TITLE:   GCN CIRCULAR
NUMBER:  23020
SUBJECT: GRB 180720B:  ISON-Castelgrande optical observations
DATE:    18/07/22 23:39:09 GMT
FROM:    Alexei Pozanenko at IKI, Moscow  <apozanen@iki.rssi.ru>

S. Schmalz (KIAM), F. Graziani (GAUSS). A. Pozanenko (IKI), A. Volnova 
(IKI),  E. Mazaeva  (IKI),  I. Molotov (KIAM) report on behalf of larger GRB 
follow-up collaboration:

We observed the field of GRB 180720B (Swift-BAT detection: Siegel et al., 
GCN 22973, GCN 22975; Fermi-LAT detection: Bissaldi and Racusin, GCN 22980; 
Fermi-GBM detection: Roberts et al., GCN 22981; MAXI/GSC detection: Negoro 
et al., GCN 22993; Konus-Wind detection:  Frederiks et al., GCN 23011) 
with  ORI-22 (22 cm) telescope of ISON-Castelgrande observatory starting on 
July 20  (UT) 23:04:30.  We obtained 150 images of 60 s exposure in Clear 
filter.  The optical afterglow (e.g. Martone et al. GCN 22976;  Sasada et 
al., GCN 22977;  Reva et al., GCN 22979; Itoh et al., GCN 22983; Kann et 
al., GCN 22985)  is  detected in  separate images up to the end of series.

The coordinates of the optical afterglow are (J2000) 
:02:06.792   -02:55:04:99  with uncertainties of about 0.5 arcsec in both 
coordinates.  Preliminary photometry  of the  afterglow at  (UT, mid time) 
23:22:21 is R =17.40 +/- 0.15. The photometry is  based on nearby USNO-B1.0 
(R2) stars.