GCN Circular 18251

J.P. Osborne (U. Leicester), D.N. Burrows (PSU), J.A. Kennea (PSU), G.
Cusumano (INAF-IASF PA), M. Perri (ASDC) and P.A. Evans (U. Leicester)
report on behalf of the Swift-XRT team:

The XRT began observing the field of GRB 150907B at 00:16:37.8 UT,
3010.0 seconds after the BAT trigger. Using promptly downlinked data we
find an uncatalogued X-ray source located at RA, Dec 255.30809,
-63.78591 which is equivalent to:
   RA(J2000)  = 17h 01m 13.94s
   Dec(J2000) = -63d 47' 09.3"
with an uncertainty of 4.0 arcseconds (radius, 90% containment). This
location is 185 arcseconds from the BAT onboard position, outside the
BAT error circle. This position may be improved as more data are
received; the latest position is available at
http://www.swift.ac.uk/sper.  We cannot determine whether the source is
fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 1.52
x 10^21 cm^-2 (Willingale et al. 2013).