GCN Circular 15441

D.N. Burrows (PSU), J.A. Kennea (PSU), V. Mangano (PSU), J.P. Osborne
(U. Leicester), K.L. Page (U. Leicester), C. Pagani (U. Leicester), B.
Sbarufatti (INAF-OAB/PSU), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC) and
J.R. Cummings report on behalf of the Swift-XRT team:

We have analysed 9.1 ks of XRT data for GRB 131103A (Cummings  et al.
GCN Circ. 15440
Not found
 
 
),  from 82 s to 25.5 ks after the  BAT trigger. The
data comprise 793 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The refined XRT position is RA, Dec =
348.9213, -44.6377 which is equivalent to:

RA (J2000): 23 15 41.11
Dec(J2000): -44 38 15.7

with an uncertainty of 3.5 arcsec (radius, 90% confidence).

The late-time light curve (from T0+5.9 ks) can be modelled with  a
power-law decay with a decay index of alpha=1.16 (+/-0.26).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.76 (+0.27, -0.25). The
best-fitting absorption column is  4.0 (+0.8, -0.7) x 10^21 cm^-2, in
excess of the Galactic value of 1.1 x 10^20 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 2.15 (+0.18, -0.17)
and a best-fitting absorption column of 3.5 (+0.7, -0.6) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 4.0 x 10^-11 (7.2 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     3.5 (+0.7, -0.6) x 10^21 cm^-2
Galactic foreground: 1.1 x 10^20 cm^-2
Excess significance: 8.9 sigma
Photon index:	     2.15 (+0.18, -0.17)

If the light curve continues to decay with a power-law decay index of
1.16, the count rate at T+24 hours will be 6.4 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.6 x
10^-13 (4.6 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/00576562.

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