Esto es lo que pone Seichii Yoshida
C/2011 C1 ( McNaught )
Brightened very rapidly. Now it is so bright as 10.2 mag and visible visually (Mar. 18, Juan Jose Gonzalez). Diffuse object, with a large coma of 4.5 arcmin. It approaches to the sun down to 0.88 A.U. in mid April, and it keeps 10-11 mag until mid May. It keeps observable until it fades out, although it keeps locating somewhat low in the morning sky. However, because it is a tiny comet, it may fade out very rapidly.
Y esto es lo que pone en
http://www.astrosurf.com/cometas-obs/COMETA FECHA MAG COMA C COLA AP INSTRUMENTO COD
------------ ---------------- ---- ----- - ----- --- ------------ ---
C/2011 C1 2011 03 18.21875 10.2 4.5M 3 100 X 203 GON
¿Podría ser un error?