodically on a time scale consistent with the rotational period of UV Ceti. During the brightest observed flare, we also detect significant linear polarization with polarization fraction $>18$%. Averaging the data in 6-minute, 10 MHz frequency bins we find that the flux density of these flares does not vary over the 30 MHz bandwidth of the Murchison Widefield Array, however we cannot rule out finer time-frequency structure. Using the measured flux densities for the flares, we estimate brightness temperatures between $(10^{13}-10^{14})\,$K, indicative of a coherent emission mechanism. The brightness temperature and polarization characteristics point to the electron cyclotron maser mechanism. We also calculate the flare rates given our four observed flares and compare them to flare rates for the set of M dwarf stars with known 100--200 MHz flares. Our measurement is the first for flares with intensities $<100$ mJy at 100-200 MHz.
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