C. Pagani (U. Leicester), G. Stratta (ASDC), P. D'Avanzo (INAF-OAB), V.
D'Elia (ASDC), D.N. Burrows (PSU), J.A. Kennea (PSU), M.C. Stroh (PSU),
A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester) and A.
Melandri report on behalf of the Swift-XRT team:
We have analysed 8.4 ks of XRT data for GRB 120722A (Melandri et al.
GCN Circ. 13499), from 161 s to 27.7 ks after the BAT trigger. The
data are entirely in Photon Counting (PC) mode. The enhanced XRT
position for this burst was given by Evans et al. (GCN. Circ 13502).
The light curve can be modelled with a power-law decay with a decay
index of alpha=0.85 (+0.12, -0.11).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.6 (+0.8, -0.7). The
best-fitting absorption column is 5.1 (+1.8, -1.5) x 10^22 cm^-2, in
excess of the Galactic value of 3.1 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 8.4 x 10^-11 (5.7 x 10^-10) erg
A summary of the PC-mode spectrum is thus:
Total column: 5.1 (+1.8, -1.5) x 10^22 cm^-2
Galactic foreground: 3.1 x 10^20 cm^-2
Excess significance: 5.6 sigma
Photon index: 2.6 (+0.8, -0.7)
The results of the XRT-team automatic analysis are available at
This circular is an official product of the Swift-XRT team.