GCN Circular 42096

D.N. Burrows (PSU), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi  (INAF-IASFPA) , M.
Capalbi (INAF-OAR), S. Lanava (PSU), S. Dichiara (PSU) and P.A. Evans
report on behalf of the Swift-XRT team:

We have analysed 6.8 ks of XRT data for GRB 251003A, from 59 s to 34.6
ks after the   trigger. The data comprise 126 s in Windowed Timing (WT)
mode (the first 8 s were taken while Swift was slewing) with the
remainder in Photon Counting (PC) mode. 

The late-time light curve (from T0+4.6 ks) can be modelled with a
power-law decay with a decay index of alpha=0.6 (+0.4, -0.3).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.67 (+0.11, -0.10). The
best-fitting absorption column is  1.4 (+3.0, -1.4) x 10^22 cm^-2, at a
redshift of 4.412, in addition to the Galactic value of 4.4 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 2.8 x
10^-11 (7.5 x 10^-11) erg cm^-2 count^-1. 

A summary of the WT-mode spectrum is thus:
Galactic foreground: 4.4 x 10^21 cm^-2
Intrinsic column:    1.4 (+3.0, -1.4) x 10^22 cm^-2 at z=4.412
Photon index:	     2.67 (+0.11, -0.10)

If the light curve continues to decay with a power-law decay index of
0.6, the count rate at T+24 hours will be 8.2 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.3 x
10^-13 (6.1 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/01400964.

This circular is an official product of the Swift-XRT team.