^Lundmark, K. Suspected New Stars Recorded in Old Chronicles and Among Recent Meridian Observations. Publications of the Astronomical Society of the Pacific. 1921, 33: 225. Bibcode:1921PASP...33..225L. doi:10.1086/123101.
^ 2.02.1Mayall, N.U. The Crab Nebula, a Probable Supernova. Astronomical Society of the Pacific Leaflets. 1939, 3: 145. Bibcode:1939ASPL....3..145M.