GCN Circular 22486

S. J. LaPorte (PSU), J.A. Kennea (PSU), A.P. Beardmore (U. Leicester),
P.A. Evans (U. Leicester), S.L. Gibson (U. Leicester), A. D'Ai
(INAF-IASFPA), A. Melandri (INAF-OAB), B. Sbarufatti (INAF-OAB/PSU) and
P. D'Avanzo report on behalf of the Swift-XRT team:

We have analysed 8.7 ks of XRT data for GRB 180314A (D'Avanzo et al.
GCN Circ. 22478
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 ), from 165 s to 37.0 ks after the  BAT trigger. The
data comprise 181 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Osborne et al. (GCN Circ. 22480
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 ).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=2.60 (+0.04, -0.17). At T+328 s  the decay
steepens to an alpha of 5.8 (+2.2, -1.0) before breaking again at T+401
s to a final decay with index alpha=0.94 (+/-0.03).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.34 (+0.08, -0.04). The
best-fitting absorption column is  consistent with the Galactic value
of 1.5 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has
a photon index of 1.77 (+/-0.07) 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 3.9 x
10^-11 (4.7 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 1.5 x 10^21 cm^-2
Intrinsic column:    1.5 (+0.8, -0.0) x 10^21 cm^-2 at z=1.445
Photon index:	     1.77 (+/-0.07)

If the light curve continues to decay with a power-law decay index of
0.94, the count rate at T+24 hours will be 0.014 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 5.7 x
10^-13 (6.9 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/00814129.

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