GCN Circular 24810

D.N. Burrows (PSU), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), A.P. Beardmore (U. Leicester), V. D'Elia (ASDC), A. D'Ai
(INAF-IASFPA), A. Melandri (INAF-OAB), A. Tohuvavohu (PSU), S. J.
LaPorte (PSU) and  report on behalf of the Swift-XRT team: report on
behalf of the Swift-XRT team:

We have analysed 8.1 ks of XRT data for GRB 190613A, from 142 s to 18.3
ks after the  BAT trigger. The data comprise 127 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.
24809
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 ).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=5.1 (+1.1, -0.9). At T+174 s  the decay
flattens to an alpha of -1.500000 (+0.905300, -0.000007). The light
curve breaks again at T+207 s to a decay with alpha=5.0 (+0.7, -0.6), 
and  again at T+372 s s to alpha=1.44 (+0.18, -0.15),  before a final
break at T+7345 s s after which the decay index is -1.5 (+0.0, -1.4).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.01 (+/-0.12). The
best-fitting absorption column is  5.1 (+2.8, -2.6) x 10^20 cm^-2, in
excess of the Galactic value of 1.5 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.75 (+0.22, -0.15)
and a best-fitting absorption column of 2.0 (+4.9, -0.5) x 10^20 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.7 x 10^-11 (3.8 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.0 (+4.9, -0.5) x 10^20 cm^-2
Galactic foreground: 1.5 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.75 (+0.22, -0.15)

If the light curve continues to decay with a power-law decay index of
-1.5, the count rate at T+24 hours will be 0.41 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.5 x
10^-11 (1.6 x 10^-11) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00908288.

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