Université de Strasbourg, CNRS, Observatoire Astronomique de Strasbourg, UMR 7550, Strasbourg, France.
Max Planck Institute for Astrophysics, Garching, Germany.
Nature. 2023 Jul;619(7968):41-45. doi: 10.1038/s41586-023-06064-x. Epub 2023 Jun 21.
The centre of the Milky Way Galaxy hosts a black hole with a solar mass of about 4 million (Sagittarius A (Sgr A)) that is very quiescent at present with a luminosity many orders of magnitude below those of active galactic nuclei. Reflection of X-rays from Sgr A by dense gas in the Galactic Centre region offers a means to study its past flaring activity on timescales of hundreds and thousands of years. The shape of the X-ray continuum and the strong fluorescent iron line observed from giant molecular clouds in the vicinity of Sgr A are consistent with the reflection scenario. If this interpretation is correct, the reflected continuum emission should be polarized. Here we report observations of polarized X-ray emission in the direction of the molecular clouds in the Galactic Centre using the Imaging X-ray Polarimetry Explorer. We measure a polarization degree of 31% ± 11%, and a polarization angle of -48° ± 11°. The polarization angle is consistent with Sgr A being the primary source of the emission, and the polarization degree implies that some 200 years ago, the X-ray luminosity of Sgr A was briefly comparable to that of a Seyfert galaxy.
银河系中心有一个太阳质量约为 400 万倍的黑洞（人马座 A*（Sgr A*）），目前非常平静，其光度比活动星系核低几个数量级。银河系中心区域密集气体对 Sgr A的 X 射线反射为研究其过去几千年的耀发活动提供了一种手段。从 Sgr A附近的大质量分子云中观测到的 X 射线连续谱和强荧光铁线的形状与反射情景一致。如果这种解释是正确的，那么反射连续谱发射应该是极化的。在这里，我们使用成像 X 射线偏振探测器（Imaging X-ray Polarimetry Explorer）报告了在银河系中心分子云方向上的极化 X 射线发射的观测结果。我们测量到的偏振度为 31%±11%，偏振角为-48°±11°。偏振角与 Sgr A是发射的主要源一致，偏振度表明大约 200 年前，Sgr A的 X 射线光度曾短暂地与塞弗特星系相当。
