GCN Circular 14403

K.L. Page (U. Leicester) and M. De Pasquale (UCL-MSSL) report on behalf
of the Swift-XRT team:

We have analysed 2.7 ks of XRT data for GRB 130418A (De Pasquale  et
al. GCN Circ. 14377
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 ),  from 119 s to 15.6 ks after the	BAT trigger.
The data comprise 262 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 Evans et al. (GCN. Circ 14383).

The light curve can be modelled with an initial power-law decay with an
index of alpha=0.72 (+/-0.11), followed by a break at T+801 s to an
alpha of 1.51 (+0.54, -0.30).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.24 (+/-0.06). The
best-fitting absorption column is  2.9 (+7.3, -2.9) x 10^20 cm^-2, at a
redshift of 1.218, in addition to the Galactic value of 2.7 x 10^20
cm^-2 (Kalberla et al. 2005). The PC mode spectrum has a photon index
of 1.70 (+0.24, -0.23) and a best-fitting absorption column of 2.6
(+3.0, -2.5) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10
keV flux conversion factor deduced from this spectrum  is 4.2 x 10^-11
(4.8 x 10^-11) erg cm^-2 count^-1.

A summary of the PC-mode spectrum is thus:
Galactic foreground: 2.7 x 10^20 cm^-2
Intrinsic column:    2.6 (+3.0, -2.5) x 10^21 cm^-2 at z=1.218
Photon index:	     1.70 (+0.24, -0.23)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00553847.

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