GCN Circular 30401

D. A. Kann (HETH/IAA-CSIC), A. de Ugarte Postigo (HETH/IAA-CSIC, 
DARK/NBI), C. Thoene, M. Blazek, J. F. Agui Fernandez (all 
HETH/IAA-CSIC), N. Maicas, and J. L. Lamadrid (COAJ report:

We observed the afterglow of GRB 210704A (BALROG localization: 
Kunzweiler et al., GCN #30369; Fermi/LAT detection: Berretta et al., GCN 
#30375; Fermi/GBM detection: Malacaria & Meegan, GCN #30382; AGILE/MCAL 
detection: Ursi et al., GCN #30372; AstroSat/CZTI detection: Prasad et 
al., GCN #30378; Konus-Wind detection: Ridnaia et al., GCN #30388; 
Swift/XRT afterglow detection: D'Ai et al., GCN #30379) with the T80 
0.8m telescope at the Observatorio de Javalambre (Teruel, Spain). 
Observations consisted of 3 x 300 s in z', i', g' r' each, at midtimes 
1.081, 1.093, 1.104, and 1.116 days after the GRB, respectively.

The afterglow (Kim et al., GCN #30384, D'Avanzo et al., GCN #30385, Kann 
et al., GCN #30391, de Ugarte Postigo et al., GCN #30392) is 
well-detected in g'r', faintly in i' and not in z'. Against four 
Pan-STARRS field stars, we measure (AB magnitudes):

g' = 22.42 +/- 0.11 mag;
r' = 22.17 +/- 0.10 mag;
i' = 22.08 +/- 0.23 mag;
z' > 21.5 mag

at the above-mentioned mid-times.