TITLE:   GCN CIRCULAR
NUMBER:  21038
SUBJECT: Swift Trigger 750044 is probably a noise fluctuation
DATE:    17/04/26 13:54:26 GMT
FROM:    David Palmer at LANL  <palmer@lanl.gov>

S. B. Cenko (GSFC), N. P. M. Kuin (UCL-MSSL), A. Y. Lien (GSFC/UMBC),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the
Swift Team:

At 13:41:41 UT, the Swift Burst Alert Telescope (BAT) deteced a marginal
peak in the image domain in the vicinity of a known source 
(trigger=750044).  Swift slewed immediately to the location. 
The BAT on-board calculated location is 
RA, Dec 255.044, -60.112 which is 
   RA(J2000) = 17h 00m 11s
   Dec(J2000) = -60d 06' 42"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed no significant activity. 

The XRT began observing the field at 13:43:44.3 UT, 123.3 seconds after
the BAT trigger. No source was detected in 300 s of promptly downlinked
data. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 126 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. Because of the density of catalogued stars, further
analysis is required to report an upper limit for any afterglow in the
sub-image. The 8'x8' region for the list of sources generated on-board covers
100% of the BAT error circle. Because of the density of catalogued stars,
further analysis is required to report an upper limit for any afterglow in the
region. No correction has been made for the expected extinction corresponding
to E(B-V) of 0.21. 

Due to the low significance of the image peak (6.00 sigma), the 
large distance to the potential associated source (10.5 arcminutes),
the lack of activity in the BAT count rates, and the non-detection 
by XRT, we believe that this is merely a noise fluctuation in
the image plane and not an astrophysical source.