TITLE: GCN CIRCULAR NUMBER: 40354 SUBJECT: GRB 250504A: Swift-XRT refined Analysis DATE: 25/05/05 21:00:16 GMT FROM: Phil Evans at U of Leicester pae9@star.le.ac.uk
J.A. Kennea (PSU), D.N. Burrows (PSU), A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), A. Melandri (INAF-OAR), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), M. A. Williams (PSU) and P.A. Evans report on behalf of the Swift-XRT team:
We have analysed 6.9 ks of XRT data for GRB 250504A, from 81 s to 56.7 ks after the BAT trigger. The data comprise 47 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode.
The light curve can be modelled with a power-law decay with a decay index of alpha=1.26 (+0.05, -0.04).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.60 (+0.24, -0.22). The best-fitting absorption column is 2.9 (+1.4, -0.7) x 10^21 cm^-2, consistent with the Galactic value of 2.1 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.8 x 10^-11 (6.0 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus: Total column: 2.9 (+1.4, -0.7) x 10^21 cm^-2 Galactic foreground: 2.1 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 1.60 (+0.24, -0.22)
If the light curve continues to decay with a power-law decay index of 1.26, the count rate at T+24 hours will be 1.7 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.3 x 10^-14 (1.0 x 10^-13) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01310284.
This circular is an official product of the Swift-XRT team.
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