[vsnet-grb-info 2167] GRB050918: Possile Swift/XRT detected afterglow

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4006
SUBJECT: GRB050918: Possile Swift/XRT detected afterglow
DATE:    05/09/21 12:55:35 GMT
FROM:    Jamie A. Kennea at PSU/Swift-XRT  <kennea at astro.psu.edu>

J. A. Kennea, D. N. Burrows, D. Grupe, P. Roming (PSU), J. Osborne (U. 
Leicester), S. T. Holland (GSFC/USRA) and N. Gehrels (GSFC) report on 
behalf of the Swift team:

At September 20th 22:08 UT, Swift began a 10ks TOO observation of the 
Integral discovered burst GRB050918 (GCN 4002). Analysis of ground 
processed data from Swift/XRT reveals a previously uncatalogued faint 
X-ray point source inside the 2.8 arcminute Integral error circle, at the 
following coordinates:

RA(J2000):   17:50:28.7,
Dec(J2000): -25:24:41.2.

The uncertainty on this position is estimated to be 7 arcseconds radius 
(90% containment). This position is 34 arcseconds from the center of the 
Integral error circle given in GCN 4002.

There is no evidence of fading in this source, however as this observation 
occured more than 2 days after the burst this result is expected. Further 
observations will be required to determine if this source is the afterglow 
of GRB050918.

A UVOT V-band image shows no new source, with respect to the DSS, inside 
the INTEGRAL 2.8 arcminute radius error circle.  The 5-sigma limiting 
magnitude in a circular aperture with a radius of six arcseconds is 
V_lim=19.3.