TITLE:   GCN CIRCULAR
NUMBER:  35588
SUBJECT: GRB 240118A: Mondy optical observations
DATE:    24/01/20 23:54:29 GMT
FROM:    Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>

N. Pankov (HSE, IKI), A. Pozanenko (IKI), E. Klunko (ISTP), S. Belkin (IKI) report on behalf of IKI GRB FuN:

We observed the field of  Fermi LAT localization of GRB 240118A (Bissaldi, GCN 35560), which was also detected by Fermi GBM (Fermi GBM team, GCN 35558; Hamburg, GCN 35563), NuSTAR (Grefenstette, GCN 35564), Konus-Wind (Frederiks, GCN 35567), Swift BAT (DeLaunay, GCN 35568), and GRBAlpha (Dafcikova et al., GCN 35580), and the localization area  observed by MASTER-Tunka observatory (Lipunov et al., GCN 35561) and Abastumani observatory (Pankov et al., GCN 35572).

Observations  started on  2024-01-18 (UT) 14:13:46 with AZT-33IK  telescope of Sayan observatory (Mondy) in the R-filter. The observations have been carried out in moderate weather conditions with FWHM of 2.5". We report observations of XRT candidates detected in the Swift TOO program (Evans et al., GCN 35573).
XRT #1 - out of FOV
XRT #2 - matches bright USNO-B1.0 star with R2=9.98 mag
XRT #3 - within the XRT #3 error circle we detect a faint source, which matches SDSS J011408.49+294753.1 source with SDSS DR12 r'= 22.117 and redshift of z_phot = 0.68
XRT #4 - out of FOV
XRT #5 - matches bright Gaia DR3 star with G=6.48 mag
XRT #6 - out of FOV
XRT #7 - out of FOV

Preliminary photometry of the faint source XRT #3 suggested as an X-ray afterglow (Beardmore et al., GCN  35587) is following

Date       UT start   t-T0    Filter Exp.    OT     Err.  UL(3sigma)
                       (mid, days)    (s)

2024-01-18 14:13:46  0.537932  R     29*120   22.1   0.3   22.1

The photometry is based on nearby USNO-B1.0 stars. 

At this time we cannot say anything about the variability of the source. The source at coordinates 01:14:08.48 +29:47:53.2, spatially coinciding with the galaxy SDSS J011408.49+294753.1 with a redshift of 0.68 could be a host galaxy of GRB 240118A.