TITLE:   GCN CIRCULAR
NUMBER:  20560
SUBJECT: GRB 170127B: Swift-XRT refined Analysis
DATE:    17/01/28 15:25:05 GMT
FROM:    Phil Evans at U of Leicester  <pae9@leicester.ac.uk>

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

We have analysed 2.8 ks of XRT data for GRB 170127B, from 60 s to 10.6
ks after the  BAT trigger. The data comprise 7 s in Windowed Timing
(WT) mode (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=1.7 (+0.5, -0.4).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.57 (+0.27, -0.23). The
best-fitting absorption column is  consistent with the Galactic value
of 2.0 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 4.1 x 10^-11 (4.2 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.0 (+/-4.2) x 10^20 cm^-2
Galactic foreground: 2.0 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.57 (+0.27, -0.23)

If the light curve continues to decay with a power-law decay index of
1.7, the count rate at T+24 hours will be 6.7 x 10^-6 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.7 x
10^-16 (2.8 x 10^-16) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00735331.

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