J. L. Tonry; A. Dressler; J. P. Blakeslee; E. A. Ajhar και άλλοι. (2001). «The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances». Astrophysical Journal546 (2): 681–693. doi:10.1086/318301. Bibcode: 2001ApJ...546..681T.
L. C. Ho; A. V. Filippenko; W. L. W. Sargent (1997). «A Search for "Dwarf" Seyfert Nuclei. III. Spectroscopic Parameters and Properties of the Host Galaxies». Astrophysical Journal Supplement112 (2): 315–390. doi:10.1086/313041. Bibcode: 1997ApJS..112..315H.
A. F. Tennant; R. F. Mushotzky (1983). «The absence of rapid X-ray variability in active galaxies». Astrophysical Journal264: 92–104. doi:10.1086/160576. Bibcode: 1983ApJ...264...92T.
A. Ptak; T. Yaqoob; P. J. Serlemitsos; R. Mushotzky και άλλοι. (1994). «Rapid X-ray spectral variability in NGC 3227». Astrophysical Journal436: L31–L34. doi:10.1086/187626. Bibcode: 1994ApJ...436L..31P.
J. L. Tonry; A. Dressler; J. P. Blakeslee; E. A. Ajhar και άλλοι. (2001). «The SBF Survey of Galaxy Distances. IV. SBF Magnitudes, Colors, and Distances». Astrophysical Journal546 (2): 681–693. doi:10.1086/318301. Bibcode: 2001ApJ...546..681T.
L. C. Ho; A. V. Filippenko; W. L. W. Sargent (1997). «A Search for "Dwarf" Seyfert Nuclei. III. Spectroscopic Parameters and Properties of the Host Galaxies». Astrophysical Journal Supplement112 (2): 315–390. doi:10.1086/313041. Bibcode: 1997ApJS..112..315H.
A. F. Tennant; R. F. Mushotzky (1983). «The absence of rapid X-ray variability in active galaxies». Astrophysical Journal264: 92–104. doi:10.1086/160576. Bibcode: 1983ApJ...264...92T.
A. Ptak; T. Yaqoob; P. J. Serlemitsos; R. Mushotzky και άλλοι. (1994). «Rapid X-ray spectral variability in NGC 3227». Astrophysical Journal436: L31–L34. doi:10.1086/187626. Bibcode: 1994ApJ...436L..31P.