TITLE: GCN CIRCULAR NUMBER: 43131 SUBJECT: GRB 251214B: VLT/X-shooter observations DATE: 25/12/15 17:56:34 GMT FROM: Antonio de Ugarte Postigo at LAM, CNRS <adeugartepostigo@gmail.com> A. de Ugarte Postigo (LAM), D. B. Malesani (DAWN/NBI and Radboud), M. Garnichey (LUX-Paris Obs.), J. An (NAOC), G. Corcoran (UCD), L. Izzo (INAF/OACn & DARK/NBI), A. Martin-Carrillo (UCD), A. Saccardi (CEA/Irfu), A. L. Thakur (INAF/IAPS), A. Torralba (ISTA) and Y. Ma (Princeton U.) report on behalf of the Stargate collaboration: We observed the optical counterpart of GRB 251214B detected by Fermi (Fermi GBM team, GCN 43088), Swift (Eyles-Ferris et al., GCN 43089) and GECAM-B (Luo et al., GCN 43113) with X-shooter mounted on the UT3 (Melipal) of ESO’s Very Large Telescope (Paranal Observatory, Chile). Observations were conducted in twilight and at large airmass. The acquisition images, which started at 00:46:54 UT of 15 Dec 2025 (15.74 hr after the burst onset) show the counterpart with the following photometry (AB magnitudes), as compared to field stars from the SDSS catalogue: g = 23.15 +/- 0.06 r = 22.19 +/- 0.04 z = 20.76 +/- 0.05 A 2x600 s spectrum followed, covering the spectral range between 3000 and 21000 AA. The spectrum shows a red continuum, consistent with the photometry, only detectable above 6000 AA, and more prominent at infrared wavelengths. We do not detect clear emission features from the underlying host galaxy (mentioned by Gress et al., GCN 43095 and Watson et al., GCN 43103), which prevents us from measuring its redshift. We note that the Legacy Survey reveals that the source underlying the afterglow is composed of two blobs, a fainter one right under the GRB and a brighter one towards the North East, at a distance of 1". The slight difference between our photometry and the one of COLIBRÍ (Watson et al., GCN 43103) could be due to the different contribution of these underlying sources within the photometric aperture. We acknowledge expert support from the ESO observing staff in Paranal, in particular Claudia Paladini, Célia Desgrange, Cecila Bustos, and Ana Jimenez-Gallardo. View this GCN Circular online at https://gcn.nasa.gov/circulars/43131. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0LW...