GCN Circular 10521
V. Rumyantsev (CrAO), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration: We observed the field of the Swift GRB 100316A (Baumgartner et al. GCN 10484) with Shajn telescope of CrAO starting (UT) March 16 19:15 under descending weather conditions and mean seeing of 2 arcsec. No object is detected in enhanced XRT error circle (Evans, GCN 10490). The upper limit of point like object in a stacked image based on USNO-B1.0 star 1618-0120609 (J2000) RA= 16:48:06.44 Dec= +71:50:15.2 (assuming R2=15.25) is following: T0+ Filter, Exposure, mag. (mid, d) (s) 0.7061 R 8x60 > 21.6 The non-detection is strongly support the object of R~20.5 reported in GCN 10487 (Gorosabel et al) is the optical afterglow of GRB100316A.