GCN Circular 11390

A. Melandri, R. Margutti and B. Sbarufatti (INAF-OAB) report on  
behalf of the Swift-XRT team:

We have analysed 7.4 ks of XRT data for GRB 101030A (Melandri et al.  
GCN Circ. 11386
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 ), from 71 s to 19.2 ks after the BAT trigger. The  
data comprise 118 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 11387).

The light curve can be modelled with a series of power-law decays.  
The initial decay index is alpha=2.32 (+0.26, -0.33). At T+112 s the  
decay steepens to an alpha of 3.97 (+0.24, -0.22). The light curve  
breaks again at T+478 s to a decay with alpha=-0.08 (+0.18, -1.43),  
before a final break at T+5105 s after which the decay index is 1.12  
(+0.22, -0.21).

A spectrum formed from the WT mode data can be fitted with an  
absorbed power-law with a photon spectral index of 2.87 (+0.15,  
-0.13). The best-fitting absorption column is 1.83 (+0.26, -0.24) x  
10^21 cm^-2, in excess of the Galactic value of 4.2 x 10^20 cm^-2  
(Kalberla et al. 2005). The PC mode spectrum has a photon index of  
2.11 (+0.12, -0.20) and a best-fitting absorption column of 8.1  
(+2.7, -3.9) x 10^20 cm^-2. The counts to observed (unabsorbed)  
0.3-10 keV flux conversion factor deduced from this spectrum is 3.6 x  
10^-11 (4.6 x 10^-11) erg cm^-2 count^-1.

If the light curve continues to decay with a power-law decay index of  
1.12, the count rate at T+24 hours will be 4.7 x 10^-3 count s^-1,  
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.7 x  
10^-13 (2.2 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/00437408.

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