TITLE:   GCN CIRCULAR
NUMBER:  35812
SUBJECT: GRB 240225B: Nanshan/HMT optical afterglow detection
DATE:    24/02/26 23:18:55 GMT
FROM:    Dong Xu at NAOC/CAS <dxu@nao.cas.cn>

X. Liu,, J. An, S.Y. Fu, S.Q. Jiang, Z.P. Zhu, T.H. Lu, D. Xu (NAOC), X. Gao (Urumqi No.1 Senior High School), J.Z. Liu (XAO) report:

We observed the field of GRB 240225B detected by MAXI (Nakajima et al., GCN 35796) and AstroSat (Joshi et al., GCN 35798) using the HMT-0.5m telescope with big FOV (~1 deg^2) located at Nanshan, Xinjiang, China. Photometry was carried out twice in the same night without any filter..

A slowly decaying uncatalogued optical transient is detected at coordinates

R.A. = 08:33:26.80 (J2000)
Dec. = +27:04:32.77 (J2000)

with an uncertainty of radius ~ 0.3 arcsec, with r ~ 18.9 +/- 0.1 mag (AB) at a median time of 18.90 hr post-burst, calibrated with the nearby PanSTAR field. This OT is positionally at the border of the error circle of Swift/XRT  "Source 1" (D'Ai  et al., GCN 35810), and is also consistent with and thus confirming the GOTO candidate (Gompertz et al., GCN 35805).

We thus think the OT is the optical afterglow of GRB 240225B.