GCN Circular 17394

M. H. Siegel (PSU), D. N. Burrows (PSU), N. Gehrels (NASA/GSFC),
C. Gronwall (PSU) and B. Sbarufatti (INAF-OAB/PSU) report on behalf of
the Swift Team:

At 00:12:42 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 150204A (trigger=629693).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 207.806, -8.686 which is 
   RA(J2000) = 13h 51m 13s
   Dec(J2000) = -08d 41' 08"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  This was an image trigger and, as usual for such
events, does not show any noticeable structure. 

The XRT began observing the field at 00:15:04.5 UT, 141.7 seconds after
the BAT trigger. No source was detected in 468 s of promptly downlinked
data. We are waiting for the full dataset to detect and localise the
XRT counterpart. 

UVOT took a finding chart exposure of  58 seconds with the White filter
starting 858 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 25% of
the BAT 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
BAT 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
0.04. 

Given the lack of a bright XRT source, it is likely that this is a
noise event and not an astrophysical source.  The full ground-linked
data set will be necessary to verify. 

Burst Advocate for this burst is M. H. Siegel (siegel AT swift.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.)