GCN Circular 7753

D. Grupe (PSU), S. D. Barthelmy (GSFC), W. H. Baumgartner (GSFC/UMBC),
A. P. Beardmore (U Leicester), J. R. Cummings (NASA/UMBC),
C. Gronwall (PSU), S. T. Holland (CRESST/USRA/GSFC),
J. A. Kennea (PSU), V. Mangano (INAF-IASFPA),
K. M. McLean (GSFC/UMD), J. P. Osborne (U Leicester),
D. M. Palmer (LANL), D. Perez (U Leicester), T. Sakamoto (NASA/UMBC),
M. Stamatikos (NASA/ORAU), M. C. Stroh (PSU) and
T. N. Ukwatta (GSFC/GWU) report on behalf of the Swift Team:

At 22:20:24 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080520 (trigger=312047).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 280.192, -55.004 which is 
   RA(J2000)  =  18h 40m 46s
   Dec(J2000) = -55d 00' 13"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows two peaks
with a duration of about 15 sec.  The peak count rate
was ~700 counts/sec (15-350 keV), at ~2 sec after the trigger. 

The XRT began observing the field at 22:22:04.3 UT, 99.5 seconds after
the BAT trigger.  Using promptly downlinked data we find a bright uncatalogued X-ray
source. The position, astrometrically enhanced by aligning promptly available
UVOT field source  positions to the USNO-B1 catalogue, is RA,Dec = 280.19337, -54.99181
(degrees) which is equivalent to:

RA  (J2000.0) = 18 40 46.41
DEC (J2000.0) = -54 59 30.5

with an uncertainty of 2.8 arcsec (radius, 90% containment). 
This position is 44.0 arcsec from the BAT position, inside the BAT
error circle. 

UVOT took a finding chart exposure of 100 seconds with the White (160-650 nm)
filter starting 106 seconds after the BAT trigger. There is a candidate
afterglow in the rapidly available 2.7'x2.7' sub-image at

RA  (J2000.0) =  18:40:46.41
Dec (J2000.0) = -54:59:31.1

with an estimated uncertainty of 0.6 arcsec (90%, radius). 
The estimated magnitude is white = 19.8 +/- 0.1 mag. No correction has been
made for Galactic extinction. 

Burst Advocate for this burst is D. Grupe (grupe 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.)