{
  "submittedHow": "web",
  "subject": "EP261007b: NOT optical observations, variable source outside the FXT region",
  "circularId": 45864,
  "createdOn": 1791474981965,
  "eventType": [
    "X-ray Transient",
    "Optical Transient"
  ],
  "format": "text/plain",
  "eventId": "EP261007b",
  "submitter": "Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>",
  "body": "J. A. Quirola-Vasquez (Radboud), A. Martin-Carrillo (UCD), D. B. Malesani (DAWN/NBI and Radboud), G. Corcoran (UCD), R. A. J. Eyles-Ferris (Leicester), P. G. Jonker (Radboud), A. J. Levan (Radboud and Warwick), J. Chacon (PUC), and F. E. Bauer (SSI and UTA) report on behalf of a larger collaboration:\n\nWe observed the field of the X-ray transient EP261007b (Wen et al., GCN 45847) using the ALFOSC camera on the Nordic Optical Telescope (NOT). Observations consisted of a sequence of 5 x 300 s exposures in the SDSS r-band, and started on 2026-10-08 at 01:57:25 UT (~10.9 hr after the EP/WXT trigger time; Wen et al., GCN 45847).\n\nAfter performing image subtraction on our stacked image against the Legacy Survey, no residuals are found within the EP-FXT error circle, although we note that the bright nearby star Gaia DR3 2763566336899590528 leaves some subtraction imperfections, affecting a small part of the EP-FXT area. We obtain an upper limit in our difference image within the EP-FXT region of r > 23.8 (AB), calibrated using nearby stars from the Pan-STARRS catalogue, and not corrected for Galactic extinction.\n\nWe do however note the presence of a transient source outside (51\" away) of the FXT region at coordinates (J2000) RA = 23:45:22.41, Dec= +11:20:25.8. For this source we measure a difference magnitude of r = 22.09 +/- 0.10. A faint object can be seen in the Legacy Survey at this position with r = 23.62 +/- 0.20 (AB). Given the low S/N of this archival detection, no morphological properties can be reliably inferred.\n\n\nIt is not expected for the FXT localization to be so far off the actual transient position, so the association between this object and EP261007b cannot be confirmed at the present time, but we encourage further monitoring as this source remains consistent with the EP/WXT localization.\n"
}