TITLE:   GCN CIRCULAR
NUMBER:  46113
SUBJECT: GRB 261029A / AT 2026ahaw: Optical upper limits from the PKU 60cm Telescope 
DATE:    26/10/30 15:02:52 GMT
FROM:    Y.C. Kang at Peking University <yckang@stu.pku.edu.cn>

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.