GCN Circular 45556
Subject
GRB 260909A: OSN 1.5m, CAHA 2.2m and GTC 10.4m optical upper limits
Event
Date
2026-09-12T21:03:53Z (3 days ago)
From
I. Perez-Garcia at Instituto de Astrofísica de Andalucía <ipg@iaa.es>
Via
Web form
I. Perez-Garcia, J. Rodrigo, M.D. Caballero-Garcia, M. Gritsevich, S.-Y. Wu, S. Guziy (IAA-CSIC), Y.-D. Hu (GXU), G. Gomez-Velarde (IAC, GRANTECAN), F. Tinaut-Ruano (CAHA) and A.J. Castro-Tirado (IAA-CSIC), on behalf of a larger collaboration
Following the detection of GRB 260909A by SVOM/ECLAIRs (Saccardi et al. GCN 45534), we triggered the 2.2m CAHA telescope (+ CAFOS) at the Calar Alto Observatory (Almeria, Spain). Images were gathered starting on Sep. 10 00:07 UT (i.e. ~12.8 hours after the trigger) in the Sloan i, Sloan z and clear bands, covering the SVOM/MXT (Saccardi et al. GCN 45534) and EP/FXT (Mao et al. GCN 45543) error circles. No optical transient is detected in the co-added images (900 s per band) down to 3-sigma limits of z = 21.13, i = 22.25 and clear = 22.43 mag.
The field was also observed with the 1.5m telescope at the Sierra Nevada Observatory (OSN, Granada, Spain). A 300 s I-band image was obtained on Sep. 10 starting at 01:49 UT (i.e. ~14.5 hours after the trigger). No optical transient is detected within the above-mentioned error boxes down to I = 20.61 mag (3-sigma).
Later on we also triggered the 10.4m GTC telescope equipped with OSIRIS in La Palma (Spain). Sloan z-band images were gathered on Sep. 10 starting at 05:33 UT (mid-time ~18.5 hours after the trigger). No optical transient is detected on the co-added image (900 s) down to z = 24.55 mag (3-sigma).
A second GTC/OSIRIS epoch in the Sloan z band was obtained on Sep. 12 (mid-time Sep. 12 03:16 UT, i.e. ~2.7 days after the trigger; 1020 s in total) under worse seeing conditions. No optical transient is detected down to z = 24.17 mag (3-sigma), and no variable source is found between both GTC epochs.
Magnitudes are in the AB system (Vega for the I band), calibrated against ATLAS-REFCAT2 (the clear band against Gaia G and the I band through the Lupton 2005 transformations), and not corrected for Galactic extinction.
These non-detections are consistent with the reports from SVOM/C-GFT (Guan et al. GCN 45535), Xinglong 2.16m (Ma et al. GCN 45536), SVOM/VT (Li et al. GCN 45539), VLT (Saccardi et al. GCN 45545), OHP/T193 (Amram et al. GCN 45546), KAIT (Zheng et al. GCN 45549) and CrAO/AbAO (Pankov et al. GCN 45554).
We thank the staff at GTC, Calar Alto and Sierra Nevada observatories for their excellent support.