Caught in the Act: Chandra Observations of Microlensing of the Radio-loud Quasar MG J0414+0534
Caught in the Act: Chandra Observations of Microlensing of the Radio-loud Quasar MG J0414+0534
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陷入困境：钱德拉对无线电响亮类星体 MG J0414 0534 微透镜的观测
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发表时间：
2002
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影响因子：
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通讯作者：
N. Morgan
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作者：
G. Chartas;E. Agol;M. Eracleous;G. Garmire;M. Bautz;N. Morgan
我们目前的监测结果的遥远（z = 2.64），引力透镜类星体MG J 0414 +0534与钱德拉X射线天文台。在最亮图像A的光谱中，在99%置信水平下检测到6.49 ± 0.09 keV（静止帧）处的Fe Kα线，等效宽度约为190 eV，与冷介质的荧光一致。在我们监测计划的最后两次观察中，我们检测到图像B光谱中窄Fe Kα线的等效宽度增加了五倍，但在较亮的图像A中没有增加，而图像C太暗了，无法分辨该线。图像B的连续发射分量在最后两次观测中没有跟随铁谱线的突然增强。我们建议，只有在图像B中的铁线强度从~190到900 eV的突然增加可以用焦散交叉来解释，由于微透镜选择性地增强了吸积盘的线发射区域的条带。图像B的光谱中连续辐射的不增强表明连续辐射区域比铁线辐射区域更靠近吸积盘的中心，并且放大焦散没有达到足够接近前一个区域以放大它。焦散交叉事件的模型预测放大光变曲线的不连续性，并提供了~ Fe Kα发射区的外半径为5 × 10 ~（-4）pc。在图像B的光谱中没有检测到任何相对论性或多普勒频移的铁谱线，这意味着最近两次观测的放大焦散位于大于约100个引力半径的半径处。对四重透镜类星体MG J 0414 +0534的每次观测都提供了四个不同时期的类星体视图，这些时期由透镜图像之间的时间延迟间隔开。我们通过将每张图像的通量归一化为该图像在所有观测中的平均通量来产生类星体X射线通量的光变曲线。我们发现归一化的光变曲线从1的显着偏差，特别是对于最暗的图像C。解释图像C的通量变化的一个合理机制是微透镜事件。最后，对MG J 0414 +0534的光谱分析表明，它有超过银河值的显著吸收。对于透镜类星体红移处的吸收，我们发现一个NH ~ 5 × 1022 cm-2的内禀柱密度，与光学波段观察到的红化一致。
We present results from monitoring of the distant (z = 2.64), gravitationally lensed quasar MG J0414+0534 with the Chandra X-Ray Observatory. An Fe Kα line at 6.49 ± 0.09 keV (rest frame) with an equivalent width of ~190 eV, consistent with fluorescence from a cold medium, is detected at the 99% confidence level in the spectrum of the brightest image A. During the last two observations of our monitoring program, we detected a fivefold increase of the equivalent width of a narrow Fe Kα line in the spectrum of image B but not in the brighter image A, whereas image C is too faint to resolve the line. The continuum emission component of image B did not follow the sudden enhancement of the iron line in the last two observations. We propose that the sudden increase in the iron-line strength from ~190 to 900 eV only in image B can be explained with a caustic crossing due to microlensing that selectively enhances a strip of the line emission region of the accretion disk. The nonenhancement of the continuum emission in the spectrum of image B suggests that the continuum emission region is concentrated closer to the center of the accretion disk than the iron-line emission region and that the magnification caustic has not reached close enough to the former region to amplify it. A model of a caustic crossing event predicts discontinuities in the light curve of the magnification and provides an upper limit of ~5 × 10-4 pc on the outer radius of the Fe Kα emission region. The nondetection of any relativistic or Doppler shifts of the iron line in the spectrum of image B implies that the magnification caustic for the last two observations was located at a radius greater than ~100 gravitational radii. Each observation of the quadruply lensed quasar MG J0414+0534 provides a view of the quasar at four different epochs spaced by the time delays between the lensed images. We produced a light curve of the quasar X-ray flux by normalizing the flux of each image to the mean flux of that image over all observations. We find significant deviations of the normalized light curve from unity especially for the faintest image C. A plausible mechanism to explain the flux variability of image C is a microlensing event. Finally, spectral analysis of MG J0414+0534 indicates the presence of significant absorption in excess of the Galactic value. For absorption at the redshift of the lensed quasar, we find an intrinsic column density of NH ~ 5 × 1022 cm-2, consistent with the reddening observed in the optical band.