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GCN Circular 20470

Subject
GRB 170115A: Swift-XRT refined Analysis
Date
2017-01-16T15:12:26Z (7 years ago)
From
Kim Page at U.of Leicester <kpa@star.le.ac.uk>
K.L. Page and P.A. Evans (U. Leicester) report on behalf of the
Swift-XRT team:

We have analysed 3.9 ks of XRT data for GRB 170115A, from 82 s to 40.4
ks after the  BAT trigger. The data comprise 224 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=1.54 (+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 2.22 (+0.17, -0.16). The
best-fitting absorption column is  1.3 (+0.5, -0.4) x 10^21 cm^-2, in
excess of the Galactic value of 6.1 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 2.9 x 10^-11 (4.0 x 10^-11) erg
cm^-2 count^-1. 

A summary of the WT-mode spectrum is thus:
Total column:	     1.3 (+0.5, -0.4) x 10^21 cm^-2
Galactic foreground: 6.1 x 10^20 cm^-2
Excess significance: 2.6 sigma
Photon index:	     2.22 (+0.17, -0.16)

If the light curve continues to decay with a power-law decay index of
1.54, the count rate at T+24 hours will be 4.1 x 10^-4 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x
10^-14 (1.7 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/00733103.

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