TITLE: GCN CIRCULAR NUMBER: 40835 SUBJECT: GRB 250625A: Swift-XRT refined Analysis DATE: 25/06/26 05:57:53 GMT FROM: Phil Evans at U of Leicester pae9@star.le.ac.uk
S. Dichiara (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), M. Capalbi (INAF-OAR), M. Perri (SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), J.A. Kennea (PSU), D.N. Burrows (PSU) and P.A. Evans report on behalf of the Swift-XRT team:
We have analysed 6.0 ks of XRT data for GRB 250625A, from 123 s to 45.1 ks after the trigger. The data comprise 58 s in Windowed Timing (WT) mode 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=0.8 (+1.1, -1.2). At T+174 s the decay steepens to an alpha of 6.3 (+/-1.7) before breaking again at T+238 s to a final decay with index alpha=1.19 (+0.17, -0.15).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.68 (+0.32, -0.29). The best-fitting absorption column is 1.7 (+1.3, -1.0) x 10^21 cm^-2, in excess of the Galactic value of 5.5 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 4.3 x 10^-11 (5.2 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus: Total column: 1.7 (+1.3, -1.0) x 10^21 cm^-2 Galactic foreground: 5.5 x 10^20 cm^-2 Excess significance: 1.9 sigma Photon index: 1.68 (+0.32, -0.29)
If the light curve continues to decay with a power-law decay index of 1.19, the count rate at T+24 hours will be 5.0 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.2 x 10^-14 (2.6 x 10^-14) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01327910.
This circular is an official product of the Swift-XRT team.
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