TITLE: GCN CIRCULAR NUMBER: 42860 SUBJECT: GRB 251126A: Swift-XRT refined Analysis DATE: 25/11/27 13:02:50 GMT FROM: Phil Evans at U of Leicester pae9@star.le.ac.uk
K.L. Page (U. Leicester), M. Capalbi (INAF-OAR), M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU), A.P. Beardmore (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team:
We have analysed 6.2 ks of XRT data for GRB 251126A, from 66 s to 56.7 ks after the trigger. The data comprise 9 s in Windowed Timing (WT) mode (taken while Swift was slewing), with the remainder in Photon Counting (PC) mode.
The light curve can be modelled with a series of power-law decays. The initial decay index is alpha=3.5 (+0.6, -0.5). At T+210 s the decay flattens to an alpha of -0.50 (+0.00, -0.17) before breaking again at T+1954 s to a final decay with index alpha=1.13 (+0.21, -0.16).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.11 (+0.25, -0.24). The best-fitting absorption column is 1.7 (+0.8, -0.7) x 10^21 cm^-2, in excess of the Galactic value of 9.5 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.3 x 10^-11 (4.6 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus: Total column: 1.7 (+0.8, -0.7) x 10^21 cm^-2 Galactic foreground: 9.5 x 10^20 cm^-2 Excess significance: 1.8 sigma Photon index: 2.11 (+0.25, -0.24)
If the light curve continues to decay with a power-law decay index of 1.13, the count rate at T+24 hours will be 8.5 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.8 x 10^-13 (3.9 x 10^-13) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at https://www.swift.ac.uk/xrt_products/01417793.
This circular is an official product of the Swift-XRT team.
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