GCN Circular 11610

D. Grupe (PSU) reports on behalf of the Swift-XRT team:

We have analyzed 11 ks of XRT data for GRB 110128A (Grupe  et al. GCN
Circ. 11603
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 ), from 125 s to 30.0 ks after the  BAT trigger. The data
comprise 9 s in Windowed Timing (WT) mode (taken while Swift was
slewing), with the remainder in Photon Counting (PC) mode. The enhanced
XRT position for this burst was given by Osborne et al. (GCN. Circ
11606).

The light curve can be modeled with an initial decay slope alpha-1 =
2.3+/-0.5 and a break at 700 (-200,+600) s followed by a decay slope of
alpha-2 = 0.6+/-0.3. Currently we are in the plateau phase. At this
point predictions of the behavior of the light curve are unreliable.


A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.64 (+0.22, -0.21). The
best-fitting absorption column is  consistent with the Galactic value
of 9.0 x 10^19 cm^-2 (Kalberla et al. 2005). The counts to observed
(unabsorbed) 0.3-10 keV flux conversion factor deduced from this
spectrum  is 4.0 x 10^-11 (4.1 x 10^-11) erg cm^-2 count^-1.

A summary of the PC-mode spectrum is thus:
Galactic foreground: 9.0 x 10^19 cm^-2
Intrinsic column:    0.0 (+3.0, -0.0) x 10^21 cm^-2
at z=2.339
Photon index:	     1.64 (+0.22, -0.21)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00443861.

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