TITLE: GCN CIRCULAR NUMBER: 42052 SUBJECT: GRB 251001B: Swift-XRT refined Analysis DATE: 25/10/02 07:52:16 GMT FROM: Phil Evans at U of Leicester pae9@star.le.ac.uk
S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB) and P.A. Evans report on behalf of the Swift-XRT team:
We have analysed 7.8 ks of XRT data for GRB 251001B, from 99 s to 40.1 ks after the trigger. The data comprise 540 s in Windowed Timing (WT) mode (the first 10 s were taken while Swift was slewing) 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=1.34 (+/-0.06).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.92 (+0.08, -0.07). The best-fitting absorption column is 8.8 (+2.0, -1.9) x 10^20 cm^-2, in excess of the Galactic value of 2.6 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.74 (+0.19, -0.18) and a best-fitting absorption column of 8.6 (+5.7, -4.8) x 10^20 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.9 x 10^-11 (4.5 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus: Total column: 8.6 (+5.7, -4.8) x 10^20 cm^-2 Galactic foreground: 2.6 x 10^20 cm^-2 Excess significance: 2.1 sigma Photon index: 1.74 (+0.19, -0.18)
If the light curve continues to decay with a power-law decay index of 1.34, the count rate at T+24 hours will be 9.6 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.8 x 10^-14 (4.3 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/01400467.
This circular is an official product of the Swift-XRT team.
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