TITLE: GCN CIRCULAR NUMBER: 39533 SUBJECT: EP250227a: NOT optical observations DATE: 25/02/28 16:36:03 GMT FROM: Antonio Martin-Carrillo at UCD,Space Science Group antonio.martin-carrillo@ucd.ie
D. B. Malesani (DAWN/NBI and Radboud Univ.), A. Martin-Carrillo (UCD), A. J. Levan (Radboud Univ and Warwick Univ.), F. E. Bauer (PUC), P. G. Jonker (Radboud Univ), M. Alejandra Diaz Teodori (NOT and Turku Univ.), Roar H. Rasmussen (NOT and Aarhus Univ.), Saskia Schlagenhauf (QUB), report for a larger collaboration:
We obtained observations of the field of the fast X-ray transient EP250227a (Wen et al. GCN 39532) using the Nordic Optical Telescope (NOT) equipped with the ALFOSC camera. Observations started on 2025 Feb 28.126 UT (22.37 hr after the EP trigger) and were carried out in the r and z filters.
No new source is visible within the EP/FXT X-ray error circle (Wen et al. GCN 39532), down to a 3-sigma limiting magnitude r > 23.7 AB, calibrated against nearby Pan-STARRS objects. At the edge of the error circle, we note the presence of a source, visible also in the Legacy Survey and whose brightness is consistent with the archival value. While this is a potential host galaxy for EP250227a, its chance association probability is not negligible.
We also performed image subtraction on our stacked r-band image using the Legacy Survey as template. A single variable source is identified at coordinates (inconsistent with those of the EP/FXT error circle):
R.A.(J2000) = 13:36:29.37 Dec.(J2000) = -13:49:00.16
This source is located about 1” to the NE of the nucleus of a galaxy visible in the Legacy Survey with magnitude r = 18.8. We measure for the variable source r = 22.5 +/- 0.1 AB.
The nature of this source and its association with EP250227a are unclear at the moment. Further observations are planned and deep r-band photometry of the field is encouraged.
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