0220033

A basic idea of the unified model is that all Seyfert 2 galaxies harbour a bright Seyfert 1 nucleus which is hidden from our view by an optically and geometrically thick obscuring torus. The difference between type 1 and 2 objects should only be due to the viewing angle that determines whetehr the galaxy nucleus is seen directly or through a torus of molecular gas and dust grains. X-ray (2-10 keV) observations have provided strong support for the obscuring torus hypothesis by measuring large (up to 1E22-23 cm-2) column densities of neutral material in Seyfert 2 galaxies. For the case of cosmic abundances the Thompson cross-section is equal to the photoelectric cross-section at around 10 keV so that this energy may be assumed to be the boundary between photoelectric and Compton dominated regimes. This energy turns out to be the practical limit of X-ray satellites which can observe Compton thick sources in the photoelectric regime where the emission is dominated by reflection/scattering components. These borderline objects turn out to be particularly bright in hard (>10 keV) X-rays as at these energies the transparency effect is coupled to a strong reflection component and are therefore interesting targets for INTEGRAL observations. INTEGRAL allows us to observe these objects well into the Compton dominated regime where the nuclear emission component can be studied and clearly separated from the reflection and absorption effects that dominate the X-ray emissions. The three Compton-obscured source targets have been selected for studies with INTEGRAL for the basic pragmatic reasons that they are nearby and very bright (~ 1E-10 ergs cm-2 s-1) in hard X-ray emission above 10 keV. Good spectral measurements will be possible with INTEGRAL enabling us to study the nuclear emission spectrum and the nature of the absorbing material for the interesting case of these borderline Compton thick objects as well as asse [truncated! Please see actual data for full text]

该统一模型的核心思路为：所有赛弗特2型星系（Seyfert 2 galaxy）均蕴含一个明亮的赛弗特1型星系核，但其被一个光学及几何厚度均较大的遮蔽环面所遮挡，无法被我们直接观测。1型与2型赛弗特天体的差异仅由观测视角决定：视角不同将决定我们是直接观测星系核，还是通过由分子气体与尘埃颗粒构成的环面进行观测。X射线（2-10 keV）观测通过测量赛弗特2型星系中中性物质的大柱密度（最高可达1×10²²~10²³ cm⁻²），为遮蔽环面假说提供了强有力的支撑。对于宇宙丰度情形，汤姆逊截面（Thompson cross-section）与光电截面（photoelectric cross-section）在约10 keV处相等，因此该能量可被视为光电主导区域与康普顿主导区域的分界能量。该能量恰好是当前X射线卫星的实用观测极限：此类卫星可在光电主导区域观测康普顿厚源，而该区域的辐射以反射/散射成分为主。这类边界源在硬X射线（>10 keV）波段表现得格外明亮——在此能量区间，透明度效应与强反射成分共同作用，因此它们是国际伽玛射线天体物理实验室（INTEGRAL）观测的极具价值的目标。INTEGRAL可让我们对康普顿主导区域开展深入观测，该区域的核辐射成分可被清晰地分离出来，与主导X射线辐射的反射与吸收效应区分开。本次研究选取了3个受康普顿遮蔽的源作为INTEGRAL观测目标，其核心实用依据为：这些源距离地球较近，且在10 keV以上的硬X射线辐射中亮度极高（约1×10⁻¹⁰ ergs·cm⁻²·s⁻¹）。借助INTEGRAL可获得优质的光谱测量数据，从而得以研究这类边界康普顿厚源的核辐射光谱与吸积物质的性质[文本已截断，请查阅原始完整数据以获取全部内容]