TITLE:   GCN CIRCULAR
NUMBER:  24823
SUBJECT: GRB 190613B: Swift-XRT refined Analysis
DATE:    19/06/13 22:01:33 GMT
FROM:    Phil Evans at U of Leicester  <pae9@leicester.ac.uk>

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

We have analysed 6.3 ks of XRT data for GRB 190613B (D'Ai et al. GCN
Circ. 24807), from 103 s to 19.3 ks after the  BAT trigger. The data
comprise 352 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Beardmore et al. (GCN Circ. 24812).

The late-time light curve (from T0+5.3 ks) can be modelled with a
power-law decay with a decay index of alpha=0.52 (+/-0.11).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.93 (+/-0.05). The
best-fitting absorption column is  3.28 (+0.24, -0.23) x 10^21 cm^-2,
in excess of the Galactic value of 6.0 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.90 (+/-0.11) and a
best-fitting absorption column of 2.6 (+0.5, -0.4) 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 (5.2 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.6 (+0.5, -0.4) x 10^21 cm^-2
Galactic foreground: 6.0 x 10^20 cm^-2
Excess significance: 7.6 sigma
Photon index:	     1.90 (+/-0.11)

If the light curve continues to decay with a power-law decay index of
0.52, the count rate at T+24 hours will be 0.091 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.5 x
10^-12 (4.8 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/00908329.

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