GCN Circular 14112

O.M. Littlejohns (U. Leicester), B. Sbarufatti (INAF-OAB/PSU), G.
Stratta (ASDC), P. D'Avanzo (INAF-OAB), D.N. Burrows (PSU), J.A. Kennea
(PSU), M.C. Stroh (PSU), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester) and H.A. Krimm report on behalf of the Swift-XRT team:

We have analysed 10 ks of XRT data for GRB 121226A (Krimm  et al. GCN
Circ. 14105
Not found
 
 
),  from 109 s to 35.4 ks after the	BAT trigger. The data
are entirely in Photon Counting (PC) mode. The best available XRT
position  (using the promptly downlinked event data, the XRT-UVOT
alignment and matching UVOT field sources to the USNO-B1 catalogue) is
RA, Dec = 168.6423, -30.4064 which is equivalent to:

RA (J2000): 11 14 34.14
Dec(J2000): -30 24 23.1

with an uncertainty of 2.1 arcsec (radius, 90% confidence).

The light curve can be modelled with  a power-law decay with a decay
index of alpha=0.98 (+/-0.06).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.4 (+/-0.4). The
best-fitting absorption column is  8.2 (+2.5, -2.1) x 10^21 cm^-2, in
excess of the Galactic value of 6.1 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 4.4 x 10^-11 (1.2 x 10^-10) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     8.2 (+2.5, -2.1) x 10^21 cm^-2
Galactic foreground: 6.1 x 10^20 cm^-2
Excess significance: 6.0 sigma
Photon index:	     2.4 (+/-0.4)

If the light curve continues to decay with a power-law decay index of
0.98, the count rate at T+24 hours will be 1.5 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.7 x
10^-14 (1.9 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/00544027.

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