TITLE:   GCN CIRCULAR
NUMBER:  20535
SUBJECT: GRB 170126A: Swift-XRT refined Analysis
DATE:    17/01/27 04:49:22 GMT
FROM:    Phil Evans at U of Leicester  <pae9@leicester.ac.uk>

D.N. Burrows (PSU), P.A. Evans (U. Leicester), S.L. Gibson (U.
Leicester), J.P. Osborne (U. Leicester), A. Melandri (INAF-OAB), P.
D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. Cholden-Brown (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 7.0 ks of XRT data for GRB 170126A, from 73 s to 40.7
ks after the  BAT trigger. The data comprise 68 s in Windowed Timing
(WT) mode (the first 7 s were taken while Swift was slewing) with the
remainder in Photon Counting (PC) mode. 

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.30 (+0.06, -0.05).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.52 (+0.33, -0.28). The
best-fitting absorption column is  2.0 (+2.5, -1.3) x 10^21 cm^-2,
consistent with the Galactic value of 7.0 x 10^20 cm^-2 (Willingale et
al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux
conversion factor deduced from this spectrum  is 4.5 x 10^-11 (5.3 x
10^-11) erg cm^-2 count^-1. 

A summary of the WT-mode spectrum is thus:
Total column:	     2.0 (+2.5, -1.3) x 10^21 cm^-2
Galactic foreground: 7.0 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.52 (+0.33, -0.28)

If the light curve continues to decay with a power-law decay index of
1.30, the count rate at T+24 hours will be 9.2 x 10^-4 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.2 x
10^-14 (4.9 x 10^-14) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00735188.

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