GCN Circular 42160

A.P. Beardmore (U. Leicester), M. Perri (SSDC & INAF-OAR), V. D'Elia
(SSDC & INAF-OAR), B. Sbarufatti (INAF-OAB), J.A. Kennea (PSU), D.N.
Burrows (PSU), S. Lanava (PSU), J.P. Osborne (U. Leicester) and P.A.
Evans report on behalf of the Swift-XRT team:

We have analysed 6.4 ks of XRT data for GRB 251007B, from 134 s to 33.2
ks after the   trigger. The data comprise 6 s in Windowed Timing (WT)
mode (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=1.68 (+0.24, -0.26).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.79 (+0.39, -0.25). The
best-fitting absorption column is  6.5 (+3.1, -0.5) x 10^21 cm^-2,
consistent with the Galactic value of 6.0 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 5.0 x 10^-11 (7.5 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     6.5 (+3.1, -0.5) x 10^21 cm^-2
Galactic foreground: 6.0 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.79 (+0.39, -0.25)

If the light curve continues to decay with a power-law decay index of
1.68, the count rate at T+24 hours will be 3.9 x 10^-5 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.9 x
10^-15 (2.9 x 10^-15) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/01402467.

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