TITLE:   GCN CIRCULAR
NUMBER:  25093
SUBJECT: GRB 190718A: Swift-XRT refined Analysis
DATE:    19/07/18 18:29:45 GMT
FROM:    Phil Evans at U of Leicester  <pae9@leicester.ac.uk>

B. Sbarufatti (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U.
Leicester), P.A. Evans (U. Leicester), P. D'Avanzo (INAF-OAB), M.G.
Bernardini (INAF-OAB), E. Ambrosi  (INAF-IASFPA) , D.N. Burrows (PSU),
J. D. Gropp (PSU) and V. D'Elia report on behalf of the Swift-XRT team:

We have analysed 6.4 ks of XRT data for GRB 190718A (D'Elia et al. GCN
Circ. 25082), from 70 s to 41.2 ks after the  BAT trigger. The data
comprise 349 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Evans et al. (GCN Circ. 25084).

The late-time light curve (from T0+4.6 ks) can be modelled with a
power-law decay with a decay index of alpha=1.03 (+0.18, -0.17).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.64 (+0.15, -0.14). The
best-fitting absorption column is  7.0 (+4.2, -3.8) x 10^20 cm^-2, in
excess of the Galactic value of 1.2 x 10^20 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 4.0 x 10^-11 (4.4 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     7.0 (+4.2, -3.8) x 10^20 cm^-2
Galactic foreground: 1.2 x 10^20 cm^-2
Excess significance: 2.5 sigma
Photon index:	     1.64 (+0.15, -0.14)

If the light curve continues to decay with a power-law decay index of
1.03, the count rate at T+24 hours will be 0.011 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.5 x
10^-13 (5.0 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/00915091.

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