A Thermal Bremsstrahlung Model for the Quiescent X-Ray Emission from Sagittarius A*
A Thermal Bremsstrahlung Model for the Quiescent X-Ray Emission from Sagittarius A*
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DOI：
10.1086/341425
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发表时间：
2002-01
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影响因子：
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通讯作者：
E. Quataert
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作者：
E. Quataert
我考虑热吸积流（邦迪/ADAFs）的热轫致辐射，考虑到观测望远镜的光束（Rbeam）相对于邦迪吸积半径（RA）的有限尺寸。对于Rbeam《RA》，来自黑洞周围热星际介质的软x射线辐射在观测到的辐射中占主导地位，而对于Rbeam《RA》，来自吸积流的硬x射线辐射占主导地位。我将这些模型应用于钱德拉对银河系中心的观测，其中Rbeam≈RA。我认为轫致辐射是钱德拉从人马座A*观测到的大部分“静止”（非耀斑）通量的原因；这种发射在空间上扩展到~RA ~ 1”尺度，并且具有相对较软的光谱。如果中心黑洞的吸积是通过邦迪流或ADAF流进行的，那么在较深的观测中应该存在硬x射线幂律，其通量为软x射线通量的~；如果没有检测到这种硬x射线成分，就会反对ADAF/Bondi模型。我简要地讨论了这些结果在其他低光度活动星系核中的应用。
I consider the thermal bremsstrahlung emission from hot accretion flows (Bondi/ADAFs), taking into account the finite size of the observing telescope's beam (Rbeam) relative to the Bondi accretion radius (RA). For Rbeam ≫ RA, soft X-ray emission from the hot interstellar medium surrounding the black hole dominates the observed emission, while for Rbeam ≪ RA, hard X-ray emission from the accretion flow dominates. I apply these models to Chandra observations of the Galactic center, for which Rbeam ≈ RA. I argue that bremsstrahlung emission accounts for most of the "quiescent" (nonflaring) flux observed by Chandra from Sgr A*; this emission is spatially extended on scales ~RA ~ 1'' and has a relatively soft spectrum, as is observed. If accretion onto the central black hole proceeds via a Bondi or ADAF flow, a hard X-ray power law should be present in deeper observations with a flux ~ of the soft X-ray flux; nondetection of this hard X-ray component would argue against ADAF/Bondi models. I briefly discuss the application of these results to other low-luminosity active galactic nuclei.