在中红外波长下解析半人马座A最内层的秒差距
Resolving the innermost parsec of Centaurus A at mid-infrared wavelengths
摘要：
我们报告了在欧洲南方天文台的VLTI望远镜阵列上用中红外干涉仪（WIRE）对半人马座A进行干涉观测的结果。干涉测量在8至13微米的波长范围内进行光谱分辨（R = 30）。它们的空间分辨率在最短波长处达到15 mas。用NACO的自适应光学仪器在近红外波段，用SEST和JCMT在毫米波段进行了补充观测。我们发现半人马座A核心的中红外辐射主要由一个未分辨的点源（<10 mas）所控制。观测的基线方向垂直于射电喷流揭示了一个扩展的组成部分，可以解释为一个几何薄，尘埃盘，其轴与射电喷流对齐。它的直径约为0.6 pc。我们认为，未解决的排放占主导地位的同步辐射源。它的整个频谱的特征是由一个ν^{-0.36}幂律，它在8 × 10 ^{13} Hz处向高频指数截止，在ν< 45 GHz处变得光学厚。基于同步辐射自康普顿（SSC）对γ射线辐射的解释，我们发现磁场强度为26微特斯拉，相对论电子的最大能量为γ c = E c/m e c^2 = 8500。在γ c附近，加速时间尺度为4天，与最快的X射线变化相一致。我们的SSC模型主张体积洛伦兹因子的上限< 2.5，与“错误定向的BL Lac对象”的概念不同。我们估计它的热核光度为1.3x10^{34} W，介于高效吸积活动星系核（如塞弗特星系）和典型FR I射电星系之间。
英文摘要：
We report the results of interferometric observations of Centaurus A with the MID-infrared Interferometer (MIDI) at ESO's VLTI telescope array. The interferometric measurements are spectrally resolved (R = 30) in the wavelength range 8 to 13 micron. Their spatial resolution reaches 15 mas at the shortest wavelengths. Supplementary observations were obtained in the near-infrared with the adaptive optics instrument NACO, and at mm wavelengths with SEST and JCMT. We find that he mid-infrared emission from the core of Centaurus A is dominated by an unresolved point source (<10 mas). Observations with baselines orientated perpendicular to the radio jet reveal an extended component which can be interpreted as a geometrically thin, dusty disk, the axis of which is aligned with the radio jet. Its diameter is about 0.6 pc. We argue, that the unresolved emission is dominated by a synchrotron source. Its overall spectrum is characterized by a ν^{-0.36} power-law which cuts off exponentially towards high frequencies at 8x10^{13} Hz and becomes optically thick at ν< 45 GHz. Based on a Synchrotron Self Compton (SSC) interpretation for the gamma-ray emission, we find a magnetic field strength of 26 microTesla and a maximum energy of relativistic electrons of γ_c = E_c/m_e c^2 = 8500. Near γ_c, the acceleration time scale is 4 days, in good agreement with the fastest X-ray variations. Our SSC model argues for an upper limit for the bulk Lorentz factor < 2.5, at variance with the concept of a "mis-directed BL Lac object". We estimate a thermal core luminosity of 1.3x10^{34} W, intermediate between the values for highly efficiently accreting AGN (e.g. Seyfert galaxies) and those of typical FR I radio galaxies.
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