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 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.