TITLE: GCN CIRCULAR NUMBER: 23601 SUBJECT: GRB 181201A: photometric signature of the SN DATE: 19/01/03 20:40:28 GMT FROM: Alexei Pozanenko at IKI, Moscow S. Belkin (IKI), E. Mazaeva (IKI), A. Pozanenko (IKI), P. Minaev (IKI), A. Volnova (IKI), N. Tominaga (Konan University), S. Blinnikov (ITEP), D. Chestnov (KIAM), E. Klunko (ISTP), I. Reva (FAPI), V. Rumyantsev (CrAO), D. Buckley (SAAO), R. Ya. Inasaridze (AbAO) report on behalf of GRB-FuN collaboration: We observed the optical afterglow (e.g. Podesta et al., GCN 23470; Kong GCN 23475) of the INTEGRAL GRB 181201A (Mereghetti et al., GCN 23469) with Gemini-N telescope on Dec. 22 in g'r'i'z and Dec. 24 in r'i'-filters. Preliminary photometry of the OT is following. Date t-T0 Filter Exp. OT Err. (mid, days) (s) 2018-12-22 21.10536 i' 3*180 21.50 0.03 2018-12-22 21.09536 r' 3*180 21.82 0.03 2018-12-24 23.09418 i' 3*180 21.32 0.06 2018-12-24 23.10793 r' 3*240 21.83 0.03 The photometry is based on the SDSS-DR12 star SDSS-DR12_id i' r' J211710.81-123706.3 16.257 16.517 Based on our previous observations and photometry reported in GCNs 23475, 23478, 23486, 23504 we plot a light curve of the afterglow in r'-filter (http://grb.rssi.ru/GRB181201A/GRB181201A_optics_fit.png). Power law approximation of the LC before 2018-12-22 has an index of 1.19 +/-0.01. The photometry obtained on 2018-12-22 and 2018-12-24 has a significance of about 2 and 6.5 sigma above the power law approximation. Additionally the i'-magnitude increases between the two epochs. We can suggest that we observed the Supernova signature associated with GRB 181201A.