Y.-D. Hu, A. Sota, A. J. Castro-Tirado, T.-R. Sun, M. D. Caballero-Garcia, R. Sanchez-Ramirez and E. Fernandez-Garcia (IAA-CSIC), on behalf of a larger collaboration, report:
Following the detection of GRB 220403B by Swift (Klingler et al. GCNC 31820) and Fermi (Hamburg et al. GCNC 31829), we triggered the 1.5m OSN telescope in Granada (Spain) starting on Apr 4 at 02:49 UT (i.e. ~6.1 h post burst). A series of images in the I band with 60 s exposure were obtained in cloudy weather. In the co-added image of selected high S/N frames, the optical afterglow is weakly detected within the position reported by UVOT (Klingler et al. GCNC 31820) and XRT (Beardmore et al. GCNC 31827) with I=20.45+-0.30 at a median time of 03:20 UT, which is consistent with previous reports of detection by Jelinek et al. (GCNC 31821), Zhu et al. (GCNC 31823), Rossi et al. (GCNC 31826) and Pankov et al. (GCNC 31837), also upper limits by Lipunov et al. (GCNC 31825), Grossan et al. (GCNC 31830). Further observations are ongoing.
We thank the staff at OSN for their excellent support.