GCN Circular 45546
Subject
GRB 260909A: OHP/T193 z-band upper limit
Event
Date
2026-09-10T09:27:50Z (5 days ago)
From
Christophe Adami at LAM <christophe.adami@lam.fr>
Via
Web form
P. Amram (LAM/Pytheas/AMU), C. Adami (LAM/Pytheas/AMU), E. Le Floc'h (CEA/Irfu), A. Saccardi (CEA/Irfu), F. Schüssler (CEA/DPhP), S. Basa (LAM/OHP/Pytheas/AMU), D. Russeil (LAM/Pytheas/AMU), report on behalf of a larger collaboration:
We observed the field of the SVOM/ECLAIRs GRB 260909A (Saccardi et al., GCN 45534; see also Mao et al., GCN 45543; Guan et al., GCN 45535; Ma et al., GCN 45536; Pankov et al., GCN 45537; Wang et al., GCN 45538; Li et al., GCN 45539; Saccardi et al., GCN 45545) with the 1.93-m T193 telescope at the Observatoire de Haute-Provence (France), equipped with the MISTRAL spectro-imager.
We obtained 52 individual exposures in the z band for a total integration time of 5.68 h. The observations started on 2026 September 9 at 20:36:43 UT (T-T_0 = 9.3 h), with a mean time on September 10 at 00:10:48 UT (T-T_0 = 13.9 h).
The stacked image reaches a 3 sigma limiting magnitude of z = 23.25.
A faint source with a magnitude of z = 23.5 +/- 0.5 is barely detected within the error region reported by Mao et al. (GCN 45543). This source is also present in the Legacy Survey and has a consistent archival magnitude of z = 23.21. Its presence at a similar brightness level in pre-existing data therefore suggests that it is unlikely to be the GRB afterglow.
The photometric calibration was performed using nearby stars from the PanSTARRS catalog and the magnitudes are not corrected for Galactic extinction. We used the STDWeb/STDPipe tools (Karpov 2025).
We acknowledge the excellent support from the Observatoire de Haute-Provence and in particular J. Balcaen.