TITLE: GCN GRB OBSERVATION REPORT NUMBER: 4202 SUBJECT: GRB 051105a: MDM Observations DATE: 05/11/06 05:04:24 GMT FROM: Jules Halpern at Columbia U. J. P. Halpern, S. Tonnesen, S. Tuttle (Columbia U.), and N. Mirabal (U. Michigan) report on behalf of the MDM Observatory GRB follow-up team: "We observed the location of Swift GRB 051105a (Mineo et al., GCN #4188) using the MDM 2.4m telescope, with a 4.6x4.6 arcminute field centered on the improved BAT position (Barbier et al., GCN #4194). A total of 2 and 30 minutes exposure were obtained in the Gunn g and r filters, respectively. The mean epoch of the observations was Nov. 6 02:39 UT, or 20 hours after the burst. The following R magnitudes of objects mentioned in previous GCN circulars were measured, referenced to the comparison star magnitude R=17.0 used by Piranomonte et al. (GCN #4201): --------------------------------------------------------------------------- R.A. (J2000) Decl. (J2000) R(mag) ID GCN ref --------------------------------------------------------------------------- 17 41 10.00 +34 55 45.2 21.15 +/- 0.03 inside XRT S1 4195,4196,4201 17 41 10.28 +34 55 41.1 22.50 +/- 0.12 outside XRT S1 4196,4201 17 41 03.28 +34 59 03.6 23.24 +/- 0.22 radio 4199 --------------------------------------------------------------------------- Positional uncertainties are 0.3" in the USNO B1.0 reference system, except for the faint object that is, nevertheless, consistent in position with the radio source of Frail & Cameron (GCN #4199). The bright object in the error circle of XRT S1 is clearly blue in g-r, as well as on the Palomar Sky Survey plates, and might therefore be an X-ray detected QSO. Our magnitude of it is consistent with that measured by Piranomonte et al. (GCN #4201) 7 hours earlier."