[vsnet-grb-info 14983] GRB 140515A: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  16277
SUBJECT: GRB 140515A: Swift-XRT refined Analysis
DATE:    14/05/15 23:58:11 GMT
FROM:    Paolo D'Avanzo at INAF-OAB  <paolo.davanzo at brera.inaf.it>

P. D'Avanzo, M. G. Bernardini (INAF-OAB), P. A. Evans (U. Leicester)
report on behalf of the Swift-XRT team:

We have analysed 7.1 ks of XRT data for GRB 140515A (D'Avanzo  et al.
GCN Circ. 16267),  from 60 s to 13.6 ks after the  BAT trigger. The
data comprise 9 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. 16270).


The light curve can be modelled with  a power-law decay with an initial
decay index of alpha=2.5 (+0.5, -0.3). Then at T0+1100 s the light
curve rises, reaching a count rate ~ 0.3 ct/sec. The remaining two
orbits show irregular rate variations likely due to an underlying
flaring activity, with a count rate ~ 0.3 ct/sec and ~ 0.1 ct/sec
respectively.

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.75 (+0.12, -0.11). The
best-fitting absorption column is  1.7 (+3.2, -1.7) x 10^22 cm^-2, at a
redshift of 6.32 (Chornock et al., GCN Circ. 16269), in addition to the
Galactic value of 2.5 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 3.7 x 10^-11 (3.9 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Galactic foreground: 2.5 x 10^20 cm^-2
Intrinsic column:    1.7 (+3.2, -1.7) x 10^22 cm^-2 at z=6.32
Photon index:	     1.75 (+0.12, -0.11)


The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00599037.

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