D.N. Burrows (PSU), C. Pagani (U. Leicester), A.P. Beardmore (U.
Leicester), P.A. Evans (U. Leicester), G. Stratta (ASDC), P. D'Avanzo
(INAF-OAB), V. D'Elia (ASDC), J.A. Kennea (PSU), M.C. Stroh (PSU) and
J.K. Cannizzo report on behalf of the Swift-XRT team:
We have analysed 11 ks of XRT data for GRB 130505A (Cannizzo et al.
GCN Circ. 14563), from 102 s to 29.4 ks after the BAT trigger. The
data comprise 503 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Evans et al. (GCN. Circ 14569).
The late-time light curve (from T0+3.7 ks) can be modelled with a
power-law decay with a decay index of alpha=1.06 (+0.03, -0.04).
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.86 (+/-0.03). The
best-fitting absorption column is 10.0 (+/-0.7) x 10^20 cm^-2, in
excess of the Galactic value of 3.6 x 10^20 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 1.92 (+/-0.07) and a
best-fitting absorption column of 8.8 (+1.6, -1.5) x 10^20 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum is 3.8 x 10^-11 (4.7 x 10^-11) erg cm^-2
A summary of the PC-mode spectrum is thus:
Total column: 8.8 (+1.6, -1.5) x 10^20 cm^-2
Galactic foreground: 3.6 x 10^20 cm^-2
Excess significance: 5.6 sigma
Photon index: 1.92 (+/-0.07)
If the light curve continues to decay with a power-law decay index of
1.06, the count rate at T+24 hours will be 0.27 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.0 x
10^-11 (1.3 x 10^-11) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at
This circular is an official product of the Swift-XRT team.