TITLE: GCN CIRCULAR NUMBER: 21145 SUBJECT: GRB 170524A: TSHAO and CrAO optical observations DATE: 17/05/25 20:28:02 GMT FROM: Alexei Pozanenko at IKI, Moscow E. Mazaeva (IKI), S. Nazarov (CrAO), A. Kusakin (Fesenkov Astrophysical Institute), A. Volnova (IKI), A. Pozanenko (IKI) report on behalf of larger GRB follow-up collaboration: We observed the field of the Swift GRB 170524A (trigger=754322) (Gropp et al., GCN 21135) with Zeiss-1000 (East) of Tien Shan Astronomical Observatory and AZT-8 telescope of CrAO. We obtained several images in R filter. The TSHAO observations started on 2017-05-24 (UT) 20:31:45 under not optimal weather conditions. Observations in CrAO started on 2017-05-25 (UT) 00:18:50. Within enhanced XRT position (Evans et al. GCN 21136) we did not detect any optical source in the first epoch. In the second epoch (CrAO observation) we detected an object which is on the edge of the enhanced XRT position. The object has coordinates (J2000) 21:17:56.30 +48:36:27.9 with uncertainties of about 1 arcsec in each coordinate and brightness of R=20.10 +/- 0.15 at 0.1992 days after the Swift trigger. For now we can not say anything about the object variability. However the object is barely visible in DSS2 (Red). The preliminary results of field photometry are as follows Date UT start t-T0 Filter Exp. UL(3 sigma) (mid, days) (s) 2017-05-24 20:31:45 0.06857 R 46*120 20.3 2017-05-25 00:18:50 0.19920 R 10*180 21.5 Photometry is based on nearby USNO-B1.0 stars USNO-B1.0_id R2 1386-0392957 16.69 1385-0394718 17.29 1386-0392907 17.11 The finding chart of the object can be found at http://grb.rssi.ru/GRB170524A/GRB170524A_CrAO_170524.png