GCN Circular 45387
Subject
EP260812a: AZT-22 optical upper limit
Event
Date
2026-08-15T14:16:38Z (3 days ago)
From
Xiaofeng Wang at Tsinghua University <wang_xf@mail.tsinghua.edu.cn>
Via
Web form
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.