TITLE: GCN CIRCULAR NUMBER: 38508 SUBJECT: GRB 241209D: Swift-XRT refined Analysis DATE: 24/12/10 00:31:53 GMT FROM: Phil Evans at U of Leicester pae9@star.le.ac.uk
K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), S. Dichiara (PSU), J.A. Kennea (PSU), D.N. Burrows (PSU) and P.A. Evans report on behalf of the Swift-XRT team:
We have analysed 6.4 ks of XRT data for GRB 241209D, from 260 s to 37.7 ks after the BAT trigger. The data comprise 22 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode.
The light curve can be modelled with an initial power-law decay with an index of alpha=4.3 (+3.4, -2.5), followed by a break at T+626 s to an alpha of 0.66 (+/-0.13).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.89 (+0.29, -0.26). The best-fitting absorption column is 5.9 (+6.9, -3.6) x 10^20 cm^-2, consistent with the Galactic value of 2.3 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 3.5 x 10^-11 (4.0 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus: Total column: 5.9 (+6.9, -3.6) x 10^20 cm^-2 Galactic foreground: 2.3 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.89 (+0.29, -0.26)
If the light curve continues to decay with a power-law decay index of 0.66, the count rate at T+24 hours will be 0.014 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.1 x 10^-13 (5.8 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/01273106.
This circular is an official product of the Swift-XRT team.
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