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GCN Circular 23633

Subject
GRB 190106A: Swift-XRT refined Analysis
Date
2019-01-07T13:45:03Z (5 years ago)
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), 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), 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).

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.
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