Observed with the 2.4 m telescope at MDM Observatory
|GCN Circular #257: GRB 990123 Optical Observations|
J. P. Halpern, Y. Yadigaroglu, K. M. Leighly, & 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 Feb. 14.50 UT using the MDM Observatory 2.4m telescope. A total of 100 minutes exposure was obtained in seeing of 0.9 arcsec. An object is detected at a position consistent with that of the GRB host galaxy as measured in the HST STIS image (Bloom et al. astro-ph/9902182). Its magnitude is R = 23.77 +/- 0.10 (referenced to the comparison star of GCN #207), equivalent to Gunn r = 24.10. Since this is consistent with the estimate of r = 24.0-24.2 for the host galaxy alone by Bloom et al., we conclude that the optical transient is no longer making a detectable contribution to the total light in ground-based images. We also report a revised magnitude on Feb. 3.54 of R = 23.55 +/- 0.24, after more detailed analysis of those data. Further HST observations are therefore needed to follow the unusual afterglow decay of this most energetic GRB. The latest MDM image will be posted at http://cba.phys.columbia.edu/grb/ This message may be cited.
|Columbia University Astronomy and Astrophysics and MDM Observatory|