GCN Circular 1155
P.A. Price, D.W. Fox, J. S. Bloom & S.R. Kulkarni, California Institute of Technology, Pasadena report on behalf of a larger collaboration: "We have registered the J-band images of the field of GRB 011121 (GCN 1147, GCN 1148) obtained at Las Campanas Observatory by K. Koviak (see GCN 1153) against nearly one hundred stars whose stellar positions are listed in the USNO-A2.0 catalog. Individual RMS errors for this registration, are 0.24" and 0.20" respectively in RA and Dec. From this analysis we derive the following position for the NIR transient reported in GCN 1149: (J2000) RA 11:34:29.669, Dec -76:01:41.56. The nominal uncertainty in each coordinate is about 0.30 arcsec; this includes the 0.17 arcsec uncertainty between USNO-A2.0 and the ICRF (the latter defines the radio frame). It is clear that the transient reported in GCN 1153 is the NIR counterpart of the optical transient first reported by Wyrzykowski et al. (GCN 1150). We therefore conclude that the coordinates reported in GCN 1150 (and based on the GSC) are in error by 2.6 arsec (east-west axis). While this difference is more than three times the nominal error for positions derived from the GSC (Deutsch 1999) we believe that our astrometry based on USNO-A2.0 is secure."