GCN Circular 14540

A. Melandri (INAF-OAB) and S. Immler (NASA/CRESST/GSFC) report on behalf of the Swift-XRT team:

We have analysed 3.4 ks of XRT data for the Fermi/LAT-detected burst:
GRB 130502B,  from 55.1 ks to 67.9 ks after the  Fermi/LAT trigger. The
data are entirely in Photon Counting (PC) mode.  An X-ray source is
detected within the Fermi/LAT error circle. Using 3614 s of PC mode
data and 6 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 = 66.76207, +71.06071 which is equivalent to:

RA (J2000): 04h 27m 02.90s
Dec(J2000): +71d 03' 38.5"

with an uncertainty of 1.5 arcsec (radius, 90% confidence). This
position is 157 arcsec from the Fermi/LAT position.  The light curve is
consistent with a constant source of mean count rate 1.1e-01 ct/sec. A
power-law fit gives an index of 0.8 (+/-1.3).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.88 (+0.28, -0.26). The
best-fitting absorption column is  2.8 (+1.0, -0.9) x 10^21 cm^-2, in
excess of the Galactic value of 1.1 x 10^21 cm^-2 (Kalberla et al.
2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 4.3 x 10^-11 (6.3 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.8 (+1.0, -0.9) x 10^21 cm^-2
Galactic foreground: 1.1 x 10^21 cm^-2
Excess significance: 3.1 sigma
Photon index:	     1.88 (+0.28, -0.26)

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00020266.

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