TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  1158
SUBJECT: GRB011121: UBRI Observations
DATE:    01/11/24 18:12:47 GMT
FROM:    Michael Brown at NOAO  <mbrown@noao.edu>

M. Brown, R. Schommer, K. Olsen, B. Jannuzi, A. Dey (NOAO), A. Fruchter,
J. Rhoads (STSci) and the NOAO Deep Wide Field Survey Team. 

The GRB011121 optical transient (Wyrzykowski et al. GCN 1150) was imaged
with the CTIO Blanco 4m with Chip2 of Mosaic-II in UBRI between 7:32 and
8:21 23 Nov 2001 UT. 

Two objects within 2" of each other were detected near the position
reported in GCN 1150.  The brighter object (located at 11:34:29.66
-76:01:41.49 J2000) is the optical transient while the fainter object
(located at 11:34:30.15 -76:01:42.26 J2000) could be the host or a
companion galaxy.

Aperture photometry of the optical transient, candidate host/companion and
Star A from GCN 1150 is provided below. The photometry is in the
Johnson-Kron-Cousins system and has been calibrated with Landolt (1992)
standards from regions SA113 and SA95.  The photometry has been corrected
for atmospheric extinction (to airmass 0) but has not been corrected for
galactic extinction where the Schlegel et al. (1998) dust maps predict
dust reddening of E(B-V)=0.496 magnitudes. 

The 1" aperture photometry misses approximately 0.6 magnitudes of the total
flux while 3" aperture photometry of the candidate host/companion galaxy
suffers from contamination from the optical transient.  Star A is ~0.8
magnitudes fainter in R-band than originally reported in the USNO
catalogue (and GCN 1150) and estimates of the fading of the optical
transient should be corrected accordingly.

Object	Band  Seeing   UT       1" radius    2" radius     3" radius
              (arcsec) (23 Nov) ap. mag.     ap. mag       ap mag.

OT      U     1.95     7:59     23.6 +/- 0.2  22.4 +/- 0.1  22.1 +/- 0.1
OT      B     1.45     7:45     23.3 +/- 0.1  22.6 +/- 0.1  22.4 +/- 0.1
OT      R     1.45     7:32     21.8 +/- 0.1  21.1 +/- 0.1  20.8 +/- 0.1
OT      I     1.50     8:16     21.2 +/- 0.1  20.3 +/- 0.1  20.0 +/- 0.1

Host?	U     1.95     7:59     24.6 +/- 0.4  23.4 +/- 0.3  22.6 +/- 0.2
Host?	B     1.45     7:45     24.4 +/- 0.1  23.1 +/- 0.1  22.5 +/- 0.1
Host?	R     1.45     7:32     22.2 +/- 0.1  21.2 +/- 0.1  20.9 +/- 0.1
Host?	I     1.50     8:16     21.3 +/- 0.1  20.3 +/- 0.1  20.0 +/- 0.1

Star A	U     1.95     7:59     21.7 +/- 0.1  20.9 +/- 0.1  20.7 +/- 0.1
Star A	B     1.45     7:45     20.5 +/- 0.1  20.0 +/- 0.1  20.0 +/- 0.1
Star A	R     1.45     7:32     18.7 +/- 0.1  18.3 +/- 0.1  18.2 +/- 0.1
Star A	I     1.50     8:16     17.6 +/- 0.1  17.6 +/- 0.1  17.5 +/- 0.1

The reduced images are available from the 1st author upon request
(mbrown@noao.edu).

This message can be cited.