GCN Circular 16510

K.L. Page (U. Leicester), C. Pagani (U. Leicester), A. Melandri
(INAF-OAB), B. Sbarufatti (INAF-OAB/PSU), P. D'Avanzo (INAF-OAB), M.C.
Stroh (PSU), D.N. Burrows (PSU), J.A. Kennea (PSU), A.P. Beardmore (U.
Leicester) and D. Kocevski report on behalf of the Swift-XRT team:

We have analysed 7.5 ks of XRT data for GRB 140703A (Kocevski  et al.
GCN Circ. 16503
Not found
 
 
),  from 104 s to 39.2 ks after the  BAT trigger. The
data comprise 126 s in Windowed Timing (WT) mode (the first 7 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 Goad
et al. (GCN Circ. 16506
Not found
 
 
).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=0.1 (+1.5, -1.6). At T+120 s  the decay
steepens to an alpha of 6.8 (+0.4, -0.3). The light curve breaks again
at T+158 s to a decay with alpha=5.1 (+/-0.4),	and  again at T+319 s s
to alpha=0.1 (+0.6, -0.4),  before a final break at T+7413 s s after
which the decay index is 1.56 (+0.14, -0.13).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.84 (+0.08, -0.07). The
best-fitting absorption column is  5.2 (+/-0.6) x 10^22 cm^-2, at a
redshift of 3.14, in addition to the Galactic value of 1.3 x 10^21
cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index
of 1.82 (+/-0.09) and a best-fitting absorption column of 5.4 (+8.0,
-5.4) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV
flux conversion factor deduced from this spectrum  is 3.8 x 10^-11 (4.6
x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 1.3 x 10^21 cm^-2
Intrinsic column:    5.4 (+8.0, -5.4) x 10^21 cm^-2 at z=3.14
Photon index:	     1.82 (+/-0.09)

If the light curve continues to decay with a power-law decay index of
1.56, the count rate at T+24 hours will be 0.022 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.4 x
10^-13 (1.0 x 10^-12) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00603243.

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