{
  "body": "J. A. Quirola-Vasquez (Radboud), R. A. J. Eyles-Ferris (Leicester), D. B. Malesani (DAWN/NBI and Radboud), G. Corcoran (UCD), A. Martin-Carrillo (UCD), L. Cotter (UCD), P. G. Jonker (Radboud), F. E. Bauer (SSI and UTA), and J. Chacón (PUC) report on behalf of a larger collaboration:\n\nWe observed the location of EP250911a (Liang et al., GCN 41788) with the Sinistro instrument mounted on the 1-m telescopes at McDonald Observatory, available via the LCO network. 6 x 200 s exposures were obtained in the SDSS r filter at a start time of 2025-09-11 UT 09:35:35 (~37.1 min post trigger).\n\nWithin the WXT and FXT error circles (Liang et al., GCN 41788) we locate a new source in our stacked r-band image, not visible in the archival Legacy Survey images. Its coordinates (0.5\" error) are:\n\nRA(J2000): 23:50:04.83\nDEC(J2000): +29:17:59.6\n\nCalibrated to nearby stars from the Pan-STARRS catalog, we measure a magnitude r = 20.04 +/- 0.07 (AB), not corrected for Galactic extinction.\n\nGiven the non-detection in the deeper archival images and the consistency with the FXT error circle, we suggest that this source is the optical counterpart of EP250911a.\n",
  "createdOn": 1757586218887,
  "submitter": "Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>",
  "circularId": 41790,
  "eventId": "EP250911a",
  "subject": "EP250911a: LCO optical counterpart discovery",
  "submittedHow": "web",
  "format": "text/plain",
  "bibcode": "2025GCN.41790....1Q"
}