TITLE: GCN CIRCULAR NUMBER: 10820 SUBJECT: GRB 100513A: CrAO optical observations DATE: 10/06/01 20:26:58 GMT FROM: Alexei Pozanenko at IKI, Moscow V. Rumyantsev (CrAO), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration: We observed the field of the Swift GRB 100513A (Baumgartner et al. GCN 10746) with Shajn telescope of CrAO in R-filter between May, 13 (UT) 18:43 -- 20:38, and in I-filter on May, 14 (UT) 19:47 -- 20:57 and on May, 16 (UT) 18:28 -- 20:20. The afterglow (Morgan et al. GCN 10747) is clearly detected on May, 13,14 and not detected on May 16. The afterglow coordinates are (J2000) RA = 11 18 26.85 Dec = +03 37 40.3 with uncertainty of 0.3 arcsec. The photometry of stacked images based on USNO-B1.0 star 0936-0206849 (RA(J2000) = 11:18:37.91 Dec(J2000)= +03:37:43.1) assuming R=18.59 I=17.88 is following: T0+ Filter, Exposure, mag. Upper Limit (mid, d) (s) 0.7313 R 104x60 23.03 +/- 0.12 24.3 1.7573 I 64x60 21.59 +/- 0.07 23.6 3.7202 I 91x60 >23.5 23.5 The combined images can be found at http://grb.rssi.ru/GRB100513A/ Using above photometry combined with reported earlier (R = 21.39 at 2.46 hours, GCN 10750; J-filter photometry in GCNs 10747, 10749; i'=21.3 at 9.89 hours, GCN 10757) one can suggest taht power law index of decay light curve in J, R and I- bandpass is compatible and equal to ~0.7 in the first day. The break of power law can be assumed in I-band between first and third days with power law decay index > 2.