对最里面喷流区的新认识：用LOFT探测极端喷流变化
A new insight into the innermost jet regions: probing extreme jet variability with LOFT
摘要：
Blazar是一种高度可变的源，其时间尺度可以低至几分钟。这就是高能峰值BL Lac（HBL）天体的情况，它在X射线中表现出很强的可变性，这与TeV发射高度相关。这种相关性的程度仍然存在争议，特别是当燃烧活动被跟踪到非常短的时间尺度时。这种相关性可能会挑战同步加速器自康普顿方案，其中一个相对论性电子种群主导了整个辐射输出。我们认为，LOFT大面积探测器（10 m $^2$，LAD），由于其前所未有的定时能力，将使我们能够检测X射线对应物（2-50 keV）的非常快的变化观察到TeV的能量，shedding光的性质的X-TeV连接。我们将讨论PKS 2155-304的测试用例，表明有可能寻找在非常短的时间尺度上发生的任何X射线变化，迄今为止从未探索过。这将对多区方案中任何额外电子群体的大小和位置施加强约束。从这个角度来看，LOFT和CTA天文台计划在同一时间段内运行，将使我们能够深入研究X射线和TeV排放之间的联系。我们还讨论了LOFT在测量HBLs中同步辐射光谱的光谱曲率变化方面的潜力，这将使直接研究高能电子的加速机制成为可能。LOFT定时能力在研究具有通量$\ge 1$ mCrab的平谱射电类星体（FSRQ）中也将是有希望的。高能量发射的位置的限制将通过秒时间尺度上的时间调查和分钟时间尺度上的光谱趋势分析给出。这代表了与CTA的进一步联系，因为最近在一些FSRQs中检测到快速（意外）TeV发射。
英文摘要：
Blazars are highly variable sources over timescales that can be as low as minutes. This is the case of the High Energy Peaked BL Lac (HBL) objects showing strong variability in X-rays, which highly correlate with that of the TeV emission. The degree of this correlation is still debated, particularly when the flaring activity is followed down to very short time scales. This correlation could challenge the synchrotron-self-Compton scenario in which one relativistic electron population dominates the entire radiative output. We argue that the LOFT Large Area Detector (10 m$^2$, LAD), thanks to its unprecedented timing capability, will allow us to detect the X-ray counterpart (2-50 keV) of the very fast variability observed at TeV energies, sheding light on the nature of X-TeV connection. We will discuss the test case of PKS 2155-304, showing as it would be possible to look for any X-ray variability occurring at very short timescales, never explored so far. This will put strong constraints on the size and the location of any additional electron population in the multi-zone scenario. Under this perspective, LOFT and the CTA observatories, planned to operate in the same time frame, will allow us to investigate in depth the connection between X-ray and TeV emissions. We also discuss the potentialities of LOFT in measuring the change in spectral curvature of the synchrotron spectra in HBLs which will make possible to directly study the mechanism of acceleration of highly energetic electrons. LOFT timing capability will be also promising in the study of Flat Spectrum Radio Quasars (FSRQs) with flux $\ge 1$ mCrab. Constraints to the location of the high energy emission will be given by temporal investigation on second timescale and spectral trend analysis on minute timescales. This represents a further link with CTA because of the rapid (unexpected) TeV emission recently detected in some FSRQs.
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