GCN Circular 11517

V. D'Elia, G. Stratta (ASDC) and S. R. Oates (MSSL-UCL) report on behalf
of the Swift-XRT team:

We have analysed 18.8 ks of XRT data for GRB 110102A (Oates et
al., GCN Circ. 11509
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 ), from 139 s to 47.5 ks after the  BAT trigger.
The data comprise 400 s in Windowed Timing (WT) mode with the
remainder in Photon Counting (PC) mode. The enhanced XRT position for
this burst was given by Goad et al. (GCN. Circ 11510).

The light curve shows an intital flaring activity, possibly associated
to the prompt event, followed by a canonical steep-flat-steep
behaviour, which can be modelled with double broken power-law
decay. The initial decay index is alpha= 8.6. At T+450 (+/- 0.05) s the
decay flattens to an alpha of 0.49 (+/-0.03). At T+11.38 (+/- 0.01) ks  
the decay steepens again to an alpha of 1.53 (+0.07 -0.09).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.48 (+/-0.04). The
best-fitting absorption column is  7.8 (+/- 1) x 10^20 cm^-2, in
excess of the Galactic value of 4.8 x 10^20 cm^-2 (Kalberla et al.
2005). The PC mode spectrum has a photon index of 2.27 (+/-0.07) and a
best-fitting absorption column of 1.28 (+/- 0.17) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.6 x 10^-11 (5.8 x 10^-11) erg cm^-2 count^-1.

If the light curve continues to decay with a power-law decay index of 1.6,
the count rate at T+48 hours will be 0.012 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of
4.3 x 10^-13 (7.0 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/00441454.

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

[GCN OPS NOTE(04jan11):  Per author's request, the "4.3 x 10^-12 (2.1 x 10^-13)"
in the 4th paragraph was changed to "4.3 x 10^-13 (7.0 x 10^-13)".]