2001ApJ...550L.163C

An observation of the gravitationally lensed system 2016+112 with the Chandra X-Ray Observatory has resolved a mystery regarding the proposed presence of a dark matter object in the lens plane of this system. The Chandra Advanced CCD Imaging Spectrometer observation has clearly detected the lensed images of 2016+112 with positions in good agreement with those reported in the optical and also detects 13 additional X-ray sources within a radius of 3'.5. Previous X-ray observations in the direction of 2016+112 with the ROSAT HRI and ASCA Solid-State Imaging Spectrometer have interpreted the X-ray data as arising from extended emission from a dark cluster. However, the present Chandra observation can account for all the X-ray emission as originating from the lensed images and additional point X-ray sources in the field. Thus, cluster parameters based on previous X-ray observations are unreliable. We place a 3 σ upper limit on the 2-10 keV flux and luminosity of the cluster of 1.6x10^–14 ergs.s^–1.cm^–2 and 1.7x10⁴⁴ ergs.s^–1, respectively. We estimate an upper limit on the mass-to-light ratio within a radius of 800 h^–1₅₀ kpc of M/L_V<190 h₅₀ (M/L_V)_☉. None of the additional point X-ray sources are associated with the galaxy cluster members recently detected in deep optical and IR observations.

The lensed object is quite unusual, with reported narrow emission lines in the optical that suggest it may be a type 2 quasar. Our modeling of the X-ray spectrum of the lensed object implies that the column density of an intrinsic absorber must lie between 3 and 85x10²² cm^–2 (3 σ confidence level). The 2-10 keV luminosity of the lensed object, corrected for the lens magnification effect and using the above range of intrinsic absorption, is from 3x10⁴³ to 1.4x10⁴⁴ ergs.s^–1.