TITLE:   GCN CIRCULAR
NUMBER:  14527
SUBJECT: GRB 130502A: Swift detection of a burst
DATE:    13/05/02 18:07:57 GMT
FROM:    Jamie A. Kennea at PSU/Swift-XRT  <kennea@swift.psu.edu>

E. Troja (NASA/GSFC/UMCP), A. A. Breeveld (UCL-MSSL),
P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), N. Gehrels (NASA/GSFC),
S. T. Holland (STScI), H. A. Krimm (CRESST/GSFC/USRA),
C. B. Markwardt (NASA/GSFC), F. E. Marshall (NASA/GSFC),
A. Melandri (INAF-OAB), B. Sbarufatti (INAF-OAB/PSU),
M. H. Siegel (PSU), M. Stamatikos (OSU/NASA/GSFC), M. C. Stroh (PSU),
C. A. Swenson (PSU) and T. N. Ukwatta (MSU) report on behalf of the
Swift Team:

At 17:50:30 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 130502A (trigger=554996).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 138.578, -0.143 which is 
   RA(J2000) = 09h 14m 19s
   Dec(J2000) = -00d 08' 35"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a double-peaked
structure with a duration of about 5 sec.  The rapidly available light
curve also shows a peak in the lowest energy at T+10 sec, but it is
not clear at this time whether or not the second peak is real. The 
peak count rate was ~3000 counts/sec (15-350 keV), at ~0 sec after 
the trigger. 

The XRT began observing the field at 17:52:01.8 UT, 91.4 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 138.5690, -0.1232 which
is equivalent to:
   RA(J2000)  = 09h 14m 16.56s
   Dec(J2000) = -00d 07' 23.7"
with an uncertainty of 2.2 arcseconds (radius, 90% containment). This
location is 78 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 (2.49 x
10^20 cm^-2, Kalberla et al. 2005), with an excess column of 2.5
(+1.77/-1.57) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 95 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers 100% of
the XRT error circle. The typical 3-sigma upper limit has been about 19.6 mag. 
The 8'x8' region for the list of sources generated on-board covers 100% of the
XRT 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
0.03. 

Burst Advocate for this burst is E. Troja (eleonora.troja AT nasa.gov). 
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.)