TITLE:   GCN CIRCULAR
NUMBER:  28021
SUBJECT: GRB 200623A: TNG optical observations
DATE:    20/06/23 23:09:31 GMT
FROM:    Paolo D'Avanzo at INAF - OAB  <paolo.davanzo@inaf.it>

P. D'Avanzo (INAF-OAB), V. D'Elia (ASI-SSDC), G. Andreuzzi, D. Carosati (INAF-TNG) on behalf of the CIBO collaboration report:

We observed the field of GRB 200623A (Fermi/GBM Team, GCN Circ. 28011; DeLaunay et al., GCN Circ. 28013; Veres and Meegan, 
GCN Circular. 28019) with the Italian 3.6m TNG telescope equipped with DOLORES in imaging mode. A series of images were 
obtained with the r-sdss filter on 2020-06-23 from 21:23:29 UT to 21:44:01 UT (i.e. about 18.3 hours after the burst) covering the entire 
Swift/BAT-GUANO error circle reported by DeLaunay et al. (GCN Circ. 28013,). Further observations are in progress. 

No obvious afterglow candidate is detected inside the BAT-GUANO error circle. 

Inside the 5" radius error circle of the Swift/XRT source #3 (see Evans, GCN Circ. 28015 and https://www.swift.ac.uk/ToO_GRBs/00021005) 
we detect a faint source at the following coordinates: 

RA(J2000), Dec (J2000) = 16:07:59.11, +53:28:39.0  (+/- 0.5").

From preliminary photometry, we estimate for this object a magnitude r ~ 24.2 (AB, calibrated against the SDSS catalogue). This source is 
apparently not visible in the SDSS and Pan-STARRS archival images of this field. Given the faintness of the source, no conclusion can be 
derived about its variability and about its association to GRB 200623A. 

We note that the 5" radius error circle of the Swift/XRT source #3 is consistent with the catalogued galaxy SDSS J160758.62+532842.2 whose 
photometric redshift is 0.33 +/- 0.05. 

The position of the the Swift/XRT source #2 is outside the field of view of our images, therefore we cannot provide information on the optical 
afterglow candidate reported by Belkin et al. (GCN Circ. 28020).