GCN Circular 6544

O. Godet, N. Lyons, K.L. Page, P.A. Evans, J. Osborne, R. Starling
(U. Leicester) and G.  Tagliaferri (INAF-OAB) report on behalf the
Swift-XRT team:

The XRT started to observe the field of the INTEGRAL burst GRB 070615
(Mereghetti et al., GCN 6537
Not found
 
 
) 10.7h after the IBAS trigger. We analysed
around 3ks of PC data. A possible weak and uncatalogued X-ray source is
detected at a position of:

RA(J2000)  =  02h 57m 15.37s 
Dec(J2000) = -04d 24' 26.6"

with an uncertainty of 7.5 arcsec (90% containment radius). This is 23
arcsec from the INTEGRAL position given by Mereghetti et al. (GCN Circ.
6537
Not found
 
 
). 

We note that there are only 5 counts detected in the error circle
centred on this position. In this region, only ~0.07 background counts
would be expected. Using the Bayesian method to find a 99.7\% level
confidence limit on the actual number of counts from the source, the
range would then be between 0.8 and 14.9 counts. We estimate the
probability that this detection is due to a background fluctuation to be
6e-7, suggesting that this is a real detection.

Since it is impossible to say whether or not the source is fading, we
cannot say with any certainty that the source is the X-ray afterglow of
GRB 070615.

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