TITLE:   GCN CIRCULAR
NUMBER:  29249
SUBJECT: GRB 210104B: BOOTES network optical upper limit
DATE:    21/01/04 23:20:22 GMT
FROM:    Youdong HU at IAA-CSIC  <huyoudong072@hotmail.com>

Y.-D. Hu, E. Fernandez-Garcia, A. J. Castro-Tirado, M.D. Caballero-Garcia (IAA-CSIC),  C. Perez del Pulgar,  A. Castellon, I. Carrasco, A. Reina (Univ. de Malaga), F. Rendon (IAA-CSIC and INTA-CEDEA) R. Fernandez-Munoz (IHSM/UMA-CSIC) and M. Jelinek (ASU-CAS) on behalf of a larger collaboration, report:

Following the Swift trigger of GRB 210104B (Laha et al., GCNC 29243), the 0.3m BOOTES-1B robotic telescope in Mazagon (Huelva), southern Spain, automatically responded to this burst. Series images were taken started 2021-01-04 21:11:00 UT (~50 s after trigger). In the co-added of 10x10 s images, no source is detected within the XRT position (Laha et al., GCNC 29243) which down to 18.1 mag (clear filter).

The 0.6m BOOTES-2/TELMA robotic telescope at IHSM La Mayora (UMA-CSIC) in Algarrobo Costa (Malaga, Spain) also automatically responded to the Swift trigger of GRB 210104B (Laha et al., GCNC 29243). A series of images were taken starting on 2021-01-04 21:11:24 UT (~74 s after trigger). No optical source is detected within the XRT position on the co-added image (10x10 s, clear filter) which down to 19.9 mag.

Those non-detections are consistent with the reports from Swift (Laha et al., GCNC 29243) and MASTER-Net (Lipunov et al., GCNC 29242). Additional observations are ongoing. We thank the staff at INTA-CEDEA and La Mayora for their excellent support.