TITLE: GCN CIRCULAR NUMBER: 23962 SUBJECT: GRB 190311A: NOT optical counterpart DATE: 19/03/12 21:47:13 GMT FROM: Jonatan Selsing at DARK/NBI J. Selsing (DAWN/NBI), Z.P. Zhu (NAOC), D. Xu (NAOC), D. Malesani  (DAWN/NBI, DARK/NBI), D. Nespral (IAC), D. Gandolfi (Univ. Turin), and  J. Telting (NOT), report on behalf of a larger collaboration: We have observed the optical afterglow of GRB 190311A (Troja et al.,  GCN 23946; Goad et al., GCN 23950; Veres & Meegan, GCN 23953) with the  2.5-m Nordic Optical Telescope (NOT). We have obtained an r+z imaging  sequence using the ALFOSC instrument, with 4x300 and 5x300 s exposure in  the r and z band, respectively. Imaging observations began 9.4 hr after  the BAT trigger. In the images we clearly detect the optical counterpart of GRB 190311A,  as previously reported (Zhu et al., GCN 23948; Pozanenko et al., GCN  23947; Gorbovskoy et al., GCN 23949; Belkin et al., GCN 23951; Mao et  al., GCN 23954; Peris & Fernandez-Soto, GCN 23959). We calibrate the photometric zeropoints against the Pan-STARRS catalog and derive the following magnitudes for the optical counterpart: r = 21.88 +- 0.03 AB mag z = 21.26 +- 0.04 AB mag The source is centred at the position: RA (J2000.0) = 14:08:15.726 DEC (J2000.0) = +53:30:02.74 with the astrometric solution calibrated against the 2MASS catalog.