Medling, A. M., Ammons, S. M., Max, C. E., Davies, R. I., Engel, H., & Canalizo, G. (2011). Mass of the southern black hole in NGC 6240 from laser guide star adaptive optics. The Astrophysical Journal, 743(1): 32, pp. 1-10. doi:10.1088/0004-637X/743/1/32.