TITLE:   GCN CIRCULAR
NUMBER:  27222
SUBJECT: GRB 200224A: Calar Alto 2.2m optical afterglow detection
DATE:    20/02/26 10:47:39 GMT
FROM:    Alexander Kann at IAA-CSIC  <kann@iaa.es>

J. F. Agui Fernandez, M. Blazek, D. A. Kann (all HETH/IAA-CSIC), A. de 
Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), C. C. Thoene (HETH/IAA-CSIC), 
E. Gallego-Cano, and A. Guijarro (both CAHA) report:

We observed the field of the Swift-detected GRB 200224A (Ukwatta et al., 
GCN #21173) with the 2.2m telescope at CAHA, Almeria, Spain. We obtained 
5 x 120 s each in Rc and Ic.

At the position of the optical afterglow reported by Sota et al. (GCN 
#27176), Stecklum et al. (GCN #21177), and Marshall & Ukwatta (GCN 
#27182), we clearly detect a source in each stack image.

We measure Rc = 21.60 +/- 0.06 mag at 0.03702 days after the GRB, and Ic 
= 21.31 +/- 0.09 mag at 0.05794 days after the GRB (Vega magnitudes), in 
good agreement with the measurements of Tautenburg at an earlier time 
(GCN #27177) and OSN at a later time (GCN #27176).

We note the optical afterglow is very faint (see also Becerra et al., 
GCN #27189), but the clear detection in u by Swift/UVOT (GCN #27182) as 
well as the blue Rc-Ic color we find indicates this GRB is neither at 
high redshift nor particularly extinguished (see also the XRT results, 
Gropp et al., GCN #27179), it is likely just intrinsically faint.