Kundic, T.; Turner, E.L.; Colley, W.N.; Gott, III; Rhoads, J.E. (1997). «A robust determination of the time delay in 0957+561A,B and a measurement of the global value of Hubble's constant». Astrophys. J.482: 75-82. doi:10.1086/304147. Bibcode: 1997ApJ...482...75K.
Young, P.; Gunn, J.E.; Oke, J.B.; Westphal, J.A.; Kristian, J. (1980). «The double quasar Q0957 + 561 A, B - A gravitational lens image formed by a galaxy at Z = 0.39». Astrophysical Journal241: 507–520. doi:10.1086/158365. Bibcode: 1980ApJ...241..507Y.
Kundic, T.; Turner, E.L.; Colley, W.N.; Gott, III; Rhoads, J.E. (1997). «A robust determination of the time delay in 0957+561A,B and a measurement of the global value of Hubble's constant». Astrophys. J.482: 75-82. doi:10.1086/304147. Bibcode: 1997ApJ...482...75K.
Young, P.; Gunn, J.E.; Oke, J.B.; Westphal, J.A.; Kristian, J. (1980). «The double quasar Q0957 + 561 A, B - A gravitational lens image formed by a galaxy at Z = 0.39». Astrophysical Journal241: 507–520. doi:10.1086/158365. Bibcode: 1980ApJ...241..507Y.