0957 + 561 A, B: twin quasistellar objects or gravitational lens?

@article{Walsh197909575,
  title={0957 + 561 A, B: twin quasistellar objects or gravitational lens?},
  author={D. Walsh and Robert F Carswell and Ray J. Weymann},
  journal={Nature},
  year={1979},
  volume={279},
  pages={381-384}
}
0957 + 561 A, B are two QSOs of mag 17 with 5.7 arc s separation at redshift 1.405. Their spectra leave little doubt that they are associated. Difficulties arise in describing them as two distinct objects and the possibility that they are two images of the same object formed by a gravitational lens is discussed. 
Direct imaging of the twin QSOs 0957 + 561 A and B: the gravitational lens interpretation
Recent observations have indicated that the twin quasistellar objects 0957+561 A and B might be images produced by a gravitational lens. New direct observations are presented, including the probable
Flux variations of QSO 0957 + 561 A, B and image splitting by stars near the light path
If the double QSO 0957 + 561 A, B is the result of gravitational lens actions by a massive galaxy, stars in its outer parts and close to the light paths may cause significant flux changes in one
Radio studies of the double QSO, 0957 + 561A, B
The radio source 0957 + 561 has at least four components. Two coincide with the optical QSOs, which is in accordance with the hypothesis that the QSOs are images of a single object due to a
Gravitational Lenses and VLBI Structures
The double quasar 00957 + 561 A,B along with bright radio arches and VLBI structures is modelled using a gravitational lens consisting of an elliptical galaxy and a cluster. The effective time-delay
Optical Photometry of Quasar 0957+561A, B
Observations of the gravitational lens system 0957+561A, B in the R band are presented in this Letter. The observations, taken with the 82 cm IAC-80 telescope, at Teide Observatory, Spain, were made
The triple QSO PG1115 + 08: another probable gravitational lens
Recently, Walsh, Carswell and Weymann1 reported the discovery of two objects (0957+56A,B) with identical spectra and separated by 6 arc min. They suggested that a gravitational lens was responsible.
The VLA Light Curves of 0957+561; 1979-1994
The gravitational lens 0957+561 has been monitored by our group for 16 years, using the VLA at 5 GHz. Since our last report in 1992, both images have returned to their quiescent flux levels, and the
VLBI Observations of the double QSO, 0957 + 561 A, B
Walsh et al.1 originally suggested that the double QSO 0957 + 561 A, B might be images of the same object formed by a gravitational lens because of their remarkably similar optical spectra.
VLBI structures of the images of the double QSO 0957 + 561
Very long baseline interferometry (VLBI) observations of the double QSO 0957 + 561 have revealed radio fine structure in the two ‘image’ components A and B. The structures are similar, both of the
The Double Quasar 0957+561: Examination of the Gravitational Lens Hypothesis Using the Very Large Array
A full 12-hour synthesis at 6-centimeter wavelength with the Very Large Array confirms the major features previously reported for the double quasar 0957+561. In addition, the existence of radio jets
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