[vsnet-grb-info 16693] GRB 150626B: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17974
SUBJECT: GRB 150626B: Swift-XRT refined Analysis
DATE:    15/06/27 15:16:40 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at leicester.ac.uk>

P.A. Evans (U. Leicester), B.P. Gompertz (U. Leicester), A. Maselli 
(INAF-IASFPA), A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB), B.
Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), T.G.R. Roegiers (PSU),
J.P. Osborne (U. Leicester) and L.M. McCauley report on behalf of the
Swift-XRT team:

We have analysed 8.9 ks of XRT data for GRB 150626B (McCauley et al.
GCN Circ. 17966), from 111 s to 23.5 ks after the  BAT trigger. The
data comprise 8 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 Goad et al. (GCN Circ. 17968).
The late-time light curve (from T0+5.3 ks) is consistent with a
constant source of mean count rate 1.9e-01 ct/sec. A power-law fit
gives an index of 0.2 (+0.6, -0.5).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.99 (+/-0.15). The
best-fitting absorption column is  9.6 (+1.4, -1.3) x 10^21 cm^-2, in
excess of the Galactic value of 1.7 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 4.8 x 10^-11 (8.8 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     9.6 (+1.4, -1.3) x 10^21 cm^-2
Galactic foreground: 1.7 x 10^20 cm^-2
Excess significance: 11.7 sigma
Photon index:	     1.99 (+/-0.15)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00646786.

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