TITLE: GCN CIRCULAR NUMBER: 42491 SUBJECT: GRB 251026B: Swift-XRT observations of GOTO25jgl/AT2025absf DATE: 25/10/27 20:04:15 GMT FROM: Phil Evans at U of Leicester pae9@star.le.ac.uk

J.P. Osborne (U. Leicester), C. Salvaggio (INAF-OAB), M. Ferro (INAF-OAB), R. Brivio (INAF-OAB), D.N. Burrows (PSU), S. Lanava (PSU), S. Dichiara (PSU), K.L. Page (U. Leicester) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:

Swift-XRT has performed follow-up observations of the Fermi/GBM-detected burst GRB 251026B, collecting 2.0 ks of Photon Counting (PC) mode data between T0+116.7 ks and T0+122.7 ks, centred on the tentative GOTO optical counterpart candidate (GCN Circ. 42470).

No X-ray sources have been detected consistent with the estimated 3-sigma GOTO error region (0.8 arcsec). The 3-sigma upper limit in the field ranges from ~0.004 to ~0.005 ct s^-1, corresponding to a 0.3-10 keV observed flux of 1.7e-13 to 2.1e-13 erg cm^-2 s^-1 (assuming a typical GRB spectrum).

The results of the XRT-team automatic analysis of the XRT observations, including a position-specific upper limit calculator, are available at https://www.swift.ac.uk/ToO_GRBs/00021872.

This circular is an official product of the Swift-XRT team.

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