{
  "format": "text/markdown",
  "createdOn": 1794412498347,
  "subject": "EP261111a: Xinglong optical upper limit",
  "body": "Junjie-Jin (NAOC), Qi-Zhao (NAOC), Dong-Xu (NAOC), Yue-Sun (NAOC), Haiyang-Mu (NAOC), Yu-Zhang (NAOC), Pengliang-Du (NAOC), Zhou-Fan (NAOC), Hong-Wu (NAOC) report on behalf of a large collaboration:\n\nThe Wide-field X-ray Telescope on Einstein Probe detected the X-ray transient EP261111a (Huang et al., GCN 46226).\n\nWe performed optical observations of the field of EP261111a at Xinglong Observatory. Our measurements are summarized below.\n\nInspection of the stacked science images and the archival-image comparison revealed no candidate optical counterpart within the EP/WXT localization region (3 arcmin radius). The representative 5-sigma point-source limiting magnitudes are listed below.\n\nTime offsets are measured from the EP/WXT trigger at 2026-11-11T13:25:10Z (GCN 46226).\n\nMid-time (UTC) | Hours after trigger | Exposure (s) | Filter | 5-sigma limiting magnitude | System | Telescope\n2026-11-11T13:48:38.264 | 0.391 | 6 x 300 | g | > 20.955 | PS1-AB-calibrated | Tsinghua-NAOC 0.8-m telescope (TNT)\n\nThe tabulated times are exposure-weighted mid-times in UTC. The representative depths were estimated from the background noise in the observed stacked images.\n\nPhotometry was calibrated using field stars from the BEST catalog (Xiao et al. 2026) on the PS1 photometric system.\n\nReferences:\nGCN 46226 · EP261111a: Einstein Probe detection of an X-ray transient — https://gcn.nasa.gov/circulars/46226",
  "submitter": "Xinglong Observatory at National Astronomical Observatories (NAOC), Chinese Academy of Sciences (CAS) <xinglong@nao.cas.cn>",
  "eventType": [
    "X-ray Transient"
  ],
  "eventId": "EP261111a",
  "submittedHow": "web",
  "circularId": 46227
}