TITLE: GCN CIRCULAR NUMBER: 39757 SUBJECT: GRB 250317B: LCO detection of the fading optical afterglow DATE: 25/03/17 09:34:57 GMT FROM: Ismael Perez-Fournon at Instituto de Astrofisica de Canarias ipf@iac.es
I. Pérez-Fournon, F. Poidevin (IAC and ULL), D. Cano-Morales, I. Correa-Plasencia, and A.E. Hernández-Díaz (ULL)
We report Las Cumbres Observatory Global Telescope network (LCOGT) observations of the field of GRB 250317B, discovered by SVOM/ECLAIRs (Zhao et al., GCN circ. 39752 and GCN circ. 39753) and SVOM/MXT (Zhao et al., GCN circ. 39752 and GCN circ. 39753; and Götz et al., GCN circ. 39756). We observed the field of GRB 250317B with one of the two LCOGT 1-m telescopes, equipped with Sinistro cameras, located at the LCOGT node at McDonald Observatory (Texas). We obtained a 300-sec exposure in the SDSS r' filter starting at 2025-03-17 07:26:01 UT, about 5.23 hours after the SVOM trigger. An uncatalogued source is clearly detected at the position of the optical afterglow detected by SVOM/F-GFT (COLIBRÍ) (Watson et al., GCN circ. 39754) and SVOM/VT (Palmerio et al., GCN circ. 39755).
We measure the following AB magnitude, calibrated against Pan-STARRS DR2 stars and not corrected for Galactic extinction:
Time (UT, mid term) | mag | error | filter | ---------------------------------------------- 2025-03-17T07:28:31 19.27 0.05 r'
This work makes use of observations from the Las Cumbres Observatory global telescope network (LCOGT observing programme IAC2025A-009, SGLF).
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