GCN Circular 45545
A. Saccardi (CEA/Irfu), B. Schneider (LAM), J. An (NAOC), D. B. Malesani (DAWN/NBI and Radboud), G. Corcoran (UCD), S. D. Vergani (LUX-Paris Obs.), A. J. Levan (Radboud and Warwick), N. R. Tanvir (U. Leicester), A. L. Thakur (INAF/IAPS), report on behalf of the Stargate collaboration:
In light of the early optical upper limits reported by Li et al. (GCN 45539), we observed the field of the SVOM GRB 260909A (Saccardi et al., GCN 45534; Wang et al., GCN 45538) using the ESO VLT UT1 (Antu) equipped with the FORS2 imager and the ESO VLT UT4 (Keyen) equipped with the HAWK-I near-infrared imager.
We obtained a multi-filter observation in the z-band and in the near-infrared YJHK bands. A preliminary analysis reveals no new sources consistent with the EP/FXT position (Mao et al., GCN 45543), down to the following 3-sigma limiting magnitudes (calibrated against Pan-STARRS and 2MASS for the optical and near-infrared bands, respectively):
| Band | Mid time (UT) | T-T0 (hr) | Exposure time (min) | Instrument | Magnitude (AB) |
|---|---|---|---|---|---|
| z | 2026 Sep 10.21 | 17.65 | 20 | VLT/FORS2 | > 24.3 |
| Y | 2026 Sep 10.19 | 17.35 | 10 | VLT/HAWK-I | > 23.9 |
| J | 2026 Sep 10.20 | 17.56 | 8 | VLT/HAWK-I | > 23.6 |
| H | 2026 Sep 10.21 | 17.76 | 8 | VLT/HAWK-I | > 23.1 |
The K-band integration was curtailed, and analysis of the frames obtained is ongoing.
We acknowledge the excellent support from the observing staff in Paranal.