TITLE: GCN CIRCULAR NUMBER: 45387 SUBJECT: EP260812a: AZT-22 optical upper limit DATE: 26/08/15 14:16:38 GMT FROM: Xiaofeng Wang at Tsinghua University <wang_xf@mail.tsinghua.edu.cn> D. Mirzakulov (UBAI), J. Baxtiyorov (UBAI), X.-F. Wang (THU), S. Ehgamberdiev (UBAI), A. Shaymanov (Maidanak Observatory/UBAI), and H.-W. Peng (THU) report on behalf of the UBAI and THU joint teams: We observed the field of the Einstein Probe fast X-ray transient EP260812a (Liu et al., GCN 45362) with the AZT-22 1.5~m telescope of the Maidanak Astronomical Observatory (MAO) starting on 2026-08-12 at 15:49:06 UTC, and obtained 4x300s exposure in the B and R filters using 4kx4k CCD SNUCAM camera (Im et al., 2010). We did not detect any optical counterpart at positions provided either by EP-WXT (Liu et al., GCN 45362) or by Corcoran et.al. (GCN 45376) in our stacked frames. We measure the following upper limits for our stacked images: DATE-OBS t-T0(hrs) Exptime(s) Filter Upperlimit(mag) Site/Telescope 2026-08-12T15:49:06 4.468 4x300 B 23.30 MAO/AZT-22 2026-08-12T16:12:58 4.866 3x300 R 23.05 MAO/AZT-22 2026-08-12T20:29:38 9.144 4x300 B 23.92 MAO/AZT-22 2026-08-12T20:36:41 9.261 4x300 R 23.72 MAO/AZT-22 2026-08-13T16:29:13 29.137 4x300 R 23.28 MAO/AZT-22 All the data have been reduced by the data processing pipeline, STDWeb (Karpov 2025). We performed images subtraction on the stacked images using the Pan-STARRS templates. The photometry was calibrated using the Gaia DR3 Synphot catalog and was not corrected for extinction. We thanks the MAO staff for supporting the observations. View this GCN Circular online at https://gcn.nasa.gov/circulars/45387. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...