TITLE: GCN CIRCULAR NUMBER: 42963 SUBJECT: EP251130a: ULL-ASTRO-MASTER late detection of the optical afterglow with LCO 1-m telescope at Teide Observatory DATE: 25/12/02 19:57:57 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias ipf@iac.es

T. Tundidor Rodríguez, J. Basurto Merino, P.G. Berdayes, A. Caballero-Almagro, A. Cerón, M. Contreras, F. Díaz-Segado, T. Ferrer-Laviña, B. Gandolfi, V. Ghiraldo, J. Hernández Fung, L. Juliá-Maroto, E. Lekaroz-Urriza, M. Manzano García, E. Mejía-Martínez, J. Prieto Polo, M. Pulido-Torres, M. Quintana-Ansaldo, A. Schenone-Zanuzzi, A. Selezneva, E. Urquijo-Rodríguez (all ULL), M. Abdul-Masih (IAC and ULL), and I. Pérez-Fournon (IAC and ULL).

We report on observations of the optical counterpart of the X-ray transient EP251130a, detected by the Wide-field X-ray Telescope (WXT) on board the Einstein Probe (EP) mission (Wu et al., GCN Circ. 42903) and with detections of Swift-XRT (Evans et al., GCN Circ. 42908) and of the EP Follow-up X-ray Telescope (FXT) (Zhang et al., GCN Circ. 42915).

We observed the field of EP251130a with one of the two Las Cumbres Observatory (LCO) 1-m telescopes equipped with Sinistro cameras located at the LCO node at Teide Observatory, Tenerife, Canary Islands, Spain. The observation, a single exposure of 500 sec in the SDSS i' filter, started on 2025-12-01 at 23:31:37 UT, about 36.40 hours after the EP-WXT trigger. The optical counterpart first reported by Dornic et al. (GCN Circ. 42904) is clearly detected in our image with a magnitude of i' = 20.68 +/- 0.14 (AB), calibrated against PanSTARRS-1 DR2 stars and not corrected for Galactic extinction. Our result is consistent with other optical observations (Lipunov et al., GCN Circ. 42906; He et al., GCN Circ. 42914; Gupta et al., GCN Circ. 42916; Zheng et al., GCN Circ. 42917; van Dalen et al., GCN Circ. 42918; Moskvitin and Spiridonova, GCN Circ. 42919; Aryan et al., GCN Circ. 42921; Volnova et al., GCN Circ. 42922; Ma et al., GCN Circ. 42940; and Corcoran et al., GCN Circ. 42951).

van Dalen et al. (GCN Circ. 42918) have reported a redshift of z = 4.035 using GTC OSIRIS+.

This work makes use of observations from the Las Cumbres Observatory global telescope network (LCO program IAC2025B-010). These observations are part of a course in Astrophysical Techniques of the Master in Astrophysics of the Astrophysics Department of the University of La Laguna in collaboration with the Instituto de Astrofísica de Canarias (La Laguna, Tenerife, Canary Islands, Spain).

This work made use of the Astro-COLIBRI platform (P. Reichherzer et al. 2021, ApJS, 256, 5).

View this GCN Circular online at https://gcn.nasa.gov/circulars/42963. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...