TITLE:   GCN CIRCULAR
NUMBER:  34271
SUBJECT: GRB 230723B: Further CAHA observations and host galaxy detection
DATE:    23/07/26 17:36:30 GMT
FROM:    Antonio de Ugarte Postigo at OCA <deugarte@oca.eu>

J.F. Agui Fernandez (IAA-CSIC), A. de Ugarte Postigo (OCA/CNRS), C.C. Thoene (ASU-CAS), J. Flores and Ana Guijarro Roman (CAHA) report:

We have performed follow-up observations on the GRB 230723B field (Page et al. GCN 34324, Osborne et al. GCN 34248) with CAFOS in the 2.2m telescope at the Calar Alto Observatory in Almeria, Spain. Observations consisted of 9x360s in i-band, starting at 2023-07-25T20:46:11 UT with a mean epoch 2.393 days after the burst. We detect the object reported in Agui Fernandez et al. (GCN 34251) at a magnitude consistent with our previous observation. 
The early optical detection of the transient at a consistent location by Sasada et al. (GCN 34268) indicates that the detection in the first Calar Alto observation was already dominated by the host galaxy contribution. The interpolation from the observation of Sasada et al. (GCN 34251) to the one of Agui Fernandez et al. (GCN 34251) indicates a decay rate of at least alpha=1.1 (where F_nu ~ t^-alpha). Extrapolating this, the GRB afterglow should be dimmer than 24 mag at the time of our follow-up observations. We do note, that the host galaxy should be in the range for emission line spectroscopy with 8-10m telescopes.