GCN Circular 10719

J. Mao (INAF-OAB) reports on behalf of the Swift-XRT team:

We have analysed 8.7 ks of Swift XRT data for GRB 100504A (Mao et al. 
GCN Circ. 10712
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 ). The data comprise 120 s in Windowed Timing (WT) mode 
with the remainder in Photon Counting (PC) mode.

The light curve shows evidence of flaring in WT mode, peaking at about 
83 s, after that, the light curve can be modelled with a broken 
power-law in PC mode, with an initial decay index of 
alpha1=3.04(+/-0.57) and breaking to a decay of index 
alpha2=0.57(+/-0.06), the break time is about 450 s.

A spectrum formed from the WT mode data can be fitted with an absorbed 
power-law with a photon spectral index of 1.95 (+/-0.09). The 
best-fitting absorption column is 9.07 (+/-0.71) x 10^21 cm^-2, in 
excess of the Galactic value of 3.77 x 10^21 cm^-2 (Kalberla et al. 
2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion 
factor deduced from this spectrum is 5.96 x 10^-11 (9.31 x 10^-11) erg 
cm^-2 count^-1.

The spectrum formed from the PC mode data can be fitted with an absorbed 
power-law with a photon spectral index of 2.40 (+/-0.37) and the 
absorption column density is consistent with the Galactic one in the GRB 
direction. The counts to observed (unabsorbed) 0.3-10 keV flux 
conversion factor deduced from this spectrum is 5.56 x 10^-11 (6.72 x 
10^-11) erg cm^-2 count^-1.

If the light curve continues to decay with a power-law decay index of 
0.57, the count rate at T+24 hours will be 6.9 x 10^-3 count s^-1, 
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.8 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/00421124.

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