GCN Circular 9331

E. A. Hoversten (PSU), S. D. Barthelmy (GSFC), D. N. Burrows (PSU),
M. M. Chester (PSU), D. Grupe (PSU), J. A. Kennea (PSU),
H. A. Krimm (CRESST/GSFC/USRA), N. P. M. Kuin (MSSL),
D. M. Palmer (LANL) and T. N. Ukwatta (GSFC/GWU) report on behalf of
the Swift Team:

At 00:23:00 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090510 (trigger=351588).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 333.555, -26.606 which is 
   RA(J2000) = 22h 14m 13s
   Dec(J2000) = -26d 36' 19"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single spike 
with a duration of about 0.5 sec.  The peak count rate
was ~21000 counts/sec (15-350 keV), at 0 sec after the trigger. 

The XRT began observing the field at 00:24:34.6 UT, 94.1 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 333.55195, -26.58345 which is
equivalent to:
   RA(J2000)  = 22h 14m 12.47s
   Dec(J2000) = -26d 35' 00.4"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 81 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 consistent with the Galactic value of
1.66e+20 cm^-2 (Kalberla et al. 2005). 

UVOT took a finding chart exposure of 150 seconds with the White 
filter  starting 97 seconds after the BAT trigger. No credible 
afterglow candidate has  been found in the initial data products. 
The 2.7'x2.7' sub-image  does not include the position  of the XRT
candidate. The 8'x8' region for the list of sources   generated
on-board covers the XRT position and 100% of the BAT error  circle. 
The list of sources is  typically complete to about 18 mag.  No
correction has been made for the  expected extinction  corresponding
to E(B-V) of 0.02. 

We note the existence of the galaxy 2dFGRS TGS176Z296 at
a distance of 140 arcsec from the XRT position. 

Burst Advocate for this burst is E. A. Hoversten (hoversten AT astro.psu.edu). 
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)