GCN Circular 17203

B.P. Gompertz (U. Leicester), M. de Pasquale (INAF-IASFPA), A. Maselli 
(INAF-IASFPA), A. Melandri (INAF-OAB), M.C. Stroh (PSU), D.N. Burrows
(PSU), J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester) and J.R. Cummings report on behalf of the Swift-XRT team:

We have analysed 6.8 ks of XRT data for GRB 141220A (Cummings  et al.
GCN Circ. 17196
Not found
 
 
),  from 87 s to 36.3 ks after the  BAT trigger. The
data comprise 42 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 refined XRT position is RA, Dec = 195.0653, +32.1466
which is equivalent to:

RA (J2000): 13 00 15.66
Dec(J2000): +32 08 47.9

with an uncertainty of 3.6 arcsec (radius, 90% confidence).

The late-time light curve (from T0+5.6 ks) can be modelled with  a
power-law decay with a decay index of alpha=1.38 (+0.26, -0.23).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.81 (+0.21, -0.20). The
best-fitting absorption column is  8.3 (+5.9, -5.1) x 10^20 cm^-2, in
excess of the Galactic value of 1.3 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 3.7 x 10^-11 (4.2 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     8.3 (+5.9, -5.1) x 10^20 cm^-2
Galactic foreground: 1.3 x 10^20 cm^-2
Excess significance: 2.3 sigma
Photon index:	     1.81 (+0.21, -0.20)

If the light curve continues to decay with a power-law decay index of
1.38, the count rate at T+24 hours will be 2.6 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 9.5 x
10^-14 (1.1 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/00621915.

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