GCN Circular 19394

L. M. Z. Hagen (PSU), S. D. Barthelmy (GSFC),
H. A. Krimm (CRESST/GSFC/USRA), F. E. Marshall (NASA/GSFC),
D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the
Swift Team:

At 03:29:15 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 160506A (trigger=685245).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 265.774, -46.117 which is 
   RA(J2000)  =  17h 43m 06s
   Dec(J2000) = -46d 07' 00"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows broad peak
with a total duration of about 50 sec.  The peak count rate
was ~1200 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 03:30:50.6 UT, 94.8 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
265.8484, -46.1340 which is equivalent to:
   RA(J2000)  = 17h 43m 23.60s
   Dec(J2000) = -46d 08' 02.3"
with an uncertainty of 2.0 arcseconds (radius, 90% containment). This
location is 195 arcseconds from the BAT onboard position, outside 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 (2.67 x
10^21 cm^-2, Willingale et al. 2013), with an excess column of 4.8
(+2.85/-2.47) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 2.68e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 250 seconds with the U filter starting
101 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 upper limit has been 19.6 mag. The
8'x8' region for the list of sources generated on-board covers 100% of the XRT
error circle. The typical upper limit has been 18.0 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.26. 

Burst Advocate for this burst is L. M. Z. Hagen (lea.zernow.hagen AT gmail.com). 
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.)