[vsnet-grb-info 28448] GRB 210724A: Early CAHA 2.2m limit

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  30551
SUBJECT: GRB 210724A: Early CAHA 2.2m limit
DATE:    21/07/30 12:37:10 GMT
FROM:    Alexander Kann at IAA-CSIC  <kann at iaa.es>

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), A. Gardini, and I. Hermelo (both CAHA) report:

We observed the in-flight XRT afterglow position (revised in Evans et 
al., GCN #30547) of GRB 210724A (D'Avanzo et al., GCN #30497) with CAFOS 
mounted at the 2.2m Calar Alto telescope (Almeria, Spain), under very 
adverse conditions (high airmass, strong Calima, clouds, bad seeing, 
strong moonlight - the works). We obtained 10 x 180 s images in r', 
starting on July 24, 21:07:08 UT (0.8831 h after the burst).

At the position of the GTC afterglow candidate (de Ugarte Postigo et 
al., GCN #30511), we detect no source down to r' > 22.0 mag (AB 
magnitude) against PanSTARRS comparison stars, at midtime 0.0482 d 
(1.1569 h) after the burst. This is of similar depth as the detection by 
de Ugarte Postigo et al., GCN #30511, perhaps indicating a slowly rising 
afterglow, or at least one that is not steeply decaying.