TITLE:   GCN CIRCULAR
NUMBER:  43112
SUBJECT: GRB 251214B: Swift-XRT refined Analysis
DATE:    25/12/15 09:28:13 GMT
FROM:    Phil Evans at U of Leicester <pae9@star.le.ac.uk>

D.N. Burrows (PSU), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), S. Campana
(INAF-OAB), S. Lanava (PSU), S. Dichiara (PSU) and P.A. Evans report on
behalf of the Swift-XRT team:

We have analysed 5.9 ks of XRT data for GRB 251214B, from 46 s to 28.7
ks after the   trigger. The data comprise 8 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 an initial power-law decay with an
index of alpha=0.72 (+0.14, -0.17), followed by a break at T+418 s to
an alpha of 1.33 (+0.10, -0.08).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.82 (+0.19, -0.18). The
best-fitting absorption column is  1.6 (+0.7, -0.6) x 10^21 cm^-2, in
excess of the Galactic value of 4.0 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 3.9 x 10^-11 (4.9 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.6 (+0.7, -0.6) x 10^21 cm^-2
Galactic foreground: 4.0 x 10^20 cm^-2
Excess significance: 3.5 sigma
Photon index:	     1.82 (+0.19, -0.18)

If the light curve continues to decay with a power-law decay index of
1.33, the count rate at T+24 hours will be 1.6 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.3 x
10^-14 (7.8 x 10^-14) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
https://www.swift.ac.uk/xrt_products/01423875.

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