GCN Circular 18215

F. E. Marshall (NASA/GSFC), S. D. Barthelmy (GSFC),
A. Y. Lien (GSFC/UMBC), D. M. Palmer (LANL) and T. Sakamoto (AGU)
report on behalf of the Swift Team:

At 22:19:27 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 150831B (trigger=653978).  Swift did not slew due to observing
constraint.  The BAT on-board calculated location is 
RA, Dec 271.021, -27.252, which is 
   RA(J2000)  =  18h 04m 05s
   Dec(J2000) = -27d 15' 07"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a couple of overlapping peaks
structure with a total duration of about 3 sec.  The peak count rate
was ~2000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

Due to an observing constraint, Swift will not slew until T0+49.6
minutes. There will be no XRT or UVOT data until this time. 

We note that this source is in the projected direction of the 
Galactic bulge (lon,lat = 3.51,-2.66) and for that reason there 
is a strong possibility that this is a Galactic source.  However, its
light curve and the presence of flux above 100 keV are more consistent 
with a cosmological GRB. 

Determination of the nature of this event will require XRT observations
and the full downlinked dataset. 

Burst Advocate for this burst is F. E. Marshall (marshall AT milkyway.gsfc.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.)