A. Rossi (INAF-OAS) and P. D'Avanzo (INAF-OA Brera) report on behalf of
the CIBO collaboration:
We observed the field of GRB200623A (DeLaunay et al., GCN 28013)
simultaneously in the r' and z' bands with the LBC imager mounted on LBT
(Mt Graham, AZ, USA). Observations started at 05:58 UT on 2020-06-25,
50.7 hr after the GRB trigger and finished at 06:24 UT and allowed us to
obtain 20min of exposure in each band. Observations were performed under
good seeing conditions (seeing ~0.9") and reached a depth of r~26 mag.
The images covered all the three sources found by XRT (Sbarufatti et
al., GCN 28023). No new point source is detected within their error circles.
Image subtraction against TNG r-band images obtained on 2020-06-23
(D'Avanzo et al., GCN 28021) using HOTPANTS (v5.1.11) does not reveal
any flux variation in the candidate found within the error circle of the
XRT source #3. The near-by galaxy at z~0.33 noticed by D'Avanzo et al.
(GCN 28021) is too close to saturation in LBC images, preventing us to
make any statement about possible flux variations within the galaxy.
We also note that a faint, extended source is present within the XRT
error circle of source #3, visible in both the r' and z' images, and not
mentioned in previous reports about this event. This is also a candidate
host galaxy of XRT source #3 though with a higher chance association
probability compared to the brighter galaxy. Further Swift/XRT
observations will help establishing variability and possibly reducing
the X-ray position uncertainty.
We acknowledge the excellent support from the LBTO and LBT-INAF staff,
particularly B. Rothberg, F. Cusano, S. Paiano and D. Paris, in
obtaining these observations.