TITLE:   GCN CIRCULAR
NUMBER:  37737
SUBJECT: EP240930a / GRB 240930B: CrAO ZTSH optical upper limit
DATE:    24/10/08 18:43:37 GMT
FROM:    Alexei Pozanenko at IKI, Moscow <grb.alex@gmail.com>

 A. Vonova (IKI), V. Rumyantsev (CrAO), A. Pozanenko (IKI), N. Pankov (HSE,
IKI), and S. Belkin (IKI) report on behalf of the GRB-IKI-FuN collaboration:

We observed EP240930a, detected by EP-WXT (Tian et al., GCN 37648) and FXT
(Peng et al., GCN 37653), and triangulated by IPN (Kozyrev et al., GCN
37696), using the 2.6-meter ZTSh telescope of CrAO, equipped with a CCD
photometer and an R-filter. The observations started on 2024-10-01 (UT)
16:48:01.

We did not detect any new optical object within the FXT (Peng et al., GCN
37653) localization area in comparison with DSS2. The preliminary
photometry is as follows:

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

2024-10-01 16:48:01 0.98182 46x120 R n/d n/d 23.6

This result is in agreement with previous reports (Kumar et al., GCN 37651;
Zheng et al., GCN 37656; Bochenek et al., GCN 37682; SVOM/C-GFT team, GCN
37720). The magnitudes were calibrated using nearby USNO-B1.0 stars (R2
magnitude). No correction has been made for Galactic extinction toward
EP240930a