Gandhi, P., Fabian, A., Suebsuwong, T., Malzac, J., Miniutti, G., & Wilman, R. (2007). Constraints on light bending and reflection from the hard X-ray background. Monthly Notices of the Royal Astronomical Society, 382, 1005-1018. https://doi.org/10.1111/j.1365-2966.2007.12462.x