GCN Circular 29971

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

The XRT began observing the field of GRB 210509A at 15:45:53.0 UT,
4412.6 seconds after the BAT trigger. Using promptly downlinked data we
find an uncatalogued X-ray source located at RA, Dec 350.37430, 6.67134
which is equivalent to:
   RA(J2000)  = 23h 21m 29.83s
   Dec(J2000) = +06d 40' 16.8"
with an uncertainty of 4.4 arcseconds (radius, 90% containment). This
location is 80 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 https://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 7.11
x 10^20 cm^-2 (Willingale et al. 2013).