GCN Circular 33111

M. Capalbi (INAF-IASFPA), M. Perri (SSDC & INAF-OAR), J.A. Kennea
(PSU), A. Tohuvavohu (U. Toronto), D.N. Burrows (PSU), P.A. Evans (U.
Leicester), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), V.
D'Elia (SSDC & INAF-OAR) and S.B. Cenko report on behalf of the
Swift-XRT team:

We have analysed 6.2 ks of XRT data for GRB 221226B (Cenko et al. GCN
Circ. 33108
Not found
 
 
), from 56 s to 40.4 ks after the  BAT trigger. The data
comprise 14 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. 33109
Not found
 
 
).

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.58 (+0.13, -0.12).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.5 (+0.4, -0.3). The
best-fitting absorption column is  7 (+23, -7) x 10^21 cm^-2, at a
redshift of 2.694, in addition to the Galactic value of 1.7 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 4.3 x
10^-11 (4.6 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 1.7 x 10^20 cm^-2
Intrinsic column:    7 (+23, -7) x 10^21 cm^-2 at z=2.694
Photon index:	     1.5 (+0.4, -0.3)

If the light curve continues to decay with a power-law decay index of
1.58, the count rate at T+24 hours will be 6.9 x 10^-5 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.0 x
10^-15 (3.2 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/01145959.

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