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 } _ { -0.05 } consistent with the range of \Gamma 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 \times 10 ^ { -13 } \hbox { erg~ { } cm$ { } ^ { -2 } $~ { } s$ { } ^ { -1 } $ } and a 0.4–8.0 keV lensed luminosity of 1.0 \times 10 ^ { 46 } \hbox { erg~ { } s$ { } ^ { -1 } $ } .
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 ^ { +0.5 } _ { -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 K \alpha line in only the spectrum of image A .
The rest frame energy , width , and equivalent width of this feature are E _ { line } = 5.7 _ { -0.3 } ^ { +0.2 } keV , \sigma _ { line } = 0.87 _ { -0.15 } ^ { +0.30 } keV , and EW = 1200 ^ { +300 } _ { -200 } eV , respectively .