[vsnet-grb-info 14938] GRB 140508A: Swift-XRT observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  16232
SUBJECT: GRB 140508A: Swift-XRT observations
DATE:    14/05/09 06:26:12 GMT
FROM:    Alex Amaral-Rogers at U.of Leicester  <aar14 at leicester.ac.uk>

 reports on behalf of the Swift-XRT team:

We have analysed 3.0 ks of XRT data for the Fermi/GBM-detected burst:
GRB 140508A,  from 69.0 ks to 75.2 ks after the  Fermi/GBM trigger. The
data are entirely in Photon Counting (PC) mode.  An X-ray source is
detected within the Fermi/GBM error circle. Using 2973 s of PC mode
data and 3 UVOT images, we find an enhanced XRT position (using the
XRT-UVOT alignment and matching UVOT field sources to the USNO-B1
catalogue): RA, Dec = 255.46650, +46.78033 which is equivalent to:

RA (J2000): 17h 01m 51.96s
Dec(J2000): +46d 46' 49.2"

with an uncertainty of 1.8 arcsec (radius, 90% confidence). This
position is 0.3 arcsec from the iPTF optical transient candidate (GCN
Circ. 16226).  The late-time light curve (from T0+69.0 ks) is
consistent with a constant source of mean count rate 2.0e-01 ct/sec.

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.01 (+0.25, -0.23). The
best-fitting absorption column is  7.8 (+5.9, -5.1) x 10^20 cm^-2, in
excess of the Galactic value of 2.1 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 3.3 x 10^-11 (3.9 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     7.8 (+5.9, -5.1) x 10^20 cm^-2
Galactic foreground: 2.1 x 10^20 cm^-2
Excess significance: 1.8 sigma
Photon index:	     2.01 (+0.25, -0.23)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00020376.

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