TITLE: GCN CIRCULAR NUMBER: 39446 SUBJECT: GRB 250221A: TNOT detection of the optical counterpart DATE: 25/02/24 09:24:45 GMT FROM: Xiaofeng Wang at Tsinghua University wang_xf@mail.tsinghua.edu.cn

A. Iskandar（XAO), H.-C. Zhu (THU)，X.-F. Wang, and L.-T. Wang (XAO) report the optical detection of the afterglow of GRB 250221A (Francile et al., GCN 39395; Caputo et al., GCN 39396; Watson et al., GCN 39397; Melandri et al., GCN 39406; Shilling et al., GCN 39409; Guo et al., GCN 39412; Muenter et al., GCN 39417; Palmerio et al., GCN 39418; Pankov et al., GCNs 39422,39424,39426,39427; Ghosh et al., GCN 39425).

We obtained the r-band images (~2.40 days after the burst) with the 80~cm Tsinghua-Nanshan Optical Telescope (TNOT) located at Nanshan Station of Xinjiang Astronomy Observatory, starting on 2025-02-23 (UT) 13:05:49. The afterglow is clearly detected on the stacked images, with the following magnitude:

r = 20.46 +- 0.17 mag (MJD =60698.5457)

The above photometric result is calibrated against the Pan-STARRS catalog without a correction for the Galactic extinction.

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