SIMBAD references

We observed B1600+434 and B1608+656 with Chandra ACIS, detecting both quasar images in B1600+434 and three of four images in B1608+656. We did not detect significant X-ray emission from nearby galaxy groups or clusters associated with each lens galaxy. The upper limits on the X-ray luminosity of any cluster within 4' of each lens and at each lens redshift are ∼2x10⁴² and ∼6x10⁴² ergs/s for B1600+434 and B1608+656, respectively. The radio-loud source quasars have power-law photon indices of Γ=1.9±0.2 and Γ=1.4±0.3 and X-ray luminosities of 1.4^+0.2_–0.1x10⁴⁵ and 2.9^+0.7_–0.4x10⁴⁴ ergs/s for B1600+434 and B1608+656, respectively, before correcting for the magnification. We detected a differential absorption column density of ΔN_H∼3x10²¹/cm2 between the two images of B1600+434, roughly consistent with expectations from differential extinction estimates of ΔE(B-V)=0.1 mag and a standard dust-to-gas ratio. The differential absorption observed in gravitational lenses may serve as an important probe to study the gas content in high-redshift galaxies, since it can separate the absorbing column originating from the lens galaxy and those intrinsic to quasars. We also detected 157 serendipitous X-ray sources in the two Chandra fields and identified the brighter optical counterparts using the Sloan Digital Sky Survey and Palomar Digital Sky Survey.