[vsnet-grb-info 19877] GRB 171001A: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  21956
SUBJECT: GRB 171001A: Swift-XRT refined Analysis
DATE:    17/10/02 11:19:25 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at leicester.ac.uk>

J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore
(U. Leicester), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB), P.
D'Avanzo (INAF-OAB), D.N. Burrows (PSU), A. Tohuvavohu (PSU), S. J.
LaPorte (PSU) and A.Y. Lien report on behalf of the Swift-XRT team:

We have analysed 6.0 ks of XRT data for GRB 171001A (Lien et al. GCN
Circ. 21946), from 176 s to 52.2 ks after the  BAT trigger. The data
comprise 11 s in Windowed Timing (WT) mode (taken while Swift was
slewing), with the remainder in Photon Counting (PC) mode. The enhanced
XRT position for this burst was given by Evans et al. (GCN Circ.
21952).

The light curve can be modelled with an initial rise, with a power-law
index of alpha=-0.13 (+0.19, -0.21), followed by a break at T+1318 s 
to an alpha of 1.88 (+0.24, -0.18).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.09 (+0.21, -0.19). The
best-fitting absorption column is  6.2 (+4.6, -2.7) x 10^20 cm^-2,
consistent with the Galactic value of 3.6 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 3.1 x 10^-11 (3.7 x
10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     6.2 (+4.6, -2.7) x 10^20 cm^-2
Galactic foreground: 3.6 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     2.09 (+0.21, -0.19)

If the light curve continues to decay with a power-law decay index of
1.88, the count rate at T+24 hours will be 2.1 x 10^-4 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.6 x
10^-15 (7.8 x 10^-15) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00775553.

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