TITLE:   GCN CIRCULAR
NUMBER:  30995
SUBJECT: GRB 211024B: CAHA 2.2m Detection; ultra-long GRB? 
DATE:    21/10/25 15:45:51 GMT
FROM:    Alexander Kann at IAA-CSIC  <kann@iaa.es>

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

We observed the optical afterglow of the very long Swift GRB 211024B 
(Gropp et al., GCN #30980; Zhu et al., GCN #30984) with CAFOS mounted on 
the 2.2m Telescope at Calar Alto, Almeria, Spain. We obtained 30 x 90 s 
in the SDSS i' band under mediocre conditions.

At the position of the GRB afterglow discovered by Nanshan/NEXT (Zhu et 
al., GCN #30984), we detect a source. Against one Pan-STARRS comparison 
star, we measure:

i' = 20.27 +\- 0.05 mag (AB) at 0.2485 d after the GRB.

We note the XRT light curve at time of writing 
(https://www.swift.ac.uk/xrt_curves/01081073/  Evans et al., GCN #30994) 
shows a certain resemblance to that of the ultra-long GRB 111209A, being 
relatively flat until 10 ks before dropping off very steeply. The lack 
of early data prevents further conclusions for now. Further follow-up is 
warranted.