{ "createdOn": 1740660558572, "editedBy": "Judith Racusin at NASA/GSFC on behalf of Daniele B. Malesani at IMAPP / Radboud University ", "eventId": "EP250225a", "submitter": "Daniele B. Malesani at IMAPP / Radboud University ", "bibcode": "2025GCN.39516....1M", "body": "Daniele B. Malesani (DAWN/NBI and Radboud Univ.), Andrew J. Levan (Radboud Univ. and DAWN/NBI), Antonio Martin-Carrillo (UCD), Franz E. Bauer (PUC), Peter G. Jonker (Radboud Univ.), Maria E. Ravasio (Radboud Univ.), M. Alejandra Diaz Teodori (NOT and Turku Univ.), Roar H. Rasmussen (NOT and Aarhus Univ.), Saskia Schlagenhauf (QUB), report on behalf of a larger collaboration:\n\nWe observed the field of the fast X-ray transient EP250225a (Jiang et al., GCN 39475) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations were carried out in the r and z filters, with mean times 2025 Feb 26.98 and 27.00 UT (1.47 and 1.49 days after the trigger, respectively).\n\nTemplate subtraction of the NOT images using the Legacy Survey as reference yields a potential faint candidate at the edge of the EP/WXT error circle, located at coordinates:\n\nRA(J2000) = 09:25:04.07\nDec(J2000) = -04:53:40.2\n\nThis position is consistent with an object in the Legacy Survey (with magnitudes g = 23.22, r = 22.48, i = 21.53, z = 21.57). The object looks point-like both in our data (PSF 0.75\" in the z band) and in the Legacy Survey. Photometry confirms a brightening of 0.50 +- 0.05 and 0.33 +- 0.10 mag in the r and z bands, respectively, when compared to the archival fluxes in the Legacy Survey.\n\nThe point-like nature of the source suggests either a transient on top of a compact host galaxy or stellar variability. Further observations are planned (and encouraged) to establish the nature of this object and its association with EP250225a.", "format": "text/plain", "version": 2, "circularId": 39516, "editedOn": 1740679251940, "subject": "EP250225a: NOT optical candidate counterpart", "submittedHow": "web" }