TITLE: GCN CIRCULAR NUMBER: 27567 SUBJECT: GRB 200412B: Tautenburg observations DATE: 20/04/13 12:26:07 GMT FROM: Sylvio Klose at TLS Tautenburg B. Stecklum, S. Klose, S. Melnikov, and A. Nicuesa Guelbenzu (all Tautenburg) report: We observed the field of GRB 200412B (Fermi GBM team, GCN 27547; Mailyan et al., GCN 27558; see also Burgess et al., GCN 27548; Longo et al., GCN 27557; Page et al., GCN 27561; Gupta et al., GCN 27563; Zheng et al., GCN 27565) with the Tautenburg 1.34m Schmidt telescope equipped with the TAUKAM 6k x 6k CCD camera and the wide V-band filter (VB). The transmission curve of this filter closely follows the Gaia GBP filter. The fading optical transient detected by MASTER Global Robotic Net (Lipunov et al., GCN 27555, 27556) is clearly detected on our images (for other optical observations see also Kumar et al., GCN 27564; Belkin et al., GCN 27566). Using Gaia DR2 stars in the field, we measure the following preliminary magnitudes (Vega system): Mean time: April 12, 21:29:48 UT, VB = 18.43 +/- 0.01 Mean time: April 13, 02:22:38 UT, VB = 19.00 +/- 0.01