[vsnet-grb-info 2136] Swift-BAT trigger 155072 ground analysis

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3975
SUBJECT: Swift-BAT trigger 155072 ground analysis
DATE:    05/09/14 18:35:54 GMT
FROM:    Jay R. Cummings at NASA/GSFC/Swift  <jayc at milkyway.gsfc.nasa.gov>

L. Barbier (GSFC), L. Angelini (GSFC), Alex Blustin (UCL-MSSL), 
D. Burrows (PSU), S. Barthelmy (GSFC), S. Campana (INAF-OAB), 
J. Cummings (GSFC/NRC), E. Fenimore (LANL), N. Gehrels (GSFC), 
O. Godet (U. Leicester), J. Greiner (MPE), D. Hullinger (UMD), 
J. Kennea (PSU), H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD), 
F. Marshall (GSFC), J. Osborne (U Leicester), K. Page (U. Leicester), 
D. Palmer (LANL), A. Parsons (GSFC), T. Sakamoto (GSFC/NRC), 
G. Sato (ISAS), J. Tueller (GSFC),
on behalf of the Swift team:

Swift-BAT trigger 155072 (Greiner et al. GCN circ. 3974) appears to be
consistent with a statistical fluctuation in the intersection of the
rate and image domains.  We cannot completely rule out that the rate and
image excesses are due to a very weak GRB, based on the BAT data.

If the excesses are due to a very weak GRB, the burst would appear to be
short (~1 sec) and to have a hard spectrum with no emission < 50 keV in
the BAT energy range. The spectral parameters are poorly constrained.

The BAT refined ground analysis position is RA, Dec 59.512d, -16.655d
(3h 58m 2.8s, -16d 39' 19") J2000, with an error radius of 4 arcmin
(90% confidence including systematic errors).

The initial XRT image (a single 2.5 sec integration at 11:28:53.8 UT, 
99 sec after the BAT trigger) has no indication of an X-ray source.  
Further XRT observations in PC mode began at 12:35:30 (T+3996 sec).  In 
2.1 ks of PC mode data there is no detectable X-ray source.  The 3-sigma 
unabsorbed flux upper limit is 2.5e-13 erg cm^-2 sec^-1 (0.3-10 keV).  We 
note that this is highly unusual for a long GRB at this epoch, but does 
not rule out a short GRB.

UVOT began observing 4084 sec after the BAT trigger.  No new source
is seen in the 100 second exposure with the V filter to a 5-sigma limit
of 18.4 magnitudes.  This magnitude is uncorrected for extinction and is
based on a preliminary zero-point, measured in orbit, and will require
refinement with further calibration.

No further observations are planned.