P. D'Avanzo (INAF-OAB), V. D'Elia (ASI-SSDC), M. Della Valle (INAF-OACN) A. Melandri (INAF-OAB), A. Rossi (INAF-OAS),
G. Tagliaferri (INAF-OOAB), A. Harutyunyan, D. Carosati (INAF-TNG) on behalf of the CIBO collaboration report:
We observed the field of GRB 210730A (Sonbas et al., GCN Circ. 30548; Prasad et al., GCN Circ. 30555; Wood et al., GCN Circ. 30577)
with the Italian 3.6m TNG telescope equipped with the optical camera DOLORES. A series of images were obtained with the r-sdss filter
on 2021-07-30 from 21:41:57 UT to 22:08:38 UT (i.e. about 17 hours after the burst).
At the edge of the XRT error circle (https://www.swift.ac.uk/xrt_positions/01062150/) we detect a faint optical source at the following
With preliminary photometry, carried out using a small aperture to minimise contamination from a nearby bright star, we derive the following
r = 22.7 +/- 0.2
(AB; calibrated against the SDSS catalogue).
In our co-added image we reach a limiting magnitude of r ~ 23.5 (AB, 3sigma c.l.).
We note that the same source is visible in archival Pan-STARRS images. Using a common set of reference stars and carrying out differential
photometry on TNG and Pan-STARRS images we find no evidence for a change in magnitude of this source.
Therefore, this source is likely not related to GRB 210730A. Alternatively, it can be the GRB host galaxy.