TITLE:   GCN CIRCULAR
NUMBER:  36168
SUBJECT: GRB 240418A: TSHAO Zeiss-1000 optical upper limit
DATE:    24/04/19 01:36:41 GMT
FROM:    Alexei Pozanenko at IKI, Moscow <apozanen@iki.rssi.ru>

A. Pozanenko (IKI), I. Reva (FAI),  N.Pankov (HSE), S. Belkin (IKI)  report on behalf of GRB-IKI-FuN:

We have observed the field of GRB 240418A (Siegel et al., GCN 36162)  with Zeiss-1000 telescope of Tien Shan Astronomical Observatory starting on 2024-04-18 (UT) 21:47:25.

We do not detect  any object within Enhanced Swift-XRT position (Evans et al., GCN 36166) up to R=21.6. Preliminary photometry of the field in a stacked image is following.

Date       UT start t-T0    Filter  Exp.   OT  Err. UL(3 sigma)
                     (mid, days)     (s)
2024-04-18 21:47:25  -      R       21*120 n/d n/d  21.6

The photometry is based on nearby USNO-B1.0 stars.
Non detection of the OT is in agreement with the observations (Lipunov et al., GCN 36163; Odeh et al., GCN 36165; Malesani et al., GCN 36167).