GCN Circular 16298

A. Melandri (INAF-OAB), M. G. Bernardini (INAF-OAB),
P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), D. Malesani (DARK/NBI),
D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB/PSU) and
M. H. Siegel (PSU) report on behalf of the Swift Team:

At 09:17:46 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 140518A (trigger=599287).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 227.269, +42.416 which is 
   RA(J2000) = 15h 09m 05s
   Dec(J2000) = +42d 24' 56"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a multiple-peaked
structure with a  duration of about 60 s.  The peak count rate
was ~1500 counts/s (15-350 keV) at ~0 sec after trigger. 

The XRT began observing the field at 09:18:55.0 UT, 69 seconds
after the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source with an enhanced position: RA, Dec 227.2519,
42.4185 which is equivalent to:
   RA(J2000)  = 15h 09m 00.45s
   Dec(J2000) = +42d 25' 06.6"
with an uncertainty of 2.0 arcseconds (radius, 90% containment). 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 (1.56 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 2.5
(+2.30/-2.03) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 3.67e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 76 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
0.02. 

Burst Advocate for this burst is A. Melandri (andrea.melandri AT brera.inaf.it). 
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.)