GCN Circular 20558

J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), V. D'Elia
(ASDC), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB), S. J. LaPorte
(PSU), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), B. Mingo (U.
Leicester) and	report on behalf of the Swift-XRT team: report on
behalf of the Swift-XRT team:

We have analysed 6.2 ks of XRT data for GRB 170127A, from 86 s to 58.8
ks after the  BAT trigger. The data comprise 168 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 an initial power-law decay with an
index of alpha=1.28 (+/-0.15), followed by a break at T+329 s to an
alpha of 8.0 (+0.0, -1.1).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.49 (+/-0.10). The
best-fitting absorption column is  1.3 (+/-0.4) x 10^21 cm^-2, in
excess of the Galactic value of 8.5 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 (5.0 x 10^-11) erg
cm^-2 count^-1. 

A summary of the WT-mode spectrum is thus:
Total column:	     1.3 (+/-0.4) x 10^21 cm^-2
Galactic foreground: 8.5 x 10^20 cm^-2
Excess significance: 2.0 sigma
Photon index:	     1.49 (+/-0.10)

If the light curve continues to decay with a power-law decay index of
5.19, the count rate at T+24 hours will be 2.0 x 10^-13 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.9 x
10^-24 (10.0 x 10^-24) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00735326.

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