GCN Circular 23633

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), D.N. Burrows (PSU), A. Tohuvavohu (PSU), S. J. LaPorte
(PSU) and V. Yurkov report on behalf of the Swift-XRT team: report on
behalf of the Swift-XRT team:

We have analysed 5.7 ks of XRT data for GRB 190106A (Yurkov et al. GCN
Circ. 23614
Not found
 
 
), from 85 s to 44.7 ks after the  BAT trigger. The data
comprise 254 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Goad et al. (GCN Circ. 23619
Not found
 
 
).

The late-time light curve (from T0+11.7 ks) can be modelled with a
power-law decay with a decay index of alpha=1.02 (+/-0.11).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.06 (+0.06, -0.05). The
best-fitting absorption column is  1.9 (+/-1.1) x 10^21 cm^-2, at a
redshift of 1.86, in addition to the Galactic value of 1.0 x 10^21
cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index
of 1.95 (+0.09, -0.06) and a best-fitting absorption column consistent
with the Galactic value. The counts to observed (unabsorbed) 0.3-10 keV
flux conversion factor deduced from this spectrum  is 3.5 x 10^-11 (4.4
x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 1.0 x 10^21 cm^-2
Intrinsic column:    1.0 (+1.6, -0.0) x 10^21 cm^-2 at z=1.86
Photon index:	     1.95 (+0.09, -0.06)

If the light curve continues to decay with a power-law decay index of
1.02, the count rate at T+24 hours will be 0.096 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.4 x
10^-12 (4.2 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/00882252.

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