GCN Circular 15993

C. Pagani (U. Leicester), A. Melandri (INAF-OAB), B. Sbarufatti
(INAF-OAB/PSU), P. D'Avanzo (INAF-OAB), V. Mangano (PSU), M.C. Stroh
(PSU), D.N. Burrows (PSU), A.P. Beardmore (U. Leicester), P.A. Evans
(U. Leicester) and S.B. Cenko report on behalf of the Swift-XRT team:

We have analysed 6.7 ks of XRT data for GRB 140318A (Cenko  et al. GCN
Circ. 15986
Not found
 
 
),  from 114 s to 46.2 ks after the	BAT trigger. The data
comprise 219 s in Windowed Timing (WT) mode (the first 9 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. The enhanced XRT position for this burst was given by Goad et al.
(GCN Circ. 15991
Not found
 
 
).

The light curve can be modelled with an initial power-law decay with an
index of alpha=0.48 (+/-0.20), followed by a break at T+263 s to an
alpha of 1.88 (+0.07, -0.06).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.21 (+0.12, -0.11). The
best-fitting absorption column is  1.14 (+0.27, -0.25) x 10^21 cm^-2,
in excess of the Galactic value of 2.6 x 10^20 cm^-2 (Kalberla et al.
2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 2.9 x 10^-11 (3.9 x 10^-11) erg
cm^-2 count^-1. 

A summary of the WT-mode spectrum is thus:
Total column:	     1.14 (+0.27, -0.25) x 10^21 cm^-2
Galactic foreground: 2.6 x 10^20 cm^-2
Excess significance: 5.8 sigma
Photon index:	     2.21 (+0.12, -0.11)

If the light curve continues to decay with a power-law decay index of
1.88, the count rate at T+24 hours will be 2.1 x 10^-4 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.2 x
10^-15 (8.3 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/00592204.

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