TITLE:   GCN CIRCULAR
NUMBER:  29847
SUBJECT: GRB 210420B: BOOTES-4/MET optical afterglow detection
DATE:    21/04/20 21:14:16 GMT
FROM:    Youdong HU at IAA-CSIC  <huyoudong072@hotmail.com>

Y.-D. Hu, T.-R. Sun, E. Fernandez-Garcia, A. J. Castro-Tirado, M.D. Caballero-Garcia, M. A. Castro Tirado (IAA-CSIC), C. Perez del Pulgar, A. Castellon, I. Carrasco (Univ. de Malaga), S. Guziy (Univ. of Nikolaev) and D. R. Xiong, Y. F. Fan, J. M. Bai, C. J. Wang, Y. X. Xin, X. H. Zhao (Yunnan Observatories of CAS) on behalf of a larger collaboration, report:

Following the detection of GRB 210420B by Swift (Moss et al. GCNC 29844), we triggered the 0.6m BOOTES-4/MET robotic telescope at Lijiang Astronomical Observatory (China) in order to follow up this event, starting on Apr 20, 19:51 UT. A series of images in clear filter was obtained. An uncatalogued optical source is found within the XRT position (Moss et al. GCNC 29844), for which we measure a magnitude of 17.9 +/- 0.1, calibrated against nearby stars in the USNO-B2 catalogue. This is consistent with the findings from MASTER (Lipunov et al, GCNC 29845) and Hankasalmi (Oksanen et al, GCNC 29846). Further observations are ongoing.

We thank the staff at Lijiang observatory for their excellent support.