[vsnet-grb-info 12399] Swift Trigger 533836 is a new Galactic transient

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  13774
SUBJECT: Swift Trigger 533836 is a new Galactic transient
DATE:    12/09/16 10:05:16 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

J. R. Cummings (NASA/UMBC), C. Gronwall (PSU), D. Grupe (PSU),
H. A. Krimm (CRESST/GSFC/USRA), C. B. Markwardt (NASA/GSFC),
D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB/PSU) and
M. Stamatikos (OSU/NASA/GSFC) report on behalf of the Swift Team:

At 09:16:06 UT, the Swift Burst Alert Telescope (BAT) triggered and
located an unidentified source near the Galactic center (trigger=533836). 
Swift slewed immediately to the source location. 
The BAT on-board calculated location is 
RA, Dec 266.322, -26.400 which is 
   RA(J2000) = 17h 45m 17s
   Dec(J2000) = -26d 23' 58"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  This is a 16 minute long image trigger,
so there is no immediately available lightcurve data.  The on-board detection
significance is 8.5 sigma. 

The XRT began observing the field at 09:36:59.0 UT, 1252.7 seconds
after the BAT trigger. XRT found a possible X-ray source
located at RA, Dec 266.2960, -26.4025 which is equivalent to:
   RA(J2000)  = +17h 45m 11.04s
   Dec(J2000) = -26d 24' 09.0"
with an uncertainty of 5.8 arcseconds (radius, 90% containment). This
location is 84 arcseconds from the BAT onboard position, within the BAT
error circle. We are waiting for the full dataset to download in order 
to confirm the existence of the source. 

The initial flux in the 2.5 s image was 8.01e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 1259 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. 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 XRT 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 large, but uncertain extinction
expected. 

Due to its position 152 arcminutes from the Galactic center,
and its duration (discovered in a 16-minute long imag trigger),
we believe that this is a previously-uncatalogued Galactic
transient.  A final determination of the status of this source
will require the downlinked data from the ground station. 

A 'Swift J' source name will be assigned based on the final 
X-ray position.