Absorption of nuclear γ-rays on the starlight radiation in FR I sources: the case of Centaurus A
Absorption of nuclear γ-rays on the starlight radiation in FR I sources: the case of Centaurus A
复制标题
FR I 源中星光辐射对核 γ 射线的吸收：以半人马座 A 为例
DOI：
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发表时间：
2006
期刊：
影响因子：
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通讯作者：
M. Ostrowski
中科院分区：
文献类型：
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作者：
Ł. Stawarz;Ł. Stawarz;F. Aharonian;S. Wagner;M. Ostrowski
几个BLLac天体被证实是在它们的相对论喷流的核部分产生可变的和强烈的多普勒增强TeV发射的来源。很可能许多Fanaroff-Riley I型(FR I)射电星系也是TeV源，对于这种星系，多普勒隐藏的核γ射线辐射可能太弱，无法直接观测到。然而，我们在这里表明，在低功率FR I射电源的活动核产生的总时间平均TeV辐射中，约有1%不可避免地被星光光子场上的光子-光子湮灭吸收和重新处理，以及随后产生的和快速各向同性的正负电子对的发射。在射电星系半人马座A的例子中，我们发现所讨论的机制可以给出一个以各向同性γ-射线晕的形式的独特的可观测特征。这是由于电子-正电子对通过吸收过程注入到椭圆形主体内部的星际介质中，并通过逆康普顿过程主要向GeV-TeV光子能量范围上散射星光辐射的结果。这样的银河系γ射线晕预计将具有在GLAST 0.1TeV光子能量处达到峰值的特征光谱，并且光子通量足够强，足以被现代切伦科夫望远镜和未来的∼探测到。这些发现应该也适用于附近的其他FR I源。
Several BL Lac objects are confirmed sources of variable and strongly Doppler-boosted TeV emission produced in the nuclear portions of their relativistic jets. It is more than probable that also many of the Fanaroff‐Riley type I (FR I) radio galaxies, believed to be the parent population of BL Lacs, are TeV sources, for which Doppler-hidden nuclear γ -ray radiation may be only too weak to be directly observed. Here we show, however, that about 1 per cent of the total time-averaged TeV radiation produced by the active nuclei of low-power FR I radio sources is inevitably absorbed and re-processed by photon‐photon annihilation on the starlight photon field, and the following emission of the created and quickly isotropized electron‐positron pairs. In the case of the radio galaxy Centaurus A, we found that the discussed mechanism can give a distinctive observable feature in the form of an isotropic γ -ray halo. It results from the electron‐positron pairs injected to the interstellar medium of the inner parts of the elliptical host by the absorption process, and upscattering starlight radiation via the inverse-Compton process mainly to the GeV‐TeV photon energy range. Such a galactic γ -ray halo is expected to possess a characteristic spectrum peaking at ∼0.1 TeV photon energies, and the photon flux strong enough to be detected by modern Cherenkov Telescopes and, in the future, by GLAST. These findings should apply as well to the other nearby FR I sources.