TITLE: GCN CIRCULAR NUMBER: 39516 SUBJECT: EP250225a: NOT optical candidate counterpart DATE: 25/02/27 12:49:18 GMT FROM: Daniele B. Malesani at IMAPP / Radboud University d.malesani@astro.ru.nl
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), report on behalf of a larger collaboration:
We 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).
Template 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:
RA(J2000) = 09:25:04.07 Dec(J2000) = -04:53:40.2
This 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.
The 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.
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