TITLE:   GCN CIRCULAR
NUMBER:  39524
SUBJECT: GRB 250226A / EP250226a: LCO detection of the afterglow
DATE:    25/02/27 23:22:56 GMT
FROM:    Ismael Perez-Fournon at Instituto de Astrofisica de Canarias <ipf@iac.es>

F. Poidevin, I. Pérez-Fournon (IAC and ULL), D. Cano-Morales, I. Correa-Plasencia, and A.E. Hernández-Díaz (ULL)

We observed the location of the long-duration GRB 250226A / EP250226a discovered by Fermi GBM (Fermi GBM team, GCN circ. 39479) and EP WXT and FXT (Jiang et al., GCN circ. 39482; Jiang et al., GCN circ. 39513) and detected also by GECAM-B (Zhang et al., GCN circ. 39492) and INTEGRAL SPI-ACS and PICsIT (Thakur et al., GCN circ. 39518) with two Las Cumbres Observatory Global Telescope network (LCOGT) 1-m telescopes, equipped with Sinistro cameras, located at the LCOGT node at Sutherland Observatory (South Africa). Simultaneous 300-sec exposures were obtained in the SDSS i' and r' filters starting at about 18.89 hr after the Fermi trigger. We detect the optical afterglow  at the location reported by An et al. (GCN circ. 39486) and with optical detections by other groups (Zhu et al., GCN circ. 39487; Magnani et al., GCN circ. 39488; Li et al.,  GCN circ. 39489; Aryan et al., GCN circ. 39509; Zou et al., GCN circ. 39511; Li et al., GCN circ. 39514; and Junjie-Jin et al., GCN circ. 39515). A redshift of z = 3.315 has been reported by Zhu et al. (GCN circ. 39487). 

We measure the following magnitudes, calibrated against Pan-STARRS DR2 stars and not corrected for Galactic extinction:

Date       |  UT start | t_mid - t0 (hours)   | mag | error | filter |
----------------------------------------------------------------------
2025-02-27   01:28:39         18.94            21.22  0.29     i'
2025-02-27   01:28:40         18.94            21.44  0.36     r'


This work makes use of observations from the Las Cumbres Observatory global telescope network (LCOGT observing programme IAC2025A-009, SGLF).