[vsnet-grb-info 19569] GRB 170710A: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  21312
SUBJECT: GRB 170710A: Swift-XRT refined Analysis
DATE:    17/07/10 12:13:53 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at leicester.ac.uk>

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

We have analysed 9.8 ks of XRT data for the Swift/BAT-detected burst
GRB 170710A (Evans et al. GCN Circ. 21308), from 114 s to 30.4 ks after
the  Swift/BAT trigger. The data comprise 102 s in Windowed Timing (WT)
mode (the first 8 s were taken while Swift was slewing) with the
remainder in Photon Counting (PC) mode. The enhanced XRT position for
this burst was given by Osborne et al. (GCN Circ. 21309).

The light curve can be modelled with an initial power-law decay with an
index of alpha=4.43 (+0.26, -0.23), followed by a break at T+446 s to
an alpha of 0.49 (+0.07, -0.08).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.81 (+/-0.10). The
best-fitting absorption column is  3.6 (+/-0.3) x 10^21 cm^-2, in
excess of the Galactic value of 1.8 x 10^21 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.96 (+0.28, -0.26)
and a best-fitting absorption column of 2.5 (+1.2, -0.7) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.7 x 10^-11 (5.1 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.5 (+1.2, -0.7) x 10^21 cm^-2
Galactic foreground: 1.8 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.96 (+0.28, -0.26)

If the light curve continues to decay with a power-law decay index of
0.49, the count rate at T+24 hours will be 0.011 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.1 x
10^-13 (5.7 x 10^-13) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00761119.

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