Columbia University Astronomy and 

MDM Observatory GRB Team

GRB 990123
Observed with the 2.4 m telescope at MDM Observatory

R-band raw image R-band smoothed image

GCN Circular #242: GRB 990123 Optical Observations
I. A. Yadigaroglu, J. P. Halpern, R. Uglesich, & J. Kemp (Columbia U.)
report on behalf of the MDM Observatory GRB follow-up team:

"We imaged the field of GRB 990123 in the R band on Jan. 30.52 using the
MDM Observatory 2.4m telescope.  A total of 40 minutes exposure was
obtained in seeing of 0.9-1.0 arcsec.  The optical transient is clearly
detected at magnitude R = 23.01 +/- 0.24 (referenced to the comparison
star of GCN #207, assuming r - R = 0.4).  An independent calibration
using a Landolt standard also gives a consistent magnitude.  The OT
position, measured with respect to the USNO-A2.0 reference system,
is (J2000) RA 15:25:30.34, Dec +44:45:59.2 with an uncertainty of
0.3 arcseconds in radius.  This position is consistent with that of the
original detection of the OT (GCN #206).  The temporal power-law decay
slope connecting our observation to the first Palomar detection is
alpha_r = -1.15 +/- 0.07, consistent with all previous observations,
which gave alpha_r = -1.13 +/- 0.03 (GCN #240).

Thus, the OT appears to be unresolved, at a fixed position, and following
a power-law decay in time.

However, we see no object corresponding to a suggested intervening
galaxy that was estimated to lie 1.8 arcsec north of the OT (GCN #206).
In fact, there is no other object on our image within 5 arcsec of the
OT, to a limiting magnitude of approximately R = 24.  Since this galaxy
was only reported to be seen marginally on one POSS II red plate with
R = 21.5 +/- 0.5 (GCN #213), we conclude that it probably does not
exist.  If true, this eliminates one of the arguments for hypothesizing
that the burst is lensed."

This message may be cited.

Ion Yadigaroglu
Jules Halpern
Robert Uglesich
Jonathan Kemp
Columbia University Astronomy and Astrophysics and MDM Observatory

MDM Observatory