GCN Circular 42052

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.