Accepted by ApJ Preprint typeset using L ATEX style emulateapj v. 11/12/01 CHANDRA OBSERVATIONS OF QSO 2237+0305
Accepted by ApJ Preprint typeset using L ATEX style emulateapj v. 11/12/01 CHANDRA OBSERVATIONS OF QSO 2237+0305
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发表时间：
2000
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通讯作者：
G. Chartas;E. Agol;M. Bautz;G. Garmire
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作者：
G. Chartas;E. Agol;M. Bautz;G. Garmire
本文介绍了2000年9月6日和2001年12月8日在钱德拉X射线天文台上用先进的电荷耦合器件成像光谱仪(ACIS)对引力透镜系统QSO2237+0305(爱因斯坦十字)分别进行了30.3k和9.5k的观测。成像分析解析了爱因斯坦十字的四张X射线图像。可能检测到第五幅图像；然而，该图像的信噪比较差，再加上附近较亮的图像产生的污染，使得该检测不太确定。我们调查了附加图像的可能来源。符合爱因斯坦十字星座所有图像的组合光谱，假设与银河系之间存在简单的幂定律，并介入透镜星系的吸收，得到的光子指数为1.9−0.05，与大样本射电安静类星体的Γ范围一致。对于第一次对爱因斯坦十字的钱德拉观测，这个光谱模型产生了0.4-8.0keV的X射线通量为4.6×10erg厘米的S和0.4-8.0keV的透镜光度为1.0×10erg的S。在两次观测之间，X射线通量下降了20%，Kolmogorov-Smirnov检验表明，在第一次观测中，图像A在97%的置信度水平上是可变的。此外，在第一次钱德拉观测中，在图像A领先的图像A和B之间可能检测到2.7−0.9小时的时间延迟。图像的X射线通量比与受微透镜影响的光学通量比一致，表明X射线发射也是微透镜的。我们测量的柱状密度与从消光测量推断的柱状密度的比较表明，透镜星系中的尘气比高于我们银河系的平均值。最后，我们报道了在99.99%的置信度水平下，仅在图像A的光谱中就探测到了Fe-K-α谱线红移能量附近的一个宽发射特征。该特征的剩余标架能量、宽度和等效宽度分别为Eline=5.7+0.2−0.3kev，σline=0.87+0.30−0.15keV，Ew=12 0 0+30 0−2 0 0 eV。
We present the observations of the gravitationally lensed system QSO 2237+0305 (Einstein Cross) performed with the Advanced CCD Imaging Spectrometer (ACIS) onboard the Chandra X-ray Observatory on 2000 September 6, and on 2001 December 8 for 30.3 ks and 9.5 ks, respectively. Imaging analysis resolves the four X-ray images of the Einstein Cross. A possible fifth image is detected; however, the poor signal-to-noise ratio of this image combined with contamination produced by a nearby brighter image make this detection less certain. We investigate possible origins of the additional image. Fits to the combined spectrum of all images of the Einstein Cross assuming a simple power law with Galactic and intervening absorption at the lensing galaxy yields a photon index of 1.90 −0.05 consistent with the range of Γ measured for large samples of radio-quiet quasars. For the first Chandra observation of the Einstein Cross this spectral model yields a 0.4–8.0 keV X-ray flux of 4.6× 10erg cm s and a 0.4–8.0 keV lensed luminosity of 1.0 × 10erg s. The source exhibits variability both over long and short time scales. The X-ray flux has dropped by 20% between the two observations, and the Kolmogorov-Smirnov test showed that image A is variable at the 97% confidence level within the first observation. Furthermore, a possible time-delay of 2.7 −0.9 hours between images A and B with image A leading is detected in the first Chandra observation. The X-ray flux ratios of the images are consistent with the optical flux ratios which are affected by microlensing suggesting that the X-ray emission is also microlensed. A comparison between our measured column densities and those inferred from extinction measurements suggests a higher dust-to-gas ratio in the lensing galaxy than the average value of our Galaxy. Finally, we report the detection at the 99.99% confidence level of a broad emission feature near the redshifted energy of the Fe Kα line in only the spectrum of image A. The rest frame energy, width, and equivalent width of this feature are Eline = 5.7 +0.2 −0.3 keV, σline = 0.87 +0.30 −0.15 keV, and EW = 1200 +300 −200 eV, respectively.