GCN Circular 15231

Dirk Grupe (Swift MOC/PSU) report on behalf of the Swift XRT team:

We report on two additional Swift XRT observations of the
INTEGRAL-discovered burst GRB 130903A (Mereghetti et al., GCN circ.
15169
Not found
 
 
). As reported in Grupe & Holland (GCN circ. 15173
Not found
 
 
), we found
an X-ray source at a level of 5e-3 counts/s within the INTEGRAL
error circle. Swift obtained a second observation on September 06
for 5.0 ks. The source reported in Grupe & Holland was still
present but at a significantly lower level at (1.1+0.5-0.4)e-3
counts/s suggesting a rather slow decay slope during the 'normal'
X-ray afterglow phase (e.g. see Grupe et al. 2013,
arXiv:1305:3236). However, a decay by a factor of 5 is still
consistent with a background AGN (e.g. Grupe et al. 2010, AJ 187,
64). Therefore we performed a third observation which was executed
on September 16 for a total of 4.6 ks. In this new observation
the source seems to be gone. The 3-sigma upper limit at the 
position of the previously detected X-ray source is at a level of 
1.25e-3 counts/s. We can conclude that the X-ray source reported 
in  Grupe & Holland (GCN circ. 15173
Not found
 
 
) is most-likely the X-ray 
afterglow of GRB 130903A. 

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