TITLE: GCN CIRCULAR NUMBER: 20591 SUBJECT: GRB 170202A: T100 observations DATE: 17/02/03 10:29:03 GMT FROM: Eda Sonbas at NASA/GSFC E. Sonbas (Adiyaman Univ.), T. Guver, M. De Pasquale (Istanbul Univ.), E. Gogus (Sabanci Univ.), O. Erece, M. Kocak, H. Kirbiyik, H. Esenoglu (TUG) report on behalf of a larger collaboration We observed the field of Swift GRB 170202A (Racusin et al., GCN#20575) with the 1.0 meter T100 telescope (Bakirlitepe, TUBITAK National Observatory, Turkey), starting February, 2, 20:12:45.56 UT (~ 1.7 hours after the trigger). Observations were carried out in the R filter. The afterglow is detected in the R band images with an exposure time of 300 s. Using USNO-B1 stars USNO-B1 0950-0184329 (R.A.=152.492, Dec=+5.028) and USNO-B1 0949-0181744 (R.A.=152.514, Dec=+4.993) in the field, the magnitude of the OT was estimated as follows; t-t0 (hr) exp.(s) filt mag err (+/-) 1.75 300 R 18.98 0.07 Analysis of further observations with the same filter is ongoing. We thank to TUBITAK National Observatory for a partial support in using T100 telescope with project number 10CT100-95 and technical support.