GCN Circular 11481

J.M. Gelbord (PSU) reports on behalf of the Swift-XRT team:

We have analysed 17 ks of XRT data for GRB 101219B (Gelbord et al.
GCN Circ. 11473
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 ), from 136 s to 65.2 ks after the BAT trigger. The
data comprise 415 s in Windowed Timing (WT) mode (the first 9 s were
taken while Swift was slewing) with the remainder in Photon Counting
(PC) mode. The enhanced XRT position for this burst was given by
Beardmore et al. (GCN. Circ 11480).

The light curve (from T0+425 s) can be modelled with a series of
power-law decays. The decay from T+425 s is steep, with an index of
alpha=4.16 (+2.3, -0.50).  At T+638 s the decay flattens to an
alpha of 2.35 (+0.31, -0.46).  Another break at T+4.7 ks is
followed by a flatter decay of alpha = 0.23 (+/-0.15).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.68 (+/- 0.04). The
best-fitting absorption column is consistent with the Galactic value
of 3.14 x 10^20 cm^-2 (Kalberla et al. 2005). The PC mode spectrum has
a photon index of 1.69 (+0.12, -0.11) and a best-fitting absorption
column consistent with the Galactic value. The counts to observed
(unabsorbed) 0.3-10 keV flux conversion factor deduced from this
spectrum  is 4.1 x 10^-11 (4.3 x 10^-11) erg cm^-2 count^-1.

A summary of the PC-mode spectrum is thus:
Total column:	     3.1 (+0.9, -3.1) x 10^20 cm^-2
Galactic foreground: 3.14 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.69 (+0.12, -0.11)

If the light curve continues to decay with a power-law decay index of
0.23, the count rate at T+24 hours will be 0.0060 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x
10^-13 (1.3 x 10^-13) erg cm^-2 s^-1.  The count rate at T+48 hours
would be 0.0051 count s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00440635.

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