GCN Circular 23857

J.A. Kennea (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U.
Leicester), P.A. Evans (U. Leicester), V. D'Elia (ASDC), A. D'Ai
(INAF-IASFPA), A. Melandri (INAF-OAB), B. Sbarufatti (INAF-OAB/PSU),
D.N. Burrows (PSU) and A.Y. Lien report on behalf of the Swift-XRT
team:

We have analysed 6.4 ks of XRT data for GRB 190204A (Lien et al. GCN
Circ. 23852
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 ), from 81 s to 13.0 ks after the  BAT trigger. The data
comprise 926 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The refined XRT position is RA, Dec =
351.4775, +54.8766 which is equivalent to:

RA (J2000): 23 25 54.59
Dec(J2000): +54 52 35.7

with an uncertainty of 3.6 arcsec (radius, 90% confidence).

The late-time light curve (from T0+4.8 ks) can be modelled with a
power-law decay with a decay index of alpha=1.36 (+/-0.16).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.740 (+0.022, -0.018). The
best-fitting absorption column is  consistent with the Galactic value
of 4.4 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has
a photon index of 1.83 (+0.12, -0.11) and a best-fitting absorption
column of 5.4 (+0.8, -0.7) x 10^21 cm^-2. The counts to observed
(unabsorbed) 0.3-10 keV flux conversion factor deduced from this
spectrum  is 4.6 x 10^-11 (6.8 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     5.4 (+0.8, -0.7) x 10^21 cm^-2
Galactic foreground: 4.4 x 10^21 cm^-2
Excess significance: 2.4 sigma
Photon index:	     1.83 (+0.12, -0.11)

If the light curve continues to decay with a power-law decay index of
1.36, the count rate at T+24 hours will be 9.9 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.5 x
10^-13 (6.8 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/00887579.

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