TITLE: GCN CIRCULAR NUMBER: 11042 SUBJECT: GRB 100802A: NOT optical observation DATE: 10/08/03 10:09:43 GMT FROM: Dong Xu at DARK,NBI D. Xu (Weizmann Inst.), D. Malesani (DARK/NBI), P. Jakobsson (Univ. of Iceland), P. A. Wilson, R. Nilsson (NOT), report on behalf of a larger collaboration: We have imaged the field of GRB100802A (Troja et al., GCN #11031) with the Nordic Optical Telescope equipped with ALFOSC. Observations started at 02:49 UT, 3rd August (~21.06 hrs after the BAT trigger) and four 900 s frames in the R band were obtained. We detect an optical source localised at RA(J2000) = 00:09:52.38 Dec(J2000) = +47:45:18.8 with an error radius of 0.4". This position is 0.96" +/- 0.85" S-W of the UVOT position (Siegel & Troja, GCN #11032). We therefore identify this source as the afterglow of GRB100802A. A finding chart is visible at the following URL: http://www.astro.ku.dk/~malesani/GRB/100802A/GRB100802A_NOT.jpg. Based on the USNO-B1 catalog (R1 magnitudes), we find R=22.9+/-0.3 at a mean epoch of 21.6 hr after the BAT trigger. Compared with the P60 detection (Cenko, GCN #11040), our measurement confirms a clear fading, and implies a rather shallow decay of the afterglow light curve with alpha = 0.34 +/- 0.08 assuming an unbroken power-law decay F(t) propto t^-alpha. This might suggest some contribution from an underlying host galaxy.