Revealing the nature of the QPO and its harmonic in GX 339-4 using frequency-resolved spectroscopy
Revealing the nature of the QPO and its harmonic in GX 339-4 using frequency-resolved spectroscopy
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DOI：
10.1093/mnras/stw464
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发表时间：
2015-06
影响因子：
4.8
通讯作者：
M. Axelsson;C. Done
中科院分区：
文献类型：
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作者：
M. Axelsson;C. Done
我们利用频率分辨光谱技术研究了GX 339-4中显著的低频准周期振荡（QPO）及其谐波的能谱。我们跟踪这些光谱的演变作为源，使从一个明亮的低/硬过渡到硬中间状态。在硬/中间态，QPO和时间平均光谱是相似的，谐波是未检测到的或类似的QPO。相比之下，在较软的状态下，谐波比QPO谱和时间平均谱明显更软，并且QPO谱比时间平均谱明显更硬。显然，这些非常不同的光谱形状的分量的存在意味着时间平均光谱是复杂的，这也可以从以下事实看出：较软的光谱不能很好地由圆盘、康普顿化及其反射来描述。我们使用的频率分辨光谱，以更好地约束模型组件，并发现数据是一致的时间平均光谱，其中有一个额外的低温，光学厚康普顿化组件。谐波可以单独用这个附加分量来描述，而QPO谱与硬康普顿化及其反射谱相似。无论是QPO，也不谐波显示的迹象，即使它是强的时间平均频谱的光盘组件。这增加了越来越多的证据，在黑洞双星的非均匀康普顿化。虽然中间态的谐波和QPO光谱之间的相似性可以从单个区域中康普顿散射的角度依赖性产生，但这不能解释在软态中看到的巨大差异。相反，我们建议，软康普顿区域主要位于光盘上方，而硬康普顿是从较热的内部流。因此，我们的研究结果指出，在功率谱中产生谐波功能的多种可能的机制。在给定的观察中，主导机制可能是倾角和内盘半径的函数。
We use frequency-resolved spectroscopy to examine the energy spectra of the prominent low-frequency quasi-periodic oscillation (QPO) and its harmonic in GX 339-4. We track the evolution of these spectra as the source makes a transition from a bright low/hard to hard intermediate state. In the hard/intermediate states, the QPO and time-averaged spectra are similar and the harmonic is either undetected or similar to the QPO. By contrast, in the softer states, the harmonic is dramatically softer than the QPO spectrum and the time-averaged spectrum, and the QPO spectrum is dramatically harder than the time-averaged spectrum. Clearly, the existence of these very different spectral shaped components mean that the time-averaged spectra are complex, as also seen by the fact that the softer spectra cannot be well described by a disc, Comptonization and its reflection. We use the frequency-resolved spectra to better constrain the model components, and find that the data are consistent with a time-averaged spectrum which has an additional low-temperature, optically thick Comptonization component. The harmonic can be described by this additional component alone, while the QPO spectrum is similar to that of the hard Comptonization and its reflection. Neither QPO nor harmonic shows signs of the disc component even when it is strong in the time-averaged spectrum. This adds to the growing evidence for inhomogeneous Comptonization in black hole binaries. While the similarity between the harmonic and QPO spectra in the intermediate state can be produced from the angular dependence of Compton scattering in a single region, this cannot explain the dramatic differences seen in the soft state. Instead, we propose that the soft Compton region is located predominantly above the disc while the hard Compton is from the hotter inner flow. Our results therefore point to multiple possible mechanisms for producing harmonic features in the power spectrum. The dominant mechanism in a given observation is likely a function of both inclination angle and inner disc radius.