GCN Circular 46113
Yacheng Kang (PKU), Fengkai Wan (PKU), Xinmiao Zhao (PKU), and Fangzhou Ren (PKU) report on behalf of the PKU HiTF (High-energy Transients Follow-up) group:
We observed the field of GRB 261029A, triggered by Fermi/GBM (Fermi GBM team, GCN 46071; T0 = 2026-10-29T01:27:03) and SVOM/ECLAIRs (Goto et al., GCN 46072), using the PKU 60cm telescope at Xinglong Observatory, NAOC. Observations in the r and i bands were obtained approximately 1.4 days after the Fermi/GBM trigger.
No significant optical counterpart is detected in the stacked r- and i-band images at the reported position of the optical/infrared counterpart (O'Neill et al., GCN 46073; He et al., GCN 46078; Wang et al. GCN 46079; De et al., GCN 46080; Cotter et al., GCN 46081; Álvarez et al., GCN 46083; Yin et al., GCN 46084; Shi et al., GCN 46088; Kang et al., GCN 46090; Ma et al., GCN 46092; De et al., GCN 46093; Novotny et al., GCN 46097; Zhao et al., GCN 46099; Dimple et al., GCN 46101; Novotny et al., GCN 46102; Rodríguez-Torres et al., GCN 46103; Hua et al., GCN 46104; Yin et al., GCN 46109). We derive 3-sigma upper limits of r > 22.14 mag and i > 21.48 mag. Preliminary photometry was calibrated against nearby Pan-STARRS field stars. The reported limits are approximate AB magnitudes and have not been corrected for Galactic extinction.
The observation log is summarized below following the time sequence:
| Date | Start_UT | T_mid - T0 (days) | Filter | Exposure (s) | 3-sigma Upper Limit |
|---|---|---|---|---|---|
| 2026-10-30 | 10:50:60 | 1.43 | r | 9 * 600 | > 22.14 |
| 2026-10-30 | 12:36:48 | 1.50 | i | 9 * 600 | > 21.48 |
Further optical follow-up observations are encouraged.
The PKU 60cm Telescope is operated by the Department of Astronomy, Peking University. The PKU HiTF group is dedicated to rapid follow-up observations of high-energy transients.