TITLE:   GCN CIRCULAR
NUMBER:  37584
SUBJECT: EP240913A/GRB 240913C: AbAO optical upper limit
DATE:    24/09/21 10:33:25 GMT
FROM:    Alexei Pozanenko at IKI, Moscow <grb.alex@gmail.com>

S. Belkin (HSE, IKI), R. Ya. Inasaridze (AbAO), A. Pozanenko (IKI), N.
Pankov (HSE, IKI) report on behalf of GRB-IKI-FuN:

We observed the field of EP240913A/GRB 240913C (Li et al., GCN 37492; Yin
et al., GCN 37493; Dasgupta et al., GCN 37505; Bissaldi et al., GCN 37509;
Pawar et al., GCN 37510) using the 70-cm AS-32 telescope at the Abastumani
Observatory (AbAO) in the R-filter, starting on 2024-09-14 at 23:44:17
(UT). We did not detect the optical counterpart in the stacked image within
the Swift-XRT error circle (Jiang et al., GCN 37497), consistent with
reports from Asquini et al., GCN 37499; Zhu et al., GCNs 37500, 37501;
Zheng et al., GCN 37511; Schneider et al., GCN 37515; Lipunov et al., GCN
37521. Preliminary photometry is as follows:

Date UT Start t-T0 (days) Filter Exposure (s) OT Err UL (3σ)
2024-09-14 23:44:17 1.53211 R 113×60 n/d n/d 22.2

The magnitudes were calibrated using nearby USNO-B1.0 stars:
RA: 01:06:52.7994912, DEC: +16:43:24.121128, R2: 15.96
RA: 01:07:11.4427176, DEC: +16:49:54.951564, R2: 17.09