TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1155
SUBJECT: GRB 011121 J-Band Astrometry
DATE:    01/11/23 23:35:28 GMT
FROM:    Shri Kulkarni at Caltech  <srk@astro.caltech.edu>

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."