太阳耀斑中的准周期脉动：来自费米伽马射线暴监测器的新线索
Quasi-Periodic Pulsations in Solar Flares: new clues from the Fermi Gamma-Ray Burst Monitor
摘要：
在过去的四十年中，已经观察到太阳耀斑显示出从最低的（即射电）到最高的（即伽马射线）的准周期脉动（QPP），这是电磁波谱的一部分。到目前为止，还不清楚是什么机制产生了这样的QPP。在本文中，我们分析了四个明亮的太阳耀斑，表现出引人注目的准周期行为的签名，并与伽马射线暴监测器（\gbm）上的费米卫星观测。由于GBM涵盖了超过30年的能量（8 keV至40 MeV），因此它可以成为了解驱动太阳耀斑的物理过程的关键仪器。我们测试了GBM观测到的太阳耀斑的时间序列的周期性应用经典的周期图分析。然而，与以前的作者相反，我们在创建功率谱密度谱（PSD）之前没有降低原始光曲线的趋势。为了评估频率的意义，我们使用了一种方法，这是通常适用于X射线双星和塞弗特星系。该技术考虑了PSD的基本连续性，对于所有这些源，PSD具有P（f）~ f^{-α}依赖性，并且通常被标记为红噪声。我们检查了这种技术的可靠性，将其应用到一个太阳耀斑，这是观察到的拉马迪高能太阳光谱成像仪（RHESSI），其中包含，除了任何潜在的周期性从太阳，4秒的旋转周期，由于航天器绕其轴旋转。虽然我们没有发现一个内在的太阳准周期性脉动，但我们确实重现了仪器的周期性。此外，采用本文所采用的方法，我们在GBM观测到的四个明亮的太阳耀斑中没有检测到显著的QPP。我们强调，为了这种分析的目的，它是最重要的是适当地占这些天体物理源的PSD中的红噪声分量。
英文摘要：
In the last four decades it has been observed that solar flares show quasi-periodic pulsations (QPPs) from the lowest, i.e. radio, to the highest, i.e. gamma-ray, part of the electromagnetic spectrum. To this day, it is still unclear which mechanism creates such QPPs. In this paper, we analyze four bright solar flares which show compelling signatures of quasi-periodic behavior and were observed with the Gamma-Ray Burst Monitor (\gbm) onboard the Fermi satellite. Because GBM covers over 3 decades in energy (8 keV to 40 MeV) it can be a key instrument to understand the physical processes which drive solar flares. We tested for periodicity in the time series of the solar flares observed by GBM by applying a classical periodogram analysis. However, contrary to previous authors, we did not detrend the raw light curve before creating the power spectral density spectrum (PSD). To assess the significance of the frequencies we made use of a method which is commonly applied for X-ray binaries and Seyfert galaxies. This technique takes into account the underlying continuum of the PSD which for all of these sources has a P(f) ~ f^{-α} dependence and is typically labeled red-noise. We checked the reliability of this technique by applying it to a solar flare which was observed by the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) which contains, besides any potential periodicity from the Sun, a 4 s rotational period due to the rotation of the spacecraft around its axis. While we do not find an intrinsic solar quasi-periodic pulsation we do reproduce the instrumental periodicity. Moreover, with the method adopted here, we do not detect significant QPPs in the four bright solar flares observed by GBM. We stress that for the purpose of such kind of analyses it is of uttermost importance to appropriately account for the red-noise component in the PSD of these astrophysical sources.
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