{
  "submittedHow": "web",
  "circularId": 40041,
  "submitter": "sqjiang at NAOC <sqjiang@bao.ac.cn>",
  "format": "text/plain",
  "bibcode": "2025GCN.40041....1J",
  "createdOn": 1743757846512,
  "subject": "GRB 250403A: JinShan optical observations",
  "eventId": "GRB 250403A",
  "body": "S.Q. Jiang, Z.P. Zhu, X. Liu, J. An, D. Xu (NAOC), S.Y. Fu (HUST), J.Z. Liu (XAO) report on behalf of a large collaboration:\n\nWe observed the field of GRB 250403A detected by SVOM/ECLAIRs (Julakanti et al., GCN 40026) and Fermi/GBM (Fermi GBM team, GCN 40025), using the 100cm-C telescope (100C) of the JinShan project, located at Altay, Xinjiang, China. Observations started at 18:03:34.11 UT on 2025-04-03, i.e., 2.80 hr after the SVOM/ECLAIRs trigger, and a series of 600 s frames were obtained in the Sloan r- and i- bands.\n\nThe optical afterglow (Starling et al., GCN 40028; Wu et al., GCN 40029; Du et al., GCN 40031; Li et al., GCN 40032; Julakanti et al., GCN 40034; Ghosh et al., GCN 40039) of GRB 250403A is clearly detected in our stacked images. Preliminary photometry results are as follows:\n\nT_mid(hr) Filter  Mag(AB)  MagErr\n4.06           r       19.77      0.05\n4.73           i       20.11      0.06\n\ncalibrated with nearby Legacy Survey stars and not corrected for Galactic extinction. \n\nWe acknowledge the excellent support from T.Q. Chen and Z.K. Feng for enabling these observations."
}