TITLE:   GCN CIRCULAR
NUMBER:  21794
SUBJECT: GRB 170903A: Swift-XRT observations
DATE:    17/09/03 14:34:05 GMT
FROM:    Phil Evans at U of Leicester  <pae9@leicester.ac.uk>

S. Campana (INAF-OAB), P.A. Evans (U. Leicester), J.P. Osborne (U.
Leicester), D.N. Burrows (PSU), J.A. Kennea (PSU) and G. Tagliaferri
(INAF-OAB) report on behalf of the Swift-XRT team:

The XRT began observing the field of GRB 170903A at 13:41:04.6 UT,
3117.5 seconds after the BAT trigger. Using promptly downlinked data we
find an uncatalogued X-ray source with an enhanced position: RA, Dec
254.5260, 34.9796 which is equivalent to:
   RA(J2000)  = 16h 58m 06.23s
   Dec(J2000) = +34d 58' 46.6"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
location is 43 arcseconds from the BAT onboard position, within 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. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (1.74 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 6.3
(+3.39/-2.89) x 10^21 cm^-2 (90% confidence).