TITLE: GCN CIRCULAR NUMBER: 40644 SUBJECT: GRB 250605A: Swift-XRT refined Analysis DATE: 25/06/06 11:02:50 GMT FROM: Phil Evans at U of Leicester pae9@star.le.ac.uk
A. Melandri (INAF-OAR), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), M.A. Williams (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team:
We have analysed 7.0 ks of XRT data for GRB 250605A, from 90 s to 50.2 ks after the trigger. The data comprise 149 s in Windowed Timing (WT) mode (the first 6 s were 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=4.36 (+0.19, -0.15). At T+164 s the decay flattens to an alpha of 3.19 (+0.29, -0.32) before breaking again at T+326 s to a final decay with index alpha=0.79 (+/-0.07).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.12 (+0.06, -0.05). The best-fitting absorption column is 2.59 (+0.20, -0.19) x 10^21 cm^-2, in excess of the Galactic value of 4.3 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.10 (+0.13, -0.12) and a best-fitting absorption column of 2.9 (+/-0.5) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.6 x 10^-11 (5.5 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus: Total column: 2.9 (+/-0.5) x 10^21 cm^-2 Galactic foreground: 4.3 x 10^20 cm^-2 Excess significance: 8.7 sigma Photon index: 2.10 (+0.13, -0.12)
If the light curve continues to decay with a power-law decay index of 0.79, the count rate at T+24 hours will be 0.085 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.0 x 10^-12 (4.7 x 10^-12) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01321323.
This circular is an official product of the Swift-XRT team.
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