Observed with the 2.4 m telescope at MDM Observatory
|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.
|Columbia University Astronomy and Astrophysics and MDM Observatory|