GRB 990712: R-band CCD image, CTIO 0.9m
1999 August 16, 50 minutes exposure
|GCN Circular #402: GRB 990712 Optical Observation|
J. Kemp & J. Halpern (Columbia U.) report on behalf of the MDM Observatory GRB follow-up team's southern extension: "We observed the optical counterpart of GRB 990712 in the R band on Aug. 16.32 UT using the CTIO 0.9m. A total of 50 minutes exposure was obtained in seeing of 2."0. An object of R = 21.73 +/- 0.06 is detected at position (J2000) RA 22:31:53.00, Dec -73:24:28.7 in the USNO-A2.0 reference system, with uncertainty of 0".4. This is consistent with the OT position as measured by Bakos et al. (GCN #387) and Hjorth et al. (GCN #389). The magnitude is referenced to the secondary standards used by Bakos et al. (IAUC #7225), although our own calibration using Landolt standards (cf. GCN #395) is about 0.08 mag brighter. The object appears only marginally extended in these images of relatively poor seeing. Revising the decay model of Hjorth et al. (GCN #389), we find a slope of -1.05 and a constant contribution of R = 21.78 from the host galaxy. An extrapolation of the OT decay with a slope of -1.05 would have predicted R = 25.5 at this time. In this model, the observed light is now dominated by the host galaxy. HST observations are needed to follow the afterglow decay, and to locate it within its relatively low-redshift host galaxy (z=0.43, Galama et al. GCN #388). An HST observation is scheduled for Aug. 29. If the OT decay continues with a slope of -1.05, it will be found at R = 25.9 on Aug. 29. The CTIO image and revised decay curve are posted at http://www.astro.bio2.edu/grb/ This message may be cited."
|Columbia University Astronomy and Astrophysics and MDM Observatory|